To get the work done from internal combustion engine,we have to burn air-fuel mixture inside the cylinder.When the combustion of air-fuel mixture takes place in the engine cylinder,a temperature as high as 2500 degree centigrade is reached.To withstand such a high temperature we have to use very high melting point material for construction of engine.Practically it is less possible because,"Platinum" a metal which has one of the highest melting point,melts at above 1800 degree centigrade.
It has been practically found that out of total heat generated by internal combustion engine due to combustion of fuel,only 30% of heat is converted in useful work,out of remaining 70% about 40 % is carried by exhaust gases into the atmosphere during exhaust stroke.The rest of 30% must be passed to atmosphere by some suitable arrangement.
Here we find the necessity of cooling.In addition to overheating,large temperature differences may lead to distortion of the engine components due to set up of thermal stresses.If the cooling system is not provided to internal combustion engine,the lubricating oil film would break down and the lubricating oil will decompose to give gummy and carbon deposits.
In lack of Cooling system,a complete seizure of the piston,bearing and other important parts will occur.Due to this,there will be more frequent replacement of the components are required.It will also increase the repairing cost and breakdown period.The engine life will be reduced considerably.
It should also be noted that higher temperatures lower the volumetric efficiency of the engine,promote pre-ignition and tendency of the engine to detonate.The object of cooling is achieved by any of the two methods,
01)Air Cooling
02)Water Cooling
Properties of an efficient cooling system:-
The following are the two main properties desired of an efficient cooling system,
01)It must be capable of removing only about 30% of the heat generated in the combustion chamber.Too much heat removal will lower the thermal efficiency of the engine.
02)It should remove heat at a fast rate when engine is hot.It is also required to be very slow cooling at the starting of the engine,so that the different working parts of the internal combustion engine reach their operating temperature in a short time period.
If you are using Water cooled engine,then are little chances of freezing of water in cold weather conditions,if we keep engine without use for very long time. To overcome this problem,we have to mix anti freezers in cooling water.
The different cooling systems employed in various automobile will be covered in next post.
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Thursday
Construction Of Spark Plug Used In Automotive Engine.
To ignite the mixture of air-petrol inside the engine cylinder,a spark plug is used.A spark plug which is screwed into the cylinder head is usually designed to withstand a pressure about 35 kilogram per centimeter square and operate under 10000 to 30000 volts.
Construction Of Spark Plug:-
The core insulating assembly is housed in the steel shell assembly.The lower threaded portion of the shell which has 18 millimeter or 14 millimetre diameter thread on standard plugs has ground electrode welded to it.The centre electrode is screwed into the insulator at its upper position.The upper end of the centre electrode is connected to the terminal which communicates with the distributor.
When high voltage is applied,the spark jumps in the small gap which is provided between the lower end of the centre electrode and the ground electrode.This spark is responsible for starting ignition in the cylinder.
Platinum,nickel are generally used as electrode material due its capacity to withstand corrosives,high temperature and has good thermal conductivity.The insulator should have a good thermal conductivity,chemical inertness to gases of combustion,high resistance,be non-brittle and able to withstand high temperature and pressure.In recent practice is to use aluminium and silicon oxides also.
In order to prevent the escaping of gases from the cylinder to the atmosphere, suitable sealing gaskets are provided between the shell and the core insulator.Another steel gasket is also provided at the area where the steel shell is to contact cylinder head when the spark plug is screwed in its proper position.The leakage of the hot gases past a defective or worn out gasket is likely to raise the temperature of the plug.
Generally 0.3 to 0.6 millimeter gap is kept in the spark plug.Under special circumstances a 0.7 millimeter gap can also be kept.The efficiency of the entire ignition system is greatly reduced both by too large or too small gap.Therefore,the gap must be kept in the desired limits.
The deposit of foreign materials such as carbon between the electrodes or on the outside of the insulator between the plug terminal and the shell are source of nuisance and permit some of the high voltage to by-pass gap resulting in a reduced intensity of spark giving decreased engine efficiency.To avoid carbon deposits,we should have to operate spark plug above 400 degree centigrade.By bending the ground electrode,we can adjust the gap of plug.
There are two types of spark plugs used for automotive purpose,
01) Hot Plug:-
In this spark plug,the path traced by the heat received by the plug,to reach the Cooling cylinder head water is longer so that the plug can be maintained at a high temperature to burn carbon deposits.
02) Cold Plug:-
It has a shorter insulating nose which increase the rate of heat transfer due to short conducting path.This type of spark plugs are suitable for the engines,running a high speed and having high compression ratio.
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Construction Of Spark Plug:-
The core insulating assembly is housed in the steel shell assembly.The lower threaded portion of the shell which has 18 millimeter or 14 millimetre diameter thread on standard plugs has ground electrode welded to it.The centre electrode is screwed into the insulator at its upper position.The upper end of the centre electrode is connected to the terminal which communicates with the distributor.
When high voltage is applied,the spark jumps in the small gap which is provided between the lower end of the centre electrode and the ground electrode.This spark is responsible for starting ignition in the cylinder.
Platinum,nickel are generally used as electrode material due its capacity to withstand corrosives,high temperature and has good thermal conductivity.The insulator should have a good thermal conductivity,chemical inertness to gases of combustion,high resistance,be non-brittle and able to withstand high temperature and pressure.In recent practice is to use aluminium and silicon oxides also.
In order to prevent the escaping of gases from the cylinder to the atmosphere, suitable sealing gaskets are provided between the shell and the core insulator.Another steel gasket is also provided at the area where the steel shell is to contact cylinder head when the spark plug is screwed in its proper position.The leakage of the hot gases past a defective or worn out gasket is likely to raise the temperature of the plug.
Generally 0.3 to 0.6 millimeter gap is kept in the spark plug.Under special circumstances a 0.7 millimeter gap can also be kept.The efficiency of the entire ignition system is greatly reduced both by too large or too small gap.Therefore,the gap must be kept in the desired limits.
The deposit of foreign materials such as carbon between the electrodes or on the outside of the insulator between the plug terminal and the shell are source of nuisance and permit some of the high voltage to by-pass gap resulting in a reduced intensity of spark giving decreased engine efficiency.To avoid carbon deposits,we should have to operate spark plug above 400 degree centigrade.By bending the ground electrode,we can adjust the gap of plug.
There are two types of spark plugs used for automotive purpose,
01) Hot Plug:-
In this spark plug,the path traced by the heat received by the plug,to reach the Cooling cylinder head water is longer so that the plug can be maintained at a high temperature to burn carbon deposits.
02) Cold Plug:-
It has a shorter insulating nose which increase the rate of heat transfer due to short conducting path.This type of spark plugs are suitable for the engines,running a high speed and having high compression ratio.
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All Petrol Engine used electric spark ignition.The compressed air-petrol mixture in a petrol engine must be fired at the correct instant so that the resulting rise in pressure acts on the piston when it is at top dead centre.A high voltage is required to jump the gap of a spark plug and give a spark of sufficient energy to ignite the mixture.
As the speed of a spark ignition engine increases,it is desirable that the spark advance increase as the ignition time stays constant but the cycle is completed in less time.Some devices are employed for this purpose.The details about such mechanism is as below,
01) Centrifugal Advance Mechanism:-
In this mechanism,the drive shaft is connected to the ignition cam through base plate,spring loaded weight and an advance cam.The latter integral with the ignition cam.When the speed of the engine increases,the centrifugal force pull the weights out against the spring force thus advancing the angular position of the cam relative to drive shaft.
This action opens the contact points earlier and the ignition timing is therefore advanced.With decrease in the speed the springs pulls the weight inwards and bring back the cam thus reducing the spark in advance.
02) Vacuum Advance Mechanism:-
In this case,flexible diaphragm is kept in the fully retarded position by the force of a spring.One face of diaphragm is exposed to the atmosphere through the air vent,the other face is exposed to vacuum in the sealed vacuum chamber which is connected by a pipe line to the induction manifold.
The part loads due to vacuum the diaphragm is pushed upwards by the air pressure and the angular position of the cam in the distributor is advanced through the actuating rod,so that the spark now occurs earlier.When the engine runs on full load,the suction in the manifold decreases and the diaphragm is pushed downwards by the spring thereby retarding the cam.
This way we can increase the timing of spark ignition in our petrol engine.
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As the speed of a spark ignition engine increases,it is desirable that the spark advance increase as the ignition time stays constant but the cycle is completed in less time.Some devices are employed for this purpose.The details about such mechanism is as below,
01) Centrifugal Advance Mechanism:-
In this mechanism,the drive shaft is connected to the ignition cam through base plate,spring loaded weight and an advance cam.The latter integral with the ignition cam.When the speed of the engine increases,the centrifugal force pull the weights out against the spring force thus advancing the angular position of the cam relative to drive shaft.
This action opens the contact points earlier and the ignition timing is therefore advanced.With decrease in the speed the springs pulls the weight inwards and bring back the cam thus reducing the spark in advance.
02) Vacuum Advance Mechanism:-
In this case,flexible diaphragm is kept in the fully retarded position by the force of a spring.One face of diaphragm is exposed to the atmosphere through the air vent,the other face is exposed to vacuum in the sealed vacuum chamber which is connected by a pipe line to the induction manifold.
The part loads due to vacuum the diaphragm is pushed upwards by the air pressure and the angular position of the cam in the distributor is advanced through the actuating rod,so that the spark now occurs earlier.When the engine runs on full load,the suction in the manifold decreases and the diaphragm is pushed downwards by the spring thereby retarding the cam.
This way we can increase the timing of spark ignition in our petrol engine.
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Wednesday
Different Ignition Systems Of Four Cylinder Engine.
For the combustion of fresh charge of mixture it must be burn in engine cylinder.This is done with the help of spark plug.A spark is produced in spark plug by ignition system.The details about various ignition system will be covered in this post.
01) Coil Ignition System:-
This ignition system consists of a 6 or 12 volt battery,resistance,ignition switch,ammeter,high tension coil,contact breaker,condenser,high tension distributor and spark plug.
The high tension coil consists of a Water proof casing containing a few turns of heavy wire forming a primary winding surrounded by about 20000 turns of fine wire forming secondary winding,both the windings being wound over a laminated soft iron core and insulated from each other.One end of secondary winding is earthed while the other end connected through a heavily insulated wire into the centre of the distributor cap.
A carbon contact carries the current to the rotor arm,made of bronze which revolves and distributes the current to the various cylinders through spark plug leads.Thus the rotor arm connects the proper spark plug to the secondary winding at the required moment.
As the flow of current through the primary winding is stopped by the contact breaker,a very high voltage( near about 8000 to 10000 volts) is induced in the secondary winding.This voltage is supplied through the high tension distributor to the appropriate spark plug gap there by producing a spark.The high tension distributor and the contact breaker,are placed in one body.
The condenser in the primary circuit prevents sparking at the contact breaker points.It also increase the electromotive force in the secondary at break while it further decrease the electromotive force in the secondary at make thus giving a high voltage unidirectional current.
The contact breaker consists of a cam with a number of lobes on it,a fixed post holding one contact while other contacts is mounted on a movable arm.The material used for contacts are platinum and tungsten.
The contact breaker points are opened only 3 to 3.5 millimeter apart.The high tension distributor is prevents the serious trouble that are likely to be developed in the high tension coil either when the current flows due to a faulty circuit or when the ignition switch is left in the "On" position,in either case the high tension coil may be heated up giving an inferior performance.
The resistance wire may also act as a fuse breaking the primary circuit thereby avoiding the discharge of the battery.
02) Magneto Ignition System:-
This system consists of a switch,a magneto,contact breaker,condenser,high tension distributor and spark plugs.
The magneto consists of a fixed armature having primary and secondary winding and a rotating magnetic assembly driven from the engine.
The electromotive force induced in the secondary is insufficient to produce a spark.Consequently it is transformed into the high voltage by the contact breaker in the primary circuit.The voltage induced may be more than 10000 volts.
The spark is produced at the correct moment in the proper cylinder with the help of high tension distributor.(As per the action takes place in coil ignition system.)
I hope,this will give you a little knowledge about ignition of your vehicle.what you say?
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01) Coil Ignition System:-
This ignition system consists of a 6 or 12 volt battery,resistance,ignition switch,ammeter,high tension coil,contact breaker,condenser,high tension distributor and spark plug.
The high tension coil consists of a Water proof casing containing a few turns of heavy wire forming a primary winding surrounded by about 20000 turns of fine wire forming secondary winding,both the windings being wound over a laminated soft iron core and insulated from each other.One end of secondary winding is earthed while the other end connected through a heavily insulated wire into the centre of the distributor cap.
A carbon contact carries the current to the rotor arm,made of bronze which revolves and distributes the current to the various cylinders through spark plug leads.Thus the rotor arm connects the proper spark plug to the secondary winding at the required moment.
As the flow of current through the primary winding is stopped by the contact breaker,a very high voltage( near about 8000 to 10000 volts) is induced in the secondary winding.This voltage is supplied through the high tension distributor to the appropriate spark plug gap there by producing a spark.The high tension distributor and the contact breaker,are placed in one body.
The condenser in the primary circuit prevents sparking at the contact breaker points.It also increase the electromotive force in the secondary at break while it further decrease the electromotive force in the secondary at make thus giving a high voltage unidirectional current.
The contact breaker consists of a cam with a number of lobes on it,a fixed post holding one contact while other contacts is mounted on a movable arm.The material used for contacts are platinum and tungsten.
The contact breaker points are opened only 3 to 3.5 millimeter apart.The high tension distributor is prevents the serious trouble that are likely to be developed in the high tension coil either when the current flows due to a faulty circuit or when the ignition switch is left in the "On" position,in either case the high tension coil may be heated up giving an inferior performance.
The resistance wire may also act as a fuse breaking the primary circuit thereby avoiding the discharge of the battery.
02) Magneto Ignition System:-
This system consists of a switch,a magneto,contact breaker,condenser,high tension distributor and spark plugs.
The magneto consists of a fixed armature having primary and secondary winding and a rotating magnetic assembly driven from the engine.
The electromotive force induced in the secondary is insufficient to produce a spark.Consequently it is transformed into the high voltage by the contact breaker in the primary circuit.The voltage induced may be more than 10000 volts.
The spark is produced at the correct moment in the proper cylinder with the help of high tension distributor.(As per the action takes place in coil ignition system.)
I hope,this will give you a little knowledge about ignition of your vehicle.what you say?
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Saturday
Valve Timings Of High Performance Engine.
It is most important to perform the engine as per our requirement.The performance of engine depends on mean effective pressure and rotational speed.Since mean effective pressure is limited by fuel and strength of materials,the only way to have higher performance is to have higher rotational speed.
In high performance engines it is usual to open the valves earlier and close them later so that the opening time is more thus ensuring the maximum amount of fresh mixture at higher rotational engine speed and greatest possible clearance of exhaust gases.
In some unsupercharged racing cars inlet valve opens as early as 25 degree before top dead centre and closes 60 degree after bottom dead centre.Exhaust valve opens 55 before bottom dead centre and closes 25 degree after top dead centre.
Thus we see that the inlet and exhaust valves open and close in four stroke Otto cycle engine as follows,
01) Inlet valve opens 10 to 30 degree in advance of top dead centre position.Closes 30 to 60 degree after bottom dead centre.
02) Exhaust valve opens 30 to 60 degree in advance of the bottom dead centre position.Closes 8 to 25 degree after the top dead centre position.
It has been found practically that the actual maximum pressure in such engine is only about half of the theoretical value,because the inlet and outlet valves do not open and close suddenly but take some time to operate.
Because of the resistance of the inlet valve of the entering charge,the actual pressure inside the cylinder during the suction stroke is slightly less than atmospheric pressure.Similarly because of the resistance of exhaust valve to exhaust gases leaving the cylinder,the actual pressure inside the cylinder during exhaust stroke is slightly higher than atmospheric pressure.
Due to this there are some losses occur which is called as "Pumping Loss".This loss is treated as negative and therefore subtracted from the positive work done,thus we get net work done during the cycle.
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In high performance engines it is usual to open the valves earlier and close them later so that the opening time is more thus ensuring the maximum amount of fresh mixture at higher rotational engine speed and greatest possible clearance of exhaust gases.
In some unsupercharged racing cars inlet valve opens as early as 25 degree before top dead centre and closes 60 degree after bottom dead centre.Exhaust valve opens 55 before bottom dead centre and closes 25 degree after top dead centre.
Thus we see that the inlet and exhaust valves open and close in four stroke Otto cycle engine as follows,
01) Inlet valve opens 10 to 30 degree in advance of top dead centre position.Closes 30 to 60 degree after bottom dead centre.
02) Exhaust valve opens 30 to 60 degree in advance of the bottom dead centre position.Closes 8 to 25 degree after the top dead centre position.
It has been found practically that the actual maximum pressure in such engine is only about half of the theoretical value,because the inlet and outlet valves do not open and close suddenly but take some time to operate.
Because of the resistance of the inlet valve of the entering charge,the actual pressure inside the cylinder during the suction stroke is slightly less than atmospheric pressure.Similarly because of the resistance of exhaust valve to exhaust gases leaving the cylinder,the actual pressure inside the cylinder during exhaust stroke is slightly higher than atmospheric pressure.
Due to this there are some losses occur which is called as "Pumping Loss".This loss is treated as negative and therefore subtracted from the positive work done,thus we get net work done during the cycle.
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Troubleshooting Of Diesel Engine.
Below are the some faults which may occur in any diesel engine.The rectification are also given below suggested go through it for better performance of engine.
01) Engine Will Not Start:-
A) Fuel-have at least six inches high in the tank and insure that the air breather is open to avoid air-lock.
B) Engine too cool.Try to warm the engine or wait for improvement in weather conditions.
C) Dirty fuel oil filters.Clean the fuel filter or replace it if necessary.
D) Cranking is too slow,run down battery.Re-charge the battery,tighten loose connections,check key switch and solenoid relay.
E) Minimum speed adjusting screw on engine Governor may be screwed out too far.Set it as per requirement.
02) Engine Starts But Stalls As Receiver Pressure Builds Up:-
A) Severe cold weather may make it necessary to open the service valve.
03) Engine Starts And Receiver Pressure Builds But Machine Will Not Slow Down Or Unload:-
A) Check the drain cock on the control unit is closed.
B)Throttle controller pipe leaking or clogged.Clean if clogged and replace/repair if leaking.
04) Engine Function Properly But compressor Does Not Load Up Or Only Partially Loads Up:-
A) Butterfly Valve Not Open.Take necessary action for free movement of butterfly valve.
B) Air cleaner elements are clogged or dirty.Clean thoroughly or replace.
05) Diesel Engine Shut Down Due To Insufficient Cooling:-
A) Low water level in indicator.Improve the water level by adding water.
B) Radiator clogged.Clean it immediately.
C) Dirt in fins.Blow out air in reverse direction to flow of air.
D) Faulty engine thermostat.Remove the fault as per instructions of manufacturer.
E) Operating pressure is above maximum allowable.Discharge the pressure and keep it in limit.
F) Engine fan belt too loose.Adjust the tension of belts as per requirement.
06) Diesel Engine Shut Down Due To Low Engine Oil Pressure Or No Oil Pressure Shown On Gauge:-
A) Oil level in crankcase of engine is low.Top up as required.
B) Compressor level setting is wrong.Level the compressor.
C) If engine running but no oil pressure shown on gauge,stop engine and check oil pressure gauge on some known pressure.Check oil filter element for clogging.Replace if required.
D) Check engine oil pump and screen.Take rectification action as per requirement.
E) Incorrect engine oil,oil line or oil pump screen can clog if incorrect oil grade is used.Use proper lubrication oil as per instruction of engine manufacturer.
07) Discharge Air Contains Excessive Lubricating Oil:-
A) Oil line from separator to air-end blocked.Clean choke in return line.
B) If separated oil is returning to intake in the proper way,it is possible that oil separator fiber glass wool discs needs replacement.Check separator shell for leak and rectify,if required.
C) Oil level in air/oil receiver is too high.Correct the oil level as required,up to middle in visual indicator.
08) Engine Speed Low During Start Up:-
A) Battery improper.check electrolyte level and specific gravity and recharge.
B) Loose wiring connection.Inspect and tighten.
09) Compressor Rotates In Reverse Direction When Shutdown With Pressure In The Receiver:-
A) Discharge valve malfunctioning.remove discharge valve.Inspect and rectify.
B) Oil check valve malfunctioning.Dismantle the oil check valve and inspect and repair.
10) Safety Valve Blows:-
A) Controller not functioning.Check control filter,strainer.Clean and adjust rotation per minute.(RPM)
B) Unloader transformer adjusted at higher pressure,adjust to proper pressure setting.
C) Butterfly valve not closing properly.Inspect and take necessary action.
D) Safety valve defective.Inspect and adjust,if necessary replace.Safety valve is to be set at 10% higher pressure than the maximum unloading pressure.
Hope this will help to rectify problems of your diesel engine.
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01) Engine Will Not Start:-
A) Fuel-have at least six inches high in the tank and insure that the air breather is open to avoid air-lock.
B) Engine too cool.Try to warm the engine or wait for improvement in weather conditions.
C) Dirty fuel oil filters.Clean the fuel filter or replace it if necessary.
D) Cranking is too slow,run down battery.Re-charge the battery,tighten loose connections,check key switch and solenoid relay.
E) Minimum speed adjusting screw on engine Governor may be screwed out too far.Set it as per requirement.
02) Engine Starts But Stalls As Receiver Pressure Builds Up:-
A) Severe cold weather may make it necessary to open the service valve.
03) Engine Starts And Receiver Pressure Builds But Machine Will Not Slow Down Or Unload:-
A) Check the drain cock on the control unit is closed.
B)Throttle controller pipe leaking or clogged.Clean if clogged and replace/repair if leaking.
04) Engine Function Properly But compressor Does Not Load Up Or Only Partially Loads Up:-
A) Butterfly Valve Not Open.Take necessary action for free movement of butterfly valve.
B) Air cleaner elements are clogged or dirty.Clean thoroughly or replace.
05) Diesel Engine Shut Down Due To Insufficient Cooling:-
A) Low water level in indicator.Improve the water level by adding water.
B) Radiator clogged.Clean it immediately.
C) Dirt in fins.Blow out air in reverse direction to flow of air.
D) Faulty engine thermostat.Remove the fault as per instructions of manufacturer.
E) Operating pressure is above maximum allowable.Discharge the pressure and keep it in limit.
F) Engine fan belt too loose.Adjust the tension of belts as per requirement.
06) Diesel Engine Shut Down Due To Low Engine Oil Pressure Or No Oil Pressure Shown On Gauge:-
A) Oil level in crankcase of engine is low.Top up as required.
B) Compressor level setting is wrong.Level the compressor.
C) If engine running but no oil pressure shown on gauge,stop engine and check oil pressure gauge on some known pressure.Check oil filter element for clogging.Replace if required.
D) Check engine oil pump and screen.Take rectification action as per requirement.
E) Incorrect engine oil,oil line or oil pump screen can clog if incorrect oil grade is used.Use proper lubrication oil as per instruction of engine manufacturer.
07) Discharge Air Contains Excessive Lubricating Oil:-
A) Oil line from separator to air-end blocked.Clean choke in return line.
B) If separated oil is returning to intake in the proper way,it is possible that oil separator fiber glass wool discs needs replacement.Check separator shell for leak and rectify,if required.
C) Oil level in air/oil receiver is too high.Correct the oil level as required,up to middle in visual indicator.
08) Engine Speed Low During Start Up:-
A) Battery improper.check electrolyte level and specific gravity and recharge.
B) Loose wiring connection.Inspect and tighten.
09) Compressor Rotates In Reverse Direction When Shutdown With Pressure In The Receiver:-
A) Discharge valve malfunctioning.remove discharge valve.Inspect and rectify.
B) Oil check valve malfunctioning.Dismantle the oil check valve and inspect and repair.
10) Safety Valve Blows:-
A) Controller not functioning.Check control filter,strainer.Clean and adjust rotation per minute.(RPM)
B) Unloader transformer adjusted at higher pressure,adjust to proper pressure setting.
C) Butterfly valve not closing properly.Inspect and take necessary action.
D) Safety valve defective.Inspect and adjust,if necessary replace.Safety valve is to be set at 10% higher pressure than the maximum unloading pressure.
Hope this will help to rectify problems of your diesel engine.
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Friday
How To Draw Valve Timing Diagram For Four Stroke Petrol Engine?
In petrol engine various strokes are performed to obtained the results from engine.By denoting the corresponding position of the piston attached to the crankshaftat which these strokes occurs,we can draw the exact moment in the sequence of events at which the valves are open and close.The graphical diagrams are known as valve timing diagram.The valve timing are modified to set better charging and exhausting performance as there is always a difference between theory and practical.
The diagram is drawn for two complete revolution of the crankshaft means for one complete cycle.
Following strokes are performed in four stroke petrol engine .
01)Suction Stroke:-
Piston starts moving from top dead centre resulting opening of inlet valve.The fresh charge of air-fuel mixture enters in cylinder.Piston moves further to bottom dead centre.
02)Compression Stroke:-
Inlet and exhaust valves are in close position and piston starts moving upward from bottom dead centre to top dead centre there by compression of charge took place.
03)Expansion Stroke:-
The ignition is started by spark plug just before the end of compression stroke.Both inlet and exhaust valves are still closed.A rapid explosion take place which is followed by expansion of hot gases pushing the piston to its bottom dead centre.In this stroke the useful work is obtained from the engine that is why ,it is also called as working stroke.
04)Exhaust Stroke:-
Piston starts moving upward from bottom dead centre resulting the burnt gases are pushed out through the exhaust valve till it reaches to top dead centre.Up to this point inlet valve remain closed.when the burnt gases totally exhausted to atmosphere, piston starts moving down,inlet valve opens,fresh charge is sucked and the cycle is again repeated as earlier.
Theoretically above cycle is well perfect but in actual practice,it is slightly modified by the opening of inlet valve and delayed closing of exhaust valve.The details are as below.
The inlet valve is opened 10 to 30 degree in advance to the top dead centre of the piston to facilitate the inrush of fresh charge and out rush of burnt gases.
The piston moves down during suction stroke which is continued up to 30 to 40 degree or even 60 degree after the bottom dead centre.The inlet valve is then closed and compression stroke starts.
To give some extra time to fuel to burn,the spark is produced at 30 to 40 degree before the top dead centre of piston.The pressure rises up and attains a maximum value when the piston is about 10 degree past to top dead centre.
The exhaust valve is open about 30 to 60 degree before piston reaches to bottom dead centre.The burnt exhaust gases pushed out of cylinder as the piston starts moving upward.This exhaust stroke continuous till the exhaust valve closed when the piston is about 8 to 10 degree or even 25 degree past the top dead centre.
The angle between the position of the crank at the inlet valve opening and that exhaust valve closing is known as valve overlap.
All this angular positions of crank can be plotted by a circular line corresponding to one vertical line;where top dead center can be taken at top of the line and bottom dead center at bottom of the vertical line.
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The diagram is drawn for two complete revolution of the crankshaft means for one complete cycle.
Following strokes are performed in four stroke petrol engine .
01)Suction Stroke:-
Piston starts moving from top dead centre resulting opening of inlet valve.The fresh charge of air-fuel mixture enters in cylinder.Piston moves further to bottom dead centre.
02)Compression Stroke:-
Inlet and exhaust valves are in close position and piston starts moving upward from bottom dead centre to top dead centre there by compression of charge took place.
03)Expansion Stroke:-
The ignition is started by spark plug just before the end of compression stroke.Both inlet and exhaust valves are still closed.A rapid explosion take place which is followed by expansion of hot gases pushing the piston to its bottom dead centre.In this stroke the useful work is obtained from the engine that is why ,it is also called as working stroke.
04)Exhaust Stroke:-
Piston starts moving upward from bottom dead centre resulting the burnt gases are pushed out through the exhaust valve till it reaches to top dead centre.Up to this point inlet valve remain closed.when the burnt gases totally exhausted to atmosphere, piston starts moving down,inlet valve opens,fresh charge is sucked and the cycle is again repeated as earlier.
Theoretically above cycle is well perfect but in actual practice,it is slightly modified by the opening of inlet valve and delayed closing of exhaust valve.The details are as below.
The inlet valve is opened 10 to 30 degree in advance to the top dead centre of the piston to facilitate the inrush of fresh charge and out rush of burnt gases.
The piston moves down during suction stroke which is continued up to 30 to 40 degree or even 60 degree after the bottom dead centre.The inlet valve is then closed and compression stroke starts.
To give some extra time to fuel to burn,the spark is produced at 30 to 40 degree before the top dead centre of piston.The pressure rises up and attains a maximum value when the piston is about 10 degree past to top dead centre.
The exhaust valve is open about 30 to 60 degree before piston reaches to bottom dead centre.The burnt exhaust gases pushed out of cylinder as the piston starts moving upward.This exhaust stroke continuous till the exhaust valve closed when the piston is about 8 to 10 degree or even 25 degree past the top dead centre.
The angle between the position of the crank at the inlet valve opening and that exhaust valve closing is known as valve overlap.
All this angular positions of crank can be plotted by a circular line corresponding to one vertical line;where top dead center can be taken at top of the line and bottom dead center at bottom of the vertical line.
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The Requirement Of Fuel Filter In Diesel Engine.
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Thursday
The Requirement Of Fuel Filter In Diesel Engine.
For smooth running of diesel engine every care must be taken right from fuel supply to maintenance of parts.The running life of engine is mostly depend up on the quality of fuel and lubrication .To obtain required quality of fuel some filters are used in diesel engine.The detail description is as below.
Dirt is dangerous for engine parts.it can be enter in the engine during suction stroke along with fuel and lubrication oil.To get rid of this unwanted dirt,filters are used.A filter cleans Air, is known as air filter,fuel filter cleans the fuel and lubrication oil is filtered by lubrication filter.
Various types of fuel filters are available to make the fuel oil free from dirt and other foreign material to suit varying conditions of operations.They included paper element,cloth element,felt element and combination of cloth and felt element.
Basically there are two types of fuel filters,
01)Preliminary Fuel filter:-
This type of filter is fitted in between fuel tank and fuel feed pump.This filter consists of a single bowl,in which a perforated tube is fitted centrally.The perforated centre tube is surrounded annular by a filter element.a gasket is placed at top of the bowl,to check against any leakage of fuel.
Due to suction created by the fuel feed pump,the fuel from fuel tank is sucked through the filter element,dropping the impurities and enter into the centre perforated tube from where it is drawn out by feed pump.
The dirt and other impurities left by the fuel at filter element collect at the bottom of the bowl from where these are removed out frequently,through drain plug fitted at the bottom of the bowl.
02)Secondary Fuel Filter:-
In dual (Two Stage) secondary filter two numbers of filter elements are employed.One having ordinary filter element and other having fine filter element.Each filter unit is supported by central bolt,known as filter element carrier.
Drain plugs are provided to remove the impurities which collects at the bottom of bowl.
The fuel enters the first filter unit (Ordinary Filter Element) where it drops large dust particles at the element,then this fuel flows out centrally.This filtered fuel is enters the next stage (Fine Filter Element) where even the finest particles of dirt etc are separated from it.Then this purified fuel flows to the feed pump.An air vent screw is provided at the top of the filter for air venting.
So,take care of engine fuel and enjoy long life of your vehicle.
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The Details About Fuel Atomiser Used In Diesel Engine.
Construction And Working Of Fuel Injection Pump.
Important Components Of Fuel Injection System For Diesel Engine.
Dirt is dangerous for engine parts.it can be enter in the engine during suction stroke along with fuel and lubrication oil.To get rid of this unwanted dirt,filters are used.A filter cleans Air, is known as air filter,fuel filter cleans the fuel and lubrication oil is filtered by lubrication filter.
Various types of fuel filters are available to make the fuel oil free from dirt and other foreign material to suit varying conditions of operations.They included paper element,cloth element,felt element and combination of cloth and felt element.
Basically there are two types of fuel filters,
01)Preliminary Fuel filter:-
This type of filter is fitted in between fuel tank and fuel feed pump.This filter consists of a single bowl,in which a perforated tube is fitted centrally.The perforated centre tube is surrounded annular by a filter element.a gasket is placed at top of the bowl,to check against any leakage of fuel.
Due to suction created by the fuel feed pump,the fuel from fuel tank is sucked through the filter element,dropping the impurities and enter into the centre perforated tube from where it is drawn out by feed pump.
The dirt and other impurities left by the fuel at filter element collect at the bottom of the bowl from where these are removed out frequently,through drain plug fitted at the bottom of the bowl.
02)Secondary Fuel Filter:-
In dual (Two Stage) secondary filter two numbers of filter elements are employed.One having ordinary filter element and other having fine filter element.Each filter unit is supported by central bolt,known as filter element carrier.
Drain plugs are provided to remove the impurities which collects at the bottom of bowl.
The fuel enters the first filter unit (Ordinary Filter Element) where it drops large dust particles at the element,then this fuel flows out centrally.This filtered fuel is enters the next stage (Fine Filter Element) where even the finest particles of dirt etc are separated from it.Then this purified fuel flows to the feed pump.An air vent screw is provided at the top of the filter for air venting.
So,take care of engine fuel and enjoy long life of your vehicle.
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The Details About Fuel Atomiser Used In Diesel Engine.
Construction And Working Of Fuel Injection Pump.
Important Components Of Fuel Injection System For Diesel Engine.
Wednesday
The Details About Fuel Atomiser Used In Diesel Engine.
The purpose of fuel atomiser in diesel engine is to atomise or break the fuel oil into fine particles and to direct the spray into the combustion chamber so that every fuel particle mixes with the air.This purpose is some what like carburettor used in petrol engine,where petrol is break in fine particle and mixes with air.
The fuel atomiser have following important parts,
01)Passage
02)Nozzle Valve
03)Nozzle
04)Nozzle Body
05)Adjusting Screw
06)Feeling Pin
07)Cap Nut
08)Spindle
09)Spring
10)Spring Cap Nut
Working Of Fuel Atomiser:-
The pressure of the fuel,supplied from fuel feed pump through the fuel passages lifts the nozzle valve.The fuel passes down to the nozzle and injected into cylinder (Combustion Chamber) in the form of a very fine spray.
When the fuel pressure drops,the nozzle valve moves down under the force of the spring and rests on its seat,closing the nozzle inlet to the passage,thus the fuel supply is cut off.
Any fuel leaked past the plunger of nozzle valve is sent back to the fuel tank through return passage.The adjusting screw enables the tension in the spring,to be adjusted.Whether the valve is working properly or not can be checked with the help of feeling pin.
To obtain various types of fuel spray,there are numerous types of injection nozzles are used.
Single hole nozzle,Conical ended single hole nozzle have just one hole,through which the fuel is sprayed.In order to achieve greater penetration of the fuel spray,the multiple hole nozzles are quite useful.Somewhere long stem nozzles are also in use.The pintle nozzle,which is used in engines employing swirl or precombustion chamber,where the fuel is not required to penetrate the Air .The stem of the valve is extended to form a pintle protruding through the mouth of the nozzle body.Such nozzles are tend to give hallow conical spray varies from 40 to 60 degree,depending up on the type of the pintle.The delay nozzle is similar in action to the pintle nozzle except that the rate of fuel injection increase towards the end of the delivery.
Due to the reduce quantity of fuel sprayed in the beginning of the combustion there are reduced chances of diesel knocks.An injection nozzle should be mounted in such a manner that it is not subjected to intense heat.
The details about fuel filter will covered in next post.
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The fuel atomiser have following important parts,
01)Passage
02)Nozzle Valve
03)Nozzle
04)Nozzle Body
05)Adjusting Screw
06)Feeling Pin
07)Cap Nut
08)Spindle
09)Spring
10)Spring Cap Nut
Working Of Fuel Atomiser:-
The pressure of the fuel,supplied from fuel feed pump through the fuel passages lifts the nozzle valve.The fuel passes down to the nozzle and injected into cylinder (Combustion Chamber) in the form of a very fine spray.
When the fuel pressure drops,the nozzle valve moves down under the force of the spring and rests on its seat,closing the nozzle inlet to the passage,thus the fuel supply is cut off.
Any fuel leaked past the plunger of nozzle valve is sent back to the fuel tank through return passage.The adjusting screw enables the tension in the spring,to be adjusted.Whether the valve is working properly or not can be checked with the help of feeling pin.
To obtain various types of fuel spray,there are numerous types of injection nozzles are used.
Single hole nozzle,Conical ended single hole nozzle have just one hole,through which the fuel is sprayed.In order to achieve greater penetration of the fuel spray,the multiple hole nozzles are quite useful.Somewhere long stem nozzles are also in use.The pintle nozzle,which is used in engines employing swirl or precombustion chamber,where the fuel is not required to penetrate the Air .The stem of the valve is extended to form a pintle protruding through the mouth of the nozzle body.Such nozzles are tend to give hallow conical spray varies from 40 to 60 degree,depending up on the type of the pintle.The delay nozzle is similar in action to the pintle nozzle except that the rate of fuel injection increase towards the end of the delivery.
Due to the reduce quantity of fuel sprayed in the beginning of the combustion there are reduced chances of diesel knocks.An injection nozzle should be mounted in such a manner that it is not subjected to intense heat.
The details about fuel filter will covered in next post.
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Construction And Working Of Fuel Injection Pump.
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Tuesday
Construction And Working Of Fuel Injection Pump.
This is another important part of fuel injection pump system in diesel engine.It is used in the individual system of a solid injection and consist of a plunger driven by a cam and tappet mechanism at the bottom.The plunger reciprocates in the barrel.The quantity of plunger varies with the number of cylinder in the engine.The plunger has a rectangular vertical groove which extends from the top to another helical groove.The delivery valve can be lifted off its seat under the pressure of liquid fuel and against the force of the spring.The passage is connected to the fuel atomiser.
When the plunger is at the bottom of its stroke and supply as well as spill ports are uncovered,oil from fuel feed pump,after filtration is forced into the barrel.The supply and the spill port are sealed at certain stage when the plunger is pushed away with the help of cam and tappet mechanism which is provided at bottom.
During the further movement of plunger the fuel above it gets compressed and the high pressure developed,lifts the delivery valve off its seat and fuel starts flowing through the passage to the atomiser.As the plunger rises up still further,at a particular moment the helical groove connects the spill port through the rectangular vertical groove,to the fuel in the upper part of the plunger.
Consequently there is a sudden pressure drop due to which the delivery valve falls back on its seat under the force of spring.This increases the volumetric capacity of the delivery system resulting in sudden pressure drop in the delivery pipe.Thus the discharge from nozzle of the injector is cut off suddenly and the fuel is prevented from dribbling into the cylinder even after the injection ceases.The cycle is repeated frequently.
During each stroke of plunger,the duration of the delivery is more or less,according to the spill port is made to communicate,earlier or later,with the high pressure fuel in the upper part of the barrel.This depends up on the position of the helical groove which can be changed by rotating the plunger with help of rack.
When engine at full load,the position of the helical groove on the plunger is kept below the passage.At partial load or normal delivery,the plunger is rotate to a position near by passage,in which the delivery takes place for shorter period.When the engine is stopped,the plunger is rotate to the position where helical groove is opposite to the passage,in which rectangular slot is in line with the spill port.There is no pressure built up above the top of the plunger,the delivery valve is not at all lifted and hence no delivery of fuel to the atomiser takes place.
The bore of the pump ranges in eight sizes from 5 mm to 10 mm but the stroke of the plunger is standardised at 9 mm.
I hope,with this details you can open and see the actual fuel injection pump without any doubt.
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When the plunger is at the bottom of its stroke and supply as well as spill ports are uncovered,oil from fuel feed pump,after filtration is forced into the barrel.The supply and the spill port are sealed at certain stage when the plunger is pushed away with the help of cam and tappet mechanism which is provided at bottom.
During the further movement of plunger the fuel above it gets compressed and the high pressure developed,lifts the delivery valve off its seat and fuel starts flowing through the passage to the atomiser.As the plunger rises up still further,at a particular moment the helical groove connects the spill port through the rectangular vertical groove,to the fuel in the upper part of the plunger.
Consequently there is a sudden pressure drop due to which the delivery valve falls back on its seat under the force of spring.This increases the volumetric capacity of the delivery system resulting in sudden pressure drop in the delivery pipe.Thus the discharge from nozzle of the injector is cut off suddenly and the fuel is prevented from dribbling into the cylinder even after the injection ceases.The cycle is repeated frequently.
During each stroke of plunger,the duration of the delivery is more or less,according to the spill port is made to communicate,earlier or later,with the high pressure fuel in the upper part of the barrel.This depends up on the position of the helical groove which can be changed by rotating the plunger with help of rack.
When engine at full load,the position of the helical groove on the plunger is kept below the passage.At partial load or normal delivery,the plunger is rotate to a position near by passage,in which the delivery takes place for shorter period.When the engine is stopped,the plunger is rotate to the position where helical groove is opposite to the passage,in which rectangular slot is in line with the spill port.There is no pressure built up above the top of the plunger,the delivery valve is not at all lifted and hence no delivery of fuel to the atomiser takes place.
The bore of the pump ranges in eight sizes from 5 mm to 10 mm but the stroke of the plunger is standardised at 9 mm.
I hope,with this details you can open and see the actual fuel injection pump without any doubt.
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Important Components Of Fuel Injection System For Diesel Engine.
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Monday
Important Components Of Fuel Injection System For Diesel Engine.
In my previous post, "How Fuel Is Supplied In Diesel Engine? " you can find brief description about fuel supply methods.In this post,I will cover the important components of fuel injection system of diesel engine.The fuel injection system has contains following important components,
01)Fuel feed Pump
02)Fuel Injection pump
03)Fuel Atomiser and nozzles
04)Fuel Filters
Out of above parts,you will come to know in detail about Fuel Feed Pump.
Construction And Working Of Fuel Feed Pump:-
The fuel which is stored in fuel storage tank is taken to injection system through fuel filters.The fuel,either by gravity or by mechanical pressure is supplied to injection system.The fuel start flowing to the injection pump under gravity head as fuel tank is placed at a higher level than engine,in gravitation feed system.this type of arrangement is most suitable for stationary engines.
In mechanical pressure system,the fuel is sucked from the fuel tank by a mechanically operated fuel feed pump and is forced to the fuel injection pump.In this case,fuel tank is placed away from engine or at lower level than the engine.This system is most useful for automobiles using diesel as fuel.The fuel placed away from the hot engine,avoids the chances of fire hazards.
The single acting fuel feed pump contains following parts
01)Pressure Chamber
02)Plunger
03)Stuffing Box
04)Cam
05)Roller Tappet
06)Leakage Channel
07)Inlet & Outlet
08)Suction Valve
09)Plunger spring
10)Pressure Valve
A plunger arrangement is fitted in pressure chamber.The plunger is activated downward by a cam through roller tappet and plunger rod.On the opposite side of plunger,a plunger spring is employed by which the return stroke of plunger is performed.The fuel is led to the plunger space through suction valve and after getting compressed,the fuel moves out through pressure valve into the pressure chamber from where it goes to the filter and then to the fuel injection pump.To avoid the wastage of fuel,a leakage channel is provided,which collects heated fuel from the stuffing box and feeds it again to the inlet pipe.
During the upward stroke of plunger suction is created in plunger space and fuel is sucked in,through suction valve.During the downward stroke,caused by cam arrangement,the fuel below the plunger is compressed ,which forces suction valve to close and pressure valve (Outlet valve) to open.The fuel thus flows out under pressure1 kilogram per centimeter square into the pressure chamber.
The construction and working of fuel feed pump is so easy that anyone can understand it easily.
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01)Fuel feed Pump
02)Fuel Injection pump
03)Fuel Atomiser and nozzles
04)Fuel Filters
Out of above parts,you will come to know in detail about Fuel Feed Pump.
Construction And Working Of Fuel Feed Pump:-
The fuel which is stored in fuel storage tank is taken to injection system through fuel filters.The fuel,either by gravity or by mechanical pressure is supplied to injection system.The fuel start flowing to the injection pump under gravity head as fuel tank is placed at a higher level than engine,in gravitation feed system.this type of arrangement is most suitable for stationary engines.
In mechanical pressure system,the fuel is sucked from the fuel tank by a mechanically operated fuel feed pump and is forced to the fuel injection pump.In this case,fuel tank is placed away from engine or at lower level than the engine.This system is most useful for automobiles using diesel as fuel.The fuel placed away from the hot engine,avoids the chances of fire hazards.
The single acting fuel feed pump contains following parts
01)Pressure Chamber
02)Plunger
03)Stuffing Box
04)Cam
05)Roller Tappet
06)Leakage Channel
07)Inlet & Outlet
08)Suction Valve
09)Plunger spring
10)Pressure Valve
A plunger arrangement is fitted in pressure chamber.The plunger is activated downward by a cam through roller tappet and plunger rod.On the opposite side of plunger,a plunger spring is employed by which the return stroke of plunger is performed.The fuel is led to the plunger space through suction valve and after getting compressed,the fuel moves out through pressure valve into the pressure chamber from where it goes to the filter and then to the fuel injection pump.To avoid the wastage of fuel,a leakage channel is provided,which collects heated fuel from the stuffing box and feeds it again to the inlet pipe.
During the upward stroke of plunger suction is created in plunger space and fuel is sucked in,through suction valve.During the downward stroke,caused by cam arrangement,the fuel below the plunger is compressed ,which forces suction valve to close and pressure valve (Outlet valve) to open.The fuel thus flows out under pressure1 kilogram per centimeter square into the pressure chamber.
The construction and working of fuel feed pump is so easy that anyone can understand it easily.
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Sunday
How Fuel Is Supplied In Diesel Engine?
You know from my previous posts that,in a petrol engine ,a carburettor is used to mix air and fuel in the required ratio and this mixture is drawn into the engine cylinder by suction stroke.
But in Diesel Engine,which is working on constant pressure cycle,the fuel has to be supplied when the air inside the cylinder is compressed to a very high pressure.Therefore the fuel must be injected at a high pressure than that developed in the cylinder at the end of compression stroke.
Only air is compressed to a pressure of about 35 kilogram per centimeter square and the temperature after this compression is reach near to 600 degree centigrade.
The fuel sprayed into this compressed air must be uniformly distributed so that enough Oxygen in the air is available to every particle of fuel for complete combustion.The distribution of the fuel is also assisted by turbulence of air which can be brought about by properly designed inlet ports,the top of the piston and the combustion chamber.Due to which there is considerable relative motion between the fuel and the air,which leads to a proper mixing.
The time for which the fuel is injected into the engine cylinder must be very small,since high injection velocities give a good atomization of fuel and the fuel has to be burnt at top dead centre position of the piston.
In compression ignition engine (diesel engine),a pressure as high as 100 to 300 kilogram per centimeter square are required to be developed for fuel injection systems.
The main advantage of diesel engine is,the maintenance cost of fuel injection equipments are less than that those of the carburettor and spark plug of petrol engine.
Requirements Of Fuel Injection System:-
The fuel injection system in diesel engine must satisfy the below requirements,
01) At beginning as well as the end of injection of fuel should take place sharply.
02) The injection of fuel must occur at the correct moment,correct rate and in correct quantity as required by the various load conditions of engines.
03) The fuel must be injected in a fine atomised condition and must be distributed uniformly in the combustion chamber of engine.
Methods Of Fuel Injection:-
01)Air Blast Injection:-
In this,air is compressed to a very high pressure by means of compressor and the blast of air the injected carrying fuel along with it into the cylinder.This method is obsolete now.
02)Solid Injection:-
In this,the fuel under pressure is directly injected into the combustion chamber in atomised state.It requires pump to deliver the fuel at very high pressure and used in all big and small diesel engines.This system is also subdivided in,
a) Individual Pump System:-
In this system,each cylinder has its own individual high pressure pump and metering unit.The cost of this system is very high.
b) Common Rail System:-
In this system,the fuel is pumped by multi-cylinder pump into a common rail,the pressure in which is controlled by a relief valve.A metered quantity of fuel is supplied to each cylinder from the rail.It requires higher accuracy during manufacturing.
I hope,this will help you to understand about the fuel supply of your diesel engine.
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But in Diesel Engine,which is working on constant pressure cycle,the fuel has to be supplied when the air inside the cylinder is compressed to a very high pressure.Therefore the fuel must be injected at a high pressure than that developed in the cylinder at the end of compression stroke.
Only air is compressed to a pressure of about 35 kilogram per centimeter square and the temperature after this compression is reach near to 600 degree centigrade.
The fuel sprayed into this compressed air must be uniformly distributed so that enough Oxygen in the air is available to every particle of fuel for complete combustion.The distribution of the fuel is also assisted by turbulence of air which can be brought about by properly designed inlet ports,the top of the piston and the combustion chamber.Due to which there is considerable relative motion between the fuel and the air,which leads to a proper mixing.
The time for which the fuel is injected into the engine cylinder must be very small,since high injection velocities give a good atomization of fuel and the fuel has to be burnt at top dead centre position of the piston.
In compression ignition engine (diesel engine),a pressure as high as 100 to 300 kilogram per centimeter square are required to be developed for fuel injection systems.
The main advantage of diesel engine is,the maintenance cost of fuel injection equipments are less than that those of the carburettor and spark plug of petrol engine.
Requirements Of Fuel Injection System:-
The fuel injection system in diesel engine must satisfy the below requirements,
01) At beginning as well as the end of injection of fuel should take place sharply.
02) The injection of fuel must occur at the correct moment,correct rate and in correct quantity as required by the various load conditions of engines.
03) The fuel must be injected in a fine atomised condition and must be distributed uniformly in the combustion chamber of engine.
Methods Of Fuel Injection:-
01)Air Blast Injection:-
In this,air is compressed to a very high pressure by means of compressor and the blast of air the injected carrying fuel along with it into the cylinder.This method is obsolete now.
02)Solid Injection:-
In this,the fuel under pressure is directly injected into the combustion chamber in atomised state.It requires pump to deliver the fuel at very high pressure and used in all big and small diesel engines.This system is also subdivided in,
a) Individual Pump System:-
In this system,each cylinder has its own individual high pressure pump and metering unit.The cost of this system is very high.
b) Common Rail System:-
In this system,the fuel is pumped by multi-cylinder pump into a common rail,the pressure in which is controlled by a relief valve.A metered quantity of fuel is supplied to each cylinder from the rail.It requires higher accuracy during manufacturing.
I hope,this will help you to understand about the fuel supply of your diesel engine.
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Saturday
Construction And Working Of Amal Carburettor.
A carburettor is a device used in petrol or similar liquid fuel engines by means of which the fuel mixed with air,is supplied into the induction manifold of the engine.The main object of the carburettor is to supply the required quantity of fuel and Air mixture of the correct strength as dedicated by the load condition of the engine.
There are three important types of carburettor available in market,
01)Zenith Carburettor
02)Solex Carburettor
03)Amal Carburettor
The details about Zenith and Solex Carburettor was covered in earlier posts.In this post,you will find details about Amal Carburettor.
An Amal carburettor is used in small petrol engines which drives motor cycles and scooters.This carburettor is capable of maintaining a uniform mixture strength throughout the throttle opening range.This is done by means of a tapered needle,adjustably attached to the throttle valve.
Construction Of Amal Carburettor:-
This carburettor has following main parts,
01) Carburettor Body
02) Throttle Valve
03) tapered Needle
04) Throttle Valve Operating Cable
05) Main Jet
06) Pilot Jet
07) Chamber For Pilot Outlet And By-pass
08) Auxiliary Air Intake
09) Pilot Outlet
10) By-pass Outlet
11) Float Chamber
12) Jet Block
13) Float
14) Needle Valve
15) Air Valve
16) Air Valve Operating Cable
A throttle valve is fitted in carburettor body,to which a tapered needle is attached.The combination of throttle valve and tapered needle is operated by means of operating cable.To set the air-fuel ratio,the position of this tapered needle can be adjusted with respect to the throttle valve.The tapered end of the needle,regulates the area of passage in the main jet,supplies fuel to a chamber who has pilot outlet and by-pass outlet.An adjustable auxiliary air intake is also supply air to this chamber.The pilot outlet and by-pass are situated in front and back side of the throttle valve respectively.
The float chamber is connected with jet block,which contains,main and pilot jet.The float governs the level of fuel in float chamber.The float chamber receives petrol from the oil tank through needle valve,attached to the float with the help of clip.The air valve,which can be operated independently by an operating cable,to obstruct the main air passage.An adjusting screw is provided on the wall of carburettor body,by which the position of the throttle valve can be preset independent of operating cable adjustment for idling purpose.
Working Of Amal Carburettor:-
The throttle valve remain closed at starting of engine.The engine draws the mixture of air-fuel through pilot outlet.This mixture carries excess fuel,such mixture is not desirable for normal running of the engine ,therefore,the throttle valve is to be slightly raised for admitting supply of air from the main air passage.
The more the throttle valve opened,the less will be the depression on the pilot outlet,but a higher depression will be created on the by-pass and now the mixture flows from this by-pass as well as pilot outlet to compensate for accelerating period.
The function of air valve to obstruct the main air passage at the time of the start which results in enriching the mixture by increasing depression of the main jet.
The mixture provided by the pilot outlet and by-pass system,is supplemented by the fuel from the main jet approximately at 13% of the throttle valve opening.After the 75% of the opening of the throttle,the main jet only provides the fuel regulation.
At the time of idling,the throttle stop screw provides a definite throttle opening for idling purpose.
By this way,air-fuel mixture is supplied to the engine cylinder of motor cycle at various operating conditions.
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There are three important types of carburettor available in market,
01)Zenith Carburettor
02)Solex Carburettor
03)Amal Carburettor
The details about Zenith and Solex Carburettor was covered in earlier posts.In this post,you will find details about Amal Carburettor.
An Amal carburettor is used in small petrol engines which drives motor cycles and scooters.This carburettor is capable of maintaining a uniform mixture strength throughout the throttle opening range.This is done by means of a tapered needle,adjustably attached to the throttle valve.
Construction Of Amal Carburettor:-
This carburettor has following main parts,
01) Carburettor Body
02) Throttle Valve
03) tapered Needle
04) Throttle Valve Operating Cable
05) Main Jet
06) Pilot Jet
07) Chamber For Pilot Outlet And By-pass
08) Auxiliary Air Intake
09) Pilot Outlet
10) By-pass Outlet
11) Float Chamber
12) Jet Block
13) Float
14) Needle Valve
15) Air Valve
16) Air Valve Operating Cable
A throttle valve is fitted in carburettor body,to which a tapered needle is attached.The combination of throttle valve and tapered needle is operated by means of operating cable.To set the air-fuel ratio,the position of this tapered needle can be adjusted with respect to the throttle valve.The tapered end of the needle,regulates the area of passage in the main jet,supplies fuel to a chamber who has pilot outlet and by-pass outlet.An adjustable auxiliary air intake is also supply air to this chamber.The pilot outlet and by-pass are situated in front and back side of the throttle valve respectively.
The float chamber is connected with jet block,which contains,main and pilot jet.The float governs the level of fuel in float chamber.The float chamber receives petrol from the oil tank through needle valve,attached to the float with the help of clip.The air valve,which can be operated independently by an operating cable,to obstruct the main air passage.An adjusting screw is provided on the wall of carburettor body,by which the position of the throttle valve can be preset independent of operating cable adjustment for idling purpose.
Working Of Amal Carburettor:-
The throttle valve remain closed at starting of engine.The engine draws the mixture of air-fuel through pilot outlet.This mixture carries excess fuel,such mixture is not desirable for normal running of the engine ,therefore,the throttle valve is to be slightly raised for admitting supply of air from the main air passage.
The more the throttle valve opened,the less will be the depression on the pilot outlet,but a higher depression will be created on the by-pass and now the mixture flows from this by-pass as well as pilot outlet to compensate for accelerating period.
The function of air valve to obstruct the main air passage at the time of the start which results in enriching the mixture by increasing depression of the main jet.
The mixture provided by the pilot outlet and by-pass system,is supplemented by the fuel from the main jet approximately at 13% of the throttle valve opening.After the 75% of the opening of the throttle,the main jet only provides the fuel regulation.
At the time of idling,the throttle stop screw provides a definite throttle opening for idling purpose.
By this way,air-fuel mixture is supplied to the engine cylinder of motor cycle at various operating conditions.
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Various Circuits In Solex Carburettor.
In old days,Fiat cars are most popular brand in India due to its very easy start in cold conditions.This easy start is obtained by Solex Craburettor which is a down draft type carburettor and has special provisions to supply,richer mixture at starting of engine and weaken it gradually till the engine reaches its normal running speed.Solex carburettor are available in many design and all have following work circuits,
01) Starting Circuit:-
The throttle valve remains in closed position during starting.The petrol is supplied to the starter petrol jet through first passage from the float chamber and the air through the starter air jet for starting operation.
Starting Valve which have different sizes hole,is made from flat disc.The position of various holes can be adjusted in front of starter petrol jet by starter lever and then air is mixed coming from starter Air jet .This air-fuel mixture,passes through another holes of starter valve,in a passage of the carburettor,below the throttle valve.The suction stroke of the engine sucks this mixture into the cylinder.This mixture is rich enough to start the engine.
After the engine starts and speed increases,a weak mixture is required,therefore,a small hole of the starter valve is brought in front of the starter petrol jet by means of starter lever,there by reducing the quantity of petrol,which weaken the air-fuel mixture.Similarly next smaller hole of the starter valve is brought in front of starter petrol jet till the engine attains its normal speed then the starter valve is closed by bringing the starter lever to its off position.
02) Normal Running Circuit:-
At normal running speed,starting circuit is closed and throttle valve is opened.The normal running circuit consist of main jet which receives the petrol through second passage,from the float chamber as the throttle valve is opened sufficiently,the air is drawn through the venturi where the petrol mixes up with it forming a suitable mixture for the normal running of the engine.In this case,only throttle valve,governed the air-fuel ratio.
03) Accelerating Circuit:-
The engine requires an extra rich mixture,during acceleration period.To obtained extra rich mixture,the fuel is pumped under pressure into the main air passage or in the venturi through an injector.
Diaphragm pump is used to create pressure,which is actuated by a lever connected to the accelerator.The pump sucks the petrol from the float chamber through the pump valve and forces it through third passage into the main passage through an injector above the venturi of the carburettor.
04) Idling And Slow Running Circuit:-
During the idling operation,the throttle valve is kept closed and the engine receives the mixture through a port opening below the throttle valve,whose area can be varied by an idle adjusting screw according to the need of the engine.The petrol is supplied to a pilot petrol jet from the main jet fuel circuit through fourth passage and the air from a pilot air jet .The petrol and air thus supplied mix up in the idle passage and go to a port situated below the throttle valve from where the mixture is sucked by engine.
During the slow running,the engine draws the mixture from the idle passage through a hole situated above the throttle valve when the throttle valve is partially opened.
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01) Starting Circuit:-
The throttle valve remains in closed position during starting.The petrol is supplied to the starter petrol jet through first passage from the float chamber and the air through the starter air jet for starting operation.
Starting Valve which have different sizes hole,is made from flat disc.The position of various holes can be adjusted in front of starter petrol jet by starter lever and then air is mixed coming from starter Air jet .This air-fuel mixture,passes through another holes of starter valve,in a passage of the carburettor,below the throttle valve.The suction stroke of the engine sucks this mixture into the cylinder.This mixture is rich enough to start the engine.
After the engine starts and speed increases,a weak mixture is required,therefore,a small hole of the starter valve is brought in front of the starter petrol jet by means of starter lever,there by reducing the quantity of petrol,which weaken the air-fuel mixture.Similarly next smaller hole of the starter valve is brought in front of starter petrol jet till the engine attains its normal speed then the starter valve is closed by bringing the starter lever to its off position.
02) Normal Running Circuit:-
At normal running speed,starting circuit is closed and throttle valve is opened.The normal running circuit consist of main jet which receives the petrol through second passage,from the float chamber as the throttle valve is opened sufficiently,the air is drawn through the venturi where the petrol mixes up with it forming a suitable mixture for the normal running of the engine.In this case,only throttle valve,governed the air-fuel ratio.
03) Accelerating Circuit:-
The engine requires an extra rich mixture,during acceleration period.To obtained extra rich mixture,the fuel is pumped under pressure into the main air passage or in the venturi through an injector.
Diaphragm pump is used to create pressure,which is actuated by a lever connected to the accelerator.The pump sucks the petrol from the float chamber through the pump valve and forces it through third passage into the main passage through an injector above the venturi of the carburettor.
04) Idling And Slow Running Circuit:-
During the idling operation,the throttle valve is kept closed and the engine receives the mixture through a port opening below the throttle valve,whose area can be varied by an idle adjusting screw according to the need of the engine.The petrol is supplied to a pilot petrol jet from the main jet fuel circuit through fourth passage and the air from a pilot air jet .The petrol and air thus supplied mix up in the idle passage and go to a port situated below the throttle valve from where the mixture is sucked by engine.
During the slow running,the engine draws the mixture from the idle passage through a hole situated above the throttle valve when the throttle valve is partially opened.
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Friday
Construction And Working Of Zenith Carburettor.
A carburettor is a device used in petrol or similar liquid fuel engines by means of which the fuel mixed with Air ,is supplied into the induction manifold of the engine .The main object of the carburettor is to supply the required quantity of fuel and air mixture of the correct strength as dedicated by the load condition of the engine.
For this purpose different types of carburettors are available in the market.Out of that,you will find here the details of Zenith Carburettor,as below.
Zenith carburettor is also known as "British Carburettor" and used by various famous car manufacturer.This carburettor has also number of designs available for different purposes.
Construction And Working Of Zenith Carburettor:-
Construction:-In this,float chamber is supplied with fuel from the fuel tank through a pipe.Whenever the float chamber falls short of fuel,the fuel from the fuel tank flows into the chamber at a fastest speed than is consumed by the engine with the result that,the float rises up,till it reaches a certain level.At this time,a needle valve moves down and rest against the seat,resulting the stoppage of fuel supply from fuel tank.
The main jet is directly connected to the float chamber while the auxiliary jet which is also called as compensating jet draws fuel from auxiliary chamber (Reservoir).This auxiliary chamber is connected to the float chamber through an orifice.Both,main and auxiliary jet are opened up in the venturi.
The air to the carburettor is supplied through the passage.The throttle valve is located at the end of the carburettor and connected to the engine suction pipe.The opening and the closing of the throttle valve controls the quantity of air-fuel mixture supplied to the engine suction manifold.
An auxiliary nozzle from auxiliary chamber (Reservoir) is located at one end of the by-pass and the other end of this nozzle,opens up near the throttle valve.
Working At Starting And Low Speed Running:-
Because of lower Velocity of air at the time of starting or slow speed of the engine,the suction produced at the venturi is quite insufficient to operate the main and the auxiliary jet in nozzle.To improve the velocity of air,the throttle valve is closed to such an extent that there is only a small contracted passage is provided near the end of by-pass.By this,the velocity of air,passing through the region increases,producing the high suction,which operates the nozzle at auxiliary chamber and the air-fuel mixture supplied through the holes.
There is starting and slow running device is fitted in reservoir (Auxiliary Chamber).To vary the supply of air to the nozzle,the set screw given is slackened and whole assembly is taken out.By the suitable number of rotation of screw joint,the position of auxiliary nozzle is set.The whole device is then again fitted to the carburettor and tightened the screw.
Working At Normal Running:-
At this condition,the throttle valve is opened about 66% and as the air entering through the passage,passes through the venturi,its velocity increases due to smaller area consequently its pressure drops,resulting the suction effect.The fuel is sprayed in the venturi by main and auxiliary nozzle.As the speed of engine increases,there by producing the greater suction.Due to this,greater fuel being supplied by the main nozzle.Since the compensating jet (Auxiliary Jet) draws fuel from reservoir (Auxiliary Chamber),which is subjected to atmosphere pressure,through the air,the quantity of fuel supplied by it to the venturi does not change to an appreciable extent.This has the effect of supplying a weaker solution than if only one jet were provide in which case,the air-fuel mixture supplied at high speed will be richer then desired.
Thus the compensating jet enables the air-fuel mixture of the desirable strength to be supplied.In fact with correctly proportioned design of various parts of this carburettor,the fuel supplied by the main and compensating nozzle can be made to bear almost a constant ratio to the air supplied.
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For this purpose different types of carburettors are available in the market.Out of that,you will find here the details of Zenith Carburettor,as below.
Zenith carburettor is also known as "British Carburettor" and used by various famous car manufacturer.This carburettor has also number of designs available for different purposes.
Construction And Working Of Zenith Carburettor:-
Construction:-In this,float chamber is supplied with fuel from the fuel tank through a pipe.Whenever the float chamber falls short of fuel,the fuel from the fuel tank flows into the chamber at a fastest speed than is consumed by the engine with the result that,the float rises up,till it reaches a certain level.At this time,a needle valve moves down and rest against the seat,resulting the stoppage of fuel supply from fuel tank.
The main jet is directly connected to the float chamber while the auxiliary jet which is also called as compensating jet draws fuel from auxiliary chamber (Reservoir).This auxiliary chamber is connected to the float chamber through an orifice.Both,main and auxiliary jet are opened up in the venturi.
The air to the carburettor is supplied through the passage.The throttle valve is located at the end of the carburettor and connected to the engine suction pipe.The opening and the closing of the throttle valve controls the quantity of air-fuel mixture supplied to the engine suction manifold.
An auxiliary nozzle from auxiliary chamber (Reservoir) is located at one end of the by-pass and the other end of this nozzle,opens up near the throttle valve.
Working At Starting And Low Speed Running:-
Because of lower Velocity of air at the time of starting or slow speed of the engine,the suction produced at the venturi is quite insufficient to operate the main and the auxiliary jet in nozzle.To improve the velocity of air,the throttle valve is closed to such an extent that there is only a small contracted passage is provided near the end of by-pass.By this,the velocity of air,passing through the region increases,producing the high suction,which operates the nozzle at auxiliary chamber and the air-fuel mixture supplied through the holes.
There is starting and slow running device is fitted in reservoir (Auxiliary Chamber).To vary the supply of air to the nozzle,the set screw given is slackened and whole assembly is taken out.By the suitable number of rotation of screw joint,the position of auxiliary nozzle is set.The whole device is then again fitted to the carburettor and tightened the screw.
Working At Normal Running:-
At this condition,the throttle valve is opened about 66% and as the air entering through the passage,passes through the venturi,its velocity increases due to smaller area consequently its pressure drops,resulting the suction effect.The fuel is sprayed in the venturi by main and auxiliary nozzle.As the speed of engine increases,there by producing the greater suction.Due to this,greater fuel being supplied by the main nozzle.Since the compensating jet (Auxiliary Jet) draws fuel from reservoir (Auxiliary Chamber),which is subjected to atmosphere pressure,through the air,the quantity of fuel supplied by it to the venturi does not change to an appreciable extent.This has the effect of supplying a weaker solution than if only one jet were provide in which case,the air-fuel mixture supplied at high speed will be richer then desired.
Thus the compensating jet enables the air-fuel mixture of the desirable strength to be supplied.In fact with correctly proportioned design of various parts of this carburettor,the fuel supplied by the main and compensating nozzle can be made to bear almost a constant ratio to the air supplied.
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Different Types Of Compensation In Simple Carburettor.
Working Principle Of Simple Carburettor Used In Petrol Engine.
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