To pass some of the heat generated due to combustion in the cylinder of internal combustion engine, air-cooling or water-cooling methods are used. The Details about air-cooling were covered in previous post (Air Cooling Of Internal Combustion Engine.). In this post you will find some more methods of water-cooling.
In water-cooling method, the advantage of superior convective and conductive properties of water is used. Water is circulated continuously through the Cylinder with an annular space known as Water Jacket. To avoid unequal expansion in the cylinder bore and burning of lubricating oil, the water jackets are so designed that they will cover the entire length of piston stroke.
For the cleaning of water jackets in large cylinders, cleaning doors are provided. This method is also employed in large reciprocating air compressor where we have to add cooling tower in addition to cool the circulating water.
Water Cooling can be done by any of the following methods,
01) Direct Method:-
In this method, water from a storage tank is directly supplied through an inlet valve to the engine cylinder. The hot water is simply discharged and not cooled for reuse. It is suitable for large industrial units and where plenty of water is easily available.
02) Thermosyphon Method:-
In this method, hot water from engine cylinder flows towards radiator, which has comparatively cold water, and get cool down.
In order to ensure that the coolest water is always made available to the water jackets the latter should be located at as low a level as possible with respect To the radiator.
This system is useful due its simplicity and automatic operation, but there is disadvantage of water freezing in cold weather condition. We have to use large Quantity of water, as there is slow rate of circulation observed.
03) Impeller Thermosyphon Method:-
Here the flow of water takes place by convection assisted by a pump. The latter is made non-positive type, which even when stationary; allows the flow of water to take place. Thus when the working of pump fails water can still circulate on the thermosyphon system.
In its simplest form, water flow from radiator to engine and back to radiator. A thermostat is employed in system, which prevents the flow of water below a certain temperature, from the engine to the radiator. This we have to do to acquire some of the temperature at starting of the engine.
This system has three major parts, (The details about this parts will be covered in coming post.)
02) Fan and Pump
04) Full Pump Circulation Method:-
In this method, a positive supply of water by a centrifugal pump placed in the system. This system works on higher Velocity of circulating water due to which less quantity of water is required hence we can use smaller radiator.
In some designs the piston is cooled by oil squirted against the piston crown underside through a nozzle located in the connecting rod small end.
05) Evaporative Cooling Method:-
In this method, the engine may be cooled by evaporating the water in the cylinder jackets, into the steam, which absorbs Large quantity of heat and raise to the top of the engine from where it flows into a tank at the bottom of the radiator and then flows upwards and gets Condensed before reaching the top.
Due to large quantity of latent heat absorbed during evaporation of water into steam the weight of the circulating water is only 40% of that in other water Cooling methods. Hence smaller radiator can be employed.
This system is quite useful where plenty of water is not available. The higher running temperature no doubt reduces the friction in the piston but the volumetric efficiency is reduced and the engine is also liable to detonate.
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