road and workshop
Page 50
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Benchwise: cool It
AMONG transport engineers one frequently hears the opinion expressed that skills and crafts are being lost and that too much is taken for granted. Some engineers believe that this is reflected by the way various forms of engine failure and other mechanical trouble are attributed to bad luck rather than to some operating or mechanical aspect which With a little more know-how would have been brought to light. There is a feeling that although trainees may grasp the workings of the parts in the time allocated for apprenticeship training, there may be no time to dwell on the special features that play such a big part in both operation and preventive maintenance.
Therefore, for the benefit of those who are learning the trade, and any others who may wish to brush up a little, I am going to have a look at engine cooling in this article. While this subject may appear simple enough, there is a lot more to it than may at first be thought.
With the internal combustion engine only about one-third of the fuel used produces useful work to turn the engine, the remaining two-thirds producing waste heat which must be dispelled, either through the engine or the exhaust.
The quantity of heat produced by any of our larger road transport engines could easily meet the winter heating demands of a school or town hall. The combustion temperature inside the engine can rise t6 around 4000deg F, and exhaust systems are able only to handle half of the waste heat generated. Other beat which spreads around the engine block, must be drawn off as fast as it is generated and before the lubricating qualities of the oil can be destroyed.
Water jackets This surplus .heat must be handled by a cooling system in one form or another, and while motorcycles and auxiliary engin successfully cope with the problem t ample finning and air cooling, the heavi engines in the main must rely upon liqu cooling via water jackets, radiators, fa] and circulating pumps.
Obviously, the liquid-cooled engine designed with ample passages around i hottest parts, that is the combustic chamber areas, and it is the water in the jackets that receives the first heat when tl engine is started. Although there is a natur action by the heated water to start movement away from the source of heat, is necessary to ensure that the right amou of coolant is on the move from the heat cylinders up to the radiator, where it is sp into small particles in passing down tl radiator core and cooled by the air rnovit through the radiator and usually aided by fan. It may be a little hard for the trainee appreciate that on the larger engines it necessary to have the water circulatir through the engine block at between 50( and 10,000 gallons an hour to dispose of tl heat generated at full-power on motorwt. running.
2000deg F
It must be remembered that in al around the combustion section it is very h indeed. In fact, an exhaust valve can operating at around 2000deg F, which near yellow-red heat, and water jacketing around the valve seat is needed to safegua it from heat transfer.
As a start in this article I have be content to take rather an elementary look cooling but it is as well to understand t size of the demand upon a cooling systei and that the margins between satisfacto operation and engine breakdown are ye narrow ones. I will go into these matters another article.