a I am preparing a thesis on air-cooled
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diesel engines and have obtained details of units, including Magirus Deutz, that are in current production. What is your opinion of the future of the air-cooled diesel?
AAdvantages of a water-cooled engine
include a greater reserve of cooling capacity than an air-cooled counterpart. While.all water-cooled engines are designed to operate without boiling of the coolant, it can
result from a fault in the cooling system such as a partial blockage of the water passages, and well-maintained vehicles operating in dusty conditions in a tropical climate may be -close to boiling" for much of their life.
When water boils a greatly increased amount of heat is extracted from the metal surface, compared with that removed by the circulation of water in the normal way, by virtue of the latent heat of evaporation of the liquid. If the water that is boiled away is replaced by a constant supply of fresh water, a high rate of heat extraction is maintained. Moreover, the steam that is produced may well be condensed before it reaches the header tank and wastage of water is thereby avoided. This reserve of cooling capacity is obviously of special importance in the case of a highly rated engine in which cylinder temperatures are higher than those of a unit with a lower rating.
In a well-designed air-cooled engine, the rate of air flow and the way in which air is distributed over the surface of the fins of the cylinder head and cylinder block provide adequate cooling and cooling is reasonably uniform. But if fan power is reduced because of a fault in the system or the surface of the fins is contaminated with dirt or oil, severe overheating is more likely than would be the case with a water-cooled unit of similar capacity and output that developed a cooling system fault.
It is probably fair to say that development of air-cooled diesel engines has lagged behind that of water-cooled units because the reserve cooling capacity of the latter is a valuable safety factor. And uprating diesels by turbocharging and other means has helped to maintain the ascendancy of the water-cooled diesel. Moreover water jacketing reduces the noise that is radiated by an engine.
Air cooling has obvious advantages and on the side of the air-cooled diesel the claim may be justified that the majority of diesel engines on the market would have been of an advanced air-cooled type if there had been greater expenditure on research and development. The success of the relatively few aircooled automotive and industrial engines on the market gives substance to the claim.