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Page 44
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Airv. water-cooled diesels
We will be most grateful for the opportunity to reply to the contents of your answer on air-cooled diesel engines in the {1 and A column of the October 15 issue of Commercial Motor. We would reply as follows:
-Your comments comparing the properties of air-cooled and water-cooled diesel engines is of interest to us and we would welcome the opportunity to amplify the case for the air-cooled c.i. engine.
Some notable advantages of the air-cooled engine include: a) Faster warm-up period.
b) Considerably less operation time in the "Dew" period from cold start, where the majority of the internal contamination (and thus wear) of the engine takesplace — as a result of (a).
c) Greater and more accurate control of combustion chamber temperatures, as well as general engine temperatures, is possible by sensitive thermostatic control of cooling fan, compared to -blanket" cooling effect of +dater and cylinder head flow thermostat in liquid-cooled system.
d) Engine running temperature maintained within close tolerances irrespective of wide variations in climatic and ambient temperature condition. ' No special cooling system equipment necessary for arctic or eouatorial use.
e) Resultant increase in thermal efficiency as a result of (c) and (d).
f) Favourable gains in specific fuel consumption.
g) Simplified engine layout with opportunity to install individual cylinders with real advantages in accessibility and repair technioues.
h) Lack of vulnerability — no freezing or boiling risk and virtually no cooling system maintenance required.
It is a known fact that inevitably the water-cooled engine is over-cooled for a sizeable amount of its operating time and of course theoretically and practically this is undesirable. For the former, the engine is not able to produce specified performance figures when not operating at optimum temperature and with reference to the latter the tendency for lubricant contamination is increased. An example of this comes to mind in the form of one modern high-speed diesel engine where, to avoid the effects of sludging, oil change periods of only 2000 miles are recommended. In practical terms, the loss of the coolant medium, whether it is water or air, can of course be disastrous to the engine and there is as much vulnerability with the water-cooled engine through gradual coolant loss, thermostat malfunction, or other technical
failure, as with the air-cooled engine. The reference to fan failure is less likely to occur with the air-cooled engine of the type manufactured by this company, as the cooling fan unit is of the hydraulic type driven from the lubrication system of the engine and therefore the vulnerable 'V' belt drive as used on the majority of water-cooled engines for cooling fan and water pump drive, is eliminated. Obviously, if the cooling fins of the engine are blocked, then this will upset the effectiveness of the cooling air flow but in practice this is less of a problem than the blocking of the fins in a water-cooled engine radiator and the incidence is very low indeed. While agreeing with the theory that a cooling water jacket assists in insulating engine noise it is our belief that development has reached such a stage with the air-cooled engine to claim that this is no longer the case. Probably the best proof of this would be to compare general noise factor of our 230 hp (DIN rating) with a similar capacity engine of the same performance.
If the correspondent preparing the thesis would care to contact us we would offer to provide any additional information or assistance he may need.
H. MUNDT. Technical Manager, Magirus Deutz (Great Britain) Ltd, Bentley Avenue, Stake Hill Estate, Middleton, Manchester M24 2RW