New Type of 'Mixed' Engine Being Developed
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SSOM E details of a new type combustion engine were given by Dr.-Ing. Siegfried Meurer of MAN, Germany, at a Press conference in Munich last week. The name given to the engine is the FM and it was explained that the unit is neither a true compressionignition engine nor a true spark-ignition engine, but has some of the features of each type.
The engine is still at the development stage and was said to be the result of work on multi-fuel engines. The name FM is derived from '' Fremdgezfindetes M-Verfahren ". which means the M-cornbustion system (as used by MAN on diesels) with applied ignition. The illustration shows the redesigned combustion chamber, which uses a special sparking plug located opposite the injector. A small quantity of fuel from the film on the combustion-chamber wall is directed of internal to the plug by a 90° groove. The fuel ignited by the sparking plug ignites the fuel injected into the chamber.
in working on multi-fuel engines, Dr. Meurer said, it was found that petrols with very high thermal efficiencies could not be burnt in petrol engines. Similarly, the limits of a former multi-fuel engine were that it could not utilize petrols with indefinitely high octane ratings requiring compression ratios of up to 25 to 1. The MAN M-combustion system was capable, said Dr. Meurer, of burning petrol without " knocking " because of its special fuel-mixing features. Injection takes place just before combustion and the fuel is deposited in an effective manner as a thin film into the combustion-chamber walls by an air swirl. irrespective of the quantity of the injected fuel, a thin "fuelmixture zone" is created alongside the combustion-chamber wall. This mixture is not dependent upon the available air in the combustion chamber so far as its mixing ration is concerned.
For Optimum Efficiency Because even the highest compression ratios do not allow the correct timing of self ignition with high-octane petrols, pure compression ignition could not be employed if the engine was to be entirely independent of octane numbers. So spark ignition had to be applied, which allowed the compression ratio to be reduced to a degree that permitted*the optimum thermal efficiency to be achieved. With the FM system the compression ratio can range from 14 to 17 to I.
Fuel-consumption tests had shown, he said, that the economy when using 100 octane petrol was little different from that when using diesel fuel. And an important point was that where a petrol engine would emit 4 to 10 per cent of carbon monoxide in its exhaust, the FM engine put out only 0-12 per cent and under full load the figure was as low as 0.065 per cent. Similar reductions were said to be achieved in respect of the emission of unburnt hydrocarbons and nitric oxides whilst the level of soot formation in the exhaust was said to be only slightly higher than that in petrol engines and distinctly
lower than in diesels. • A.J.W.