Scaling down the conventional four stroke diesel engine to arrive at the small efficient engine needed for the economic automotive market, presents limitations, which are fundamentally better overcome by the two stroke diesel.
As design consultants specialising in the opposed piston two stroke diesel, Armstrong Whitworth have many years of experience studying and developing small high speed diesel engines.
In the truck sizes the two stroke has had many successes, General Motors in the U.S.A. and the three litre Tilling Steven opposed piston engine in the U.K. are examples. To meet the ever increasing demands on emissions and noise, however, the two stroke diesel has inherent limitations which have held back its use for the automotive application.
The initial objectives of the Armstrong Whitworth Swing Beam Engine were directed towards overcoming these limitations. This engine layout was designed to create a low noise structure, arising from a balanced linkage system, other advantages of easy start and the potential use of low grade fuel derive from its variable compression ratio and slow piston motion near inner dead centre. Test results so far show that it has the potential for more advanced development.
The developments in the application of ceramics to diesel engines could be a major advance for the small high output diesel engine. They are also seen as a possible major breakthrough for the opposed piston engine in two aspects - firstly because only the piston and liner will need making in ceramics - the absence of the cylinder head eliminates the difficult valve plate and port passage of the four stroke; secondly the potential to run without piston lubrication eliminates the problem of loss of oil in the ported liner.
Low piston side thrust forces of the Swing Beam engine will benefit the unlubricated ceramic liner and also lends itself to introducing the short crosshead piston and piston rod-seals exclude crankcase oil from the cylinder.
Ceramics will also extend the power range of this engine. Increased exhaust temperatures compensate for the lower efficiency of the small turbocharger and so reduce blower power and raise thermal efficiency.
Developments are going on with quiet scavenge blowers and blowers utilising the flywheel which is seen as another important breakthrough for the two stroke diesel. Servo-operated fuel systems also have been run which would give injection characteristics well suited to the (DI) O.P. engine.