Extended, and Variable, Stroke Reciprocating Internal Combustion Engines

A description is given, with a supporting thermodynamic analysis, of a four-stroke Diesel engine concept with the expansion and exhaust strokes exceeding the induction and compression strokes due to the use of a novel linkage connecting the piston to the crankshaft. The advantage of such an arrangement, after allowing for engine internal friction losses, is a reduction of about 8% in specific fuel consumption relative to an otherwise similar conventional Diesel engine. There is also a corresponding reduction of emissions. An extension of the concept, incorporating a slightly more complex linkage, is applicable to spark-ignition engines. In this case the arrangement can be operated more flexibly since the expansion ratio can be adjusted with the engine running. This capability also allows a constant compression ratio to be maintained independently of the selected expansion ratio. Reducing, for spark-ignition engines, the induction and compression strokes while extending the expansion and exhaust strokes correspondingly allows the brake specific fuel consumption to be reduced by about 20% at 30 % of full load. This conclusion was also supported by detailed thermodynamic studies with due allowance being made for engine friction losses.