Search Results

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.

A study was carried out to investigate, experimentally using a wind tunnel, the drag contribution (base drag) due to the flat-end of most van-type semi-trailers used for inter-city tractor-semi-trailer transportation. The study was focused on high cruise-speed operation of such vehicles at about 100 km/h (62.2 mile/h) a speed that can often be maintained for long distances on inter-city runs. It was found that it is possible to reduce overall aerodynamic drags significantly using a modestly tapered after-body terminating in a flat base. It was also shown that such after-bodies can be arranged to permit easy aft-end loading or unloading of trailers and that a reduction of engine fuel consumption at high-speed cruise on a level road of about 14% should be achievable when due allowance is also made for vehicle rolling resistance.

The potential advantages of incorporating an extended expansion-stroke in Diesel engines are discussed. It is shown that Diesel engines with extended expansion strokes can be expected to have specific fuel consumptions up to about 8% lower, for typical automotive size units, than those achievable with conventional Diesel engines employing equal compression and expansion strokes. A description is also given of the essential mechanical linkage necessary to achieve an extended expansion stroke in engines of the four-stroke type. The application of the extended expansion concept to engines of the two-stroke, uniflow, type is also described.