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The pursuit of flexibility is a recurring theme in engine design and development. Engines that are able to switch between the two-stroke operating cycle and four-stroke operation promise a great leap in flexibility. Such 2S-4S engines could then continuously select the optimum operating mode - including HCCI/CAI combustion - for fuel efficiency, emissions or specific output. With recent developments in valvetrain technology, advanced boosting devices, direct fuel injection and engine control, the 2S-4S engine is an increasingly real prospect. The authors have undertaken a comprehensive feasibility study for 2S-4S gasoline engines. This study has encompassed concept and detailed design, design analysis, one-dimensional gas dynamics simulation, three-dimensional computational fluid dynamics, and vehicle simulation. The resulting 2/4SIGHT concept engine is a 1.04 l in-line three-cylinder engine producing 230 Nm and 85 kW.

The influences of injector nozzle geometry, injection pressure and ambient air conditions on a diesel fuel spray were examined using back-lighting techniques. Both stills and high speed imaging techniques were used. Operating conditions representative of a modern turbocharged aftercooled HSDI diesel engine were achieved in an optical rapid compression machine fitted with a common rail fuel injector. Qualitative differences in spray structure were observed between tests performed with short and long injection periods. Changes in the flow structure within the nozzle could be the source of this effect. The temporal liquid penetration lengths were derived from the high-speed images. Comparisons were made between different nozzle geometries and different injection pressures. Differences were observed between VCO (Valve Covers Orifice) and mini-sac nozzles, with the mini-sac nozzles showing a higher rate of penetration under the same conditions.

An experimental study of the mixture response performance of novel, port-fuel injection strategies upon combustion stability in a gasoline engine was undertaken at low engine load and speed conditions in the range of 1.0 bar to 1.8 bar GIMEP and 1000 rpm to 1800 rpm. The aim was to improve the thermal efficiency of the engine, by extending the lean limit of combustion stability, through promotion of stable charge stratification. The investigation was carried out using a modified 4-valve single-cylinder head, derived from a 4-cylinder, pent-roof, production, gasoline engine. The cylinder head was modified by dividing the intake tract into two, separate and isolated passages; each incorporating a production fuel injector. The fuel injection timing and duration were controlled independently for each injector.