Combustion and Emissions Characteristics of Orbital's Combustion Process Applied to Multi-Cylinder Automotive Direct Injected 4-Stroke Engines 980153

Orbital have been developing their stratified combustion process (Orbital Combustion Process OCP) for direct injection gasoline engines over the last 15 years, with successful production releases of the system in both the marine and automotive 2-stroke applications in 1996. This paper discusses how the same basic qualities of the air-assist fuel system and combustion process have been applied to automotive 4-stroke engines. The inherent qualities of the air- assist fuel system in combination with careful design of the combustion chamber has enabled high charge stratification with late injection timings and very stable combustion over a wide range of operating conditions. Experimental test data from a 4-cylinder, 16 valve 4-stroke development engine demonstrates the ability of this low pressure system to operate at very lean air/fuel ratios, with part load fuel economy improvements of up to 34 % at an operating condition equivalent to a vehicle speed of 40 km/hr.

Results presented from steady state simulation of the New European Drive Cycle also demonstrate an overall base engine fuel economy improvement of over 20%, whilst achieving NOx emissions reductions of over 85% and HC emissions comparable to the baseline port injected (MPI) engine.

As a result of the combined NOx, fuel economy and HC control of the Orbital Combustion process, the authors have proposed an alternative exhaust aftertreatment strategy to the still unproven and expensive lean NOx catalyst options. In particular, steady state results show how the low raw emissions of the air-assisted DI system developed could enable a conventional 3-way catalyst system to be utilised to meet Stage 3 European emissions levels with a minimal impact on the DI fuel economy advantage.