Combustion and emissions characteristics of Orbital's combustion process applied to multi-cylinder automotive direct-injected, 4-stroke engines

摘要

Orbital has been developing its 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 he 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 NO_x emissions reductions of over 85% and HC emissions comparable to the baseline port-injected (MPI) engine. As a result of the combined NO_x, 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 NO_x 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 utilized to meet Stage 3 European emissions levels with a minimal impact on the DI fuel economy advantage.