A New Approach to Meeting Future European Emissions Standards with the Orbital Direct Injection Gasoline Engine 2000-01-2913

This paper discusses the development of a new approach to achieving EURO 4 emission standards with a simplified exhaust after-treatment system in combination with an air-assisted lean stratified Direct Injection system.

The results presented demonstrate the ability of the air-assist DI system to operate in highly stratified conditions at very lean A/F ratios, with excellent control of the raw HC and NOx emissions. In most cases the authors illustrate that with good stratified combustion control, the HC emissions can be lower than the baseline port injected stoichiometric engine. Further, the high tolerance to EGR and accurate A/F control at the spark plug enable the raw NOx emissions to be reduced by up to 85% over the European drive cycle in comparison to the baseline port injected engine with EGR.

The vehicle calibration strategy is discussed in detail, with particular attention being paid to the catalyst light-off strategy developed for the air-assist system, which enables feed exhaust gas temperatures to reach 600°C during the first 10 second idle period, while also maintaining good control of raw emissions. Also highlighted is the development of the ability to control canister vapour purge throughout both lean stratified and stoichiometric operation. This further enables good control of HC emissions while maintaining a high purge flow through the catalyst, independent of any specific catalyst regeneration requirements.

The low raw emissions of the vehicle are then applied to a single underbody catalytic converter located 1.3m from the cylinder head face. This was fitted with a combination of three-way and lean NOx traps, which had been aged under lean hydrothermal conditions. The authors discuss the systematic approach applied to the catalyst choice, in combination with the understanding of the air-assist DI modal raw HC and NOx emissions. In particular, the very low raw NOx emission burden during stratified operation is discussed, which enabled a reduced reliance on the Lean NOx trap (hereinafter LNT) storage function. Euro 4 emissions compliance is demonstrated with aged catalysts where the degradation of NOx emissions is considered to be very low, due to reduced reliance on the NOx catalyst efficiency.

The results show how, with a systematic approach, the combined ability of the underbody TWC/LNT catalyst and air-assist DI combustion system can meet future emissions standards.