Fuel Effects on SIDI Efficiency and Emissions

Spark ignition direct injection (SIDI) engines have the potential to realize significant thermal efficiency improvements compared to conventional port fuel injection engines. The effects of fuel properties on efficiency and emissions have been investigated in a prototype of an Avensis Wagon equipped with a 2.0 liter, 4 cylinder spark ignition, direct injection (SIDI) engine designed to meet US 2000 emission standards. The vehicle employed a close coupled three-way catalyst and a NOx storage and reduction catalyst. Seven matrix fuels were blended to the same RON with varying levels of aromatics, olefins, ethanol, and volatility. Relative thermal efficiency, fuel economy, and tailpipe emissions were measured for the matrix fuels and a base fuel under the FTP LA4 driving cycle. The engine was operated in a lean burn mode in light load condition for approximately half of the driving cycle. Fixed speed/load engine bench tests were also carried out for three of the matrix fuels to complement the vehicle tests. In addition, laminar burning velocity measurements of all seven matrix fuels were made in a constant volume combustion vessel. The vehicle tests showed a 2% spread in relative thermal efficiency, with increased efficiency correlating with higher olefins and lower aromatics. In the bench engine tests, a 2 % increase in peak torque was observed, with the fuel having the highest olefins plus aromatics content yielding the highest torque. The influence of the primary fuel properties autoignition resistance and burn rate (laminar burning velocity) on these results is discussed. Lower aromatic levels directionally correlated with decreased NOx emissions, and lower driveability index (DI) directionally correlated with decreased non-methane hydrocarbon emissions.