Yoshihiro Iwashita

Fuel Octane and Composition Effects on Efficiency and Emissions in a High Compression Ratio SIDI Engine

The effects of fuel octane have been assessed on the efficiency and emissions of a high compression ratio (e=13) spark ignition direct injection (SIDI) engine. Under low load stratified operation (1200 rpm, ∼20% load), a low octane fuel (RON=84, comprised of toluene, iso-octane, and n-heptane) yielded higher brake thermal efficiency and significantly lower hyd carbon emissions than a base gasoline (RON=91). The indicator diagram for the low octane fuel showed evidence for two stage heat release, suggesting the presence of spark induced compression ignition (SICI). These results suggest that higher efficiency under low load stratified conditions can be obtained with lower octane fuels that undergo SICI combustion. The effect of fuel octane under high load was assessed at WOT with a high RON model fuel (RON=103, comprised of toluene, iso-octane, and n-heptane). This high octane fuel exhibited a torque benefit compared to pure iso-octane (RON=100) and premium gasoline (RON=99) that is significantly greater than expected based on RON alone. The results suggest that a high RON fuel, in particular one that is high in aromatics, yields significant torque benefits under high load.

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.

Measurement of Flame Temperature Distribution in Engines by Using a Two-Color High Speed Shutter TV Camera System

A two-color high speed shutter TV camera system has been developed as a new sensing device for measuring the flame temperature in engines. The TV camera system can measure the radiant intensities of high temperature substances accurately and rapidly. And, the two-dimensional temperature distribution can be easily calculated from the radiant intensities by using an image processor. This system is applicable to measurement of flame temperature in diesel and gasoline engines. The relation between the progress of combustion phenomena and the measured temperature distribution is clearly explained. It is confirmed that the system is effective for measurement of the flame temperature distribution in engines.

OBSERVATION OF KNOCK USING A HIGH SPEED SHUTTER TV CAMERA SYSTEM

An ultra-high speed shutter TV camera including an image intensifier which has a light magnification of 20,000, and an image analysis system have been developed and applied to knock research with a transparent piston engine. Irregularity in the flame configuration was observed just when the pressure vibration began. The causes of cycle to cycle variation of knock intensity were examined through the simultaneous recording of the pressure vibration and the image of the flame.