Infrared absorption technique for measuring local fuel concentration near the spark plug of a port injection gasoline engine

Abstract

Abstract

The mixture concentration in the vicinity of the spark plug at the time of spark ignition is a critical parameter for the performance of SI engines. Infrared absorption is often used to measure this parameter in firing cycles. Although it is well known that the mixture concentration near the spark plug is a primary factor explaining combustion stability in direct injection engines, the effect of the local mixture concentration has not been confirmed for nearly homogeneous mixtures. In this research, the mixture concentration in the vicinity of the spark plug was measured quantitatively using infrared absorption with an optical fibre sensor built into the spark plug of a port injection engine. Measurements were made across a range of air—fuel ratios for both steady state conditions at three different overall air—fuel ratios and for a rich-to-lean transient condition. It was experimentally confirmed that the mixture concentration near the spark plug has little impact on combustion stability for steady state operation with a homogeneous mixture distribution. It has also been confirmed that fibre-sensor-based infrared absorption can be used for cycle-by-cycle analysis of the local mixture concentration even for a homogeneous mixture distribution.