In-situ Residual Gas Concentration Measurement near a Spark Plug in a Motorcycle SI Engine 2007-32-0049

This paper describes the development and application of a spark plug sensor using an infrared absorption technique to quantify the instantaneous residual gas concentration near the spark plug. The residual gas fraction inside engine cylinder is assumed to be proportional to CO₂ concentration. The relationship between CO₂ concentration and absorption strength of CO₂ was determined for various pressures and temperatures in advance using a constant volume vessel with electric heating system. The spark plug sensor for in-situ CO₂ concentration measurement was applied to a compression-expansion engine and also to a port injected motorcycle SI engine. It was possible to qualify the CO₂ concentration inside residual gas during the compression stroke using the developed optical system with new spark plug sensor in compression-expansion machine. Cycle-resolved measurements were made to investigate the effects of the residual gas concentration near the spark plug on the combustion characteristics of the commercial motorcycle engine. It was possible to measure the cycle-resolved CO₂ concentration near the spark plug and investigate the cycle-to-cycle fluctuations of mixture formation to achieve stable operation using the newly developed spark plug sensor.