In-situ fuel concentration measurement near spark plug by 3.392 mm infrared absorption method - Pressure and temperature dependence of the gasoline molar absorption coefficient

This paper describes the development and application of a spark plug sensor using a 3.392 μm infrared absorption technique to quantify the instantaneous gasoline concentration near the spark plug. We developed an in situ laser infrared absorption method using a spark plug sensor and a 3.392 μm He-Ne laser as the light source; this wavelength coincides with the absorption line of hydrocarbons. First, we established a database of the molar absorption coefficients of premium gasoline at different pressures and temperatures, and determined that the coefficient decreased with increasing pressure above atmospheric pressure. We then demonstrated a procedure for measuring the gasoline concentration accurately using the infrared absorption technique. The history of the molar absorption coefficient of premium gasoline during the experiment was obtained from the established database using measured in-cylinder pressures and temperatures estimated by taking the residual gas into consideration. These values provided instantaneous fuel concentrations in the engine cylinder. We examined the mixture formation process near the spark plug in a port-injected spark-ignition (SI) engine for different fuel injection timings, and determined that when the injection timing was delayed, a rich mixture remained near the top of the combustion chamber.