CO₂ concentration measurements inside expansion-compression engine under high EGR conditions using an infrared absorption method

The purpose of this study is to measure the high concentrations of CO₂ near a spark plug inside an internal combustion engine, and an infrared absorption method is used for the measurement. The spark plug sensor was adapted to a compression-expansion machine, and the CO₂ concentration near the spark plug was measured by adding a gas mixture, including CO₂ to imitate EGR. Next, the EGR ratio was changed from 10 to 40%, and the CO₂ concentration was measured. The effect of the CO₂ on the flame propagation was investigated by visualizing the bottom view of the compression-expansion machine. The measurements of CO₂ mass concentration are in agreement with those predicted by direct-absorption spectroscopy fundamental theory from the crank angle −60 to −15 deg ATDC. The error was less than 20%, and under the conditions with an EGR ratio of 20–40%.