Abstract
Optical engine indication synchronized with standard pressure recording allows a much more detailed characterization of the in-cylinder charge formation process. Information on the gas composition and temperature of the in-cylinder charge at a given crank angle is of upmost importance to improve engine performance. A fiber optical probe integrated in a spark plug or glow plug allows a real-time, crank angle resolved recording of the entire mixture formation process over hundreds of subsequent individual cycles. The in-cylinder probe measures simultaneously fuel and exhaust gas density as well as the gas temperature during the in-cylinder charge formation process. The measurement principle of optical engine indication is based on absorption spectroscopy of water, carbon dioxide and hydrocarbon fuel molecules. The measurement takes place in unmodified gasoline or diesel engines under real fuel conditions. The carbon dioxide detection reveals information about the internal Exhaust Gas Recirculation (EGR) rate for each individual cycle and cylinder, while the local air/fuel ratio measurement identifies misfire behavior during cold start. The knowledge of the gas temperature profile during the compression stroke provides important feedback for engine optimization like the HCCI pre-combustion temperature analysis.
