Measurement of the Equivalence Ratio in the Spark Gap Region of a Gasoline Direct Injection Engine With Spark Emission Spectroscopy and Tracer-LIF

The complexity of the mixture formation in direct injection engines requires - according to a suitable mixture transportation and vaporization of the fuel - detailed knowledge of the in-cylinder processes to reliably place an ignitable mixture at ignition timing near the spark plug for any speed and load. Two different optical measurement techniques were adapted to a single cylinder engine and the spray propagation was observed from the start of injection until ignition. 3-pentanone tracer-LIF signals (laser-induced fluorescence) and CN spark emission signals were detected simultaneously in order to get information about the local equivalence ratio at the spark plug and compare the two methods. While there is a good correlation for homogeneous operating conditions of the engine, the results diverge in the stratified mode.