In-cylinder mixture distribution measurement in a GDI engine using laser-induced fluorescence

The laser-induced fluorescence (LIF) technique for measurement of in-cylinder mixture distribution and the characteristics of tracer were discussed and an improved calibration method was developed. No assumption in absorption attenuation was needed in this method. A planar laser-induced fluorescence (PLIF) test bench was built for measurement of air-fuel mixture distribution at ignition moment in different injection strategies. Measured results of equivalence ratio in the zone near the spark plug at ignition moment were imaged. The result shows that for the lean burn mode, the early injection in intake stroke leads to a low concentration homogenous mixture which is hard to be ignited. While the later injection in compression stroke forms an over-rich zone of equivalence ratio above 2. The two-stage injection brings about a relative homogenous mixture with a rich zone of equivalence ratio around 1.2 near the spark plug which is suitable for a steady lean burn. Mixture in the rich zone near the spark plug shows its variation is below 10%.