High-speed imaging analysis of misfires in a spray-guided direct injection engine

This study is an experimental investigation of rare misfire and partial burn cycles in a spray-guided spark-ignited direct-injection optical engine. Spark discharge energy, discharge duration, flame imaging, velocity and equivalence ratio were measured every crank angle degree. Imaging was performed using high-speed 2-D particle image velocimetry (PIV) and planar laser inducted fluorescence (PLIF). The engine was operated near its optimum but produced rare and random partial burn and misfire cycles. Spark energy and spark duration for the partial burn and misfire cycles fell within the range of those for the well-burned cycles, with a slight bias toward low-energy, short-duration discharges, indicating no abnormal spark discharge events. PIV and PLIF measurements extracted from a 4 mm × 4 mm region adjacent to and downstream of the spark plug at spark timing revealed that the partial burn and misfire cycles occur under lean mixtures and low velocities, but still within the range of values for the well-burned cycles. PIV and PLIF images of partial burn and misfire cycles were compared to well-burned cycles, which had similar velocities and equivalence ratios near the spark plug at the onset of spark. Observations of the fuel distribution and flame areas for the partial burns and misfires showed that an early flame kernel was always formed, but failed to develop sufficiently to propagate to the fuel in the bowl. A flame kernel arriving late within the piston bowl found significantly leaner conditions and the mixture was not fully consumed leading to a partial burn. For misfire cycles, the mixture in the measurement plane was significantly leaner surrounding the flame kernel, which disappeared shortly after the spark discharge. It is concluded that the partial burns and misfires are not the result of failed ignition, but failure during the flame propagation process.