Experimental study on spark ignition of flowing combustible mixtures

Cycle variability in spark-ignition engines is mainly attributable to the occurrence of poor ignited and misfired cycles. The non-ordinary ignited cycles were previously observed to occur when either, the flame did not move away from the electrodes, and therefore had much contact with electrodes, or when large portions of the flame were rapidly convected away from the electrodes and therefore the flame was quenched in the flow field. Cycle variability can also occur due to turbulence or non-homogeneity in the mixture strength. Experiments showed that the degree of the cyclic variability depends very much on the characteristics of the introduced spark, the flow regime in the electrodes' gap, and the spark plug design. In the present work, we investigated the effect of the amount of energy supplied to the spark plug, the law of energy deposition during glow phase, the mean velocity vector in the spark gap and the spark plug orientation, on the mixture lean misfire limit. The experiments were carried out on a test flow facility under atmospheric conditions. Premixed butane-air mixtures were studied under variable flow rate and air-fuel ratio. The results reveal the important role that both the glow phase duration and the glow phase current play in the ignition process. It was also shown that the preferable law of energy release depends on the spark gap and spark plug orientation, in particular under high flow velocities (7-9 m/s). The crossflow plug orientation was found to be preferable in the entire range of experimental conditions. The upstream plug orientation is better than the downstream one at low flow velocities, but the trend inverses at high flow velocities. There is an optimal range of flow velocities across the spark gap for minimum ignition energy. In our experiments a flow velocity between 5 and 8 m/s was found to be preferable.