Combustion fluctuation mechanism involving cycle-to-cycle spark ignition variation due to gas flow motion in S.I. Engines

Recent experimental observations of in-cylinder gas flow motion in spark ignition engines are presented, elucidating the causes of combustion fluctuations. For this purpose, simultaneous local mixture strength, initial combustion duration and spark ignition were measured by the use of a spark plug built-in gas sampling valve. Pressure, current and voltage measurements for each cycle were recorded by a multi-data acquisition system. As a result, it became evident that one of the causes of combustion fluctuations is the variation in local mixture strength near the spark gap at the ignition timing. That is each flame kernel was influenced by mixture strength during its process of growth. In addition, spark duration was affected by gas flow velcoity at the spark gap. Especially, misfire occurred by shortening the spark duration, when gas flow velocity was too large. Spark path acquired an arch shape under the influence of gas flow velocity, but spark duration became reduced due to the restriking effect, as the gas flow was increased. Consequently, a new aspect of combustion fluctuation mechanism has been identified. Its major component is derived from mixture motion associated with both mixture strength and gas flow velocity, as well as the concomitant variation of spark ignition.