In-cylinder combustion in spark-ignited natural gas engine and its dependence on engine running conditions

摘要

An experimental study was made to investigate in-cylinder combustion in a spark-ignited natural gas engine and its dependence on engine running conditions. Flame propagation in a single-cylinder visualization engine was measured from the cylinder axis direction by the high speed schlieren method, over the wide range of spark timing and excess air ratio. The results showed that flame did not propagate concentrically around spark plug electrode, but was shifted by swirl flow. The gravity center of flame area moves corresponding to flow field in the combustion chamber. In the case of partial-burning, flame left from the spark plug electrode, resulting in no more propagation. Cylinder pressure increase is delayed compared to flame propagation. Heat release is detected when flame area occupies around 4% of the combustion chamber area. Heat release shows its maximum when flame area occupies around 70% of the combustion chamber area. Flame area varies cycle-to-cycle within±10% to its average, which is smaller than cycle variation of swirl velocity. Spark timing had little effect on flame propagation and its speed. larger excess air ratio resulted in more slender flame, slower and more shifted flame propagation. Flame propagation speed, which is negatively proportional to excess air ratio, gets half from about 10m/s to about 5m/s as excess air ratio changes from 1.3 to 1.6.