Influence of the Velocity Near the Spark Plug on Early Flame Development

The objective of this paper is to investigate how the velocity and turbulence within different locations close to the spark plug influence the combustion at individual cycles in a SI-engine.

2-D cycle-resolved laser doppler velocimetry (LDV) measurements have been done both inside the spark gap and around the spark tip to extract velocity information. The pressure in the cylinder was measured with a piezo-electric transducer connected to an A/D-card in a standard PC.

The velocity information was filtered to get “mean velocity” and “turbulence”. The pressure signal was used in a one-zone heatrelease model to get different levels of mass fraction burned etc.

The results show a significant influence of both the “mean velocity” and the “turbulence” on the early part of the combustion when the velocity was measured close to the spark plug tip. The influence was less significant when the velocity was measured at some distance from the electrodes for both a pancake and a high squish combustion chamber. The correlation between the velocity close to the spark plug and the early flame development showed no dependence on the air-fuel ratio and a modest dependence on ignition timing.