Measurement of Local Mixture Strength at Spark Gap of S. I. Engines

In spark ignition engines, local fuel concentration of the mixture occupying the electrode spacing at the instant of spark discharge may be one of the important factors to dominate the combustion process and the cycle-by-cycle variation of combustion.

To make clear the above problems, a special sampling device has been developed. The sampling valve is equipped with the central electrode of the spark plug, which enables us to sample the mixture formed near the electrode spacing of the spark plug in the ordinary engine operation.

By applying this device, the mixture existing just before the occurrence of spark discharge can be taken repeatedly every cycle, and the cycle-by-cycle variation of mixture strength in the immediate vicinity of the electrode spacing was made clear. Further, it was found that the cycle-by-cycle variation of mixture strength formed in the electrode spacing at the instant of spark discharge increases by the engine operation with EGR.