This study investigates the effect of ignition parameters on the cyclic dispersion and the specific fuel consumption of a carburetted single-cylinder engine. Ignition energy measurements were made on the low- and high-voltage sides of the ignition coil, and the performance was predicted satisfactorily by a simple model with passive elements. The spark energy was varied by changing the spark plug gap and the coil-on-time. The spark energy was measured in a special calorimeter: the aim was to find a correlation between engine performance and the spark energy measured by the calorimeter. The tests were conducted at part load and low speed with a weak mixture, as these conditions are known to give high levels of cyclic dispersion.
The spark calorimeter showed a higher spark plug conversion efficiency for spark plugs with large gaps. However, the spark plug gap was found to be a more significant determinant of engine performance than the spark energy measured by the calorimeter. The experimental results are preceded by a review of ignition phenomena and their influence on combustion.
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