Effects of High Compression Ratio and Combustion Chamber Shape on Cycle-to-Cycle Variability

The effect of high compression ratio on cycle-to-cycle variability was studied using two different combustion chamber shapes, with natural gas operation. A single cylinder Ricardo E6 test engine was run over a range of operating conditions and compression ratios. The different combustion chamber shapes were achieved by using different pistons. At each operating condition detailed cylinder pressure data were recorded for two hundred consecutive cycles allowing for a detailed study of this chaotic phenomenon.

The effect of compression ratio on cyclic variation was contradictory for the two combustion chambers, and it is concluded that the real effect was not compression ratio but combustion chamber shape, since the combustion chamber geometry was changed with altering compression ratio for both combustion chambers.

Although good correlation between variations of maximum pressure and indicated mean effective pressure was not found, the pattern of the plot of peak cylinder pressure versus its location was found to have strong correlation with variation of indicated mean effective pressure.