Experimental investigations on the cyclic variability of a large bore CNG engine

Experiments were used to explore the cyclic variability of a CNG engine. The experiments were conducted on a large bore (12V190) engine fuelled with pre-mixed natural gas. The influences of the ignition advance angle, the excess air ratio and the ignition energy on the cyclic variability were investigated. At each test condition there were acquired in-cylinder pressure traces of 100 consecutive cycles. Cyclic variability was quantified by the variation of indicated mean effective pressure (IMEP) in this paper. The experimental results showed that the cyclic variation was increased while increasing the dilution levels. And, the cyclic variation was reduced with the increase of the ignition advance angle. Meanwhile, the cyclic variation could not be significantly reduced just by increasing the ignition energy on the specified engine. The reason can be that the most important influence exerted by the ignition energy is the formation of early flame kernel. In order to significantly reduce the cyclic variations, there is also necessary the improvement of the gas mixture's motion state in the cylinder.