A novel combustion evaluation method based on in-cylinder pressure traces for diesel/natural gas dual fuel engines

To better understand the combustion process of the dual fuel engines, a novel evaluation method based on the in-cylinder pressure traces was proposed in this study. Two evaluation parameters, the in-cylinder pressure standard deviation and the coefficient of variation, were calculated from the measured in-cylinder pressure traces at every crank angle. The profile of in-cylinder pressure standard deviation shows that there is an obvious jump representing the overall combustion process. The effect of diesel injection timing shows that, by advancing diesel injection timing, the start of jump shows an initial advancing and then retarding trend. The profiles of in-cylinder pressure standard deviation or coefficient of variation show the change of combustion process as the pilot diesel injection timing is advanced. When the pilot diesel injection timing is later than 30°CA BTDC, there is a rapid rise and a higher main peak in the profiles of in-cylinder pressure standard deviation with the injection timing advancing. As the diesel injection timing is further advanced, the initial rapid rise shows an increasing trend while the main peak shows a weakening trend; and both of them finally overlap together when the diesel injection timing is earlier than 40°CA BTDC.