Research on the influence of dual spark ignition strategy at combustion process for dual cylinder free piston generator under direct injection

The direct injection technology is easy to achieve stratified combustion and greatly improves the fuel economy and power of free piston generator (FPG), but it also exacerbates the cyclic combustion fluctuation caused by the structure. Therefore, based on the dual spark ignition strategy, the influence of the ignition position and ignition time on the combustion process for dual cylinder FPG under direct injection was studied. The research results show that compared with the changes in the ignition angle position, the combustion process of direct injection FPG is more sensitive to changes in moment of ignition. Furthermore, with the ignition timing advances from 6°CA BTDC to 18°CA BTDC, the indicated thermal efficiency rises constantly at a rate of 25.1% and reached a high value of 33.9% in the same ignition position, although the uniformity of the mixture in the cylinder and the concentration of the mixture around the spark plug decrease gradually. While, in the same time of ignition, the increase rate of the indicated thermal efficiency reaches 6.6% at the maximum along with the increase of the spark plug angle and the increasing rate drops continuously along with the advancement of the ignition timing. Furthermore, compared with single spark ignition, the dual spark ignition can increase the cylinder pressure by 30% and the indicated thermal efficiency by 2% respectively.