Stratified combustion characteristics analysis and assisted-ignition strategy optimization in a natural gas blended diesel Wankel engine

It is important to improve the combustion performance of the diesel Wankel engine for its further engineering applications. Therefore, the main objective of this study was to study the dual-fuel mixture formation and stratified combustion process in the novel natural gas blended diesel Wankel engine. Meanwhile, the effects of assisted-ignition timing and assisted-ignition position on engine combustion characteristics were investigated. The results indicated that when the assisted-ignition timings and positions were changed, natural gas distribution near assisted-spark plugs changed slightly, while the variation of diesel distribution was conspicuous. Moreover, adopting dual assisted-ignition spark plugs could accelerate the fuel burning rate and improve engine combustion performance. Besides, it was found that more mixture concentrated near the assisted-spark plugs was beneficial to increase the pressure in-cylinder and combustion rate. The symmetrical arranged dual assisted-ignition spark plugs that were respected to the X-axis (Case 4) and assisted-ignition timing of 35°CA BTDC (Case 6) were the preferred practical application schemes. Compared to the schemes of single spark plug ignition (Case 1) and 20°CA BTDC ignition timing (Case 9), the peak pressure in-cylinder of the preferred application schemes increased by 42.96% and 10.91%, respectively.