Effect of Auxiliary Hydrogen Injection in the Prechamber on the Combustion Process of a Natural Gas Engine

Abstract

Prechamber jet ignition, as an efficient ignition technology, can enhance ignition stability and enable rapid combustion. The mixture formation and flow dynamics inside the prechamber are very important for the jet ignition process and engine performance. Active prechamber is an effective method to achieve turbulent jet ignition, but at present there is currently limited understanding of the impact of auxiliary fuel injection (AFI) in an active prechamber. In this study, it is suggested to use auxiliary hydrogen injection to improve the mixture in the prechamber, thereby improving the ignition performance of the prechamber jet. The influences of AFI on the combustion process and engine performance are studied by numerical simulation. Under different AFI strategies, the in-cylinder flow, ignition, and combustion processes are simulated. The effect of different AFI schemes on prechamber combustion, jet characteristics, combustion process in the main chamber, active radicals, and engine performance are compared. The results show that operating the natural gas engine under lean burn conditions increases the indicated thermal efficiency and lowers NO_x emissions. The introduction of an auxiliary hydrogen injection shortens the time interval between the spark ignition timing and the injection timing of the hot jet, thereby advancing the ignition timing for lean combustion in the main chamber. As the amount of hydrogen injected rises, the injection velocity and temperature of the prechamber jet increase, so the jet ignition performance is strengthened. Moreover, the auxiliary hydrogen that flows into the main chamber increases the chemical activity of the lean mixture present there. The combination of the prechamber jet ignition with auxiliary hydrogen injection significantly improves the ignition performance and accelerates the lean burn rate in the main chamber, showing the potential to expand the lean burn limit of natural gas engines.