Effects of control strategies for mixture activity and chemical reaction pathway coupled with exhaust gas recirculation on the performance of hydrogen-enriched natural-gas fueled spark ignition engine

Abstract

The excellent physicochemical properties of the hydrogen make it a promising fuel in the clean energy systems, including engines. In this study, the performance of a heavy-duty lean-burn natural gas (NG)-fueled spark ignition (SI) engine with hydrogen addition are examined through experiments. Then, a full-size one-dimensional (1D) GT-Power simulation model of the SI engine is established, and the feasibility of the model is validated by comparing the experimental and simulation results. In addition, control strategies for mixture reactivity and chemical reaction pathway are realized by using various exhaust gas recirculation (EGR) ratios and hydrogen injection timings, which applied in this validated simulation mode. The results reveal that the in-cylinder pressure, peak heat release rate (HRR), and in-cylinder averaged temperature of the hydrogen-enriched NG-fueled SI engine decrease with the increase in the EGR ratio by using the port fuel injection (PFI), early direct injection (DI), or late DI strategy. In addition, the volumetric efficiency, combustion efficiency and NOx emissions are reduced, while the ignition delay period is prolonged with the increase of the EGR ratio if the three strategies are used. Specifically, under the same operating conditions and EGR ratio of 18%, the volumetric efficiency the NG SI engine is obtained to be 66.6% and 70.9% by using the PFI strategy and late DI strategy, respectively. Obviously, compared to the PFI strategy, the volumetric efficiency of the NG SI engine is increased by using the late DI strategy. In addition, the combustion efficiency of the NG is 92.7% by using the PFI strategy, while it is 95.4% by using the late DI strategy. This suggests that the late DI strategy is also more conducive to enhancing the combustion efficiency of the NG SI engine. Furthermore, the NOx emissions are reduced by introducing the EGR strategy due to the control of the chemical reaction pathway. Overall, compared to the PFI and early DI strategies, by adopting the late DI strategy in the simulation model of the hydrogen-enriched NG-fueled SI engine, the in-cylinder pressure, peak HRR, and in-cylinder averaged temperature can be effectively increased based on the control of the mixture reactivity.