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A numerical investigation of hydrogen’s effects on the performance of a heavy-duty natural-gas engine for a combined hydrogen, heat and power system
Wonjun Yoon, Eunhee Ko, Honghyun Cho, Jungsoo Park
A combustion model is introduced with a 1D engine-cycle model, and a parametric study is performed by varying the hydrogen content in a heavy-duty engine with reformed-gas injection. The effect of hydrogen on the engine combustion and performance is investigated by adding hydrogen to a natural-gas-fueled engine system. The in-cylinder pressure and torque could be enhanced up to 15% in volume with the hydrogen addition. However, the nitric oxide (NOx) emissions increased slightly due to the increase in in-cylinder temperature caused by the thermal NOx formation mechanism. To suggest engine-design points, multi-objective Pareto optimization was performed by varying the valve overlap. Throughout the Pareto fronts’ optimization results, conceptual engine-design possibilities were suggested by sweeping the operating parameters. Adding 15% hydrogen improved the fuel consumption; however, the resulting higher temperature caused an increase in NOx emissions. Moreover, considering the NOx emissions, it was not a good option to add hydrogen at less than 1000 rpm.
Keywords: Hydrogen; reforming; CHHP; multi-objective Pareto; CNG; spark ignition