Investigation of the control strategy for hydrogen addition in all operating conditions of a high compression ratio liquid methane heavy-duty engine

The hydrogen addition to liquid methane gas (LMG) engines based on the rational control strategy is considered to be a promising approach to improve the performance of LMG engines. However, the current studies are limited to a few operating points. To comprehensively develop a control strategy of hydrogen addition for high compression ratio LMG engines, the effects of hydrogen addition on the emissions, combustion, and performance of an LMG engine are experimentally investigated under all operating conditions in this study. Furthermore, to achieve the optimal performance of the hydrogen-LMG engine with the optimal hydrogen blending, the coupled simulation model of MATLAB/Simulink and GT-Power is established based on the test bench, and the multiple operating parameters of the calibrated numerical model are optimized by using genetic algorithm. The results show that the maximum increases in the brake thermal efficiency with increasing hydrogen energy share (HES) are 1.6, 0.9 and 0.6 percentage points under low, medium and high loads, respectively. Correspondingly, the maximum reduction in EBSFC under low, medium and high loads is 6.5 %, 2.2 % and 1.4 %, respectively. The ignition delay is reduced and the combustion is promoted with the increase in HES. As a result, the cylinder pressure and HRR rise faster and reach a higher peak earlier. In addition, the 50 % combustion location is advanced and the 10-90 % combustion duration is shortened. In terms of emissions, the increasing HES promotes the NOx emissions and reduces the HC emissions. Especially at medium and high loads, the NOx emissions rise sharply with increasing HES. It is desirable that HES should not exceed 15 %, 4 % and 2 % at low, medium and high loads, respectively. In addition, by co-optimizing the intake valve opening timing, exhaust valve opening timing and the spark angle, the BSFC of the hydrogen-LMG engine with the optimal HES under 1200 rpm and BMEP of 6 bar is still improved by 2.2 %. This study provides new insights to further explore the energy-saving potential of hydrogen-LMG engines.