Experimental study of thermal efficiency and NOx emission of turbocharged direct injection hydrogen engine based on a high injection pressure

摘要

The direct injection (DI) hydrogen-fueled internal combustion engine (H2-ICE), as a promising carbon-neutral power device, has attracted more and more attention. However, the effects of the hydrogen injection strategy on the performance of H2-ICE lack in-depth analysis, even under the high injection pressure. Therefore, the present work investi-gated the thermal efficiency and NOx emissions with a single-hole injector over a wide range of high injection pressure and injection timing in a 3-cylinder turbocharged DI H2- ICE. The results show the strong dependence of high thermal efficiency on turbocharging and lean-burn strategies. The late-injection strategy can achieve higher thermal efficiency than the early-injection strategy, which can be applied at a wide range of loads. The effect of injection strategy on the brake thermal efficiency (BTE) mainly depends on the wall heat loss. Hydrogen late injection can reduce the wall heat loss by about 2 through strong mixture stratification. Furthermore, hydrogen late injection is always accompanied by a sharp increase in NOx emissions, even by orders of magnitude. This trade-off relationship between thermal efficiency and NOx emissions can be well optimized by a moderate late-injection strategy with an end-of-injection (EOI) of about 40 degrees CA. At the given load and start of injection (SOI), increasing the injection pressure from 5 MPa to 15 MPa can reduce the hydrogen injection duration by about 3 times. Under the higher injection pressure, the BTE performs a strong sensitivity to SOI. The BTE is improved by about 0.5 by optimizing SOI at PInj = 5 MPa mainly due to the reduced compression loss caused by further delay to the SOI allowed by higher injection pressure, while this improvement increases to about 2.3 at PInj = 15 MPa. However, at a given SOI, the highest BTE at PInj = 5 MPa is nearly 1.5 higher than that at PInj 1/4 15 MPa, which implies the potential of low-pressure injection coupled with large-flow injectors. Finally, the DI H2-ICE performs well in terms of efficiency with a maximum BTE of 44.08. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.