Experimental and simulation research on the lean combustion characteristics of direct-injection hydrogen engine.

At a constant engine speed of 2000 r/min and 5 bar gross indicated mean effective pressure, experiments were carried out on a 1.5 L engine with a variable geometry turbocharger to examine the combustion and emission characteristics of a direct injection hydrogen engine under lean combustion conditions. Additionally, a CFD simulation model was established to investigate the formation process of the air-fuel mixture and the generation of nitrogen oxides (NOx). The findings demonstrated that the uniformity of the hydrogen-air mixture in the cylinder descended with a delay in SOI (start of injection), and that the thermal efficiency often rose initially before declining. When SOI was set at −80°CA ATDC, the engine achieved maximum indicated thermal efficiency, brake thermal efficiency, and output torque values of 40.8%, 36.22%, and 61.2 Nm, respectively. However, as the SOI was delayed, the combustion variability ascended, and when the SOI was delayed to −20°CA ATDC, there was a significant chance that abnormal phenomena like pre-ignition would occur. BTE achieves a maximum of 36.38% when λ is 2.2 and SOI is −40°CA ATDC. Under lean combustion conditions, temperature was a major factor in the generation of NOx, and homogenous combustion can substantially reduce NOx emissions. NOx emissions are always less than 100 ppm when SOI is before −80°CA ATDC. • The uniformity coefficient is used to quantify the stratification degree of mixture. • The thermal efficiency generally increased initially before declining with the SOI delay. • A high possibility of abnormal combustion emerged when SOI was postponed until −20°CA ATDC. • Homogeneous combustion can effectively reduce NOx emissions under lean burn condition. [ABSTRACT FROM AUTHOR]