A comprehensive experimental study to analyze the cyclic variation of a hydrogen-blended ammonia engine with the Miller cycle

Abstract

The effects of multiple operating parameters (including speed, valve timing, λ, manifold absolute pressure, spark timing, and hydrogen injection timing) on the coefficient of variation of indicated mean effective pressure (CoVIMEP) of a hydrogen-blended ammonia engine have not been adequately evaluated, which motivates this study. Specifically, CoVIMEP is decreased from exceeding 2.4 % to approximately 0.7 % when the speed increases from 1300 rpm to 2000 rpm. Optimizing valve timing keeps CoVIMEP below 0.8 % by improving the airflow exchange process, and the engine tends to realize lower CoVIMEP at close stoichiometric ratio conditions and low pumping loss. Furthermore, adjusting spark timing affects CoVIMEP by varying the ignition process's stability, with a combustion center of gravity around 9°CA ATDC being suggested. The hydrogen direct-injection timing influences the combustion process's instability by varying the mixture concentration gradient, and the late injection strategy allows the engine to achieve a CoVIMEP of less than 0.9 %.