Experimental study on negative valve overlap condition and Miller cycle on combustion characteristics of ammonia-alcohol dual-fuel ignition engine

Aiming at the problems of low reactivity and slow combustion rate in ammonia engine, in this study, the effect of ammonia substitution ratio, NVO condition and Miller cycle on the combustion characteristics of ammonia were investigated based on a four-cylinder dual-fuel ignition engine. The results show that the methanol-assisted ammonia combustion can maintain high ITE and low BSFC at large ammonia substitution ratio under low load condition. The ethanol and n-butanol assisted ammonia combustion exhibit a synergistic effect on ITE improvement at medium and high loads, respectively. The BSFC and ITE under NVO condition are smaller and larger than those under single injection condition, respectively. The combined effect of residual exhaust heat and high-temperature anoxic environment can effectively promote the fuel pyrolysis and increase the reaction rate of the composite combustion. The BSFC and ITE in Miller cycle are smaller and larger than that of the conventional combustion condition, respectively. The maximum engine ITE of 45.11 %, 44.42 % and 44.33 % for ammonia-methanol, ammonia-ethanol and ammonia-n-butanol are achieved at IVC of 169 ° CA BTDC. The BSFC and ITE of alcohol assisted ammonia combustion are superior to that of gasoline assisted combustion under Miller cycle condition. The ITE of the dual-fuel ammonia engine can be effectively improved by the NVO condition and Miller cycle combustion mode, and a combustion regulation strategy to realize efficient combustion of ammonia engine is proposed.