Effect of Ignition Timing on Combustion Characteristics in Ammonia-Hydrogen Blended Fuel Engine with Passive Pre-Chamber

Against the backdrop of energy structure transformation and upgraded environmental protection requirements, ammonia has been gaining significant traction for its potential application as a zero-carbon fuel. However, it faces challenges such as difficult ignition, slow combustion rate, and low heating value. Thus, researching efficient combustion strategies suitable for ammonia as a fuel holds great significance. In this study, a two-cylinder diesel engine was modified into an ammonia-hydrogen blended fuel engine. Experimental study coupled with numerical simulations were carried out to investigate the effects of varying ignition timing on the combustion characteristics employed a passive pre-chamber ammonia-hydrogen fuel engine. The results show that the peak in-cylinder pressure exhibits a "first increase then decrease" trend as the ignition timing is retarded, reaching a maximum value of 7.42 MPa at the ignition timing of -27.5°CA ATDC. When the ignition timing is retarded beyond -15°CA ATDC, a double-peak phenomenon appears in the in-cylinder pressure curve. The peak heat release rate (HRR) gradually increases with the retardation of ignition timing, but excessively retarded ignition diminishes the proportion of constant-volume combustion in the combustion process. The combustion rate is the fastest when the ignition timing is -20°CA ATDC under the operating conditions of an engine speed of 1800 r·min-1, a hydrogen energy fraction (HEF) of 11.6%, and a λ of 1.0, with the shortest combustion duration (CA10~CA90) of 22.5°CA, which leads to the highest indicated thermal efficiency of 42.5%.