An optical study of the combustion and flame development of ammonia-diesel dual-fuel engine based on flame chemiluminescence

Abstract

Under the background of the “carbon peak and carbon neutrality”, the development and utilization of zero-carbon fuels, represented by green ammonia and green hydrogen, has gained attention from all walks of life. Among them, the problems of transportation and storage of hydrogen restrict its industrial development, while ammonia has significant advantages as a suitable hydrogen energy carrier for the power systems. The ammonia-diesel dual-fuel engine enables the mixture to be stratified in a time-activated multi-point ignition mode to promote efficient and clean combustion of ammonia. To investigate the combustion and flame development of the ammonia-diesel dual-fuel engine, an optical diagnostic study was carried out on a self-refit dual-fuel optical engine. The results show that the combustion inertia and lower flame temperature of ammonia can inhibit combustion and lead to lower cyclic heat release in the ammonia-diesel dual-fuel combustion (ADDC) mode, which in turn reduces the indicated mean effective pressure (IMEP). Different from the yellow-white flame produced by the high-temperature soot radiation in pure diesel combustion (PDC) mode, the flame in the ADDC mode appears orange. The peak of flame area (FR) percentage and flame natural luminosity (FNL) of the 80% ammonia ratio ADDC mode decrease by 60% and 92%, respectively, compared to the peaks at PDC mode. The ammonia combustion flame is mainly concentrated around the diesel flame, and at the same time achieves good ignition performance at all ammonia ratios. In contrast to the PDC mode where the FR and FNL decrease rapidly as the diesel injection timing (DIT) advances, the flame pattern of the ADDC mode does not respond significantly to the DIT.