To improve thermal efficiency of internal combustion engines, combustion system of the direct-injection and spontaneous-ignition operation may be preferable. This research aims to provide the fundamental data of ignition and combustion characteristics of unsteady jets with hydrogen H2 together with natural-gas NG and methane CH4. Experiments under a variety of conditions in a constant-volume vessel are made to investigate the effects of ambient temperature on ignition delay for different nozzle-hole diameters and oxygen concentrations.
Attached figure shows the typical result of H2, NG and CH4 at the base condition. Every curve exhibits the similar trend; As an ambient temperature Ti decreases, ignition delay τ increases slightly at higher Ti and increase largely at lower Ti. Among these fuels, H2 has the shortest ignition delay for the same Ti, and can be ignited at a lower temperature of Ti =780 K. In contrast, CH4 has the longest ignition delay over the whole range of Ti and suffers from misfiring at a higher Ti of 910 K. NG has a shorter delay than CH4 due to a small amount of C4H10 with good ignitability.
From the obtained results in the hydrogen jet, shorter ignition delay is observed in the case of a larger hole nozzle, a higher ambient pressure and a higher oxygen concentration. Also, based on them, the feasibility of hydrogen fuel for the direct-injection compression-ignition engine is discussed from the viewpoint of mixture formation and chemical reaction.