Optical investigation on diesel-methane dual-fuel combustion using high-pressure direct injection

This paper focuses on a dual-fuel injector to characterize the ignition delay time (IDT), flame propagation, and flame spectral distribution of diesel and methane combustion. To gain an insight into the combustion characteristics of diesel pilot-ignited methane dual-fuel combustion with a high-pressure direct injection (HPDI) strategy under various conditions, the ignition and combustion processes are obtained by a high-speed color camera. The variables such as diesel injection pressure (DIP), diesel injection duration (DID), fuel relative injection interval time (RIT), ambient temperature (AT), and ambient pressure (AP) are varied according to enginelike conditions for a better understanding of the relation between the operating conditions and combustion characteristics. The results show that methane jets inhibited the IDT of diesel, while the conditions and ignition of diesel also determined the ignition of methane. Premixed flame always exists at the initial combustion, the development of the flame propagation indicates that the entrainment between diesel and methane plays a crucial role in the flame velocity and combustion intensity. According to sensitivity analysis, the IDT, Flame tip penetration (P), Flame tip velocity (V), and Flame area (FA) are most sensitive to the AT, and at least 4, 3, 2, and 7 times to the other variables each. However, the area ratio of chemiluminescence to soot incandescence (B/R) is most sensitive to AP, which is at least 14 times the other variables.