Ignition and Combustion Characterization of Hydrogen/Methane Blends in Direct-Injection Compression-Ignition Conditions

Abstract

This work investigates the jet penetration, ignition, and combustion characteristics of methane (CH4), hydrogen–methane blend (H2–CH4), and hydrogen (H2) under various simulated direct-injection compression-ignition engine-relevant conditions. High-speed schlieren, pressure trace, and photodiode measurements were employed within a constant volume combustion chamber (CVCC). Experimental parameters were set to fixed values of the ambient density (24 kg/m3), oxygen concentration (21%), and reservoir pressure (20 MPa). The ambient temperature was maintained at 1060 K, a condition at which the jets were previously observed to exhibit varied ignition and flame stabilization behaviors. The study begins with an analysis of the injection system and nonreactive fuel jet penetration. The measurements show that introducing H2 into CH4 consistently reduces the ignition delay and shifts the ignition location upstream. Optical imaging shows that all fuel jets exhibit different ignition patterns, namely, single-kernel, multi-kernel, and voluminous ignition patterns, with proportion-dependent on fuel compositions. The ignition pattern, as well as fuel composition, appear to impact the ensuing apparent heat release and flame stabilization characteristics. Flame luminosity measurements show the H2 jet yielding the strongest broad-band emission among tested fuels.