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.