Characterizing injection and ignition of hydrogen and hydrogen-methane blend fuels in a static combustion chamber

• Pressure ratio between injector and chamber dominant factor for jet penetration, small effect of jet composition; • Minimum hot surface temperature for stable ignition of transient hydrogen jets was 760 °C; • Hot surface temperature of approximately 1116 °C reliably ignited jets with at least 60 % hydrogen by volume; • Ignition delay increased with higher chamber pressure and lower injection pressure due to increased transport time. Hydrogen offers a pathway to significant reductions in greenhouse gas emissions from transportation. Burning hydrogen in an internal combustion engine, either as the sole fuel or as a blend with natural gas, can leverage existing and accepted vehicle propulsion technologies. High net system efficiencies can be achieved with direct fuel injection late in the compression stroke to retain a diesel-like non-premixed combustion. Both hydrogen and methane have strong resistance to auto-ignition, meaning that a positive ignition source is required for reliable ignition. Understanding the interaction between ignition source and the gaseous fuel jet is critical to ensuring stable and robust ignition. In this work, the injection and ignition of hydrogen and blends with methane are evaluated in an optically accessible static combustion chamber. Schlieren imaging and in-chamber pressure were used to quantify the jet penetration and subsequent ignition. The impacts of changing gaseous fuel composition and injection parameters on jet penetration, momentum and dispersion are found to be minimal. Compared to methane, the lower density of hydrogen was offset by a higher nozzle exit velocity, leading to similar penetration rates. The transient jets were then ignited using a hot surface element in the path of the jet. The ignition delay was found to decrease with higher nozzle pressure ratios, with shorter transit time from the injector to the ignitor being the main factor. Reductions in chemical delay, quantified as the time between the arrival of the jet at the hot surface and subsequent ignition was primarily impacted by hot surface temperature. Under the conditions in the static chamber, ignition occurred primarily on the downstream side of the hot surface and the subsequent flame propagated in the downstream direction. Ignition delays increased substantially with methane-hydrogen blends, with stable ignition detected for concentrations of 60 % or more hydrogen by volume at the hot surface ignitor’s maximum temperature of 1116 °C, while hydrogen jets were ignitable at temperatures as low as 760 °C. The results demonstrate the importance of the geometry, chamber pressure, and transit time on the ignition of the jet.