Parametric Study of Autoigniting Hydrogen–Methane Jets in Direct-Injection Engine Conditions

Abstract

This work investigates the effects of ambient and injection parameters on the ignition and combustion characteristics of hydrogen (H 2 )− methane (CH 4 ) jet (50% H 2 by volume, with the remaining CH 4 ) in simulated direct-injection, compression-ignition conditions. Parameter variations include ambient gas temperature (1060−1200 K), ambient oxygen (O 2 ) concentration (10−21 vol %), and injection pressure (10−20 MPa reservoir pressure). The results show that the ignition delay of the H 2 −CH 4 jet decreases with increasing ambient temperature. In most cases, the ignition initiates from a localized kernel before spreading across the jet volume downstream. The lower ambient O 2 cases display a more voluminous ignition sequence. The results also show that the jet flame recesses upstream to attach or stabilize close to the nozzle but becomes increasingly lifted with lower ambient temperature and O 2 conditions. The flame autoignition process displays increased variation at the lowest tested ambient temperature condition in this work, which affects the ensuing flame evolution and heat release profile.

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

“…It is noted that this work builds upon recent research by the present group, expanding the experimental data set on H 2 , CH 4 , and their blends in conditions relevant to CI engines. ,− Previous studies employed a single-hole injector within a CVCC to inject fuels under varying injection and ambient conditions. Figure summarizes the parametric variations explored in these earlier investigations.…”

“…The dual fuel DI approach involves direct natural gas injection into the engine, with ignition provided by a small quantity of diesel pilot fuel . The combustion in these engines primarily occurs in a nonpremixed mode, similar to diesel combustion. − …”

“…However, to achieve this, there needs to be more DI experimental research on the corresponding ignition and flame structure in conditions resembling CI engines to improve understanding . A notable finding in previous studies is the substantial variability in ignition and combustion characteristics at lower ambient temperatures, ,, which are particularly relevant to modern CI engines operating at top dead center temperatures below 1000 K. For the methane (CH 4 , as a natural gas surrogate) jet, a prolonged ignition delay of 6.12 ms was observed, accompanied by a substantial run-to-run variation of 0.99 ms. Quasi-steady states were absent in most repetitions, resulting in transient flame stabilization positions. Introducing 50% H 2 to CH 4 reduced the ignition delay to 4.37 ms, with a comparable run-to-run variation of 0.98 ms.…”