A 2019 experimental and numerical study of pre-chamber turbulent jet ignition (TJI) of methane/air mixtures in a large-bore constant-volume chamber with a six-orifice pre-chamber identified four unresolved issues: (1) developing an auxiliary pre-chamber fueling system that maintains a rich pre-chamber while the main chamber is lean, and quantifying its effect on hot-jet discharge timing and orifice-to-orifice uniformity; (2) pre-chamber geometry and spark-plug placement that avoid the asymmetric spark-kernel formation and unequal jet discharge observed with a side-mounted spark plug; (3) simulation fidelity at engine-relevant pressures, including chemistry valid at elevated pressure, wall heat losses, and turbulence–chemistry treatments beyond the early-stage-LES/RANS-later approach that overpredicted flame propagation; and (4) transfer of constant-volume-chamber findings to fired large-bore engine conditions.

Background

Liquefied natural gas (LNG), composed mainly of methane, is a leading substitute for diesel in heavy-duty marine engines, but methane/air mixtures are hard to ignite and burn slowly in a large combustion chamber, especially under lean conditions (excess air relative to the stoichiometric, chemically balanced mixture). Pre-chamber turbulent jet ignition (TJI) addresses this: a small cavity (the pre-chamber) attached to the main combustion chamber is spark-ignited, and the burning gases vent through one or more small orifices as high-temperature turbulent jets that act as distributed, high-energy ignition sources in the main chamber. A pre-chamber that receives fuel only through the main-chamber mixture is called passive; an active (auxiliary-fueled) pre-chamber receives additional fuel so it can run rich (fuel-rich relative to stoichiometric) while the main chamber runs lean. Because a fired engine is hard to instrument, such systems are commonly studied in a constant-volume combustion chamber (CVC), a closed rigid vessel with optical access where initial pressure and mixture composition can be controlled precisely; the air-fuel equivalence ratio (lambda) is the actual air/fuel ratio divided by the stoichiometric one, so lambda above 1 means a lean mixture. Li and co-workers (2019) studied a six-orifice pre-chamber discharging into a large-bore CVC, varying lambda and initial pre-mixed pressure, with companion experiments and simulations; a companion paper by the same group (Ju et al., 2020) compared this pre-chamber ignition with open-chamber spark ignition in the same vessel and found the pre-chamber's advantage grows toward lean conditions. Their simulations combined large-eddy simulation (LES, which resolves the large turbulent eddies and models only the small ones) for the early stage with Reynolds-averaged Navier–Stokes (RANS, which models all turbulent scales) for later times, used the GRI-Mech methane oxidation mechanism (a widely used reaction mechanism fitted mainly at low pressures), and assumed adiabatic (thermally insulating) walls; these choices produced faster simulated flame propagation than measured. The experiments also used identical initial mixtures in the pre-chamber and main chamber, because separate premixing was impractical, so the practically important rich-pre-chamber/lean-main-chamber configuration was never tested. The study closed by listing what it left unresolved.

Problem Statement

As stated by the source study, four issues must be addressed for the multi-orifice pre-chamber turbulent jet ignition concept it investigated (a six-orifice pre-chamber discharging hot turbulent jets into a large-bore constant-volume chamber filled with methane/air): (1) develop and test an auxiliary pre-chamber fueling system that maintains a rich pre-chamber composition while the main chamber is lean — the experiments used identical initial conditions in both chambers because separate premixing was difficult — and quantify how this separate fueling affects jet discharge timing and the uniformity of jet discharge across the multiple orifices; (2) identify pre-chamber geometry and spark-plug placement modifications that preserve auxiliary fueling while avoiding the asymmetric spark-kernel formation and resulting unequal jet discharge caused by the side-mounted spark plug; (3) establish higher-fidelity combustion simulations at engine-relevant pressures that reproduce the experimentally measured flame propagation rather than overpredicting it, addressing the identified limitations in chemistry validity at elevated pressure, wall heat losses, and turbulence–chemistry treatment; and (4) transfer these constant-volume-chamber findings to real large-bore engine conditions — moving piston, cycle-to-cycle variation, and the full range of engine pressures and temperatures — through testing in more realistic engine rigs or full-scale hardware, including long-term engine performance and emissions. These four issues are coupled and are to be addressed together as one research program.

References

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