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The medium and heavy-duty powertrain industry trend is to reduce reliance on diesel fuel and is aligned with continued efforts of achieving ultra-low emissions and high brake efficiencies. Compression Ignition (CI) of late cycle Directly Injected (DI) Natural Gas (NG) shows the potential to match diesel performance in terms of brake efficiency and power density, with the benefit of utilizing a lower carbon content fuel. A primary challenge is to achieve stable ignition of directly injected NG over a wide engine speed and load range without the need for a separate ignition source. This project aims to demonstrate the CI of DI NG through experimental studies with a Single Cylinder Research Engine (SCRE), leading to the development of a mono-fueled NG engine with equivalent performance to that of current diesel technology, 25% lower CO2 emissions, and low engine out methane emissions.

A constant volume spray and combustion vessel utilizing the pre-burn mixture procedure to generate pressure, temperature, and composition characteristic of near top dead center (TDC) conditions in compression ignition (CI) engines was modified with post pre-burn gas induction to incorporate premixed methane gas prior to diesel injection to simulate processes in dual fuel engines. Two variants of the methane induction system were developed and studied. The first used a high-flow modified direct injection injector and the second utilized auxiliary ports in the vessel that are used for normal intake and exhaust events. Flow, mixing, and limitations of the induction systems were studied. As a result of this study, the high-flow modified direct injection injector was selected because of its controlled actuation and rapid closure. Further studies of the induction system post pre-burn were conducted to determine the temperature limit of the methane auto-ignition.

The quenching of premixed laminar flames at various constant pressures was studied through numerical simulation, with the Trajectory Generated Lower Dimensional Manifold (TGLDM) method used to employ detailed chemical mechanisms for stoichiometric methane and heptane flames. The method was validated at lower pressures and wall temperatures. The laminar flame speed predicted by the TGLDM method agrees reasonably well with experimental data reported in the literature. The peak heat flux at quenching was found to be under-predicted by 30-40% of the most current experimental data. The quench distance was calculated for pressures of 1, 2, 20 and 40 bar, with wall temperatures of 300 and 600 K and fresh gas temperature of 300 K. The quench distance was found to decrease with increasing pressure in a manner similar to previous studies. The value of quench distance for heptane was found to be smaller than that of methane by a factor of ~30% over all pressures.