High-fidelity simulations of turbulent combustion relevant to gas turbines and compression ignition engines

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It is unlikely that gas turbines (GTs) and compression ignition (CI) engines will be displaced from the transportation and energy sectors within decades to come as they provide unmatched levels of energy and power density and are highly suitable to complement intermittent renewables (e.g., wind turbines, solar). Despite continuous improvements, GTs and CI engines suffer from particulate matter (PM), NOx, CO2, and unburnt hydrocarbon (UHC) emissions. In the current environmental, economical and political context, it is essential for engine manufacturers to drastically reduce these undesirable pollutants, while increasing fuel flexibility and efficiency, but this challenging task is constrained by our poor understanding of the highly complex combustion processes involved in these engines. Historically, experimental studies have only provided qualitative results at GT and CI engine conditions due to the extremely challenging environments (optical access, high pressure, etc.). As a result, despite their importance, the mechanisms that control the combustion process and pollutant formation remain superficially understood. Direct numerical simulation (DNS), a high-fidelity simulation approach that resolves all relevant time and length scales of the turbulent combustion process, has only recently emerged as an alternative to unravel these complex mechanisms. In the proposed research, DNS will be used to explore key scientific questions that currently limit the potential of GT and CI engine strategies to reduce pollutant emissions. A first portion of the program will focus on GT combustion. To reduce CO2 emissions and to benefit from the growing alternative fuel market, hydrogen is being used as a fuel additive. However, the high reactivity of hydrogen changes completely the combustion dynamics. It is unclear what role intense turbulence (relevant to GT operating conditions) plays on these dynamics, especially at high pressure and temperature conditions, which has been little explored fundamentally. In this context, a series of DNS will be conducted to expose the effects of fuel composition, thermochemical conditions and turbulence intensity on the structure/stabilization and NOx formation of turbulent flames at GT conditions. The second portion will address the stabilization mechanism of jet flames at CI engine conditions. These flames ignite, develop, and stabilize at a distance away from the fuel injector, which controls the amount of fuel-air mixing prior to combustion and, as a result, the level of pollutants produced (PM and UHC). As little is understood about the complex stabilization mechanism, CI engines suffer from fuel flexibility. The proposed DNS will first explore the sensitivity of the stabilization mechanism of CI jet flames to important in-cylinder controlling parameters (e.g., temperature and exhaust gas dilution) and fuel effects will be investigated with a focus on alternative fuels such as bio-diesel.