Reducing the Emissions and Efficiency Penalties of Low Temperature Combustion through Low Heat Rejection Operation
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Low temperature combustion (LTC) is popular among diesel engine researchers because it dramatically reduces NOx and smoke emissions. However, LTC is limited by increased CO and hydrocarbon emissions as well as by reduced efficiency. At the same time, low heat rejection (LHR) operation has tantalized researchers with the promise of large efficiency improvements, but it has often failed to meet simulated expectations. Since LHR techniques inevitably increase combustion chamber temperatures, the ratio of specific heats of the cylinder contents is decreased, reducing the potential conversion of thermal energy to work. Combining LTC and LHR allows for low heat transfer losses and a high ratio of specific heats, providing the opportunity for increased efficiency. An experiment was conducted to evaluate potential improvements to a mild LTC mode’s combustion efficiency and thermal efficiency. The experiment used elevated engine coolant temperatures (ECT) to reduce the temperature gradient across the cylinder walls in a 1.9L four-cylinder DI diesel engine. In particular, NOx, smoke, CO, and hydrocarbon emissions were compared between LTC and conventional conditions over the ECT range (from 90 °C to 120 °C), and various measures of efficiency were compared as well. Elevated coolant temperatures reduced the carbon monoxide and hydrocarbon emissions penalties of the LTC mode, improving LTC combustion efficiency. The thermal efficiency of the mild LTC mode was not significantly different from that of the conventional mode, and brake thermal efficiency for both modes improved at higher coolant temperatures.
low temperature combustion
low heat rejection engines
Kroeger, Timothy Herbert (2017). Reducing the Emissions and Efficiency Penalties of Low Temperature Combustion through Low Heat Rejection Operation. Master's thesis, Texas A & M University. Available electronically from