Reducing the emissions and efficiency penalties of low temperature combustion (LTC) through low heat rejection (LHR)
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© 2017 Eastern States Section of the Combustion Institute. All rights reserved. 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. The experiment uses elevated engine coolant temperatures 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 are compared between LTC and conventional conditions over the engine coolant temperature range, and brake thermal efficiencies are compared as well. Preliminary results (for coolant temperatures up to 120°C) show that elevated coolant temperatures cause nearly identical thermal efficiencies for LTC and conventional combustion and significant improvements in hydrocarbon and CO emissions for LTC.
author list (cited authors)
Kroeger, T., & Jacobs, T.