Low-Temperature Combustion with Biodiesel: Its Enabling Features in Improving Efficiency and Emissions
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Low-temperature combustion is gaining interest for use in production reciprocating internal combustion engines because of its feature of simultaneously decreasing nitrogen oxides and smoke emissions. It faces, however, challenges of increased hydrocarbon (HC) and carbon monoxide (CO) emissions and decreased fuel conversion efficiency. In parallel, biodiesel is also gaining interest for use in production diesel engines as a potentially augmenting fuel to reduce petroleum-based fuel consumption. Combining the two, biodiesel and low-temperature combustion, results in improvements to both the emissions and efficiency challenges observed with petroleum-diesel-based low-temperature combustion. This work highlights the use of biodiesel with low-temperature combustion, in comparison to the same with petroleum diesel (ultralow sulfur diesel no. 2). The approach relies on experimental investigation of each fuel (in 100% concentrations) in a production medium-duty diesel engine as the exhaust gas recirculation level varies. Additionally, two fuel injection timings are studied: a "conventional combustion" timing of -8 after top dead center and a low-temperature combustion timing of 0 after top dead center. Biodiesel substantially improves combustion phasing, relative to petroleum diesel, of later-phased high-dilution low-temperature combustion for similar nitric oxide emissions and further improves cylinder-cylinder variations, both which mostly cause gross indicated fuel conversion efficiency to be about 6.5 percentage points (from 32.5 to 39%) higher for biodiesel than petroleum diesel. The improved combustion phasing with biodiesel is believed to result from both its decreased tendency of low-temperature heat release and its oxygenated feature, the latter which allows for the transition to rapid heat release to occur much sooner than petroleum diesel. Increased CO and HC concentrations are also observed with petroleum diesel at the low-temperature combustion condition (about 24 times higher for HC and 8 times higher for CO, relative to biodiesel); this is believed to result from the later-phased combustion of petroleum diesel and also causes its gross indicated fuel conversion efficiency to be lower relative to biodiesel. Finally, rates of heat transfer are substantially lower for petroleum diesel at the low-temperature combustion condition, which would tend to improve its gross indicated fuel conversion efficiency. The lower rates of heat transfer of petroleum diesel, however, result from its poorly phased combustion at this condition, which ultimately deteriorates efficiency. 2013 American Chemical Society.
author list (cited authors)
Tompkins, B. T., & Jacobs, T. J.
complete list of authors
Tompkins, Brandon T||Jacobs, Timothy J