Journal
PROCEEDINGS OF THE COMBUSTION INSTITUTE
Volume 37, Issue 4, Pages 4955-4963Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.proci.2018.07.073
Keywords
Refractive index matching; Direct injection spark ignition engine; Wall wetting; Combustion; Coolant temperature
Funding
- National Natural Science Foundation of China [51476011]
- Deutsche Forschungsgemeinschaft (DFG) [SFB-Transregio 150]
- U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office
- U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office
- U.S. Department of Energy's National Nuclear Security Administration [DE-NA0003525]
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A late-injection strategy is typically adopted in stratified-charge direct injection spark ignition (DISI) engines to improve combustion stability for lean operation, but this may induce wall wetting on the piston surface and result in high soot emissions. E30 fuel, i.e., gasoline with 30% ethanol, is a potential alternative fuel that can offer a high Research Octane Number. However, the relatively high ethanol content increases the heat of vaporization, potentially exacerbating wall-wetting issues in DISI engines. In this study, the Refractive Index Matching (RIM) technique is used to measure fuel wall films in the piston bowl. The RIM implementation uses a novel LED illumination, integrated in the piston assembly and providing side illumination of the piston-bowl window. This RIM diagnostics in combination with high-speed imaging was used to investigate the impact of coolant temperature on the characteristics of wall wetting and combustion in an optical DISI engine fueled with E30. The experiments reveal that the smoke emissions increase drastically from 0.068 FSN to 1.14 FSN when the coolant temperature is reduced from 90 degrees C to 45 degrees C. Consistent with this finding, natural flame luminosity imaging reveals elevated soot incandescence with a reduction of the coolant temperature, indicative of pool fires. The RIM diagnostics show that a lower coolant temperature also leads to increased fuel film thickness, area, and volume, explaining the onset of pool fires and smoke. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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