The Influence of Intake Pressure and Ethanol Addition to Gasoline on Single- and Dual-Stage Autoignition in an HCCI Engine
Dibble, Robert W.
KAUST DepartmentChemical and Biological Engineering Program
Clean Combustion Research Center
Mechanical Engineering Program
Physical Sciences and Engineering (PSE) Division
Online Publication Date2018-09-11
Print Publication Date2018-09-20
Permanent link to this recordhttp://hdl.handle.net/10754/628737
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AbstractAutoignition in HCCI engines is known to be controlled by the combustion kinetics of the in-cylinder fuel/air mixture which is highly influenced by the amount of low-temperature and intermediate-temperature heat release (LTHR and ITHR) that occurs. At lower intake pressures (typically <1.4 bar absolute), it has been observed that gasoline behaves as a single-stage heat release fuel, while at higher intake pressures (typically >1.8 bar absolute) gasoline behaves as a two-stage heat release fuel. Furthermore, ethanol blending into gasoline strongly affects heat release characteristics, and this warrants further investigation. This paper experimentally investigates the conditions under which gasoline transitions from a single-stage heat release fuel to a two-stage heat release fuel as intake pressure is increased. Experiments were performed in single-cylinder HCCI engine fueled with two research-grade gasolines, FACE A and FACE C. These gasolines were tested neat, and with 10% and 20% (by volume) ethanol addition. In addition, these results were compared to results previously obtained for PRF 85, and new results for PRF 84 with 10% and 20% ethanol addition. Moreover, the engine experiments were supported by rapid compression machine (RCM) ignition delay data for the same fuels. The engine experiments revealed that there were minimal differences between the heat release profiles of the two gasolines, FACE A and FACE C, a result which was supported by the RCM experiments that showed similar ignition delay times for the two FACE fuels and PRF 84. On the other hand, with ethanol addition to these gasolines and PRF 84, the occurrence of LTHR shifted to higher intake pressures compared to ethanol-free cases, from 1.4 bar intake pressure for neat fuel to 2.2 bar with 20% ethanol. Consequently, the intake temperatures required to achieve constant combustion phasing for all mixtures were drastically altered. Simulations using a detailed chemical kinetic model were utilized to understand the effects of ethanol blending on the ignition characteristics of PRF 84. The addition of ethanol was found to act as a radical sink where it inhibits the radical pool formation during the low (<850 K) and intermediate (850–1050 K) temperature chemistry regimes resulting in lower reactivity. These results help explain ethanol’s significant antiknock qualities under boosted conditions in spark-ignition engines.
CitationVuilleumier D, Atef N, Kukkadapu G, Wolk B, Selim H, et al. (2018) The Influence of Intake Pressure and Ethanol Addition to Gasoline on Single- and Dual-Stage Autoignition in an HCCI Engine. Energy & Fuels. Available: http://dx.doi.org/10.1021/acs.energyfuels.8b00887.
SponsorsThis work at the University of California Berkeley was partially supported by NSF/DOE Award No. CBET-1258653 entitled ‘‘Advancing Low Temperature Combustion and Lean Burning Engines for Light- and Heavy-Duty Vehicles with Microwave Assisted Spark Plugs and Fuel Stratification.” The work at UCONN was supported by the National Science Foundation under Grant No. CBET-1402231. Part of the work performed by G.K. was under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under contract no. DE-AC52-07NA27344 through the Special Employee Strategic Mission Support Program. The work at King Abdullah University of Science and Technology (KAUST) was funded by Saudi Aramco under the FUELCOM program.
PublisherAmerican Chemical Society (ACS)
JournalEnergy & Fuels