Numerical Investigations on the Combustion Characteristics of N-Heptane Spray under Premixed Ethanol and Iso-Octane Atmosphere in a Combustion Vessel 2017-01-2269

Based on a composed PRF/ethanol/PAH mechanism, simulations were conducted to investigate the combustion characteristics of n-heptane spray under premixed ethanol/air and iso-octane/air atmosphere in a combustion vessel. The effects of premixed ethanol and iso-octane on ignition delay, important soot precursors and soot volume fraction of n-heptane spray were studied. Also, simulated results with and without considering the cooling effects of premixed fuel vaporization were compared. When the cooling effect of premixed fuel vaporization was not considered, simulations showed that premixed ethanol could increase the ignition delay of n-heptane spray at ambient temperatures below 850K. However, premixed iso-octane showed little inhibition effect on ignition of n-heptane spray. Also, it was found that both premixed ethanol and iso-octane contributed to faster ignition under high ambient temperatures. The soot volume fraction and soot precursor concentration were significantly reduced under premixed ethanol atmosphere at 800K. For cases under premixed iso-octane atmosphere, the soot volume fraction was increased under all the simulated ambient temperatures. When the cooling effect of premixed fuel vaporization was considered, simulations showed that premixed ethanol could retard the ignition of n-heptane spray even at initial ambient temperature of 1000K. Also, the soot volume fraction was significantly reduced under premixed ethanol atmosphere at 850K. However, under premixed iso-octane atmosphere, the simulated results with and without considering the cooling effect of iso-octane vaporization show smaller difference. Therefore, the simulations show that the high vaporization heat of ethanol also has an obvious effect on soot reduction of dual-fuel combustion.