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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.

In this paper, experiments and simulations were conducted to investigate the cyclic variations of gasoline/diesel and ethanol/diesel dual-fuel combustion. For both dual-fuel modes, gasoline and ethanol were injected into the intake port during the intake stroke and diesel was directly injected into the cylinder. The influences of engine load and port fuel proportion on the cyclic variability of both dual-fuel modes were investigated. At each test condition, in-cylinder pressure traces of 150 consecutive cycles were acquired. Then the cyclic variations of ignition timing (CA5), combustion phasing (CA50), accumulated heat release (Qf) and indicated mean effective pressure (IMEP) were calculated based on the in-cylinder pressure. The experimental results showed that the cyclic variation of IMEP was mainly caused by the variation of Qf for both dual-fuel modes.