Impact of octane sensitivity and thermodynamic conditions on combustion process of spark-ignition to compression-ignition through an optical rapid compression machine

Investigation into ethanol effects on combustion and particle number emissions in a spark-ignition to compression-ignition (SICI) engine

“…The KI of 70# is significantly larger than those of 70#E10 and 82# except for the cases with the highest EGR rate under low engine loads. The KI of 70#E10 is always slightly larger than that of 82# until the EGR rate gets more than 20% where their KIs are almost identical due to the low EGR tolerance of ethanol [36]. CA50 has a positive correlation with KI for all fuels.…”

“…Based on the HRR profile, auto-ignition timing (φ auto ) was identified as the maximum curvature position of HRR [4], which is more sensitive to the first peak of d 2 p/dt 2 [36]. As seen in Eqs.…”

“…The auto-ignition intensity decreases significantly and φ auto also gets delayed drastically. Both phenomena can be attributed to ethanol's high sensitivity to exhaust dilution [36]. That is to say, ethanol has low EGR tolerance, and the flame propagation along with the reactivity in ethanol-gasoline mixtures becomes more significantly restricted with increasing EGR rate.…”

“…Among the aforementioned methods, spark assistance along with fuel stratification has a relatively low cost and only requires one fuel supply system, which has the potential to be applied in the combustion modes involving controlled auto-ignition, such as spark-ignition to compression-ignition (SICI) mode, in the near future. SICI combustion has been substantially studied in engines and fundamental research devices, e.g., rapid compression machines (RCM), using pure high-RON gasolines [1][2][3][4][5][6][26][27][28][29], ethanol-gasoline blends [24,31] and their surrogate fuels [32][33][34][35][36][37] in the past decade. Specifically, Wang et al [1] achieved SICI combustion at medium-high loads using commercial 93# gasoline and external exhaust gas recirculation (EGR), an indicated specific fuel consumption (ISFC) less than 225 g/kW•h was obtained at about 22% EGR.…”

“…Ethanol-gasoline fuels prepared by splash blending have different ethanol contents, so the RON of the mixed fuel rises with increasing ethanol content, which can directly reflect the influence of ethanol. RON-controlled blending compares a blended fuel to another pure gasoline with the same RON, so it can reveal fuel-to-fuel interaction on auto-ignition [36,37,51]. Three base gasolines with different aromatics and olefins concentrations were prepared, indicating different unsaturation degrees.…”