Impact of Blending Oxygenated Fuels on the Formation of Intermediate Products in Diesel Combustion Process

Employing the Chemkin-Pro diesel engine combustion model, n-heptane was chosen as a surrogate fuel to represent diesel, and a combustion mechanism encompassing ethanol/dimethyl ether/n-heptane was developed. The investigation delved into the effects of varying molar blending ratios of ethanol and dimethyl ether, two oxygenated fuels, on the combustion temperature, pressure, and resulting products of n-heptane. The outcomes revealed that ethanol blending led to a more pronounced reduction in reaction temperature and pressure compared to dimethyl ether. Notably, when ethanol and dimethyl ether were blended concurrently, the blending ratio of dimethyl ether emerged as a determinant factor in shaping the reaction timing. Specifically, as the dimethyl ether blending ratio rose from 15% to 35%, the combustion reaction advanced by approximately 10°(Crank Angle). Furthermore, the blending ratio of dimethyl ether exerted a significant influence on the genesis timing of oxidizing free radicals, with a higher ratio precipitating an earlier formation. Conversely, the peak molar fractions of free radicals were primarily influenced by the blending ratio of ethanol. As the ethanol blending ratio increased, the peak molar fractions of all three free radicals exhibited a rising trend. In terms of combustion products, ethanol blending effectively mitigated the formation of formaldehyde and acetaldehyde, while dimethyl ether blending primarily reduced acetaldehyde levels but potentially increased formaldehyde production. Intriguingly, when ethanol and dimethyl ether were blended in tandem and the proportion of dimethyl ether was enhanced, both the peak molar fractions of formaldehyde and acetaldehyde decreased, and the ultimate production of CO₂ also diminished.