The effects of ester-based oxygenates, including dimethyl carbonate (DMC), biodiesel, and diethyl adipate (DEA), on combustion and emissions were investigated. For each oxygenate, four blends with the baseline of ultralow sulfur diesel (ULSD) were designed containing oxygen by weight of 2%, 4%, 6%, and 8%, respectively. In term of combustion, the combustion phase was advanced by biodiesel, whereas it was delayed by DMC and DEA. Particulate matter (PM) and geometric mean diameter (GMD) were reduced by all oxygenates, whereas the reduction efficiency in PM was highest with DMC but lowest with DEA. Biodiesel resulted in the highest total particle number (PN) with the smallest GMD. Additionally, DMC decreased HC emissions but increased CO, formaldehyde (HCHO), and acetaldehyde (CH3CHO). Biodiesel increased NOx emissions but decreased other pollutants. DEA showed the similar results to that of DMC, except for HC emissions. At the same oxygen content, DMC emitted the lowest PM, PN, and CH3CHO but the highest HCHO level. DEA fuels exhibited the highest PM, HC, CO, HCHO, and CH3CHO emissions, primarily due to the significant incomplete combustion. Cubic polynomials were fitted as a function of oxygen content for PM, HC, CO, HCHO, and CH3CHO, with all R2 values greater than 0.9, which could serve as basic models to predict emission with these three ester-oxygenates within the validated boundary. Based on the analysis, still multiple factors, except for oxygen content and the ester functional group, strongly impact engine performance, whereas the multidimensional model should be further researched.
Di et al. (2026) studied this question.