Using Carbon-14 Isotope Tracing to Investigate Molecular Structure Effects of the Oxygenate Dibutyl Maleate on Soot Emissions from a DI Diesel Engine

The effect of oxygenate molecular structure on soot emissions from a DI diesel engine was examined using carbon-14 (¹⁴C) isotope tracing. Carbon atoms in three distinct chemical structures within the diesel oxygenate dibutyl maleate (DBM) were labeled with ¹⁴C. The ¹⁴C from the labeled DBM was then detected in engine-out particulate matter (PM), in-cylinder deposits, and CO₂ emissions using accelerator mass spectrometry (AMS). The results indicate that molecular structure plays an important role in determining whether a specific carbon atom either does or does not form soot. Chemical-kinetic modeling results indicate that structures that produce CO₂ directly from the fuel are less effective at reducing soot than structures that produce CO before producing CO₂. Because they can follow individual carbon atoms through a real combustion process, ¹⁴C isotope tracing studies help strengthen the connection between actual engine emissions and chemical-kinetic models of combustion and soot formation/oxidation processes.