The Influence of Fuel Properties and Engine Load Upon the Carbon and Hydrocarbon Fractions of Particulate Emissions from a Light-Duty Diesel Engine

This paper reports on the relative contributions of diesel fuel aromatic content and 90 percent distillation temperature to particulate exhaust emissions (both carbon and hydrocarbon) from a single-cylinder, indirect-injection, light-duty diesel engine as a function of engine load. The carbon and hydrocarbon fractions of particulates were determined by using a vacuum oven to heat filters on which particulates had been collected.

As expected, multiple linear regression analysis showed that the carbon particulate emission index (grams of particulates emitted per kilogram of fuel consumed) correlated well with a combination of aromatic carbon content and 90 percent distilled temperature of the eight fuels at all six loads tested. A new finding is that the relative contributions of these two fuel properties to the carbon particulate emission index depended strongly upon engine load (overall equivalence ratio). A speculative explanation, which is consistent with the theory that carbonaceous soot condenses from rich gas-phase combustion, is proposed to account for the observation that increased levels of high-boiling fuel fractions decreased the carbon particulate emission index at very heavy engine loads.

An unexpected finding was that within the normal ranges of diesel fuel properties, the hydrocarbon particulate emission index could not be correlated with fuel properties. In general agreement with other work, the hydrocarbon particulate emission index for each fuel correlated with its corresponding gaseous hydrocarbon emission index; however, the relationship between the gaseous and the particulate hydrocarbon emission indices was greatly dependent upon engine load. Data obtained using the same engine and constant fuel properties showed that the timing of combustion also strongly influenced the relationship between the gaseous and the particulate hydrocarbon emission indices.