Mechanisms of Particulate Matter Formation in Spark-Ignition Engines. 3. Model of PM Formation

Abstract

A combined experimental and modeling effort was performed in order to understand how particulate matter (PM) is formed in spark-ignition (SI) internal combustion engines. Application of the model allows quantification of the amount of PM nucleated at sites of burning liquid fuel (either droplets or pools) and in homogeneous gas-phase chemical reactions. Moreover, it quantifies PM growth by condensation and absorption/adsorption of hydrocarbon (HC) vapors as well as PM reduction by oxidation both in the cylinder and in the exhaust pipe. Model parameters, fit by comparison to experimental data, show the strong dependence of PM formation on the presence of liquid fuel in the cylinder and HCs in the exhaust, temperatures in the intake port and cylinder, air/fuel ratio, and propensity of the fuel molecule to break down into soot precursors. PM emissions calculated by the 13-parameter model compare to 84 experimental data sets with an R 2 correlation coefficient of 0.81, demonstrating good correlation. The effects of individual engine, fuel, and dilution parameters on modeled PM emissions are discussed, elucidating the mechanisms causing experimentally measured trends in PM emissions as a function of the respective parameters.