Mechanisms of particulate matter formation in spark-ignition engines. 1. Effect of engine operating conditions

A combined experimental and modeling effort was performed in order to under stand how particulate matter (PM) is formed in spark-ignition (SI) internal combustion engines. Parameters that affect global and local air/fuel ratio s strongly affect PM. Minimum PM number and mass concentrations are emitted at a global air/fuel ratio within 10% of stoichiometric, and concentration s increase by as many as 3 orders of magnitude when the air/fuel ratio is e ither increased or decreased 30% from stoichiometric. Burning liquid fuel i s a significant source of PM, as evidenced by the fact that open valve fuel injection increases PM concentrations by up to 3 orders of magnitude relat ive to closed valve injection. Coolant and oil temperatures, spark timing, and exhaust gas recirculation (EGR) affect PM through their effect on intak e port and cylinder temperatures as well as through the effect on the avail ability of liquid fuel in the cylinder. Particle sizes as a function of eng ine operating conditions are discussed.