Growing demands have been placed on emissions from passenger cars and light-duty trucks using diesel engines. In the U.S., an 0.2 g/mile particulate emission standard is mandatory starting with the 1987 model year. Two approaches to meeting this requirement are: filtration methods which trap engine-out particulate, and engine modification techniques which improve combustion and reduce such emissions. The filtration (and regeneration) technique is suitable for medium and larger vehicles due to cost, available space, and efficiency considerations. One engine modification approach uses an electronically-controlled system to optimize such parameters as fuel flow, injection timing, and exhaust gas recirculation (EGR) ratio.