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As part of the Auto/Oil Air Quality Improvement Research Program (AQIRP), a fleet of 299 1983-1993 “real world” light duty vehicles and trucks were acquired from inspection and maintenance (I/M) lanes and tested at prevailing ambient temperatures for their hot soak emissions for the first hour after the engine was turned off. When found, high-emitters were repaired and retested to quantify the effectiveness of the repairs. Also, I/M pressure-purge tests were performed to determine whether such tests could properly identify high-emitting vehicles. Measured hot soak emissions ranged from less than 0.1g HC to as high as 49g HC. Twenty percent of the vehicles tested accounted for nearly 80 percent of the total hot soak emissions, with no single common hardware component identified as the primary cause.

The role of the catalyst in regeneration of catalytic particulate traps was found to be the oxidation of gaseous fuel species, such as carbon monoxide and hydrocarbons, in the exhaust. Energy released by the oxidation of fuel on the catalyst surface heats the trap to the temperature at which combustion of trapped particulate matter can occur. Experiments with both commercial and prototype catalytic particulate traps demonstrated that the traps could be reliably regenerated by enriching the exhaust with either propane or diesel fuel. Using a DD6V-71N coach engine and a prototype catalytic particulate trap, a trap regeneration system was developed which delivers vaporized diesel fuel to the exhaust, upstream of the catalytic particulate trap. The system has no moving parts in contact with the exhaust gas and allows reliable trap regeneration under full exhaust flow. An un-optimized fuel efficiency penalty of less than 1.6% was demonstrated for this regeneration method.