Spark ignited direct injection (SIDI) gasoline engines have been in commercial production since the late 1990’s but have only become common in the U.S. light-duty fleet in the past five years. SIDI engines can be more fuel efficient, in particular under fuel lean operating conditions, and also offer a performance benefit due to the higher volumetric efficiency at high load. However, SIDI engines tend to make more PM than their port-injected counterparts, with PM mass levels exceeding those of diesels equipped with diesel particulate filters.
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