Exhaust Emissions of a Vehicle with a Gasoline Direct-Injection Engine

Their high fuel economy is making light-duty vehicles with spark-ignition direct-injection (SIDI) engines attractive. However, the implications for exhaust emissions and the effects of fuel quality on emissions are not clear for this type of engine. A Mitsubishi Legnum with a 1.8-L GDI™ engine was tested on federal test procedure (FTP) and highway fuel economy cycles. The results were compared with those for a production Dodge Neon vehicle with a 2.0-L port fuel-injection (PFI) engine. The Mitsubishi was tested with Indolene, Amoco Premium Ultimate, and a low-sulfur gasoline. The Neon was tested only with Indolene. Both engine-out and tailpipe emissions were measured. Second-by-second emissions and hydrocarbon speciation were also evaluated. The SIDI engine provided up to 24% better fuel economy than the PFI engine on the highway cycle. Tailpipe emissions of oxides of nitrogen (NO_x) from the SIDI vehicle using low-sulfur fuel were 40% less than those when using Indolene. Tailpipe weighted-average emissions of total hydrocarbons (THC) and NO_x from the SIDI vehicle were 2.9 and 9.5 times more than those from the PFI vehicle, respectively. The SIDI vehicle, as tested, did not meet the Tier II (year 2004) emissions limits for NMHC and NO_x, but it did meet the limit for CO emissions. Second-by-second emissions data show that the SIDI catalyst required more than 200 s to warm up, while the PFI catalyst required about 60 s. The ozone-forming potential of the SIDI vehicle running on Indolene was 13% more than that of the PFI vehicle. It appears that, from a fuel economy standpoint, the SIDI engine is a viable alternative to a turbocharged DI diesel for the U.S. Department of Energy's Partnership for a New Generation of Vehicles program, but simply replacing a PFI engine with a SIDI engine is not sufficient to achieve either the 80-mpg or the strict emissions goals.