Emissions and Fuel Economy of a 1998 Toyota with a Direct Injection Spark Ignition Engine

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Abstract
A 1998 Toyota Corona passenger car with a direct injection spark ignition (DISI) engine was tested via a variety of driving cycles using California Phase 2 reformulated gasoline. A comparable PFI vehicle was also evaluated. The standard driving cycles examined were the Federal Test Procedure (FTP), Highway Fuel Economy Test, US06, simulated SC03, Japanese 10-15, New York City Cycle, and European ECE+EDU. Engine-out and tailpipe emissions of gas phase species were measured each second. Hydrocarbon speciations were performed for each phase of the FTP for both the engine-out and tailpipe emissions. Tailpipe particulate mass emissions were also measured. The results are analyzed to identify the emissions challenges facing the DISI engine and the factors that contribute to the particulates, NOx, and hydrocarbon emissions problems of the DISI engine. The NOx emissions difficulties for the FTP and Supplemental FTP stem from the low efficiency of the lean NOx trap/catalyst on the DISI vehicle, in spite of its' lower engine-out NOx. The DISI vehicle has both higher engine-out and tailpipe HCs for essentially all modes of operation during the FTP, and thus the HC emissions problems are not dominated by the first 1-2 minutes of operation. The Specific Reactivity of the HCs is lower, but due to the high HC emissions, the Ozone Forming Potential is higher for the DISI vehicle. Relative to the PFI vehicle, the engine-out NMOG is more abundant in aromatics and less abundant in alkenes. Tentative evidence is presented that relates the abundance of the engine-out HC species to their volatility. It is also found that the fuel economy advantage of this vehicle is not as high as expected, but is quite good for the New York City Cycle and the Japanese cycle. It is shown that much of the fuel economy potential of lean unthrottled operation is sacrificed to light-off and regenerate the lean NOx trap/catalyst. Implications for use of a DISI engine in a hybrid electric vehicle are discussed.

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