API PUBL 4650-1997

$22.75

Analysis of High-Mileage-Vehicle Emissions Data from Late-Model, Fuel-Injected Vehicles

Published By	Publication Date	Number of Pages
API	1997	58

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Description

A recent analysis of the Environmental Protection Agency's (EPA) on-road vehicle emission factors model, MOBILE5Z4suggested that exhaust emissions of newer model, fuel-injected vehicles were over-predicted at high mileage. That over-prediction, which results in over predictions of fleet-average emission rates for future calendar years, was related to the paucity of data from modem technology, high-mileage vehicles available for the development of MOBILE5a. To bolster the database available for the next version of the MOBILE model, the American Petroleum Institute (API) sponsored a test program to investigate the exhaust emission control system deterioration characteristics of late-model, fuel-injected vehicles. Seventy-five light-duty vehicles were procured and tested over the Federal Test Procedure in this program. Vehicles included in the program were from the 1985 to 1992 model years, had accumulated at least 100,000 miles, and had never been subject to an inspection and maintenance (I/M) program. Vehicles were recruited at a site in Chicago Heights (CH), Illinois, and two separate sites in Phoenix, Arizona. The test program was conducted from April 1995 to August 1996.

Analysis of the data collected in this High-Mileage Vehicle (HMV) project revealed that model year was a more important determinant of emissions than fuel-injection technology (i.e., port fuel injection versus throttle body injection), with vehicles in the 1988 and later model year group demonstrating substantially lower emissions than vehicles in the 1985 to 1987 model year group. A comparison of emissions results from vehicles tested in this program to predictions from EPA's TECH5 model (which was used to generate base emission rate equations for MOBILE5a) indicated that TECH5 may be over predicting emissions of late-model vehicles at high mileage, which has a significant impact on fleet-average emission rates calculated by MOBILE5a for future analysis years. Finally, a comparison of high-mileage vehicle emissions data from this project to data collected by EPA in Hammond, Indiana (which were collected approximately four to five years prior to the HMV project and were the basis of MOBlLE5a) indicated that newer model year vehicles are more durable (from an emissions perspective) at equivalent age and mileage.

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