Analysis of Modal Emissions From Diverse In-Use Vehicle Fleet

Abstract

Research Program. This paper describes the initial phase of a longterm project with national implications for the improvement of transportation and air quality. The overall objective of the research is to develop and verify a comprehensive modal emissions model that accurately reflects the impacts of a vehicle's operating mode. The model is comprehensive in the sense that it will be able to predict emissions for a wide variety of light-duty vehicles (LDVs, i.e., cars and trucks) in various states of condition (e.g., properly functioning, deteriorated, malfunctioning). Other efforts and further background on modal emission modeling have been described elsewhere (1) and elsewhere in this Record by An et al.A specific modal emissions testing protocol has been developed that reflects both real-world driving and specific modal events associated with different levels of emissions. This testing protocol (described later in this paper) is being applied to more than 300 vehicles to provide the foundation for the modal emissions model. As a preliminary step, the test cycle has been applied to an initial fleet of 30 vehicles, where at least 1 vehicle falls into each of the 28 defined vehicle/technology categories. The preliminary analysis of the initial test fleet is described. VEHICLE/TECHNOLOGY CATEGORIZATIONThe conventional emission inventory models are based on bag emissions data (FTP) collected from certification tests of new cars, surveillance programs, and inspection/maintenance programs. These large sets of emissions data provide the basis for the conventional emission inventory models and are indexed primarily by model year. For LDVs, groupings are based on a few different vehicle classes and technology groups.In developing a modal emission model, we cannot base the model on these bag data and must collect second-by-second emissions data from a sample of vehicles to build a model that predicts emissions for the national fleet. The choice of vehicles for this sample is therefore crucial, since only a small sample (300+ vehicles) will be the basis for the model.The determination of the vehicle/technology categories in the modal model is a critical task, not only for vehicle recruitment and testing but also for the development of the model. Because the eventual output of the model is emissions, the vehicle/technology categories and the sampling proportions of the major vehicle/technology groups (normal versus high emitter, and carbureted versus fuel injected versus Tier 1) have been chosen based on each major category's contribution to total emissions, as opposed to a group's actual population in the national fleet. Recent results from both remote sensing and surveillance studies have indicated that a small population of vehicles contribute a substantial fraction of the total emissions The initial phase of a long-term project with national implications for the improvement of transportation and air quality is described. The overall objective of the research is to develop and verify a computer model that accurately esti...

Real-World Carbon Dioxide Impacts of Traffic Congestion

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A Modal Approach to Vehicular Emissions and Fuel Consumption Model Development

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Characterizing the effects of driver variability on real-world vehicle emissions

“…Inspection/maintenance program smog-check inspections provide data on in-use vehicles, but are inadequate indicators of on-road emissions since the tests are performed over only two no-load engine operating conditions (2500 rpm and idle). While more recent research has focused on correlating driving mode with emissions (Hansen et al, 1995;Jensen, 1995;Joumard et al, 1995;Sjodin and Lenner, 1995;Barth et al, 1997;Washington et al, 1997;Young et al, 1997), emissions were usually estimated from emission models rather than measured directly in the ®eld. The few studies that have used on-board gas analyzers (Schurmann and Staab, 1990;Kelly and Groblicki, 1993;Guenther et al, 1996) demonstrated the capabilities of these instruments to measure second-by-second emission levels to aid in repair of malfunctioning emission systems, but made no e ort to correlate driving style and emission levels.…”

“…Denis et al, 1994;Ross et al, 1995). New driving cycles are currently being proposed since it has recently become apparent that the FTP cycle is too limited to account for today's real-world driver behavior (Ross et al, 1995;Barth et al, 1997;Washington et al, 1997), but adoption of a new cycle awaits widespread ®eld data collection and analysis. Key to adoption of a new cycle is demonstration that it adequately represents today's real-world driving.…”