On-road heavy-duty diesel vehicles are a major contributor of oxides of nitrogen (NO) emissions. In the US, many heavy-duty diesel vehicles employ selective catalytic reduction (SCR) technology to meet the 2010 emission standard for NO. Typically, SCR needs to be at least 200°C before a significant level of NO reduction is achieved. However, this SCR temperature requirement may not be met under some real-world operating conditions, such as during cold starts, long idling, or low speed/low engine load driving activities. The frequency of vehicle operation with low SCR temperature varies partly by the vehicle's vocational use. In this study, detailed vehicle and engine activity data were collected from 90 heavy-duty vehicles involved in a range of vocations, including line haul, drayage, construction, agricultural, food distribution, beverage distribution, refuse, public work, and utility repair. The data were used to create real-world SCR temperature and engine load profiles and identify the fraction of vehicle operating time that SCR may not be as effective for NO control. It is found that the vehicles participated in this study operate with SCR temperature lower than 200°C for 11-70% of the time depending on their vocation type. This implies that real-world NO control efficiency could deviate from the control efficiency observed during engine certification.
The Kansas City Light-Duty Vehicle Emissions Study (KCVES) measured exhaust emissions of regulated and unregulated pollutants from 496 vehicles recruited in the Kansas City metropolitan area in 2004 and 2005. Vehicle emissions testing occurred during the summer and winter, with the vehicles operated at ambient temperatures. One key component of this study was the investigation of the influence of ambient temperature on particulate matter (PM) emissions from gasoline-powered vehicles. A subset of the recruited vehicles were tested in both the summer and winter to further elucidate the effects of temperature on vehicle tailpipe emissions. The study results indicated that PM emissions increased exponentially as temperature decreased. In general, PM emissions doubled for every 20 degrees F drop in ambient temperature, with these increases independent of vehicle model year. The effects of temperature on vehicle emissions was most pronounced during the initial start-up of the vehicle (cold start phase) when the vehicle was still cold, leading to inefficient combustion, inefficient catalyst operation, and the potential for the vehicle to be operating under fuel-rich conditions. The large data set available from this study also allowed for the development of a model to describe temperature effects on PM emission rates due to changing ambient conditions. This study has been used as the foundation to develop PM emissions rates, and to model the impact of ambient temperature on these rates, for gasoline-powered vehicles in the EPA's new regulatory motor vehicle emissions model, MOVES.
Despite much work in recent years, vehicle emissions remain a significant contributor in many areas where air quality standards are under threat. Policy-makers are actively exploring options for next generation vehicle emission control and local fleet management policies, and new monitoring technologies to aid these activities. Therefore, we report here on findings from two separate but complementary blind evaluation studies of one new-to-market real-world monitoring option, HEAT LLC's Emission Detection And Reporting system or EDAR, an above-road open path instrument that uses Differential Absorption LIDAR to provide a highly sensitive and selective measure of passing vehicle emissions. The first study, by Colorado Department of Public Health and Environment and Eastern Research Group, was a simulated exhaust gas test exercise used to investigate the instrumental accuracy of the EDAR. Here, CO, NO, CH and CH measurements were found to exhibit high linearity, low bias, and low drift over a wide range of concentrations and vehicle speeds. Instrument accuracy was high (R 0.996 for CO, 0.998 for NO; 0.983 for CH; and 0.976 for CH) and detection limits were 50 to 100ppm for CO, 10 to 30ppm for NO, 15 to 35ppmC for CH, and, depending on vehicle speed, 100 to 400ppmC for CH. The second study, by the Universities of Birmingham and Leeds and King's College London, used the comparison of EDAR, on-board Portable Emissions Measurement System (PEMS) and car chaser (SNIFFER) system measurements collected under real-world conditions to investigate in situ EDAR performance. Given the analytical challenges associated with aligning these very different measurements, the observed agreements (e.g. EDAR versus PEMS R 0.92 for CO/CO; 0.97 for NO/CO; ca. 0.82 for NO/CO; and, 0.94 for PM/CO) were all highly encouraging and indicate that EDAR also provides a representative measure of vehicle emissions under real-world conditions.
Recent measurements and modeling of primary exhaust particulate matter (PM) emissions from both gasoline and diesel-powered motor vehicles suggest that many vehicles produce PM at rates substantially higher than assumed in the current EPA PM emission factor model, known as “PART5.” The discrepancy between actual versus modeled PM emissions is generally attributed to inadequate emissions data and outdated assumptions in the PART5 model. This paper presents a study with the objective of developing an in-house tool (a modified PART5 model) for the Texas Natural Resource Conservation Commission (TNRCC) to use for estimating motor vehicle exhaust PM emissions in Texas. The work included chassis dynamometer emissions testing on several heavy-duty diesel vehicles at the Southwest Research Institute (SwRI), analysis of the exhaust PM emissions and other regulated pollutants (i.e., HC,CO,NOx), review of related studies and exhaust PM emission data obtained from literature of similar types of light and heavy-duty vehicle tests, a review of the current PART5 model, and analysis of the associated emission deterioration rates. Exhaust PM emissions data obtained from the vehicle testing at SwRI and other similar studies (covering a relatively large number and wide range of vehicles) were merged, and finally, used to modify the PART5 model. The modified model, which was named PART5-TX1, was then used to estimate new exhaust PM emission factors for in-use motor vehicles. Modifications to the model are briefly described, along with emissions test results from the heavy-duty diesel-powered vehicles tested at SwRI. Readers interested in a detailed understanding of the techniques used to modify the PART5 model are referred to the final project report to TNRCC (Eastern Research Group 2000).
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