EPA 600/R-18/299 | September 2019 | www.epa.gov/research United States Environmental Protection Agency v>EPA Cold Temperature Effects on Speciated VOC Emissions from Modern GDI Light-Duty Vehicles Office of Research and Development ------- Cold Temperature Effects on Speciated VOC Emissions from Modern GDI Light-Duty Vehicles Ingrid George, Michael Hays, Richard Snow, James Faircloth, Thomas Long, Richard Baldauf Office of Research and Development United States Environmental Protection Agency 109 T.W. Alexander Drive Research Triangle Park, NC 27711 george.ingrid@epa.gov Disclaimer: This product has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. ABSTRACT In this study, speciated volatile organic carbon (VOC) emissions were characterized from three modern gasoline direct injection (GDI) light-duty vehicles. The vehicles were tested on a chassis dynamometer housed in a climate-controlled chamber at two temperatures (20 and 72 °F) over the EPA Federal Test Procedure (FTP) and a portion of the Supplemental FTP (i.e. US06) that represents more aggressive driving conditions. The vehicles operated on gasoline blended with 10% ethanol. VOC emissions from diluted vehicle exhaust were sampled with SUMMA canisters for EPA Method TO-15 analysis and with 2,4-Dinitrophenylhydrazine (DNPH) cartridges for carbonyl analysis by EPA Method TO-11 A. This presentation will report the impact of ambient cold temperature, driving cycle, and GDI technology on speciated VOC emissions. INTRODUCTION The transportation sector contributes approximately 20% of total non-biogenic volatile organic compound (VOC) emissions in the United States. Therefore, it is imperative to obtain a detailed understanding of speciated VOC emissions from mobile sources to accurately assess the air quality and health impacts of the transportation sector. To address the need for mobile source speciated VOC emissions data, one major goal of the U.S. EPA's Office of Research and Development vehicle emissions research is to comprehensively characterize speciated emissions from modern vehicles and assess the impacts of various fuels, temperatures, newer engine, and aftertreatment technologies. This study focused on measurements of speciated exhaust emissions from gasoline direct injection (GDI) vehicles representing newer engine technologies. GDI engines were introduced into the vehicle market in the U.S. in 2007, and the technology has since quickly risen in popularity. Currently, GDI vehicles represent nearly a half of the U.S. light-duty vehicle market share. However, the speciated emissions data on these types of vehicles is extremely sparse and the effect of cold temperature on GDI vehicle emissions is unknown. Therefore, the objective of this study was to characterize speciated emissions from three GDI vehicles at two ambient temperatures. ------- METHODS Three light-duty GDI vehicles were tested during this vehicle emissions study. All vehicles were in the U.S. EPA Tier 2 Bin 5 emission standard class and each vehicle represented different types of GDI technologies. The model years (MY), odometer readings at the study start (ODO), engine displacements (ED), and GDI technology types are given below for the three vehicles (VI, V2, V3). 1) VI: MY 2014 (Tier 2, Bin 5), ODO=12,700 miles, ED = 2.4 liter, GDI technology: Naturally aspirated, wall-guided GDI engine 2) V2: MY 2015 (Tier 2, Bin 5), ODO=10,500 miles, ED = 1.5 liter, GDI technology: Spray-guided, turbocharged GDI engine 3) V3: MY 2014 (Tier 2, Bin 5), ODO=9,200 miles, ED = 1.8 liter, GDI technology: Wall and air guided, turbocharged GDI engine Vehicles were operated on 10% ethanol blended with gasoline (E10) sourced from a local distributor. Vehicle testing was conducted on a 48 inch roll chassis dynamometer housed inside a climate controlled chamber. Vehicles were tested at two ambient temperatures (20 and 72 °F). Each vehicle was driven on the Federal Test Procedure (FTP) followed by a portion of the Supplemental Federal Test Procedure (also called US06) and vehicle testing for each test condition was conducted in triplicate. The vehicle exhaust was diluted by approximately 20-30 times in a constant volume sampling dilution tunnel, where the flow was controlled by a critical flow venturi. Real-time emissions were characterized by continuous emissions monitors for carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), total hydrocarbon (THC) and nitrogen oxides (NOx). Time- integrated samples for VOCs were taken from the dilution tunnel for the three phases of the FTP (FTP1, FTP2, FTP3) and US06. VOC samples taken included SUMMA canisters for EPA Method TO-15 analysis and 2,4-Dinitrophenylhydrazine (DNPH) cartridges for gas-phase carbonyls by TO-11A analysis. Canister samples were analyzed by gas chromatography-mass spectrometry (GC/MS). DNPH cartridges were extracted with acetonitrile and extracts were analyzed by high-performance liquid chromatography (HPLC). RESULTS Real-time Hydrocarbon Emissions Real-time non-methane hydrocarbon (NMHC) emissions determined from the difference between the THC and CH4 measurements from a representative test for V2 were evaluated to better understand how the VOC emissions varied over the driving cycles. The NHMC trace over the FTP driving cycle for V2 showed that there was an extremely large spike early in the cold ------- start FTP1 phase. The majority of the total NMHC emissions over the FTP were represented by this early cold start peak within the first 200 s of the FTP. After this initial peak, a few minor peaks in NHMC emissions were observed during the FTP during driving accelerations. The US06 driving cycle represents substantially more aggressive driving compared to the FTP. As a result, the NMHC trace over the US06 for the same test showed numerous spikes in NHMC emissions that coincided with intensive accelerations during the driving cycle. Time-integrated VOC emissions Time-integrated emission rates were calculated for 134 individual VOCs over each driving cycle and test condition for VI, V2 and V3. Figure 1 shows the sum of all speciated VOC emission rates (XVOCs) that were averaged over three replicate tests for each condition. It was observed that cold start FTP1 had substantially higher EVOC emissions compared to other phases of the FTP and US06, and were between 4 to 400 times higher than warm start FTP3 tests. EVOC emission rates during FTP1 20 °F tests, as represented by the striped bars in Figure 1, were strongly enhanced compared to FTP1 72 °F tests, where the cold temperature enhancements varied for each vehicle. However, cold temperature enhancements in VOC emissions were modest for other driving phases and US06. It was also found that VOC emission rates for V2 were substantially higher than for the other two vehicles with the exception of FTP 1 V3 testing at 20 °F. Figure 1. Sum of speciated VOC emission rates for each test condition and vehicle. 1.20 1.00 - 0) 0.80 - E cn — 0.60 - ui C) / o > 0.10 - 0.05 - 0.00 - i a v\ Vi ! FTP1 mamf2 FTP2 iEI V1 72F F7Z7I V1 20F V2 72F rzzz] V2 20F V3 72F V3 20F FTP3 US06 VOC emission profiles for the three vehicles during FTP1 cold start of the 25 highest emitted VOCs are shown in Figure 2 for 72 °F (top panel) and 20 °F (bottom panel). The highest emitted VOCs during the FTP1 include a number of hazardous air pollutants, such as benzene and toluene, as well as a number of hydrocarbons found in E10 gasoline. During the warm temperature tests, VOC emission rates from V2 were substantially higher than for the other two vehicles across all VOCs measured. However, during cold temperature tests V3 emissions were higher for most of the major VOCs shown in Figure 2. It is currently unclear what the underlying ------- mechanism for these vehicle specific temperature effects might be. Real-time measurements and other ancillary data acquired during the study will be further examined to better understand these observed trends. Figure 2. VOC profiles for FTP1 at 72 °F (top) and 20 °F (bottom) CONCLUSIONS In this study, detailed speciated VOC emissions from three GDI vehicles at two ambient temperatures (20 and 72 °F) were measured. We observed substantial differences in VOC emissions between vehicles that were temperature dependent and VOC emissions were higher during the cold start FTP1 compared to other driving phases and cold temperature FTP1 tests compared to warm temperature test conditions. This work significantly increases the available emissions data for modern light-duty GDI vehicles that will improve emission inventories and air quality model predictions. ------- Key Words Volatile organic compounds Vehicle exhaust Gasoline direct injection Chassis dynamometer ------- |