Cold Temperature and Biodiesel Fuel Effects on Speciated Emissions of Volatile Organic Compounds from Diesel Trucks
Ingrid GeorgeMichael D. HaysRichard SnowJames FairclothBarbara Jane GeorgeThomas C. LongRichard Baldauf
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Abstract:
Speciated volatile organic compounds (VOCs) were measured in diesel exhaust from three heavy-duty trucks equipped with modern aftertreatment technologies. Emissions testing was conducted on a chassis dynamometer at two ambient temperatures (-7 and 22 °C) operating on two fuels (ultra low sulfur diesel and 20% soy biodiesel blend) over three driving cycles: cold start, warm start and heavy-duty urban dynamometer driving cycle. VOCs were measured separately for each drive cycle. Carbonyls such as formaldehyde and acetaldehyde dominated VOC emissions, making up ∼ 72% of the sum of the speciated VOC emissions (∑VOCs) overall. Biodiesel use led to minor reductions in aromatics and variable changes in carbonyls. Cold temperature and cold start conditions caused dramatic enhancements in VOC emissions, mostly carbonyls, compared to the warmer temperature and other drive cycles, respectively. Different 2007+ aftertreatment technologies involving catalyst regeneration led to significant modifications of VOC emissions that were compound-specific and highly dependent on test conditions. A comparison of this work with emission rates from different diesel engines under various test conditions showed that these newer technologies resulted in lower emission rates of aromatic compounds. However, emissions of other toxic partial combustion products such as carbonyls were not reduced in the modern diesel vehicles tested.Keywords:
Driving cycle
Cold start (automotive)
Ultra-low-sulfur diesel
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Oxygenate
The passage of the amended Clean Air Act on November 15, 1990, established a permanent role for oxygenates in U.S. gasoline for the foreseeable future. This status for oxygenates was confirmed approximately a month later by analytical results from the first phase of the Auto/Oil Air Quality Improvement Research Program. In view of these events, this article, the second of a two part series, presents an estimate of oxygenate requirements for 1995 ozone and carbon monoxide attainment.
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Spark-ignition (SI) engines are highly susceptible to excess emissions when started at low ambient temperatures, a phenomenon which has been widely discussed in the literature. Direct injection diesel engines feature a markedly different fuelling and combustion strategy, and as such their emissions behaviour is somewhat different from gasoline engines. The excess emissions of diesel engines at low ambient temperatures should also differ. The aim of this study was to compare excess emissions of gaseous and solid pollutants over a legislative driving cycle (the New European Driving Cycle, NEDC) following cold start at a low ambient temperature for both engine types. This paper examines emissions at low ambient temperatures with a special focus on cold start; emissions are also compared to start-up at a higher ambient temperature (24 °C). The causes of excess emissions andfuel consumption are briefly discussed. A series of tests were performed on European Euro 5 passenger cars on a chassis dynamometer within an advanced climate-controlled test laboratory at BOSMAL Automotive Research and Development Institute, Poland. Emissions data obtained over the Urban Driving Cycle by testing at 24 °C and at -7 °C, are presentedfor a selection ofmodern Euro 5 gasoline and diesel vehicles representative of the European passenger carfleet. A full modal emissions analysis was also conducted at 24 °C and at -7 °C over the NEDC. Emissions andfuel consumption were substantially higher at -7 °C than at 24 °C.
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Co-processing of H2O, CO2, and light (C1–2) oxygenates with CH4 at 950 K over Mo/H-ZSM-5 catalysts results in complete fragmentation of the oxygenate and CO as the sole oxygen-containing product. The C/Heff accounts for removal of O as CO and describes the net C6H6 and total hydrocarbon synthesis rates at varying (0.0–0.10) oxygenate and H2 to CH4 co-feed ratios.
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After an inquiry to 39 European laboratories, 15 500 measurements (1 measurement corresponds to 1 vehicle, 1 normalised or representative cycle and 1 pollutant) concerning 661 vehicles were analysed in order to model the pollutant over-emission (C02, CO, HC, NOx) during cold start and fuel over-consumption. Using these data, we propose an equation describing the relation between over-emission and the following parameters technology (diesel, catalyst and conventional cars), average speed, ambient temperature and travelled distance. The obtained data were measured for passenger cars and an extension to duty vehicles proposed. The model is a part of an emission inventory model.
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Most vehicle tailpipe emissions are related to the cold-start condition. In the present study, a novel methodology is introduced to trap the cold-start emissions. A numerical model is used to investigate the method implementation on the vehicle’s cold-start emissions. Model is validated with the experimental data. Three different driving cycles are simulated to understand the effects of the employed method. The results show that the light-off temperature is independent of the driving cycle, while the light-off time is highly dependent on the driving behavior. The presented concept is more effective for traffic conditions and the low required powers of the vehicle. The most emission reduction is related to the emissions with moderate increment after catalyst light off. Therefore, the most considerable reduction is related to the NOx emission in all driving conditions, while method implementation is not beneficial for CO reduction compared to NOx. The emission reduction varies from 20% (WLTC) to 35% (NEDC) for CO emission, from 25% (WLTC) to 34% (NEDC and FTP75) for HC emission and 41% (FTP75) to 51% (NEDC) for NO X emission. This idea would help gasoline-powered vehicles to pass more strict emissions such as Euro7 in the coming future.
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