UVM Theses and Dissertations
Format:
Print
Author:
Sentoff, Karen M.
Dept./Program:
Civil and Environmental Engineering
Year:
2013
Degree:
MS
Abstract:
A significant proportion of anthropogenic air pollution can be attributed to the tailpipe emissions of the light-duty vehicle fleet. As new technologies are introduced to address fuel consumption and pollution concerns, methods for estimating tailpipe emissions from hybrid vehicles become more pertinent. Current literature has emphasized the importance of quantifying the influence of ambient temperature and road grade along widely varying terrain on vehicle tailpipe emissions, but few researchers have investigated their effects on hybrid electric vehicles. This study aimed to (1) quantify the tailpipe emission rates from a hybrid vehicle compared to its conventional counterpart, (2) identify real-world operating ranges where hybrid pollutant emission rates were equivalent to or exceed those of the conventional, and (3) quantify the influence of both road grade and ambient temperature on the operation and the tailpipe emissions of the hybrid as compared to the conventional vehicle.
Tailpipe emissions data from hybrid and conventional model year 2010 Toyota Camry vehicles were collected during real-world driving on a single, 32-mile route over a period of 18 months. Samples from the tailpipe were transferred into the vehicles and analyzed for gas-phase pollutants in real-time by an MKS MultiGas 2030 Analyzer, a commercially available Fourier Transform Infrared Spectrometer (FTIR). Additional measurements including vehicle and engine operating parameters, tailpipe flow rate, GPS location, road grade, ambient temperature, and relative humidity were collected simultaneously, second-by-second.
Carbon monoxide (CO), carbon dioxide (CO₂), ammonia (NH₃), nitric oxide (NO), and nitrogen dioxide (NO₂) were the focus of the study as they were routinely quantifiable during stabilized operation of the Toyota Camry vehicles, both of which had low mileage accumulation and little wear on emission control devices at the time of sampling. These detectable pollutants were categorized by operating modes (OpModes), defined by the EPA MOVES model using vehicle specific power (VSP) and speed, to quantify the differences in tailpipe emission rates between the hybrid and conventional vehicles. Hybrid pollutant emission rates were equivalent to or greater than the conventional vehicle for OpModes with VSP at or exceeding 30 kW/ton, an important consideration for adjusting current models to estimate hybrid emissions. Engine-off operation of the hybrid vehicle (propulsion with no associated tailpipe emissions) was sensitive to both road grade and temperature.
The steepest road grades encountered along the route were associated with 100% engine-off operation for downhill (down to -13% grade) and 0% engine-off operation for uphill (up to 11% grade). Percent engine-off operation increased by 7% for high temperatures (above 22°C) as compared to cold temperatures (below 5°C). Although high CO, NH₃, NO, and NO₂ emission events for the hybrid were evident for cold ambient temperatures and positive road grades, these pollutants did not have significant relationships with the components of VSP (speed, acceleration, and grade), limiting the ability to model these emissions. A model of CO₂ emission rates was developed as a function of VSP neglecting road grade, and was improved with the addition of road grade, increasing the explanatory power of the model by 29%. When CO₂ emissions were modeled as a function of VSP components, addition of temperature to the model was inconsequential compared to the addition of road grade. Although road grade initially appeared to have a greater influence on the CO₂ emission rates of the conventional vehicle, excluding engine-off operation from the hybrid model resulted in an increase of 705 mg/s CO₂ for every 1% increase in road grade, greater than the 633 mg/s increase for the conventional vehicle.
Tailpipe emissions data from hybrid and conventional model year 2010 Toyota Camry vehicles were collected during real-world driving on a single, 32-mile route over a period of 18 months. Samples from the tailpipe were transferred into the vehicles and analyzed for gas-phase pollutants in real-time by an MKS MultiGas 2030 Analyzer, a commercially available Fourier Transform Infrared Spectrometer (FTIR). Additional measurements including vehicle and engine operating parameters, tailpipe flow rate, GPS location, road grade, ambient temperature, and relative humidity were collected simultaneously, second-by-second.
Carbon monoxide (CO), carbon dioxide (CO₂), ammonia (NH₃), nitric oxide (NO), and nitrogen dioxide (NO₂) were the focus of the study as they were routinely quantifiable during stabilized operation of the Toyota Camry vehicles, both of which had low mileage accumulation and little wear on emission control devices at the time of sampling. These detectable pollutants were categorized by operating modes (OpModes), defined by the EPA MOVES model using vehicle specific power (VSP) and speed, to quantify the differences in tailpipe emission rates between the hybrid and conventional vehicles. Hybrid pollutant emission rates were equivalent to or greater than the conventional vehicle for OpModes with VSP at or exceeding 30 kW/ton, an important consideration for adjusting current models to estimate hybrid emissions. Engine-off operation of the hybrid vehicle (propulsion with no associated tailpipe emissions) was sensitive to both road grade and temperature.
The steepest road grades encountered along the route were associated with 100% engine-off operation for downhill (down to -13% grade) and 0% engine-off operation for uphill (up to 11% grade). Percent engine-off operation increased by 7% for high temperatures (above 22°C) as compared to cold temperatures (below 5°C). Although high CO, NH₃, NO, and NO₂ emission events for the hybrid were evident for cold ambient temperatures and positive road grades, these pollutants did not have significant relationships with the components of VSP (speed, acceleration, and grade), limiting the ability to model these emissions. A model of CO₂ emission rates was developed as a function of VSP neglecting road grade, and was improved with the addition of road grade, increasing the explanatory power of the model by 29%. When CO₂ emissions were modeled as a function of VSP components, addition of temperature to the model was inconsequential compared to the addition of road grade. Although road grade initially appeared to have a greater influence on the CO₂ emission rates of the conventional vehicle, excluding engine-off operation from the hybrid model resulted in an increase of 705 mg/s CO₂ for every 1% increase in road grade, greater than the 633 mg/s increase for the conventional vehicle.