Semester

Summer

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Gregory Thompson

Committee Member

Melissa Abbott

Committee Member

Marc Besch

Committee Member

Nigel Clark

Committee Member

Arvind Thiruvengadam

Abstract

Light-duty diesel vehicles have received significant public and governmental scrutiny recently for violating emissions regulations. Similar to the heavy-duty diesel manufacturers during the late 1990’s, some light-duty manufacturers were implementing different control strategies between laboratory certification tests and customer on-road operation. These devices allowed the vehicle to pass certification tests but then use alternative operation on the road during normal use. The alternative operation would allow for better fuel economy but higher oxides of nitrogen (NOx) emissions. Light-duty vehicles are currently certified in the US using chassis dynamometer testing. The effects of all on-road driving conditions are not mimicked in the chassis dynamometer test cycles, and, in particular, the terrain is not considered during these certification tests. Certification in Europe now includes a real driving emissions (RDE) component that attempts to include the emissions levels of a broader range of driving conditions. However, the testing constraints of the on-road tests attempt to make the driving conditions similar to the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) chassis test by utilizing a CO2 criterion. This study's primary objective is to develop a grade-based weighting system for calculating on-road emissions of light-duty vehicles. The secondary objective is to analyze the effects of road grade on overall emissions and EURO RDE calculated emissions. A variety of routes, including city, rural, and interstate driving, were included. Each category of driving included routes with a various levels of road grade. The overall distance-based NOx emission results revealed that road grade had little effect during city driving. However, a clear trend of increased NOx emission with increased road grade could be seen for rural and interstate routes. As road grade is increased, the NOx increased by 20 and 4 times for rural and interstate routes, respectively. Individual hill climb events indicated that the certification value of NOx emissions would be exceeded at a road grade above 1.5%. The NOx emissions then increase exponentially as road grade increased further. The EURO RDE method also showed an increase of NOx emissions with road grade. In some moderate road grade cases, the EURO RDE calculation produced NOx emissions that were 11% higher than the actual overall emissions calculation. A grade-based weighting system was developed utilizing the road grade distribution of US highways. On-road test runs are analyzed using a fixed distance moving window. Windows having a grade of less than 1% are given a weighting factor of one. Windows with grade greater than 1% are given a lower weighting factor based on US highways' road grade distribution. The grade-based method produced similar results compared to the EURO RDE method with as much as 40% lower weighted distance-based NOx emission for higher grade routes. In all cases, the grade-based method calculated distance-based NOx emissions lower than the actual overall distance-based NOx calculation. In higher road grades, the grade-based method retains as much as 30% more of the actual emissions data when compared to the EURO RDE method. The grade-based method also shows less variation of NOx emissions when road grade is increased.

Embargo Reason

Publication Pending

Available for download on Saturday, July 30, 2022

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