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Automobile Emissions: A Problem-Based Learning Activity Using the Clean Air Act

Abstract

A problem-based learning activity has been developed using automotive engineering and requirements of the Clean Air Act to examine complex environmental issues involving automobiles. After an introductory study, students sample the O2, CO, NO, and NO2 levels of automobile exhaust and analyze the results. The activity employs a constructivist approach and is appropriate for entry-level engineering classes. It can be modified for use in upper level engineering classes as well. To prepare for the emissions analysis lab, students study the composition of atmospheric gases, products of combustion, and the measurement of automotive emissions. The laboratory component is the actual sampling of engine exhaust from student selected automobiles using an exhaust emissions analyzer. Students use sample values of emission concentrations for O2, CO, NO, and NO2, combustion kinetics, and fluid dynamics to calculate the engine fuel flow rate, exhaust flow rate, and mass emission rates for CO and NOX. This paper presents an overview of the introductory studies followed by a description of the automobile exhaust sampling activity. Representative sample data of automobile emissions are presented along with a discussion of the sampling results, a method for approximating pollutant mass emission rate levels, and comparison to EPA standards.

Introduction

Media coverage of environmental issues and global climate change occurs daily. Engineering students are continuously exposed to environmental topics and many are interested in pursuing environmental engineering careers. How can engineering educators incorporate contemporary issues in environmental engineering into the classroom? The activity described in this paper is designed to introduce students to automobile exhaust pollutant issues in a problem-based learning activity. The activity takes advantage of the growing availability and ease of use of portable emissions analyzers for exhaust testing. For the first part of the activity, students investigate the topic and associated issues. The second part of the activity is a laboratory component, consisting of sampling engine exhaust from student selected automobiles using an exhaust emissions analyzer. The analyzer includes a probe that is inserted into the exhaust stream from the tailpipe of a stationary automobile. Students collect concentrations of selected exhaust gases; in this case O2, CO, NO, and NO2. Calculations are performed to convert the concentrations in parts per million to mass emission rates in grams per mile or grams per brake horsepower-hour using estimates of the operating conditions of the engines, combustion kinetics, and fluid dynamics. The method for sampling and calculating levels of exhaust gases used in this in this activity is an approximation. It does not represent EPA test guidelines and is not considered a standardized method. But it does provide students the opportunity for useful experience that is needed to develop and guide understanding of the topic along with experience in making assumptions and estimates for rapid problem solving. For the third part of the activity, students are asked to develop their own problem to examine such as testing additional vehicles or examining the difference between emissions from cold and hot engines.

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Grauer, B., & Grauer, D. (2010, June), Automobile Emissions: A Problem Based Learning Activity Using The Clean Air Act Paper presented at 2010 Annual Conference & Exposition, Louisville, Kentucky. 10.18260/1-2--15960