The Health Effects Institute

Synopsis
Research Report Number 76

Effects of Fuel Modification and Emission Control Devices on Heavy-Duty Diesel Engine Emissions

Susan T. Bagley, Kirby J. Baumgard, Linda D. Gratz, John J. Johnson, and David G. Leddy
Department of Biological Sciences, Department of Mechanical Engineering and Engineering Mechanics, and Department of Chemistry, Michigan Technological University, Houghton, MI

BACKGROUND

Diesel engine exhaust contains small carbonaceous particles and a large number of chemicals that are adsorbed onto these particles or present as vapors. Diesel exhaust is a public health concern because (1) the particles are an important component of air pollution, (2) the particles are small enough to be inhaled deeply into the lungs where they may persist, and (3) the vapors and particles include mutagens, carcinogens, lung irritants, and contributors to ozone formation. Epidemiologic studies of workers in certain occupations suggest a weak association between exposure to diesel exhaust and lung cancer. Other studies have found that daily increases in mortality from heart and lung diseases are correlated with increases in particulate air pollution.

The Clean Air Act of 1970 mandates decreased particle emissions from vehicles with diesel engines. Although engine manufacturers have reduced emissions substantially by improving engine designs, fuel composition may need to be modified and emission control devices may need to be added to achieve further reductions in the future. Because the Clean Air Act requires that such devices contribute no new risks, the Health Effects Institute sponsored this study to help evaluate whether using low-sulfur fuel with emission control devices might alter diesel emissions in ways that could affect human health.

APPROACH

Dr. Susan Bagley and colleagues conducted a laboratory study to characterize the physical and chemical composition and the mutagenicity of emissions from a heavy-duty 1988 diesel engine equipped with a ceramic particle trap. This engine was operated with low-sulfur fuel at a constant speed under two different load conditions. The investigators compared their results to those obtained in an earlier study (HEI Research Report Number 56) in which they had used the same engine and a conventional, high-sulfur fuel. They also studied the effects of an oxidation catalytic converter on emissions from a heavy-duty 1991 diesel engine using a low-sulfur fuel. A unique aspect of this study was that the investigators determined the number and size of particles within the two typical classes of diesel particulate matter: the small, primary particles (nuclei mode) and the larger particle agglomerates (accumulation mode).

RESULTS AND IMPLICATIONS

The ceramic particle trap substantially decreased the weight and number of particles emitted, and as a result, lowered the levels of organic chemicals associated with particles and the mutagenicity of diesel exhaust. Use of the trap caused an increase in the amount of one chemical (fluoranthene) in the emission vapors, but no statistically significant changes were noted in the amounts or types of other vapor-phase chemicals. Regenerating the particle-loaded trap by heating it to combust the particles produced negligible increases in emission constituents and mutagenicity. Compared with results from conventional, high-sulfur fuel in the earlier study, low-sulfur fuel decreased sulfate emissions and the number of small sulfate particles, but had little effect on the weight of total particulate matter. The oxidation catalytic converter on the other hand had no effect on the number of particles, but decreased the amount of organic chemicals in the vapors and adsorbed onto the particles. Because most of the chemicals adsorbed onto the particles were removed, the weight of the total particulate matter decreased. These results indicate that the use of low-sulfur fuel in combination with emission control devices reduces selected pollutants in heavy-duty diesel engine exhaust without significantly increasing emissions of other pollutants.

Preliminary results show that, despite a substantial reduction in the weight of total particulate matter, the total number of particles in emissions from the more advanced 1991-model engine was 15 to 35 times greater than the number of particles from the 1988 engine when both engines were operated without emission control devices. This unexpected finding was due to a 30- to 60-fold increase in the number of small, primary particles. These data are of concern because the smaller particles in emissions are more likely to be trapped and retained in human lungs. However, these findings need to be validated because only one engine of each type was tested and the main objective of this study was not to compare different engines. Further inquiry, including studies with new diesel engine designs, is needed to clarify this potentially important result.

Characterization of Fuel and Aftertreatment Device Effects on Diesel Emissions

TABLE OF CONTENTS

Investigators' Report
Susan T. Bagley, Kirby J. Baumgard, Linda D. Gratz, John H. Johnson, and David G. Leddy

Commentary
Health Review Committee

CODE: BAGLEY76

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