Masters Theses

Date of Award

12-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

David K. Irick

Committee Members

Jeffrey W. Hodgson, Ke Nguyen, John M. Storey

Abstract

The primary objective of this study is to investigate the characteristics of nanoparticle formation in dilute exhaust streams from diesel engines. Nanoparticle formation may be due to condensation, homogenous nucleation, coagulation and adsorption from low temperature, sulfate and water in exhaust system. After being released from the tail pipe, new nanoparticles also might be formed due to nucleation growth from low dilution ratio and long residence time. On the other hand, nanoparticles might be formed from dilution tunnels themselves. The artifact formation in dilution tunnels is due to specific problems that may occur in a dilution device, such as dilution ratio, dilution air temperature, dilution air pressure, residence time and critical flow orifice. The experimental apparatus consists of a variable residence time, micro dilution system for exhaust dilution. Particle detection instruments consist of a scanning mobility particle sizer (SMPS), a condensation particle counter (CPC), and a NOx analyzer. Exhaust from modern diesel and gasoline engines was analyzed. Two dilution devices were designed to simulate the process of engine exhaust into the atmosphere. For high dilution ratio from 5 to 10,000:1 and variable long residence time of 50 to 2000 ms, a first dilutor, Dilutor I, was used. For low dilution ratio from 5 to 300:1 and short fixed residence time of 50 ms, a second dilutor, Dilutor II, was used. Temperature, dilution ratio, and residence time were controllable. A NOx analyzer was used to check dilution ratio. A series of experiments was done to calibrate the dilutors. The results showed that the dilution devices alter particle size if particles were not solid. Particle size measurements were taken upstream and downstream of a diesel particulate filter (DPF) with residence time changing from 50 ms to 700 ms, which increased nanoparticle concentrations by up to two orders of magnitude. Nanoparticles below about 20 nm in diameter were higher than in Microwave Regeneration Particulate Filter (MRPF) exhaust engine out during DPF regeneration. The research should help for any future measurements of nanoparticles. The nanoparticle formation and growth under different dilution conditions needs to be investigated further. A nanoparticle formation model could be built to understand homogenous nucleation. Due to the complex nature of the atmospheric dilution process, a dilution system could be developed in the laboratory to imitate the atmospheric processes. The University of Tennessee, Knoxville (UTK) and the Oak Ridge National Laboratory have joined in this research. The Graduate Automotive Technology Education (GATE) Center of UTK, sponsored by U.S. Department of Energy (DOE), was the main participant, and the research was be conducted at Advanced Propulsion Technology Center (APTC), a research and evaluation laboratory for new internal combustion engines and emissions controls technologies. The DOE Office of Heavy Vehicle Technologies sponsored the research.

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