Emission Reduction and Assisted Combustion Strategies for Compression Ignition Engines with Subsequent Testing on a Single-Cylinder Engine

Abstract

Due to increasingly stringent regulations set forth by the Environmental Protection Agency, engine researchers and manufacturers are testing and developing various emission reduction strategies for compression ignition engines. This thesis contains three sections where the author details two separate strategies for emission reduction and assisted combustion. Combustion resulting from compression ignition diesel engines contains high levels of nitrogen oxides (NOx) due to their lean operating characteristics. A common NOx reduction strategy used by most automotive manufactures involves the use of cooled EGR (exhaust gas recirculation) to reduce combustion temperatures. However, a downfall to this method is the formation of particulate matter (PM) from the reduced combustion temperatures. This reduction in NOx emissions with resulting increasing PM emissions describes the well-known NOx-PM tradeoff. Typically, a reduction in one of the emissions will result in an increase in the other. Chapter two documents the construction and testing of a cooled EGR system for a single cylinder diesel engine along with subsequent performance and emission analysis. The result of the cooled EGR system demonstrates a reduction in brake specific NOx due to reduced combustion temperatures, while decreasing brake specific PM due to increased turbulence. Resulting performance calculations displayed a slight increase in fuel consumption. Chapter three analyzes the effects of ozone-assisted combustion on a single cylinder diesel engine. This work starts with a summarization of the literature in the field, which supports the simplified combustion model for determination of trends. Experimentation results demonstrate the addition of ozone causes a decrease in ignition delay, which produces slightly higher in-cylinder temperatures. Due to the elevated temperatures and ozone decomposition, NOx production increases, while PM decreases through radial atomic oxygen chemistry. Additionally, carbon monoxide emissions increase while hydrocarbon levels decrease. The changes in fuel consumption resulting from ozone injection are negligible. Of additional importance, this work verifies findings in the literature that demonstrate the effects of adding more ozone is negligible above a certain level of ozone injection (20 ppm in this effort). This is due to high concentrations of ozone facilitating its own destruction during the compression process of the engine.