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Five small two-stroke engine designs were tested at different air/fuel ratios, under steady state and transient cycles. The effects of combustion chamber design, carburetor design, lean burning, and fuel composition on performance, hydrocarbon and carbon monoxide emissions were studied. All tested engines had been designed to run richer than stoichiometric in order to obtain satisfactory cooling and higher power. While hydrocarbon and carbon monoxide emissions could be greatly reduced with lean burning, engine durability would be worsened. However, it was shown that the use of a catalytic converter with acceptably lean combustion was an effective method of reducing emissions. Replacing carburetion with in-cylinder fuel injection in one of the engines resulted in a significant reduction of hydrocarbon and carbon monoxide emissions.

EGR coolers are widely used in reciprocating engines to reduce NOx emission. Thermophoresis-an important transport mechanism for submicron particles such as soot-drives gas-suspended particles from hot regions towards cool surfaces and is responsible for soot deposition and build-up in EGR coolers and related devices. Although much is known about thermophoresis in steady flow, little is known about soot deposition in flows with oscillatory heat and mass transfer. In this paper we present new results for the model problem of thermophoretic particle transport in a thin pulsatile shear layer above a flat, cold wall. The transport equations for this sublayer flow with oscillating shear have been solved numerically and, in the case of steady flow, are in excellent agreement with the exact solution for the steady wall shear.