Abstract
Exhaust gas recirculation (EGR) and high-pressure fuel injection are key technologies for reducing diesel engine emissions in the face of reinforced regulations. With the increasing need for advanced EGR technologies to achieve low-temperature combustion and low emission, the adverse etableffects of EGR must be addressed. One of the main problems is fouling of the EGR cooler, which involves the deposition of particulate matter (PM) due to the thermophoretic force between the cooler wall and flow field. A large amount of deposited PM can reduce the effectiveness of the heat exchanger in the EGR cooler and the de-NOx efficiency. In the present study, the effects of the variables that affect EGR cooler fouling are investigated by a comparison of laboratory-based and engine-based experiments. In the laboratory experiment, a soot generator that could readily provide separate control of the variables was used to generate the model EGR gas. Through control of the soot generator, it was possible to perform a parametric study by varying the particle size, the EGR gas flow rate, and the coolant temperature as the dominant parameters. A decrease in these factors caused an increase in the mass of the deposit and a drop in the effectiveness of the heat exchanger, related to fouling of the EGR cooler. In the engine-based experiment, engine-like conditions were provided to analyze real exhaust gas without a soot generator. Different variables were found to induce fouling of the EGR cooler, and the results of the engine-based experiment differed from those of the laboratory experiment. For example, in the engine-based experiment, a decrease in the EGR gas flow rate did not lead to a more pronounced drop in the effectiveness of the heat exchanger because of the increase in the concentration of PM in the EGR gas. This result shows that the conditions of the engine exhaust gas are different from those of the soot generator.
Highlights
The diesel engine offers several advantages over the gasoline engine in terms of combustion efficiency, fuel consumption, and durability
The purpose of this study is to evaluate the effects of different variables on exhaust gas recirculation (EGR) cooler fouling using exhaust gas from an engine and to compare the results of laboratory and engine-bench experiments
A laboratory experiment was conducted by using a particulate matter (PM) generator to evaluate the effects of the coolant temperature, flow rate, and DOC catalyst on EGR cooler fouling
Summary
The diesel engine offers several advantages over the gasoline engine in terms of combustion efficiency, fuel consumption, and durability. The former is favorable in terms of environmental considerations because it discharges less carbon dioxide (CO2 ), carbon monoxide (CO), and total hydrocarbon (THC) than the gasoline engine. In order to satisfy the requirements of the regulations, NOx and soot emissions must simultaneously be reduced, and exhaust gas recirculation (EGR) is one method of achieving this goal. EGR technology reduces NOx emission by lowering the flame temperature in the cylinder and the oxygen concentration. Cooled-EGR technology has been used to further reduce the rate of NOx emission [3,4]. Zeng et al reported that the main effects of EGR are the dilution effect, whereby the
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