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Research Papers: Air Emissions From Fossil Fuel Combustion

# Effects of Cooled EGR on a Small Displacement Diesel Engine: A Reduced-Order Dynamic Model and Experimental Study

[+] Author and Article Information
Christopher Simoson

General Electric Transportation, Erie, PA 16531

John Wagner

Automotive Research Laboratory, Department of Mechanical Engineering, Clemson University, Clemson, SC 29634jwagner@clemson.edu

J. Energy Resour. Technol 130(1), 011102 (Feb 04, 2008) (11 pages) doi:10.1115/1.2824286 History: Received November 15, 2006; Revised July 31, 2007; Published February 04, 2008

## Abstract

Diesel engines are critical in fulfilling transportation and mechanical/electrical power generation needs throughout the world. The engine’s combustion by-products spawn health and environmental concerns, so there is a responsibility to develop emission reduction strategies. However, difficulties arise since the minimization of one pollutant often bears undesirable side effects. Although legislated standards have promoted successful emission reduction strategies for larger engines, developments in smaller displacement engines has not progressed in a similar fashion. In this paper, a reduced-order dynamic model is presented and experimentally validated to demonstrate the use of cooled exhaust gas recirculation (EGR) to alleviate the tradeoff between oxides of nitrogen reduction and performance preservation in a small displacement diesel engine. EGR is an effective method for internal combustion engine oxides of nitrogen $(NOx)$ reduction, but its thermal throttling diminishes power efficiency. The capacity to cool exhaust gases prior to merging with intake air may achieve the desired pollutant effect while minimizing engine performance losses. Representative numerical results were validated with experimental data for a variety of speed, load, and EGR testing scenarios using a $0.697l$ three-cylinder diesel engine equipped with cooled EGR. Simulation and experimental results showed a 16% drop in $NOx$ emissions using EGR, but experienced a 7% loss in engine torque. However, the use of cooled EGR realized a 23% $NOx$ reduction while maintaining a smaller performance compromise. The concurrence between simulated and experimental trends establishes the simplified model as a predictive tool for diesel engine performance and emission studies. Further, the presented model may be considered in future control algorithms to optimize engine performance and thermal and emission characteristics.

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## Figures

Figure 6

Simulated and experimental engine radiator coolant temperatures for Tests 1–3

Figure 7

Experimental EGR temperatures for Tests 2 and 3 and mixed gas temperatures for Tests 1–3. Note that Test 1 does not have EGR.

Figure 8

Simulated and experimental NOx exhaust emission levels for Tests 1–3

Figure 9

Experimental exhaust concentrations of oxygen (top) and carbon dioxide (bottom) for Tests 1–3

Figure 1

Three-cylinder diesel engine with EGR valve, EGR cooler, and sensors

Figure 2

Block diagram of diesel engine model structure where [XX] denotes multiple species entering the emission block

Figure 3

Thermal network architecture for diesel engine cooling

Figure 4

Diesel engine and EGR cooler with attached valve

Figure 5

Simulated and experimental torque-speed curve for Tests 1–3 with torque variations attributed to the engine’s mechanical fueling protocol

Figure 10

Simulation and experimental engine coolant temperatures under varied loadings at N=1250rpm for Tests 4–6

Figure 11

Simulation and experimental engine coolant temperatures under varied loadings at N=2000rpm for Tests 7–9

Figure 12

Experimental EGR and mixed air/EGR gas temperatures under varied loadings at N=1250rpm for Tests 4–6

Figure 13

Experimental EGR and mixed air/EGR gas temperatures under varied loadings at N=2000rpm for Tests 7–9

Figure 14

Figure 15

Figure 16

Experimental exhaust concentrations of oxygen (top) and carbon dioxide (bottom)

Figure 17

Experimental exhaust concentrations of oxygen (top) and carbon dioxide (bottom)

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