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Research Papers

Condensation Analysis of Exhaust Gas Recirculation System for Heavy-Duty Trucks

[+] Author and Article Information
Bing-Jian Yang, Orhan Altin

 Caterpillar Inc., Mossville, IL 61552

Shaolin Mao1

T-5, Theoretical Division,  Los Alamos National Laboratory, MS-B284, Los Alamos, NM 87545 e-mail: slm_wvu@yahoo.com

Zhi-Gang Feng, Efstathios E. Michaelides

Department of Mechanical Engineering,  University of Texas at San Antonio, San Antonio, TX 78249

1

Corresponding author.

J. Thermal Sci. Eng. Appl 3(4), 041007 (Nov 07, 2011) (9 pages) doi:10.1115/1.4004745 History: Received January 21, 2011; Revised July 18, 2011; Published November 07, 2011; Online November 07, 2011

The exhaust gas recirculation (EGR) system has been widely used in the automotive and heavy-duty trucks to reduce NOx , SOx , and other controlled emissions. A liquid-cooled or air-cooled heat exchanger is the main constituent of the EGR system. The heat exchanger decreases the temperature of the exhaust gases mixture that flows through the EGR channels and the lower temperatures reduce the content of the controlled gas emissions. Condensation of water vapor is an undesirable by-product of the EGR systems because, in combination with the emission gases, it forms the corrosive sulfuric and nitric acids. The U.S. EPA has suggested that engine makers should turn off their EGR systems periodically to avoid the formation of the corrosive sulfuric and nitric acids. In order to accurately predict the corrosion process, a condensation model has been developed to investigate the rates of formation and diffusion of nitric acid and sulfuric acid to the cold tube surface. A three-dimensional computational fluid dynamics (CFD) simulation has been conducted for a typical EGR cooler during normal operating conditions of Tier 4 heavy-duty trucks. A lumped, 1D heat and mass transfer model has also been developed to study the most important physical aspects of the condensation process. The CFD and the analytical results of the rate of condensation and local fluid properties are an important and inexpensive complement to more expensive experimental measurements and testing. Such models may be used to improve the design and to optimize the operating conditions of the EGR systems and may become valuable tools in the design and manufacturing of the next generation of EGR systems for diesel engines. The model developed is general and the techniques and numerical results of this study may be extended to engine reliability, corrosion reduction, and damage prevention of other industrial engines.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of diesel engine with EGR valve and EGR cooler for heavy-duty trucks

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Figure 2

Schematic of one-dimensional model mass fraction of noncondensable gases and temperature profiles on the cold surface in a tube (shape factor considered), water film occupies the bottom layer to the wall

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Figure 3

Typical EGR cooler used in off-highway trucks, water condensation and acid corrosion occurred at the exit part (left panel); a single flat tube of EGR cooler with dimple and rough surface for purpose of enhancement of heat transfer (right panel). The length of the tube is 325 mm, width of 21 mm and thickness of 4.7 mm, while the tube wall is 0.5 mm thickness.

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Figure 4

Distribution of dew point on the cold tube surface for 15 ppm fuel (maximum value of 386 K or 113°C) the dew point is not constant and nonuniform along the axial direction

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Figure 5

Dew point temperatures and wall temperature of the tube which shows the starting location of the condensations. Plate results are also included for comparison [15].

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Figure 6

Distribution of condensation flux on the cold surface of a tube (3D CFD model) with 15 ppm sulfur fuel

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Figure 7

condensation fluxes of sulfuric acid variations versus distance from inlet and three mass flow rates of bulk mixture in the tube

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Figure 8

Variation of total condensation of sulfuric acid with different exhaust gases mass flow rates in the same tube of 1 foot long (Tin  = 351°C; Tout  = 94°C; Pin  = 0.97 atm, and Pout  = 0.93 atm)

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Figure 9

Condensation rate after 1 h run for 15 ppm sulfuric fuel with a constant inlet temperature of 415 K and varied outlet temperature

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Figure 10

Comparison sulfuric acid condensation with different fuels blue (lower column): 15 ppm sulfur fuel; red (higher column): 500 ppm sulfur fuel for 500 h duration in a flat tube

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Figure 11

Influence of the inlet Schmidt number on the condensation flux obtained by the 1D condensation model for laminar and turbulent flow. The difference between the mass fraction of the fluid bulk and that of the liquid–gas interface was assumed to be constant.

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Figure 12

Condensation flux comparison between the analytical 1D lumped model and the 3D CFD simulation results

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