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Research Papers: Internal Combustion Engines

Thermodynamic Considerations Regarding the Use of Exhaust Gas Recirculation for Conventional and High Efficiency Engines

[+] Author and Article Information
Jerald A. Caton

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843–3123

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 14, 2017; final manuscript received February 15, 2017; published online April 11, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(9), 092803 (Apr 11, 2017) (8 pages) Paper No: GTP-17-1062; doi: 10.1115/1.4036102 History: Received February 14, 2017; Revised February 15, 2017

During the last several decades, investigations of the operation of internal combustion engines utilizing exhaust gas recirculation (EGR) have increased. This increased interest has been driven by the advantages of the use of EGR with respect to emissions and, in some cases, thermal efficiency. The current study uses a thermodynamic engine cycle simulation to explore the fundamental reasons for the changes of thermal efficiency as functions of EGR. EGR with various levels of cooling is studied. Both a conventional (throttled) operating condition and a high efficiency (HE) operating condition are examined. With no EGR, the net indicated thermal efficiencies were 32.1% and 44.6% for the conventional and high efficiency engines, respectively. For the conditions examined, the cylinder heat transfer is a function of the gas temperatures and convective heat transfer coefficient. For increasing EGR, the gas temperatures generally decrease due to the lower combustion temperatures. For increasing EGR, however, the convective heat transfer coefficient generally increases due to increasing cylinder pressures and decreasing gas temperatures. Whether the cylinder heat transfer increases or decreases with increasing EGR is the net result of the gas temperature decreases and the heat transfer coefficient increases. For significantly cooled EGR, the efficiency increases partly due to decreases of the heat transfer. On the other hand, for less cooled EGR, the efficiency decreases due at least partly to the increasing heat transfer. Two other considerations to explain the efficiency changes include the changes of the pumping work and the specific heats during combustion.

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References

Heywood, J. B. , 1988, Internal Combustion Engine Fundamentals, McGraw-Hill, New York.
Caton, J. A. , 2006, “ Utilizing a Cycle Simulation to Examine the Use of EGR for a Spark-Ignition Engine Including the Second Law of Thermodynamics,” ASME Paper No. ICEF2006-1508.
Shyani, R. G. , and Caton, J. A. , 2009, “ A Thermodynamic Analysis of the Use of EGR in SI Engines Including the Second Law of Thermodynamics,” Proc. Inst. Mech. Eng., Part D, 223(1), pp. 131–149. [CrossRef]
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Caton, J. A. , 2015, An Introduction to Thermodynamic Cycle Simulations for Internal Combustion Engines, Wiley, Chichester, UK.
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Caton, J. A. , 2015, “ Heat Transfer Characteristics of Conventional and High Efficiency IC Engines Using External or Internal Gas Dilution,” ASME Paper No. ICEF2015-1012.
Caton, J. A. , 2013, “ Thermodynamic Considerations for Advanced, High Efficiency IC Engines,” ASME Paper No. ICEF2013-19040.
Caton, J. A. , 2015, “ Thermodynamic Comparison of External and Internal Exhaust Gas Dilution for High Efficiency IC Engines,” Int. J. Engine Res., 16(8), pp. 935–955. [CrossRef]
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Figures

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Fig. 9

The ratio of the average (720 deg CA) heat transfer coefficient and the average coefficient for 0% EGR as functions of the EGR level for the cooled and adiabatic EGR configurations for the high efficiency operating condition

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Fig. 8

The partition of the fuel energy for the conventional and high efficiency operating conditions for 0% EGR

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Fig. 7

The net indicated thermal efficiencies as functions of the percentage EGR for four levels of EGR cooling

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Fig. 6

The gross and net indicated thermal efficiencies for the adiabatic and cooled EGR configurations as functions of the percentage EGR for the conventional operating condition

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Fig. 5

The pumping work (as a percentage of the fuel energy) for the five levels of EGR cooling as functions of the percentage EGR for the conventional engine operating condition

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Fig. 4

The ratio of the relative heat transfer and the relative heat transfer for 0% EGR as functions of EGR for various EGR cooling levels for the conventional operating condition

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Fig. 3

The ratio of the average (720 deg CA) heat transfer coefficient and the average coefficient for 0% EGR as functions of the EGR level for the cooled and adiabatic EGR configurations for the conventional operating condition

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Fig. 2

The average combustion and exhaust gas temperatures as functions of the EGR level for the adiabatic and cooled EGR configurations for the conventional operating case

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Fig. 1

The inlet mixture temperature as functions of the EGR level for various levels of EGR cooling for the conventional operating case

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Fig. 12

Gross and net indicated thermal efficiencies as functions of the EGR level for both the adiabatic and cooled EGR configurations for the high efficiency operating condition

Grahic Jump Location
Fig. 10

The ratio of the relative heat transfer and the relative heat transfer for 0% EGR as functions of EGR for various EGR cooling levels for the high efficiency operating condition

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Fig. 11

Pumping work (as a percentage of the fuel energy) as functions of EGR for the cooled and adiabatic EGR configurations for the high efficiency engine

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