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Research Papers: Energy Systems Analysis

Waste Heat Recovery Potential of Advanced Internal Combustion Engine Technologies

[+] Author and Article Information
Timothy J. Jacobs

Department of Mechanical Engineering,
Texas A&M University,
3123 TAMU,
College Station, TX 77843-3123
e-mail: tjjacobs@tamu.edu

Contributed by the Internal Combustion Engine Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received November 17, 2014; final manuscript received March 16, 2015; published online April 17, 2015. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 137(4), 042004 (Jul 01, 2015) (14 pages) Paper No: JERT-14-1379; doi: 10.1115/1.4030108 History: Received November 17, 2014; Revised March 16, 2015; Online April 17, 2015

Coupling waste heat recovery with internal combustion engines creates opportunities to improve overall system efficiency and power output. The internal combustion engine has multiple pathways for dissipating thermal energy; the engine's exhaust is one that is conveniently accessible for converting to useful work via waste heat recovery. Coincident with increased waste heat recovery efforts, however, is increased engine efficiency improvement efforts. Anecdotally, an increase in engine efficiency will typically result in a decrease in exhaust exergy, thus decreasing the power capability of a waste heat recovery system. Further, other developments are taking place with internal combustion engines, such as the use of alternative fuels and combustion modes designed to decrease engine emissions, which may affect engine exergy. This article explores the relationships that may exist, both fundamentally and in practical application, between engine parameters and the corresponding effect on the maximum waste heat recovery potential (i.e., exergy) of the engine's exhaust. Specifically, the objectives of this study are to quantify (1) the effects of typical trends in internal combustion engine technology (i.e., increased compression ratio, decreased fuel–air equivalence ratio, and increased exhaust gas recirculation level) on waste heat recovery potential, (2) the role certain alternative fuels, particularly biodiesel, may have on waste recovery, and (3) the influence of and opportunities created by certain advanced modes of combustion, particularly low temperature combustion (LTC), on waste heat recovery potential. The study finds that fundamental engine parameters that typically result in increases in engine efficiency (i.e., increased compression ratio, decreased fuel–air equivalence ratio, and increased exhaust gas recirculation level) result in decreased exhaust exergy that decreases both efficiency and maximum power capability of a waste heat recovery system. Practical application of alternative fuels, such as biodiesel, seems to have small to no effect on the waste heat recovery. Application of novel modes of combustion, such as LTC, may result in decreases in waste heat recovery due to decreased exhaust mass flow rates typical of such combustion modes. Waste heat recovery may, however, create an opportunity to increase efficiency of LTC by exploiting chemical-to-thermal exothermic generation associated with the typically observed high concentrations of unburned fuel in the exhaust.

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Figures

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Fig. 1

Illustration of the control system under study and corresponding to Eq. (1); measurement locations of temperature, pressure, enthalpy, and entropy are provided. Exit state assumes equilibrium with the surroundings. Flow exergy assumes control system is adiabatic and work transfer is reversible.

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Fig. 2

Ideal thermodynamic efficiency of an IC engine (F/A analysis) and WHR heat engine as functions of (a) compression ratio, (b) fuel–air equivalence ratio (φ), and (c) EGR level. Calculations were performed at 1400 rev/min engine speed, 4.5 L engine displacement, 1 bar pressure boundary conditions, and 300 K inlet temperature. Compression ratio, φ, and EGR level vary depending on the control parameter.

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Fig. 3

Ideal thermodynamic power of an IC engine (F/A analysis) and WHR heat engine as functions of (a) compression ratio, (b) fuel–air equivalence ratio (φ), and (c) EGR level. Calculations were performed at 1400 rev/min engine speed, 4.5 L engine displacement, 1 bar pressure boundary conditions, and 300 K inlet temperature. Compression ratio, φ, and EGR level vary depending on the control parameter.

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Fig. 4

Ideal thermodynamic exhaust heat flow from of an IC engine (F/A analysis) for a WHR heat engine as functions of (a) compression ratio, (b) fuel–air equivalence ratio (φ), and (c) EGR level. Calculations were performed at 1400 rev/min engine speed, 4.5 L engine displacement, 1 bar pressure boundary conditions, and 300 K inlet temperature. Compression ratio, φ, and EGR level vary depending on the control parameter.

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Fig. 5

Ideal thermodynamic exhaust temperature and mass flow rate from of an IC engine (F/A analysis) for a WHR heat engine as functions of (a) compression ratio, (b) fuel–air equivalence ratio (φ), and (c) EGR level. Calculations were performed at 1400 rev/min engine speed, 4.5 L engine displacement, 1 bar pressure boundary conditions, and 300 K inlet temperature. Compression ratio, φ, and EGR level vary depending on the control parameter.

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Fig. 6

Experimental comparison of (a) exhaust exergy, (b) exhaust temperature, and (c) exhaust flow rate at several engine operating speeds and loads and (d) rate of heat release, mass fraction burned, and fuel needle lift profile as functions of engine crank angle at 2400 rev/min, midload condition for petroleum diesel (reference) and palm olein biodiesel fuels. Engine control parameters, such as injection timing, EGR level, and fuel injection pressure, vary among operating conditions and may vary between fuels as described in this study.

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Fig. 7

Experimental comparison of (a) main injection timing [28], (b) EGR level [28], and (c) air–fuel ratio at several engine operating speeds and loads for petroleum diesel (reference) and palm olein biodiesel fuels

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Fig. 8

Experimental comparison of (a) exhaust exergy, (b) exhaust temperature, and (c) exhaust flow rate as functions of EGR level and (d) rate of heat release as a function of engine crank angle at 0% and 45% EGR level for petroleum diesel and biodiesel fuels. Engine speed is 1400 rev/min, engine load is nominally 2 bar BMEP, injection timing is 0 deg ATDC, and injection pressure is 816 bar.

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Fig. 9

Unburned hydrocarbon concentrations as a function of EGR level for petroleum diesel and biodiesel fuels. Engine speed is 1400 rev/min, engine load is nominally 2 bar BMEP, injection timing is 0 deg ATDC, and injection pressure is 816 bar.

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