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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Understanding Loss Mechanisms and Identifying Areas of Improvement for HCCI Engines Using Detailed Exergy Analysis

[+] Author and Article Information
Samveg Saxena

Lawrence Berkeley National Laboratory,
One Cyclotron Road, 90-2138
Berkeley, CA 94720
e-mail: samveg@berkeley.edu

Iván Dario Bedoya

University of Antioquia,
Calle 67 No. 63-108,
Medellin, Colombia
e-mail: ibedoyac@udea.edu.co

Nihar Shah

e-mail: nkshah@lbl.gov

Amol Phadke

e-mail: aaphadke@lbl.gov
Lawrence Berkeley National Laboratory,
One Cyclotron Road, 90-2148
Berkeley, CA 94720

A table of mass fraction and external heat transfer area fraction for each zone is presented in the Appendix.

A parametric study of the influence of number of simulated zones upon exergy analysis results is presented in the Appendix. The results show that the number of simulated zones do not significantly impact the exergy analysis results; thus 10 zones are used throughout the paper.

For the simulations that were run as part of this research, misfire is defined as a failure to achieve hot ignition thereby causing a pressure trace that looks like a motoring pressure trace. This simplified definition of misfire is sufficient for this research because ethanol displays virtually no low or intermediate temperature heat release [21].

The physical exergy in the exhaust gases could be partially recovered through various means, including: (1) a longer expansion stroke, (2) turbocharging, and (3) a heat exchanger in the exhaust.

Figure 8 shows that at TDC exergy loss from heat loss decreases with increasing intake pressure, showing a 1.5% decrease in exergy loss from heat loss going from 1.0 to 2.0 bar intake pressure.

From Fig. 8 note that at CA50 = 365 deg, exergy losses from incomplete combustion have just started to show their intake pressure dependence.

It is important to note that the absolute amount of exergy loss from heat loss is increasing as equivalence ratio is increased, however as a fraction of total fuel availability there is no increase in exergy loss from heat losses.

The combustion timing threshold for increases in exergy loss from incomplete combustion tends to be further delayed with higher engine speeds, although the trend is very subtle.

Contributed by the Combustion and Fuels Committee of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received April 14, 2013; final manuscript received May 16, 2013; published online July 31, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(9), 091505 (Jul 31, 2013) (10 pages) Paper No: GTP-13-1102; doi: 10.1115/1.4024589 History: Received April 14, 2013; Revised May 06, 2013

This paper presents a detailed exergy analysis of homogeneous charge compression ignition (HCCI) engines, including a crank-angle resolved breakdown of mixture exergy and exergy destruction. Exergy analysis is applied to a multizone HCCI simulation including detailed chemical kinetics. The HCCI simulation is validated against engine experiments for ethanol-fueled operation. The exergy analysis quantifies the relative importance of different loss mechanisms within HCCI engines over a range of engine operating conditions. Specifically, four loss mechanisms are studied for their relative impact on exergy losses, including (1) the irreversible combustion process (16.4%–21.5%), (2) physical exergy lost to exhaust gases (12.0%–18.7%), (3) heat losses (3.9%–17.1%), and (4) chemical exergy lost to incomplete combustion (4.7%–37.8%). The trends in each loss mechanism are studied in relation to changes in intake pressure, equivalence ratio, and engine speed as these parameters are directly used to vary engine power output. This exergy analysis methodology is proposed as a tool to inform research and design processes, particularly by identifying the relative importance of each loss mechanism in determining engine operating efficiency.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Comparison of experimental and simulated in-cylinder pressure traces

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Fig. 2

Comparison of gross indicated power output for experimental and simulated cases for several intake pressures, equivalence ratios, and combustion timings. 1800 rpm, ethanol fueled.

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Fig. 3

Comparison of combustion efficiency for experimental and simulated cases for several intake pressures, equivalence ratios, and combustion timings. 1800 rpm, ethanol fueled.

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Fig. 4

Comparison of carbon monoxide emissions for experimental and simulated cases for several intake pressures, equivalence ratios, and combustion timings. 1800 rpm, ethanol fueled.

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Fig. 5

Comparison of exhaust (experimental) and EVO (simulated) temperatures for several intake pressures, equivalence ratios, and combustion timings. 1800 rpm, ethanol fueled.

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Fig. 6

Crank-angle resolved exergy (total, physical, and chemical) for a single operating point with PBDC = 1.8 bar, ϕ = 0.40, 1800 rpm, ethanol fuel

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Fig. 7

Crank-angle resolved cumulative exergy destruction for a single operating point with PBDC = 1.8 bar, ϕ = 0.40, 1800 rpm, ethanol fuel

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Fig. 8

BDC pressure and combustion timing sweep of exergy loss mechanisms for ϕ = 0.40, 1800 rpm, ethanol fuel

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Fig. 9

BDC pressure sweep of exergy loss mechanisms for ϕ = 0.40, 1800 rpm, CA50 = 365 deg and 370 deg, ethanol fuel

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Fig. 10

Equivalence ratio and combustion timing sweep of exergy loss mechanisms for PBDC = 1.0 bar, 1800 rpm, ethanol fuel

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Fig. 11

Equivalence ratio sweep of exergy loss mechanisms for PBDC = 1.0 bar abs, 1800 rpm, CA50 = 365 deg and 370 deg, ethanol fuel

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Fig. 12

Equivalence ratio and combustion timing sweep of exergy loss mechanisms for PBDC = 1.8 bar, 1800 rpm, ethanol fuel

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Fig. 13

Equivalence ratio sweep of exergy loss mechanisms for PBDC = 1.8 bar abs, 1800 rpm, CA50 = 365 deg and 370 deg, ethanol fuel

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Fig. 14

Engine speed and combustion timing sweep of exergy loss mechanisms for PBDC = 1.8 bar, ϕ = 0.40, ethanol fuel

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Fig. 15

Engine speed sweep of exergy loss mechanisms for PBDC = 1.8 bar abs, ϕ = 0.40, CA50 = 365 deg and 370 deg, ethanol fuel

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Fig. 16

Comparison of intake and exhaust physical availability to provide insight for turbocharger design for PBDC = 1.8 bar, 1800 rpm, ethanol fuel

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Fig. 17

In-cylinder pressure for 10, 20, and 40 zones

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Fig. 18

In-cylinder temperature for 10, 20, and 40 zones

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Fig. 19

Contribution of each exergy loss mechanism for 10, 20, and 40 zones

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