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Research Papers: Internal Combustion Engines

The Impact of Low Octane Primary Reference Fuel on HCCI Combustion Burn Rates: The Role of Thermal Stratification

[+] Author and Article Information
Luke Hagen

Hiltner Combustion Systems,
Ferndale, WA 98248
e-mail: lmh@hiltnercombustionsystems.com

George Lavoie

Department of Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: glavoie@umich.edu

Margaret Wooldridge

Department of Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: mswool@umich.edu

Dennis Assanis

Office of the President,
University of Delaware,
Newark, DE 19716
e-mail: assanis@udel.edu

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 15, 2017; final manuscript received March 17, 2017; published online May 9, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(10), 102807 (May 09, 2017) (10 pages) Paper No: GTP-17-1064; doi: 10.1115/1.4036319 History: Received February 15, 2017; Revised March 17, 2017

A new experimental method was developed which isolated charge composition effects for wide levels of internal exhaust gas recirculation (iEGR) at constant total EGR (tEGR) for homogeneous charge compression ignition (HCCI) combustion. The effect of changing iEGR was examined for both gasoline (research octane number (RON) = 90.5) and PRF40 at constant charge composition at multiple engine speeds. For this study, the charge composition was defined as the total mass of fresh air, fuel, and tEGR. Experimental results showed that for a given iEGR level, PRF40 had a reduced burn duration and higher maximum heat release rate (HRR) when compared with gasoline. PRF40 was found to have a nearly constant burn duration and HRR for a given load and CA50, largely independent of engine speed and iEGR level. Gasoline, for equivalent conditions, showed an increased burn duration at higher iEGR levels. When comparing PRF40 to gasoline at fixed combustion phasing and iEGR level, the increased HRR for PRF40 was correlated with reduced intake valve closing (IVC) temperatures. To examine the impact of thermal gradients (as distinct from fuel chemistry effects) due to IVC temperature differences, a multizone “balloon model” was used to evaluate experimental conditions. The model results demonstrated that when the in-cylinder temperature profiles between fuels were matched by adjusting wall temperature, the heat release rates were nearly identical. This result suggested the observed differences in burn rates between gasoline and PRF40 were influenced to a large degree by differences in thermal stratification and to a lesser extent by differences in fuel chemistry.

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References

Figures

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Fig. 1

Schematic of the FFVA experimental setup

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Fig. 2

Conceptual representation of in-cylinder constituent masses as they relate to ϕ and ϕ′

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Fig. 3

Advancing and retarding IVC across NVO sweep to match total EGR and ϕ′ for gasoline at 2000 RPM. IVC timing was maintained constant for the red (diamond) curve. For the black (circle) curve, IVC was varied with iEGR to maintain a constant tEGR fraction (see figure online for color).

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Fig. 4

Heat release rate for gasoline at 1000 RPM. Total EGR = 43%, 43%, and 46% for iEGR = 32%, 39%, and 46%, respectively.

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Fig. 5

Heat release rate for gasoline at 2000 RPM. Note theiEGR = 19% and 32% curves overlap on the plot. Total EGR = 42%, 42%, 43%, and 44% for iEGR = 19%, 32%, 38%, and 43%, respectively.

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Fig. 6

Comparison of 10–90% burn duration of gasoline with 10–90% burn duration of PRF40, where the M subscript refers to the main burning event for the PRF40 fuel as explained further in the text

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Fig. 7

Heat release rate for PRF40 at 1000 RPM. Total EGR = 42% for all three iEGR cases.

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Fig. 8

Heat release rate for PRF40 at 2000 RPM. Total EGR = 42%, 44%, and 45% for iEGR = 17%, 27%, and 38%, respectively.

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Fig. 9

Removing LTHR portion of MFB curve and rescaling: example for PRF40 at 1000 RPM

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Fig. 10

CA burn locations with LTHR portion of MFB removed (PRF40 at 1000 RPM)

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Fig. 11

Rate of heat release for PRF40 and gasoline with 38% iEGR at 2000 RPM. Total EGR = 43% for gasoline and 45% for PRF40. NVO duration for both cases was 135 deg CA.

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Fig. 12

Estimated IVC temperature compared with TDC temperature for gasoline and PRF40 at 1500 and 2000 RPM. iEGR = 38% for all cases.

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Fig. 13

Comparison of simulated heat release rates at 1000 RPM

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Fig. 14

Simulation results for in-cylinder temperature profiles at 700 CA deg at 1000 RPM. The hottest zone is at cumulative mass fraction of 0. The coldest zone is near the wall at cumulative mass fraction 1. Note the lower overall temperatures for both PRF40 cases.

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Fig. 15

Simulation results for PRF40 at 1000 RPM with normalized heat release rates of zones at cumulative mass fractions of 0.0, 0.1, 0.3, 0.7, 0.9, and 1.0. The average heat release is shown as the dashed curve.

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Fig. 16

Simulation results for PRF87 at 1000 RPM with normalized heat release rates of zones at cumulative mass fractions of 0.0, 0.1, 0.3, 0.7, 0.9, and 1.0. The average heat release is shown by dashed curve.

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Fig. 17

Simulation results for PRF40* (reduced IVC temperature) at 1000 RPM with normalized heat release rates of zones at cumulative mass fractions of 0.0, 0.1, 0.3, 0.7, 0.9, and 1.0. Average heat release is shown by dashed curve.

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