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Research Papers: Internal Combustion Engines

Modeling Cyclic Variability in Spark-Assisted HCCI

[+] Author and Article Information
C. Stuart Daw, Robert M. Wagner, Johney B. Green

Fuels, Engines, and Emissions Research Center, Oak Ridge National Laboratory, 2360 Cherahala Boulevard, Knoxville, TN 37932-6472

K. Dean Edwards

Fuels, Engines, and Emissions Research Center, Oak Ridge National Laboratory, 2360 Cherahala Boulevard, Knoxville, TN 37932-6472edwardskd@ornl.gov

J. Eng. Gas Turbines Power 130(5), 052801 (May 30, 2008) (6 pages) doi:10.1115/1.2906176 History: Received October 26, 2007; Revised February 07, 2008; Published May 30, 2008

Spark assist appears to offer considerable potential for increasing the speed and load range over which homogeneous charge compression ignition (HCCI) is possible in gasoline engines. Numerous experimental studies of the transition between conventional spark-ignited (SI) propagating-flame combustion and HCCI combustion in gasoline engines with spark assist have demonstrated a high degree of deterministic coupling between successive combustion events. Analysis of this coupling suggests that the transition between SI and HCCI can be described as a sequence of bifurcations in a low-dimensional dynamic map. In this paper, we describe methods for utilizing the deterministic relationship between cycles to extract global kinetic rate parameters that can be used to discriminate multiple distinct combustion states and develop a more quantitative understanding of the SI-HCCI transition. We demonstrate the application of these methods for indolene-containing fuels and point out an apparent HCCI mode switching not previously reported. Our results have specific implications for developing dynamic combustion models and feedback control strategies that utilize spark assist to expand the operating range of HCCI combustion.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Illustration of the possible role of the initial SI flame in spark-assisted HCCI. The SI flame stimulates subsequent HCCI by compressing and preheating the remaining unburned gases.

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Figure 2

General combustion trends observed in the SI-HCCI transition experiments

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Figure 3

HR profiles for the limiting cases of (a) no EGR (SI) and (b) maximum EGR (HCCI)

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Figure 4

First return maps of cyclic HR for (a) pure indolene and (b) E85 (85% ethanol, 15% indolene) at conditions near the maximum COV in HR

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Figure 5

Convergence of iterated residual fuel-air balances for a wide range of assumed initial residual charges. Convergence is driven by repeated input from observed values of HR(i).

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Figure 6

Characteristic patterns seen in the residual charge based on cycle-by-cycle mass balances

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Figure 7

Relationship between the estimated global post-TDC burn rate constant and unburned gas temperature at TDC

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Figure 8

Comparison of (a) observed post-TDC burn time (1∕kp) with (b) computed ignition delay for n-heptane

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