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Internal Combustion Engines

Assessment of Residual Mass Estimation Methods for Cylinder Pressure Heat Release Analysis of HCCI Engines With Negative Valve Overlap

[+] Author and Article Information
Elliott A. Ortiz-Soto, Jiri Vavra, Aristotelis Babajimopoulos

 University of Michigan – Ann Arbor, Ann Arbor, MI 48109-2133 Czech Technical University in Prague, Prague, 166 07, Czech Republic University of Michigan – Ann Arbor, Ann Arbor, MI 48109-2133

J. Eng. Gas Turbines Power 134(8), 082802 (Jun 11, 2012) (9 pages) doi:10.1115/1.4006701 History: Received October 31, 2011; Revised November 05, 2011; Published June 11, 2012; Online June 11, 2012

Increased residual levels in homogeneous charge compression ignition (HCCI) engines employing valve strategies such as recompression or negative valve overlap (NVO) imply that accurate estimation of residual gas fraction (RGF) is critical for cylinder pressure heat release analysis. The objective of the present work was to evaluate three residual estimation methods and assess their suitability under naturally aspirated and boosted HCCI operating conditions: (i) the simple state equation method employs the ideal gas law at exhaust valve closing (EVC); (ii) the Mirsky method assumes isentropic exhaust process; and (iii) the Fitzgerald method models in-cylinder temperature from exhaust valve opening (EVO) to EVC by accounting for heat loss during the exhaust process and uses measured exhaust temperature for calibration. Simulations with a calibrated and validated “virtual engine” were performed for representative HCCI operating conditions of engine speed, fuel-air equivalence ratio, NVO and intake pressure (boosting). The state equation method always overestimated RGF by more than 10%. The Mirsky method was most robust, with average errors between 3–5%. The Fitzgerald method performed consistently better, ranging from no error to 5%, where increased boosting caused the largest discrepancies. A sensitivity study was also performed and determined that the Mirsky method was most robust to possible pressure and temperature measurement errors.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental engine setup schematic

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Figure 2

Cylinder pressure heat release analysis results versus experimental data at 1200 rpm for firing and motored runs

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Figure 3

Integral simulation results against experimental data for various engine operating conditions

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Figure 4

Intake, exhaust and cylinder pressure traces during exhaust process for recompression valve strategy

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Figure 5

RGF estimation using different pressures in the state equation compared with cycle simulation result

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Figure 6

Cylinder temperatures for determination of calibration factor in Fitzgerald method

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Figure 7

Trapped air and fuel mass used in the RGF estimation methods against virtual engine simulation results for the engine speed sweep

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Figure 8

Estimation of RGF for state equation, Mirsky and Fitzgerald methods as a function of engine speed

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Figure 9

Estimation of RGF for state equation, Mirsky and Fitzgerald methods as a function of fuel-air equivalence ratio

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Figure 10

Estimation of RGF for state equation, Mirsky and Fitzgerald methods as a function of negative valve overlap

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Figure 11

Estimation of RGF for state equation, Mirsky and Fitzgerald methods as a function of intake pressure

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Figure 12

Sensitivity analysis results for state equation, Mirsky and Fitzgerald methods as a function of pressure and temperature (error bars) offsets

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