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Internal Combustion Engines

The Effects of Fuel Characteristics on Stoichiometric Spark-Assisted HCCI

[+] Author and Article Information
Adam J. Weall, James P. Szybist

Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory, NTRC Building, 2360 Cherahala Blvd., Knoxville, TN 37932

J. Eng. Gas Turbines Power 134(7), 072805 (May 23, 2012) (9 pages) doi:10.1115/1.4006007 History: Received November 16, 2011; Revised November 18, 2011; Published May 23, 2012; Online May 23, 2012

The characteristics of fuel lean homogeneous charge compression ignition (HCCI) operation using a variety of fuels are well known and have been demonstrated using different engine concepts in the past. In contrast, stoichiometric operation of HCCI is less well documented. Recent studies have highlighted the benefits of operating at a stoichiometric condition in terms of load expansion combined with the applicability of three way catalyst technology to reduce NOx emissions. In this study the characterization of stoichiometric HCCI using gasoline-like fuels was undertaken. The fuels investigated are gasoline, a 50% volume blend of iso-butanol and gasoline (IB50), and an 85% volume blend of ethanol and gasoline (E85). A single cylinder engine operating with direct injection (DI) and spark assist combined with a fully variable hydraulic valve actuation system allowed a wide range of operating parameters to be studied. The resultant fuel properties, which differed in terms of octane rating, fuel oxygenation, and heat of vaporization, show that stoichiometric HCCI is possible using a range of fuels but that these fuel characteristics do have some effect on the combustion characteristics. How these fuel properties can enable an increased engine operating envelope to be achieved, in comparison with both fuel lean HCCI and conventional spark ignited combustion, is then discussed.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Engine-out indicated specific NOx emissions (SA-HCCI and SI)

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Figure 2

Engine-out indicated specific HC emissions (SA-HCCI and SI)

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Figure 3

In-cylinder pressure: stoichiometric operation without spark assistance (comparable phasing and maximum pressure rise rate)

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Figure 4

MPRR for spark timing variation (valve timing held constant)

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Figure 5

CA50 for spark timing variation (valve timing held constant)

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Figure 6

In-cylinder pressure: comparable combustion phasing (valve timing held constant and spark timing varied)

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Figure 7

Apparent heat release rate: comparable combustion phasing (magnification of Fig. 6)

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Figure 8

In-cylinder pressure moderate load (E85)

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Figure 9

Cyclic variation of maximum pressure rise rate (MPRR), peak pressure (PP), and end of initial slow heat release (EO_ISHR) (E85)

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Figure 10

Cyclic variation of maximum pressure rise rate (MPRR), peak pressure (PP), and end of initial slow heat release (EO_ISHR) (IB50)

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Figure 11

Cyclic variation of maximum pressure rise rate (MPRR), peak pressure (PP), and end of initial slow heat release (EO_ISHR) (UTG91)

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Figure 12

Indicated thermal efficiency (SI)

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Figure 13

Indicated thermal efficiency (SA-HCCI)

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