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Research Papers: Internal Combustion Engines

Pressure Sensitivity of HCCI Auto-Ignition Temperature for Oxygenated Reference Fuels

[+] Author and Article Information
Bengt Johansson

Lund University,
223 63 Lund, Sweden

William Cannella

Chevron,
Richmond, CA 94802

Manuscript received November 23, 2012; final manuscript received January 8, 2013; published online June 10, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(7), 072801 (Jun 10, 2013) (13 pages) Paper No: GTP-12-1449; doi: 10.1115/1.4023614 History: Received November 23, 2012; Revised January 08, 2013

The current research focuses on creating a homogeneous charge compression ignition (HCCI) fuel index suitable for comparing different fuels for HCCI operation. One way to characterize a fuel is to use the auto-ignition temperature (AIT). The AIT can be extracted from the pressure trace. Another potentially interesting parameter is the amount of low temperature heat release (LTHR) that is closely connected to the ignition properties of the fuel. The purpose of this study was to map the AIT and the amount of LTHR of different oxygenated reference fuels in HCCI combustion at different cylinder pressures. Blends of n-heptane, iso-octane, and ethanol were tested in a cooperative fuels research (CFR) engine with a variable compression ratio. Five different inlet air temperatures ranging from 50 °C to 150 °C were used to achieve different cylinder pressures and the compression ratio was changed accordingly to keep a constant combustion phasing, CA50, of 3 ± 1 deg after top dead center (TDC). The experiments were carried out in lean operation with a constant equivalence ratio of 0.33 and with a constant engine speed of 600 rpm. The amount of ethanol needed to suppress the LTHR from different primary reference fuels (PRFs) was evaluated. The AIT and the amount of LTHR for different combinations of n-heptane, iso-octane, and ethanol were charted.

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Figures

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Fig. 1

Temperature at the IVC and corresponding compression ratios

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Fig. 2

Rate of heat release with the start of combustion for PRF70. The black box marks the magnified area for Fig. 3.

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Fig. 3

The LTHR for PRF70. The black dots indicate the start of combustion as 0.2 J/CAD.

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Fig. 4

Temperatures and pressures at auto-ignition for PRF 70

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Fig. 5

The LTHR for H40E60 The five lines represent the different intake air temperatures. The black dots indicate the start of combustion as 0.2 J/CAD.

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Fig. 6

Temperatures and pressures at auto-ignition for H40E60

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Fig. 7

Amount of the LTHR as a function of ethanol fraction. The marks for each fuel represent the different IATs, with 50 °C at the top and 150 °C at the bottom. Zero means no LTHR at one or more temperatures.

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Fig. 8

The LTHR as a function of ethanol/n-heptane proportions. The marks for each fuel represent the different IATs, with 50 °C at the top and 150 °C at the bottom. Zero means no LTHR at one or more temperatures.

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Fig. 9

The LTHR as a function of the difference between the amounts of n-heptane and ethanol

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Fig. 10

When the iso-octane is replaced with ethanol the amount of LTHR is reduced

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Fig. 11

Temperature and pressure at auto-ignition; 0.2 J/CAD. The five marks for each fuel correspond to the five different inlet air temperatures.

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Fig. 12

Temperature and pressure at auto-ignition; 1% burnt. The five marks for each fuel correspond to the five different inlet air temperatures.

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Fig. 13

Crank angle at the start of combustion

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Fig. 14

Amount of the LTHR as a function of the calculated ON; ON0 = 108.6

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Fig. 15

Auto-ignition temperature as a function of the calculated ON; ONethanol = 108.6

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Fig. 16

Amount of the LTHR as a function of the calculated ON; ONethanol = 190

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Fig. 17

Auto-ignition temperature as a function of the calculated ON; ONethanol = 190

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Fig. 18

The LTHR for H20E10 run and repetition

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Fig. 19

Temperatures and pressures at auto-ignition for H20E10 and repetition

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Fig. 20

The CAD at the SOC for the experiment with the constant SOC compared to the original experiment with the constant CA50

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Fig. 21

Temperatures and pressures at auto-ignition (using the 0.2 J/CAD definition)

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Fig. 22

The LTHR for PRF 80

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Fig. 23

The LTHR for H20E1

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Fig. 24

The LTHR for H20E5

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Fig. 25

The LTHR for H20E10

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Fig. 26

The LTHR for H20E20

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Fig. 27

The LTHR for PRF 70

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Fig. 28

The LTHR for H30E1

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Fig. 29

The LTHR for H30E5

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Fig. 30

The LTHR for H30E10

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Fig. 31

The LTHR for H30E20

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Fig. 32

The LTHR for H60E40

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Fig. 33

The LTHR for H55E4

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Fig. 34

The LTHR for H50E5

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Fig. 35

The LTHR for H45E5

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Fig. 36

The LTHR for H40E60

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Fig. 37

Auto-ignition temperatures for PRF 80

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Fig. 38

Auto-ignition temperatures for H20E1

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Fig. 39

Auto-ignition temperatures for H20E5

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Fig. 40

Auto-ignition temperatures for H20E10

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Fig. 41

Auto-ignition temperatures for H20E20

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Fig. 42

Auto-ignition temperatures for PRF 70

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Fig. 43

Auto-ignition temperatures for H30E1

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Fig. 44

Auto-ignition temperatures for H30E5

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Fig. 45

Auto-ignition temperatures for H30E10

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Fig. 46

Auto-ignition temperatures for H30E2

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Fig. 47

Auto-ignition temperatures for H60E40

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Fig. 48

Auto-ignition temperatures for H55E45

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Fig. 49

Auto-ignition temperatures for H50E50

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Fig. 50

Auto-ignition temperatures for H45E55

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Fig. 51

Auto-ignition temperatures for H40E60

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