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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Optical Investigation of the Effects of Ethanol/Gasoline Blends on Spark-Assisted HCCI

[+] Author and Article Information
Mohammad Fatouraie

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

Margaret Wooldridge

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

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 6, 2014; final manuscript received February 7, 2014; published online March 17, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(8), 081507 (Mar 17, 2014) (13 pages) Paper No: GTP-14-1069; doi: 10.1115/1.4026862 History: Received February 06, 2014; Revised February 07, 2014

Spark assist (SA) has been demonstrated to extend the operating limits of homogeneous charge compression ignition (HCCI) modes of engine operation. This experimental investigation focuses on the effects of 100% indolene and 70% indolene/30% ethanol blends on the ignition and combustion properties during SA HCCI operation. The spark assist effects are compared to baseline HCCI operation for each blend by varying spark timing at different fuel/air equivalence ratios ranging from Φ = 0.4–0.5. High speed imaging is used to understand connections between spark initiated flame propagation and heat release rates. Ethanol generally improves engine performance with higher net indicated mean effective pressure (IMEPn) and higher stability compared to 100% indolene. SA advances phasing within a range of ∼5 crank angle degrees (CAD) at lower engine speeds (700 rpm) and ∼11 CAD at higher engine speeds (1200 rpm). SA does not affect heat release rates until immediately (within ∼5 CAD) prior to auto-ignition. Unlike previous SA HCCI studies of indolene fuel in the same engine, flames were not observed for all SA conditions.

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Figures

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Fig. 1

Engine setup schematic

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Fig. 2

Example of one of the imaging processing methods used in the current work. From left to right: (1) the original color image, with color enhanced for clarity; (2) the image after conversion to monochrome; and (3) the equivalent area of the monochrome image represented as a disk.

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Fig. 3

Example of the second image processing method used in the current work. From left to right: (1) the original color image, with color enhanced for clarity; (2) the image after conversion to gray scale; and (3) the result of averaging the intensity values of 30 consecutive combustion cycles at the same crank angle after applying a low pass filter to the intensity. The range of the false color scale is 0 to 5 (arbitrary units).

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Fig. 4

Average maximum in-cylinder pressure and average phasing of Pmax as a function of ϕ. The data have been offset from the nominal ϕ values for clarity. The error bars are the standard deviations of the measured data.

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Fig. 5

Experimental results of the effects of SA on CA50, IMEPn, and the indicated thermal efficiency of the two fuel blends at 700 rpm. The error bars are the standard deviations for the cycle averaged data.

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Fig. 6

Normalized pressure, heat release rate, and mass fraction burned as a function of SA timing and fuel for ϕ = 0.4

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Fig. 7

Cycle-to-cycle variation of effective radius and heat release rate for E30-SA60 and ϕ = 0.40 at 700 rpm. Cycles 7 and 10 exhibited the minimum and maximum HRRs at these operating conditions.

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Fig. 8

Results of imaging data from four cycles for E30 with SA at 60 deg bTDC and ϕ = 0.40 at 700 rpm. Results for cycle 7 with IMEPn = 1.46 bar and HRRmax = 12.6 J/CAD are presented in (a), results for cycle 8 with IMEPn = 1.49 bar and HRRmax = 15.2 J/CAD are presented in (b), results for cycle 9 with IMEPn = 1.49 bar and HRRmax = 14.0 J/CAD are presented in (c), and results for cycle 10 with IMEPn = 1.52 bar and HRRmax = 18.2 J/CAD are presented in (d).

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Fig. 9

Results of imaging data from two cycles for E0 with SA at 40 deg bTDC and ϕ = 0.45 at 700 rpm. Results for cycle 8 data with IMEPn = 1.43 bar and HRRmax = 15.1 J/CAD are presented in (a), and results for cycle 27 data with IMEPn = 1.03 bar and HRRmax = 20.2 J/CAD are presented in (b). The location of the first local auto-ignition sites are highlighted in the panels.

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Fig. 10

Results of imaging data from for E30 with SA at 40 deg bTDC and ϕ = 0.45 at 700 rpm for cycle 10 with IMEPn = 1.75 bar and HRRmax = 19.6 J/CAD

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Fig. 11

Results for average chemiluminescent intensity for E0 HCCI and ϕ = 0.45 at 700 rpm

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Fig. 12

Results for average chemiluminescent intensity for E0 with SA at 20 deg bTDC and ϕ = 0.45 at 700 rpm

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Fig. 13

Results for average chemiluminescent intensity for E0 with SA at 40 deg bTDC and ϕ = 0.45 at 700 rpm

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Fig. 14

Results for average chemiluminescent intensity for E0 with SA at 40 deg bTDC and ϕ = 0.40 at 700 rpm

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Fig. 15

Results for average chemiluminescent intensity for E30 with SA at 40 deg bTDC and ϕ = 0.45 at 700 rpm

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Fig. 16

The effect of SA on CA50, IMEPn and indicated thermal efficiency for the two fuel blends at 1200 rpm. The error bars are the standard deviations for the cycle averaged data.

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Fig. 17

Results for average chemiluminescent intensity for E30 HCCI and ϕ = 0.45 at 1200 rpm

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Fig. 18

Results for average chemiluminescent intensity for E30 with SA at 40 deg bTDC and ϕ = 0.45 at 1200 rpm

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Fig. 19

Single cycle raw images for E0 (a) and E30 (b) at ϕ = 0.50 and 700 rpm. The numbers at the bottom of frames indicate the crank angle (°aTDC).

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