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

Modeling Investigation of Different Methods to Suppress Engine Knock on a Small Spark Ignition Engine

[+] Author and Article Information
Jiankun Shao

Engine Research Center,
Department of Mechanical Engineering,
University of Wisconsin–Madison,
Madison, WI 53705
e-mail: jshao6@wisc.edu

Christopher J. Rutland

Professor
Engine Research Center,
Department of Mechanical Engineering,
University of Wisconsin–Madison,
Madison, WI 53705
e-mail: rutland@engr.wisc.edu

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 18, 2014; final manuscript received October 15, 2014; published online December 9, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(6), 061506 (Jun 01, 2015) (15 pages) Paper No: GTP-14-1492; doi: 10.1115/1.4028870 History: Received August 18, 2014; Revised October 15, 2014; Online December 09, 2014

Knock is the main obstacle toward increasing the compression ratio and using lower octane number fuels. In this paper, a small two-valve aircraft spark ignition engine, Rotax-914, was used as an example to investigate different methods to suppress engine knock. It is generally known that if the octane number is increased and the combustion period is shortened, the occurrence of knock will be suppressed. Thus, in this paper, different methods were introduced for two effects, increasing ignition delay time in end-gas and increasing flame speed. In the context, KIVA-3V code, as an advanced 3D engine combustion simulation code, was used for engine simulations and chemical kinetics investigations were also conducted using chemkin. The results illustrated gas addition, such as hydrogen and natural gas addition, can be used to increase knock resistance of the Rotax-914 engine in some operating conditions. Replacing the traditional port injection method by direct injection strategy was another way investigated in this paper to suppress engine knock. Some traditional methods, such as adding exhaust gas recirculation (EGR) and increasing swirl ratio, also worked for this small spark ignition engine.

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References

Figures

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Fig. 1

Schematic illustration of knocking combustion in spark ignition engines [2]

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Fig. 2

Validation of ignition delay times of submechanisms for different hydrocarbons [13-17]

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Fig. 3

Validation of laminar flame speeds of submechanisms for different hydrocarbons [18-20]

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Fig. 4

Laminar flame speed, SL, of PRF87-air with hydrogen addition as a function of mole fraction of hydrogen in fuel blends, xH, for different equivalence ratios

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Fig. 5

Laminar flame speed, SL, of PRF87-air with natural gas addition as a function of mole fraction of natural gas in fuel blends, xadd, for different equivalence ratios

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Fig. 6

Computational mesh of the Rotax-914 engine [2] and model validations in two different operating conditions with the engine mesh

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Fig. 7

Effects of hydrogen addition on ignition delay time for PRF87 + H2 + air mixture

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Fig. 8

Reaction rate of H-abstraction of PRF87 fuel with initial temperature equals to 800 K and initial pressure equals to 50 atm

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Fig. 9

Reaction rate of OH consumption with hydrogen addition and mole fraction of OH in the WSR

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Fig. 10

Comparison of HO2 distribution among case 1, case 5, and case 6 in weak knock operating condition, see Table 2 (the left column shows case 1, the center column shows case 5, and the right column shows case 6)

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Fig. 11

Comparison of HO2 distribution among case 1 and case 3 in strong knock operating condition, see Table 3 (the left column shows case 1 and the right column shows case 3)

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Fig. 19

Comparison of HO2 distribution of the case with port injection (left column) and the case with direct injection (right column), see Table 6

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Fig. 18

Comparison of swirl flow and tumble flow between the case with port injection and the case with direct injection, see Table 6

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Fig. 17

Comparison of pressure trace, PRR, and HRR between port injection case and direct injection case, see Table 6

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Fig. 16

Comparison of HO2 distribution among case 1 and case 6 for natural gas addition (the left column shows case 1 and the right column shows case 6, see Table 5)

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Fig. 15

Comparison of pressure trace, PRR, and HRR among cases with different natural gas additions, see Table 5

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Fig. 14

Comparison of ignition delay time between natural gases addition cases (50% PRF87 and 50% natural gas in mole fraction) with pure PRF87 case for natural gas blends 1–6 in Table 4

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Fig. 13

Comparison of net reaction rates of hydrocarbon H-abstraction between cases with methane addition (50% PRF87 and 50% methane in mole fraction) and without methane addition (100% PRF87 in mole fraction)

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Fig. 12

Comparison of ignition delay time between cases with methane addition (50% PRF87 and 50% methane in mole fraction) and without methane addition (100% PRF87 in mole fraction)

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Fig. 20

2D contours of flame propagation and knock propensity showed by HO2 of direct injection case, see Table 6

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Fig. 21

2D contours of flame propagation and knock propensity showed by HO2 of upper left corner of direct injection case, see Table 6

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Fig. 22

Injection strategy of direct injection condition, see direct injection case of Table 6

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Fig. 23

Comparison of pressure traces and HRR of the cases with different dilution gases

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Fig. 24

Comparison of pressure traces, PRR, and HRR of cases with different swirl ratios

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Fig. 25

2D top-view plots of HO2 distribution of weak knock condition (hydrogen addition). Row 1 is case 1, row 2 is case 2, row 3 is case 3, row 4 is case 4, row 5 is case 5, and row 6 is case 6.

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Fig. 26

2D top-view plots of HO2 distribution of strong knock condition (hydrogen addition). Row 1 is case 1, row 2 is case 2, and row 3 is case 3.

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Fig. 27

2D top-view plots of HO2 distribution of natural gas addition. Row 1 is case 1, row 2 is case 2, row 3 is case 3, row 4 is case 4, row 5 is case 5, and row 6 is case 6.

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