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Research Papers: Gas Turbines: Industrial & Cogeneration

The Low Load Limit of Gasoline Partially Premixed Combustion Using Negative Valve Overlap

[+] Author and Article Information
Patrick Borgqvist

e-mail: patrick.borgqvist@energy.lth.se

Bengt Johansson

Department of Energy Sciences,
Faculty of Engineering,
Lund University,
Lund SE-221 00, Sweden

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 19, 2012; final manuscript received November 22, 2012; published online May 22, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(6), 062002 (May 22, 2013) (7 pages) Paper No: GTP-12-1440; doi: 10.1115/1.4023613 History: Received November 19, 2012; Revised November 22, 2012

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in partially premixed combustion mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline. A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

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References

Figures

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Fig. 1

The valve lift curves of the Cargine valves with negative valve overlap

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Fig. 2

Graphical representation of the experimental factors and their levels

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Fig. 3

Pareto chart of the standard deviation of IMEPnet second order regression model coefficients, xn, from Eq. (1). A is the coded letter for NVO, B is the coded letter for the fuel mass ratio between the injections, and C is the separation in crank angles between the start of the two injections.

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Fig. 4

Pareto chart of the combustion efficiency second order regression model coefficients, xn, from Eq. (1). A is the coded letter for NVO, B is the coded letter for the fuel mass ratio between the injections, and C is the separation in crank angles between the start of the two injections.

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Fig. 5

Representation of fuel injection signal from the engine control system over the different injection strategies

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Fig. 6

Standard deviation of IMEPnet of the single injection strategy compared to the optimized split main injection strategy

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Fig. 7

Combustion efficiency of the single injection strategy compared to the optimized split main injection strategy

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Fig. 8

Standard deviation of IMEPnet of the single injection strategy compared to the single injection with pilot strategy

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Fig. 9

Combustion efficiency of the single injection strategy compared to the single injection with pilot strategy

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Fig. 10

Unburned hydrocarbon (UHC) emissions of the single injection strategy compared to the single injection with pilot strategy

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Fig. 11

Combustion timing of the single injection strategy compared to the single injection with pilot strategy

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Fig. 12

Combustion duration of the single injection strategy compared to the single injection with pilot strategy

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Fig. 13

Standard deviation of IMEPnet of the split main strategy compared to the split main injection with pilot strategy

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Fig. 14

Combustion efficiency of the split main strategy compared to the split main injection with pilot strategy

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Fig. 15

Standard deviation of IMEPnet for a split main injection test case with and without the glow plug

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Fig. 16

Combustion efficiency for a split main injection test case with and without the glow plug

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