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

A Refined Model for Knock Onset Prediction in Spark Ignition Engines Fueled With Mixtures of Gasoline and Propane

[+] Author and Article Information
Emiliano Pipitone

Department of Chemical, Management,
Computer Science and Mechanical Engineering,
University of Palermo,
Viale delle Scienze,
edificio 8,
Palermo 90128, Italy
e-mail: emiliano.pipitone@unipa.it

Stefano Beccari

Department of Chemical, Management,
Computer Science and Mechanical Engineering,
University of Palermo,
Viale delle Scienze,
edificio 8,
Palermo 90128, Italy
e-mail: stefano.beccari@unipa.it

Giuseppe Genchi

Department of Chemical, Management,
Computer Science and Mechanical Engineering,
University of Palermo,
Viale delle Scienze,
edificio 8,
Palermo 90128, Italy
e-mail: giuseppe.genchi@unipa.it

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 11, 2014; final manuscript received March 4, 2015; published online May 12, 2015. Assoc. Editor: Song-Charng Kong.

J. Eng. Gas Turbines Power 137(11), 111501 (Nov 01, 2015) (9 pages) Paper No: GTP-14-1615; doi: 10.1115/1.4030262 History: Received November 11, 2014; Revised March 04, 2015; Online May 12, 2015

In the last decade, gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), widely spread in many countries, thanks to their prerogative of low cost and reduced environmental impact. Hence, bi-fuel engines, which allow to run either with gasoline or with gas (LPG or NG), became very popular. Moreover, as experimentally demonstrated by the authors in the previous works, these engines may also be fueled by a mixture of gasoline and gas, which, due to the high knock resistance of gas, allow to use stoichiometric mixtures also at full load, thus drastically improving engine efficiency and pollutant emissions with respect to pure gasoline operation without noticeable power loss. This third operation mode, called double fuel combustion, can be easily introduced in series production engine, since a simple electronic control unit (ECU) programing is required. The introduction into series production would require the availability of proper models for thermodynamic simulations, nowadays widely adopted to reduce research and development efforts and costs. To this purpose, the authors developed a quite original knock onset prediction model for knock-safe performances optimization of engines fueled by propane, gasoline, and their mixtures. The ignition delay model has been properly modified to account for the negative temperature coefficient (NTC) behavior exhibited by many hydrocarbon fuels such as gasoline and propane. The model parameters have been tuned by means of a considerable amount of light knocking in-cylinder pressure cycles acquired on a modified cooperative fuel research (CFR) engine, fueled by gasoline–propane mixtures. The adoption of many different compression ratios (CRs), inlet mixture temperatures, spark advances (SAs), and fuel mixture compositions allowed to use a very differentiated set of pressure and temperature curve, which gives the calibrated model a general validity for using different kinds of engines, i.e., naturally aspirated or supercharged. As a result, the model features a maximum knock onset prediction error around four crank angle degrees (CAD) and a mean absolute error always lower than 1 CAD, which is a negligible quantity from an engine control standpoint.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Typical auto-ignition delay measurement, carried out on a rapid compression machine using gasoline surrogate [16]

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Fig. 2

ID diagram obtained from RCM [16] (Gasoline surrogate, 20 bar, three different values of the equivalence ratio ϕ)

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Fig. 3

Comparison between measured ignition delay [16] and model adopted in the present paper

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Fig. 4

Experimental system layout

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Fig. 5

Fuel supply systems: carburettor, LPG injector, and gasoline injectors

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Fig. 6

Power spectrum of the raw pressure signal (propane mass fraction 40%, SA = 35 CAD BTDC, TMIX = 80 °C)

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Fig. 7

Raw and filtered pressure with ϑKO,exp evaluation (propane mass fraction 40%, SA = 35 CAD BTDC, TMIX = 80 °C)

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Fig. 8

Surface of the minimum εMA as a function of the model constants B and n (gasoline, TNTC = 720 K)

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Fig. 9

Contour map of the minimum εMA as a function of the model constants B and n (gasoline, TNTC = 720 K)

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Fig. 10

Model parameter A as function of the propane mass fraction

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Fig. 11

Fuel mixture MON as function of the propane mass fraction

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Fig. 12

Model parameter A as function of the mixture MON (propane mass fraction is also reported)

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Fig. 13

Comparison between estimated and experimental KOCAs for gasoline (operative conditions reported in Table 3, first column)

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Fig. 14

Comparison between estimated and experimental KOCAs for propane (operative conditions reported in Table 3, last column)

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Fig. 15

Comparison between estimated and experimental knock onset for double fuel operation (operative conditions reported in Table 3, from 20% to 80% of propane mass fraction)

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