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

Experimental Determination of Liquefied Petroleum Gas–Gasoline Mixtures Knock Resistance

[+] Author and Article Information
Emiliano Pipitone

Dipartimento di Ingegneria Chimica,
Gestionale, Informatica, Meccanica,
University of Palermo,
Viale delle Scienze,
Palermo 90128, Italy
e-mail: emiliano.pipitone@unipa.it

Giuseppe Genchi

Dipartimento di Ingegneria Chimica,
Gestionale, Informatica, Meccanica,
University of Palermo,
Viale delle Scienze,
Palermo 90128, Italy
e-mail: giuseppe.genchi@unipa.it

The air–fuel mixture portion most distant from ignition point, which undergoes auto-ignition if not promptly reached by the flame front.

The research octane number [32] is another ASTM knock rating method that prescribes the use of a CFR engine under different and less heavy test conditions respect to MON method [11]. For this reason, the RON of a fuel is usually higher than its MON.

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 November 27, 2013; final manuscript received June 5, 2014; published online July 2, 2014. Assoc. Editor: Stani Bohac.

J. Eng. Gas Turbines Power 136(12), 121502 (Jul 02, 2014) (7 pages) Paper No: GTP-13-1432; doi: 10.1115/1.4027831 History: Received November 27, 2013; Revised June 05, 2014

The results of previous experimental researches showed that great advantages can be achieved, both in terms of fuel consumption and pollutant emissions, in bifuel vehicles by means of the double-fuel combustion, i.e., the simultaneous combustion of gasoline and a gaseous fuel, such as liquefied petroleum gas (LPG) or natural gas (NG). The substantial increase in knock resistance pursued by adding LPG to gasoline, which allowed to maintain an overall stoichiometric proportion with air also at full load, is not documented in the scientific literature and induced the authors to perform a proper experimental campaign. The motor octane number (MON) of LPG–gasoline mixtures has been hence determined on a standard cooperative fuel research (CFR) engine, equipped with a double-fuel injection system in order to realize different proportions between the two fuels and electronically control the overall air–fuels mixture. The results of the measurement show a quadratic dependence of the MON of the mixture as function of the LPG concentration evaluated on a mass basis, with higher increase for the lower LPG content. A good linear relation, instead, has been determined on the basis of the evaluated LPG molar fraction. The simultaneous combustion of LPG and gasoline may become a third operative mode of bifuel vehicles, allowing to optimize fuel economy, performances, and pollutant emissions; turbocharged bifuel engines could strongly take advantage of the knock resistance of the fuels mixture thus adopting high compression ratio (CR) both in pure gas and double-fuel mode, hence maximizing performance and reducing engine size. The two correlations determined in this work, hence, can be useful for the design of future bifuel engines running with knock safe simultaneous combustion of LPG and gasoline.

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References

Figures

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Fig. 6

Scheme of the injection system

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Fig. 5

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

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Fig. 4

Experimental system layout

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Fig. 1

Raw CO emission measured at WOT for pure gasoline (same λ values of Fig. 1) and double-fuel mode (λ = 1) on a series production S.I. engine [1]

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Fig. 3

CFR engine combustion chamber: the knock sensor is placed on the opposite side to the spark plug

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Fig. 2

HC emissions after catalytic converter at WOT for both pure gasoline mode (λ values reported on the right axis) and double-fuel mode (λ = 1) on a series production S.I. engine [1]

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Fig. 7

Measured MON as function of the LPG mass fraction

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Fig. 8

Measured MON as function of the LPG molar fraction

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Fig. 9

Engine CR and spark advance adopted in the tests

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