The Underlying Physics and Chemistry behind Fuel Sensitivity

Mittal, Vikram; Heywood, John B.; Green, William

doi:10.4271/2010-01-0617

Cited by 36 publications

(16 citation statements)

References 9 publications

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“…difference between RON and MON is called sensitivity, S = RON -MON, and represents the sensitivity of the fuel autoignition kinetics to the unburned gas temperature [8]. Kalghatgi [12], and Mittal and coworkers [13] have shown that fuels with higher S have slower autoignition kinetics at lower temperatures and faster autoignition kinetics at higher temperatures, compared to fuels with lower S.…”

mentioning

confidence: 99%

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

Chupka¹,

Christensen²,

Fouts³

et al. 2015

SAE Int. J. Fuels Lubr.

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The introduction of more stringent standards for fuel economy as well as greenhouse gas emissions [1] is driving research to increase the efficiency of spark ignition (SI) engines. Approaches for increasing SI engine efficiency include increased compression ratio, direct injection (DI), turbocharging, downsizing, and down-speeding. Higher octane number (more highly knock resistant) fuels allow improved combustion phasing and operation at higher loads at the same engine speed, while also allowing the higher in-cylinder temperature and pressure generated by increased compression ratio and turbocharging which are critical for downsizing and down-speeding [2,3,4]. At the same time, renewable fuel usage is mandated to increase in the United States under the Renewable Fuel Standard [5], and globally under laws enacted in other countries. Ethanol, the most commonly used renewable fuel, has a research octane number (RON) of approximately 110 [6] compared to typical U.S. regular gasoline at 91-93 [2]. Accordingly, high octane number ethanol blends containing from 20 volume percent (vol%) to 40 vol% ethanol are being extensively studied [3,7,8,9,10]. A unique property of ethanol is its high heat of vaporization (HOV), which significantly increases charge cooling for DI engines, providing additional knock resistance.The tendency of a spark-ignited engine fuel to autoignite and cause knock is measured as the octane number, a critical performance parameter for SI engines. In the United States, octane number at the retail pump is given as the anti-knock index, the average of two octane number measurements: research octane number (RON) (ASTM D2699-13b) and motor octane number (MON) (ASTM D2700-13b). The primary differences between the RON and MON measurements are fuel-air charge temperature and engine speed, with the RON test using a comparatively low fuel-air charge temperature (that is dependent on the fuel's latent heat of evaporation) and slower engine speed while the MON test is conducted at a significantly higher fuel-air charge temperature (149°C) and faster engine speed. Recent studies have demonstrated that MON is correlated with different effects in modern engines than was the case when these tests were introduced in 1932, and in fact increasing MON at constant RON may actually lower the fuel knock resistance [11]. The ABSTRACTThe objective of this work was to measure knock resistance metrics for ethanol-hydrocarbon blends with a primary focus on development of methods to measure the heat of vaporization (HOV). Blends of ethanol at 10 to 50 volume percent were prepared with three gasoline blendstocks and a natural gasoline. Performance properties and composition of the blendstocks and blends were measured, including research octane number (RON), motor octane number (MON), net heating value, density, distillation curve, and vapor pressure. RON increases upon blending ethanol but with diminishing returns above about 30 vol%. Above 30% to 40% ethanol the curves flatten and converge at a RON of about 103 to 105, even for...

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confidence: 99%

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

Chupka¹,

Christensen²,

Fouts³

et al. 2015

SAE Int. J. Fuels Lubr.

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“…The latter observation was attributed to the time that the droplets spent in the cylinder before impacting on the combustion chamber walls. This period was not greater than the heat-up period required before the droplets reached the wet-bulb temperature 2 . Increased heat transfer through increased cylinder temperatures did not speed up evaporation.…”

Section: Current Questions Surrounding Os Knock and Evaporative Coolingmentioning

confidence: 92%

“…During knocking combustion, the auto-ignition of the unburnt gas creates localized pressure spikes and gas turbulence, which can be harmful to the engine due to the associated increase in the combustion chamber heat transfer. Engine knock can thereby cause damage to expensive engine components [1,2].…”

Section: Combustion and Knock In Si Enginesmentioning

confidence: 99%

A CFD Study of Fuel Evaporation and Related Thermo-fluid Dynamics in the Inlet Manifold, Port and Cylinder of the CFR Octane Engine

Thiart¹,

Floweday²,

Meyer³

2012

SAE Int. J. Fuels Lubr.

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“…11 can be estimated to cause a RON difference of approximately 10 points in the RON scale. This extra resistance to autoignition for the high OS fuel 3-hexene, relative to the comparable zero-OS fuel PRF80, with its "functional extra octane rating" of 10 octane numbers, is responsible for the attractiveness of high OS fuels for knock avoidance in modern high compression ratio SI engines [3,6,75]. In other words, the lack of low temperature reactivity and the corresponding high value of Octane Sensitivity increases the knock resistance of 3-hexene by about 10 Octane numbers, compared to a PRF fuel with Octane numbers in the range of 80 -95.…”

Section: Octane Sensitivity Of Branched Fuelsmentioning

confidence: 99%

Analysis of the filtered non-premixed turbulent flame

Wang

2017

Combustion and Flame

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This paper uses a chemical kinetic modeling approach to study the influences of fuel molecular structure on Octane Sensitivity (OS) in Spark Ignition (SI) engines. Octane Sensitivity has the potential to identify fuels that can be used in next-generation high compression, turbocharged SI engines to avoid unwanted knocking conditions and extend the range of operating conditions that can be used in such engines. While the concept of octane numbers of different fuels has been familiar for many years, the variations of their values and their role in determining Octane Sensitivity have not been addressed previously in terms of the basic structures of the fuel molecules. In particular, the importance of electron delocalization on low temperature hydrocarbon reactivity and its role in determining OS in engine fuel is described here for the first time. The role of electron delocalization on fuel reactivity and Octane Sensitivity is illustrated for a very wide range of engine fuel types, including n-alkane, 1-olefin, n-alcohol, and n-alkyl benzenes, and the unifying features of these fuels and their common trends, using existing detailed chemical kinetic reaction mechanisms that have been collected and unified to produce an overall model with unprecedented capabilities.

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The Underlying Physics and Chemistry behind Fuel Sensitivity

Cited by 36 publications

References 9 publications

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

A CFD Study of Fuel Evaporation and Related Thermo-fluid Dynamics in the Inlet Manifold, Port and Cylinder of the CFR Octane Engine

Analysis of the filtered non-premixed turbulent flame

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