Estimating fuel octane numbers from homogeneous gas-phase ignition delay times

Naser, Nimal; Chung, Suk Ho

doi:10.1016/j.combustflame.2017.09.037

Cited by 33 publications

(15 citation statements)

References 120 publications

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“…The NTC behvior exhibited by PRFs and the absence of NTC behavior for practical gasolines [23] is attributed to OS of practical gasolines as shown in many studies [20,[32][33][34]. NTC behavior is observed for certain fuels in the IQT [35][36][37][38] and other CVCCs [39,40].…”

Section: Introductionmentioning

confidence: 92%

Ignition delay time sensitivity in ignition quality tester (IQT) and its relation to octane sensitivity

Naser

Sarathy

Chung

2018

Fuel

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Cetane number (CN) is a commonly used metric to rate the ignition quality of distillate fuels. In this work, a concept of sensitivity in ignition delay time (IDT) obtained with an ignition quality tester (IQT) is proposed, which is correlated to octane sensitivity (OS), i.e., the difference between research octane number (RON) and motor octane number (MON). The concept is based on the determination of IDT using the ASTM D6890 standard and IDT obtained at a temperature lower than that prescribed by the standard. The IDT measured at this lower temperature is referred to as IDT l , which is obtained via a calibration procedure similar to the ASTM D6890 standard, but with a higher value of reference IDT for calibration with n-heptane. The IDT h (measured at the derived cetane number (DCN) ASTM D6890 condition) of a given test fuel and a binary primary reference fuel (PRF) mixture of iso-octane and n-heptane was measured to identify a PRF with matching IDT h as the test fuel. The ratio of low temperature IDTs of the non-PRF test fuel and PRF, i.e., IDT l,non-PRF /IDT l,PRF was defined as IDT sensitivity (IDS), which was correlated

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Section: Introductionmentioning

confidence: 92%

Ignition delay time sensitivity in ignition quality tester (IQT) and its relation to octane sensitivity

Naser

Sarathy

Chung

2018

Fuel

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“…In this case, the nonlinear regression model was a feedforward neural network [22]. The regression was an approximation, but it could balance the error in the chemical kinetic model with the error correlating octane numbers to ignition delay times [23][24][25][26][27][28]. The model could be evaluated in less than 10 s on a single CPU thread for compositions containing any combination of the more than 50 hydrocarbons and biofuels represented in the detailed chemical kinetics model developed by Mehl et al [21].…”

Section: Numerical Approachmentioning

confidence: 99%

Numerical Investigation of Fuel Property Effects on Mixed-Mode Combustion in a Spark-Ignition Engine

Pal

Ren

et al. 2020

Journal of Energy Resources Technology

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In this work, lean mixed-mode combustion is numerically investigated using computational fluid dynamics (CFD) in a spark-ignition engine. A new E30 fuel surrogate is developed using a neural network model with matched octane numbers. A skeletal mechanism is also developed by automated mechanism reduction and by incorporating a NOx sub-mechanism. A hybrid approach that couples the G-equation model and the well-stirred reactor model is employed for turbulent combustion modeling. The developed CFD model is able to predict pressure and apparent heat release rate (AHRR) traces. Two types of combustion cycles (namely, purely-deflagrative and mixed-mode cycles) are observed. The mixed-mode cycles feature earlier flame propagation and end-gas auto-ignition, leading to two distinctive AHRR peaks. The validated CFD model is then employed to investigate the effects of NOx chemistry. The NOx chemistry is found to promote auto-ignition through residual gas, while the deflagration phase remains largely unaffected. Sensitivity analysis is finally performed to understand effects of fuel properties, including heat of vaporization (HoV) and laminar flame speed (SL). An increased HoV tends to suppress auto-ignition through charge cooling, while the impact of HoV on flame propagation is insignificant. In contrast, an increased SL is found to significantly promote both flame propagation and end-gas auto-ignition. The promoting effect of SL on auto-ignition is not a direct chemical effect; it is rather caused by an advancement of the combustion phasing, which increases compression heating of the end-gas.

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“…Westbrook et al used experimentally obtained pressure data to find ignition delay times corresponding to RON and MON values of pure and compound mixtures [28,29]. Correlating homogenous gas-phase IDT with RON has also been attempted for mixtures of ethanol with PRFs, previously [30].…”

Section: Introductionmentioning

confidence: 99%

Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels

et al. 2019

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The synergistic octane blending behavior of ethanol with gasoline and its surrogates has been observed by many researchers. The non-linear octane boosting tendency is observed at mid and high molar blends of ethanol in primary references fuels. The present work aims to provide chemical insight into this non-linear blending behavior of ignition processes when ethanol is blended with primary reference fuels. To this end, ignition delay time calculations, using a wellvalidated mechanism, were performed for several fuel blends of iso-octane, n-heptane, and ethanol. Temperature and pressure values were found, correlating experimentally measured octane numbers and simulated homogenous batch reactor ignition delay times. The temperature and pressure conditions obtained, were then used to study the evolution of heat release and reactivity before the onset of auto-ignition in a homogeneous premixed reactor. Markers of low and high temperature reactivity (OH and HO2) were analyzed for various molar blends of n-heptane with ethanol/iso-octane. Ethanol was observed to be better at radical scavenging than iso-octane at higher mole fraction. A computational singular perturbation analysis was conducted for a selection of blends to clarify the reactions responsible for the synergistic blending behavior of ethanol in nheptane. The role of the H-abstraction reactions was highlighted during the first ignition stage; reactions related to n-heptane were found to compete with the H-abstraction reactions of iso-octane or ethanol. Notably, the H-abstraction path of ethanol was more favored than that of the iso-octane, as a result of the smaller activation energies of the related reactions in the ethanol. The competition of the H-abstraction paths resulted in a smaller radical pool in the n-heptane-iso-octane-air case, and an even smaller pool in the n-heptane-ethanol-air. In all the cases considered, the second stage was dominated mainly by hydrogen-related reactions, regardless of the initial mixture, with the H2O2 (+ M) → 2OH (+ M) and H + O2 → O + OH playing the most important roles. This work employed a novel approach to examine specific reactions responsible for auto-ignition in ethanol blends, which can be used for fuel design, primarily around the generation/consumption of radical pool intermediates by interaction with fuel components.

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Estimating fuel octane numbers from homogeneous gas-phase ignition delay times

Cited by 33 publications

References 120 publications

Ignition delay time sensitivity in ignition quality tester (IQT) and its relation to octane sensitivity

Ignition delay time sensitivity in ignition quality tester (IQT) and its relation to octane sensitivity

Numerical Investigation of Fuel Property Effects on Mixed-Mode Combustion in a Spark-Ignition Engine

Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels

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