Intermediate temperature heat release in an HCCI engine fueled by ethanol/n-heptane mixtures: An experimental and modeling study

Vuilleumier, David; Kozarac, Darko; Mehl, Marco; Saxena, Samveg; Pitz, William J.; Dibble, Robert W.; Chen, Jyh-Yuan; Sarathy, S. Mani

doi:10.1016/j.combustflame.2013.10.008

Cited by 86 publications

(58 citation statements)

References 44 publications

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“…It is well-known that iso-paraffins (e.g., iso-octane) display less low-temperature reactivity as compared to n-paraffins (e.g., nheptane) because the presence of multiple methyl substitutions inhibits the kinetics of low chain branching reactions in isoparaffins. 53,67,68 The simulation results for PRF91 at 750 K, shown in Figure 6a, clearly display the prominent two-stage ignition characteristic expected for paraffinic mixtures. The production of OH and HO 2 radicals shows a sharp increase up to the LTHR regime.…”

Section: Methodsmentioning

confidence: 99%

Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

2017

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Gasoline octane number is a significant empirical parameter for the optimization and development of internal combustion engines capable of resisting knock. Although extensive databases and blending rules to estimate the octane numbers of mixtures have been developed and the effects of molecular structure on autoignition properties are somewhat understood, a comprehensive theoretical chemistry-based foundation for blending effects of fuels on engine operations is still to be developed. In this study, we present models that correlate the research octane number (RON) and motor octane number (MON) with simulated homogeneous gas-phase ignition delay times of stoichiometric fuel/air mixtures. These correlations attempt to bridge the gap between the fundamental autoignition behavior of the fuel (e.g., its chemistry and how reactivity changes with temperature and pressure) and engine properties such as its knocking behavior in a cooperative fuels research (CFR) engine. The study encompasses a total of 79 hydrocarbon gasoline surrogate mixtures including 11 primary reference fuels (PRF), 43 toluene primary reference fuels (TPRF), and 19 multicomponent (MC) surrogate mixtures. In addition to TPRF mixture components of iso-octane/n-heptane/toluene, MC mixtures, including n-heptane, iso-octane, toluene, 1-hexene, and 1,2,4-trimethylbenzene, were blended and tested to mimic real gasoline sensitivity. ASTM testing protocols D-2699 and D-2700 were used to measure the RON and MON of the MC mixtures in a CFR engine, while the PRF and TPRF mixtures' octane ratings were obtained from the literature. The mixtures cover a RON range of 0−100, with the majority being in the 70−100 range. A parametric simulation study across a temperature range of 650−950 K and pressure range of 15−50 bar was carried out in a constant-volume homogeneous batch reactor to calculate chemical kinetic ignition delay times. Regression tools were utilized to find the conditions at which RON and MON best correlate with simulated ignition delay times. Furthermore, temperature and pressure dependences were investigated for fuels with varying octane sensitivity. This analysis led to the formulation of correlations useful to the definition of surrogates for modeling purposes and allowed one to identify conditions for a more in-depth understanding of the chemical phenomena controlling the antiknock behavior of the fuels.

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Section: Methodsmentioning

confidence: 99%

Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

2017

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“…The combustion chemistry of ethanol has also been clarified by the use of detailed chemical kinetic modeling [33]. As previously mentioned, single zone chemical kinetic modelling of HCCI engines can be a useful tool for understanding the fuel effect [34,35]. The current study aims to investigate the effect of ethanol addition of a PRF70 mixture.…”

Section: Introductionmentioning

confidence: 99%

Simulating HCCI Blending Octane Number of Primary Reference Fuel with Ethanol

Singh¹,

Waqas²,

Johansson³

et al. 2017

SAE Technical Paper Series

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The blending of ethanol with primary reference fuel (PRF) mixtures comprising n-heptane and iso-octane is known to exhibit a non-linear octane response; however, the underlying chemistry and intermolecular interactions are poorly understood. Well-designed experiments and numerical simulations are required to understand these blending effects and the chemical kinetic phenomenon responsible for them. To this end, HCCI engine experiments were previously performed at four different conditions of intake temperature and engine speed for various PRF/ethanol mixtures. Transfer functions were developed in the HCCI engine to relate PRF mixture composition to autoignition tendency at various compression ratios. The HCCI blending octane number (BON) was determined for mixtures of 2-20 vol % ethanol with PRF70. In the present work, the experimental conditions were considered to perform zerodimensional HCCI engine simulations with detailed chemical kinetics for ethanol/PRF blends. The simulations used the actual engine geometry and estimated intake valve closure conditions to replicate the experimentally measured start of combustion (SOC) for various PRF mixtures. The simulated HCCI heat release profiles were shown to reproduce the experimentally observed trends, specifically on the effectiveness of ethanol as a low temperature chemistry inhibitor at various concentrations. Detailed analysis of simulated heat release profiles and the evolution of important radical intermediates (e.g., OH and HO 2 ) were used to show the effect of ethanol blending on controlling reactivity. A strong coupling between the low temperature oxidation reactions of ethanol and those of n-heptane and iso-octane is shown to be responsible for the observed blending effects of ethanol/PRF mixtures.

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“…Formaldehyde starts to accumulate during the LTHR period and present at a significant concentration during ITHR. 45 The formation of hydrogen The intake temperature sensitivity test for PRF75 with C 5 alcohols was conducted to investigate the effect of alcohol addition by sweeping T in from an advanced combustion phasing to a retarded combustion phasing, as shown in Figure 15. Simulations were performed at intake pressures (P in ) of 150 kPa, a CR of 14, an engine speed of 1200 RPM, and an equivalence ratio of 0.3.…”

Section: Skeletal Mechanism For Hcci Simulationmentioning

confidence: 99%

“…37,44 The required intake temperature of reactive fuels is lower than that for less reactive fuels at constant desired combustion phasing. To quantify the boundaries of ITHR, the heat release rate (HRR) derivative-based method 45 was employed to identify the sudden change in HRR. The start of the ITHR is defined at the point where the second derivative of the heat release is equal to zero with an upper limit set at 0.004 (1/deg 2 ).…”

Section: Autoignition Delay Timesmentioning

confidence: 99%

Combustion Characteristics of C₅ Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation

Park

Chung

et al. 2015

Energy Fuels

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KEYWORDS2-methylbutanol, iso-pentanol, ignition delay, intermediate temperature heat release, skeletal mechanism, HCCI engine combustion 2 ABSTRACT C 5 alcohols are considered alternative fuels because they emit less greenhouse gases and fewer harmful pollutants. In this study, the combustion characteristics of 2-methylbutanol (2-methyl-1-butanol) and iso-pentanol (3-methyl-1-butanol) and their mixtures with primary reference fuels (PRFs) were studied using a detailed chemical kinetic model obtained from merging previously published mechanisms. Ignition delay times of the C 5 alcohol/air mixtures were compared with PRFs at 20 and 40 atm. Reaction path analyses were conducted at intermediate and high temperatures to identify the most influential reactions controlling ignition of C 5 alcohols. The direct relation graph with expert knowledge methodology was used to eliminate unimportant species and reactions in the detailed mechanism, and the resulting skeletal mechanism was tested at various homogeneous charge compression ignition (HCCI) engine combustion conditions. These simulations were used to investigate the heat release characteristics of the methylsubstituted C 5 alcohols, and the results show relatively strong reactions at intermediate temperatures prior to hot ignition. C 5 alcohol blending in PRF75 in HCCI combustion leads to a significant decrease of low temperature heat release (LTHR) and a delay the main combustion.The heat release features demonstrated by C 5 alcohols can be used to improve the design and operation of advanced engine technologies.3

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Intermediate temperature heat release in an HCCI engine fueled by ethanol/n-heptane mixtures: An experimental and modeling study

Cited by 86 publications

References 44 publications

Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

Simulating HCCI Blending Octane Number of Primary Reference Fuel with Ethanol

Combustion Characteristics of C₅ Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation

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Intermediate temperature heat release in an HCCI engine fueled by ethanol/n-heptane mixtures: An experimental and modeling study

Cited by 86 publications

References 44 publications

Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

Simulating HCCI Blending Octane Number of Primary Reference Fuel with Ethanol

Combustion Characteristics of C5 Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation

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Product

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Combustion Characteristics of C₅ Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation