Diesel Surrogate Fuels Research Articles

Enhanced Ni-Al-Based Catalysts and Influence of Aromatic Hydrocarbon for Autothermal Reforming of Diesel Surrogate Fuel

Aromatic hydrocarbons along with sulfur compounds in diesel fuel pose a significant threat to catalytic performances, due mainly to carbon deposition on the catalytic surface. In order to investigate the influence of an aromatic hydrocarbon on the autothermal reforming of diesel fuel, 1-methylnaphthalene (C11H10) was selected as an aromatic hydrocarbon. Two types of diesel surrogate fuel, i.e., DH (dodecane (C12H26) and hexadecane (C16H34) mixture) as well as DHM (DH fuel and C11H10 mixture) fuel, were prepared. A Rh-Al-based catalyst (R5A-I) was prepared using a conventional impregnation method. Various Ni-Al-based catalysts with Fe and Rh promoters were prepared via a polymer modified incipient method to improve the carbon coking resistance. These catalysts were tested under conditions of S/C = 1.17, O2/C = 0.24, 750 °C, and GHSV = 12,000 h-1 at DH or DHM fuel. R5A-I exhibited excellent catalytic performance in both DH and DHM fuels. However, carbon coking and sulfur poisoning resistance were observed in our previous study for the Ni-Al-based catalyst with the Fe promoter, which became deactivated with increasing reaction time at the DHM fuel. In the case of the Rh promoter addition to the Ni-Al-based catalysts, the catalytic performances decreased relatively slowly with increasing (from 1 wt.% (R1N50A) to 2 wt.% (R2N50A)) content of Rh2O3 at DHM fuel. The catalysts were analyzed via scanning electron microscopy combined with energy dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. Gas chromatography-mass spectrometry detected various types of hydrocarbons, e.g., ethylene (C2H4), with catalyst deactivation. The results revealed that, among the produced hydrocarbons, C2H4 played a major role in accelerating carbon deposition that blocks the reforming reaction. Therefore, Rh metal deserves consideration as a carbon coking inhibitor that prevents the negative effects of the C2H4 for autothermal reforming of diesel fuel in the presence of aromatic hydrocarbons.

바이오 디젤의 첨가가 대용 디젤연료의 예혼합화염에 미치는 영향

대기압 조건에서 대용 디젤 연료의 예혼합 화염에 바이오 디젤 첨가의 효과를 이해하기 위해 수치 연구를 수행하였다. 대용 디젤 연료로 n-dodecane과 m-xylene 및 바이오 디젤로 methyl decanoate에 대한 상세 화학 반응 메커니즘을 사용하였다. 주어진 당량비 범위에서 각 성분의 화염 속도가 계산되었고 다른 연구자의 실험 결과와 비교되었으며, 그 결과는 잘 일치하였다. 대용 디젤 연료에 methyl decanoate을 첨가하면 희박영역보다 과농영역에서 화염 속도가 증가한다. 이는 산소원자 및 OH 라디칼의 농도를 증가시키는 H + O₂=OH + O의 반응 속도가 증가하기 때문이다. Methyl decanoate의 첨가는 계산 된 모든 당량비에서 질소산화물의 최대 농도를 감소시킨다. 또한 methyl decanoate의 첨가량이 증가함에 따라 NO 배출계수도 감소한다.

Prediction of transport properties of fuels in supercritical conditions by molecular dynamics simulation

Developing reliable method for predicting transport properties of fuels in supercritical environments has long been a matter of serious practical concern in combustion science and technology mainly due to the necessity of developing high-pressure combustion device. Two basic transport properties, i.e. shear viscosity and thermal conductivity, of methane and diesel surrogate fuels in conditions both near to and far from critical point are predicted. The computed values agree well with experimental results in supercritical conditions except for the deviation of shear viscosity in neighborhood of critical region due to critical divergences. The transport properties of n-Heptane in “Spray-H” and n-Dodecane in “Spray-A” conditions are also predicted using the same simulation settings with uncertainty quantification analysis. The statistical errors of density, viscosity and thermal conductivity are estimated to be less than 1.1%, 1.88%, 1.47% and 0.5%, 0.84%, 1.46% under these two conditions.

Numerical Investigation of Combustion and Emission With Different Diesel Surrogate Fuel by Hybrid Breakup Model

Injection flow dynamics plays a significant role in fuel spray; this process controls the fuel–air mixing, which in turn is critical for the combustion and emissions process in diesel engine. In the current study, an integrated spray, combustion, and emission numerical model is developed for diesel engine computations based on the general transport equation analysis (GTEA) code. The model is first applied to predict the effect of turbulence inside the nozzle, which is considered by the submodel of hybrid breakup model on diesel spray process. The results indicate that turbulence term enhances the rate of breakup, resulting in more new droplets and smaller droplet sizes, leading to high evaporation rate with more evaporated mass. The model is also applied to simulate combustion and soot formation process of diesel. The effects of ambient density, ambient temperature, oxygen concentration and reaction mechanism on ignition delay, flame lift-off length, and soot formation are analyzed and discussed. The results show that although higher ambient density and temperature reduce the ignition delay and cause the flame stabilization location to move upstream, this is not helpful for fuel–air mixing because it increases the soot level in the fuel jet. While higher oxygen concentration has negative effects on soot formation. In addition, the model is employed to simulate the combustion and emission characteristics of a low-temperature combustion engine. The overall agreement between the measurements and predictions of in-cylinder pressure, heat release, and emission characteristics are satisfactory.

Development of a reduced n-heptane-n-butylbenzene-polycyclic aromatic hydrocarbon (PAH) mechanism for engine combustion simulation and soot prediction

A reduced n-heptane-n-butylbenzene-PAH mechanism consisting of 111 species and 542 reactions was developed for diesel engine combustion and soot modeling. The reduced mechanism was formulated based on a detailed n-butylbenzene (BBZ) mechanism and a published reduced n-heptane-PAH mechanism. The reduced BBZ sub-mechanism was constructed using the directed relation graph with error propagation, sensitivity analysis, reaction pathway analysis and rate of production analysis methods. An evaluation system of the most sensitive reactions was proposed and sensitivity coefficient maps of ignition delay were depicted for the optimization of the proposed mechanism. The present mechanism was extensively validated with experimental results of ignition delay in shock tubes and rapid compression machines, species concentration in premixed flames and jet stirred reactors, laminar flame speed, and with new direct injection compression ignition engine combustion and emission data. The results of prediction are in good agreement with experiments and suggest that the proposed mechanism can be applied for combustion and soot predictions in engines. The soot particle size distribution of BRF30 (30%BBZ+70%n-heptane in volume) is closer to D100 (real diesel) than TRF20 (20%toluene+80%n-heptane in volume). It is indicated that BBZ may be more appropriate as the representative of aromatic compounds than toluene in diesel surrogate fuels.

Density and Speed of Sound Measurements of Surrogate Diesel Fuels

The densities and speeds of sound of four surrogate diesel fuels of varying compositional accuracy were measured at atmospheric pressure over the combined temperature range 278.15–343.15 K. Measurement results for the surrogate fuels were compared to results obtained for the target fuel as well as to predicted values. For both density and sound speed, the least compositionally accurate four-component surrogate was the most dissimilar to the target fuel, with average absolute deviations (AADs) of 3.3 and 2.1%, respectively, while the most compositionally accurate nine-component surrogate was the most similar, with AADs of 0.8 and 0.4%, respectively. However, the relative behavior of the other two surrogates implies that greater complexity is not always required in a surrogate; the minimal number of components required for a given surrogate fuel will ultimately be determined by the specific research goals it is meant to achieve.

Development of an optimization methodology for formulating both jet fuel and diesel fuel surrogates and their associated skeletal oxidation mechanisms

In this study, an optimization methodology was developed for formulating both jet fuel and diesel fuel surrogates along with their associated skeletal oxidation mechanisms. Based on this methodology, new jet fuel surrogate (JFS) and diesel fuel surrogate (DFS) are formulated with same five components (n-dodecane/iso-octane/iso-cetane/decalin/toluene) by emulating practical fuel properties including liquid density, viscosity, surface tension, cetane number (CN), hydrogen-carbon (H/C) ratio, molecular weight (MW), lower heating value (LHV) and threshold sooting index (TSI). Based on the newly developed JFS and DFS, their associated chemical skeletal mechanisms were developed, which are described with same chemical reaction structure: five skeletal sub-mechanisms are employed into the skeletal fuel mechanisms, including decalin (C10H18), n-dodecane (C12H26), iso-cetane (C16H34), iso-octane (C8H18) and toluene (C7H8) sub-mechanisms. By describing the chemistries for the oxidation of large molecules C4-Cn and small H2/CO/C1 molecules respectively, the skeletal mechanisms are significantly compacted into 74 species and 189 reactions, which makes them practical to be used in 3-D engine combustion simulations. In addition to sufficient 0-D validations of ignition delay times, species concentrations and laminar flame speed in various environments, 3-D validations of constant volume spray and engine combustion were also performed for the new JFS and DFS skeletal mechanisms. It can be observed that the agreements between the computational results predicted by the present mechanisms and all the experimental data are reasonably good, which proves that the newly proposed JFS and DFS skeletal mechanisms are robust and accurate to be used in engine combustion computational fluid dynamics (CFD) studies.

On models for predicting thermodynamic regimes in high-pressure turbulent mixing and combustion of multispecies mixtures

The thermodynamic regime of a complex mixture depends on the composition, the pressure and the temperature; the spinodal locus separates the regime of thermodynamic instability from the remainder of the phase space. Since diffusion is one of the phenomena affecting the local chemical composition, the first focus is here on evaluating diffusion models in the context of high-pressure (high-$p$) multispecies mixing and combustion. It is shown that the diffusion model equations previously used to create two high-$p$ direct numerical simulation (DNS) databases can reproduce classical experimental observations of uphill diffusion in an accurate spatiotemporal manner, whereas the popular model which has a diagonal diffusion matrix and uses a velocity correction lacks spatiotemporal accuracy. Further, a mathematical formalism is used to compute the spinodal locus for mixtures for which either experimental data or previous computations from the literature are available, and it is shown that the agreement of the present calculations with that previously existing information is excellent. Using the spinodal-calculation mathematical formalism, the aforementioned DNS databases are then examined to determine the thermodynamic regime of the mixture at important stages of the simulations. In the first subset of the DNS databases that portrays mixing of five species under high-$p$ conditions, this stage is that of the transitional state representing the individual time station at which each simulation, having been initiated in a laminar state, transitions to a state having turbulent characteristics. In the second subset of the DNS databases that portrays high-$p$ turbulent combustion, this stage represents the individual time station at the peak $p$ achieved during the calculations. In both databases, the influence of the initial Reynolds number, the free-stream composition and the free-stream $p$ is studied. The results show that in all cases the mixture is in the single-phase regime. The present DNS databases have only five species, but it is shown that the methodology for computing the spinodal locus can be applied to very complex mixtures, with examples given for a twelve-species mixture and surrogate diesel fuels, thereby boding well for determining the thermodynamic regime of practical mixtures in high-$p$ turbulent flow simulations for engineering applications. According to these calculations, diesel-fuel surrogates are always in the single-phase regime at injection-conditions $p$ and temperatures existing in diesel-engine combustion chambers.

Development of a Diesel Surrogate Fuel Library

Diesel fuel is composed of a complex mixture of hundreds of hydrocarbons that vary globally depending on crude oil sources, refining processes, legislative requirements and other factors. In order to simplify the study of this fuel, researchers create surrogate fuels to mimic the physical and chemical properties of Diesel fuels. This work employed the commercial software Reaction Workbench – Surrogate Blend Optimizer (SBO) to develop a Surrogate Fuel Library containing 18 fuels. Within the fuel library, the cetane number ranges from 35 to 60 (in increments of 5) at threshold soot index (TSI) levels representative of low, baseline and high sooting tendency fuels (TSI = 17, 31 and 48, respectively). The Surrogate Fuel Library provides the component blend ratios and predicted properties for cetane number, threshold soot index, lower heating value, density, kinematic viscosity, molar hydrogen-to-carbon ratio and distillation curve temperatures from T10 to T90. A market petroleum Diesel fuel with a cetane number of 50 and a threshold soot index of 31 was selected as the Baseline Diesel Fuel. The combustion, physical and chemical properties of the Baseline Diesel Fuel were precisely matched by the Baseline Surrogate Fuel. To validate the SBO predicted fuel properties, a set of five surrogate fuels, deviating in cetane number and threshold soot index, were blended and examined with ASTM tests. Good agreement was obtained between the SBO predicted and ASTM measured fuel properties. To further validate the Surrogate Fuel Library, key properties that were effected by altering the component blend ratios to control cetane number and TSI were compared to a set of five market Diesel fuels with good results. These properties included density, viscosity, energy density and the T10 and T90 distillation temperatures. The Surrogate Fuel Library provided by this work supplies Diesel engine researchers and designers the ability to analytically and experimentally vary fuel cetane number and threshold soot index with fully-representative surrogate fuels. This new capability to independently vary cetane number and threshold soot index provides a means to further enhance the understanding of Diesel combustion and design future combustion systems that improve efficiency and emissions.

Simulated Kinetics and Chemical and Physical Properties of a Four-Component Diesel Surrogate Fuel

Real diesel fuels are mixtures composed of hundreds to thousands of components; thus, developing surrogate fuels composed of a few representative hydrocarbon components is essential for multidimensional computational fluid dynamics spray combustion simulation purposes. Surrogates that can characterize the thermophysical properties and evaporation processes of real fuel are the “physical” surrogates. Surrogates that are able to mimic fuel chemical-kinetics-related properties are viewed as the “chemical” surrogate models. For spray combustion modeling, fuels experience thermophysical (heating and evaporation) and chemical kinetics (ignition and combustion) processes. To model the multiphase spray combustion process, a “unified” diesel surrogate, which can emulate both the physical and chemical (kinetics) properties of the real diesel fuel, is proposed in this study. A group of hydrocarbon species was selected, using an inversed batch distillation methodology, to match the experimental distillation curve of ...

The evolution of soot morphology and nanostructure in laminar diffusion flame of surrogate fuels for diesel

The morphology and nanostructure of soot particles in laminar diffusion flame has been investigated in this work. The fuels considered were diesel surrogate fuels, including n-heptane, n-butanol and the volumetric mixture 50% n-heptane/50% n-butanol (H50B50). Thermophoretic sampling and TEM (transmission electron microscopy) analysis were utilized to study the morphology and nanostructure of soot particles at different points on the centerline inside the flames. The soot morphological characteristics include primary particle diameter, projected area of aggregate, and fractal dimension. The nanostructure is quantitatively described by fringe length, tortuosity and inter-fringe spacing.Overall, n-butanol flame produced smaller primary particles and aggregates, followed by H50B50, and n-heptane flames. The primary particle diameter shows a trend of increasing first and then decreasing due to soot growth and oxidation respectively. The fractal dimension of aggregates almost keeps increasing along the centerline, indicating more and more compact soot structure. As the particles travel along the flame, a graphitic ‘onion-like’ structure develops where the core remains amorphous and the outer shell graphitises. In the process of soot growth, the fringes become shorter and less curved, meanwhile inter-fringe spacing increases due to electron repulsion between the adjacent carbon layers. Subsequently, the degree of graphitization would increase, concretely, fringe length increases, while tortuosity and inter-fringe spacing decrease. At the flame tip, most microcrystalline carbon layers in the outer shell are oxidized, which causes a sharp increase in the tortuosity, but does not have obvious effect on the other two parameters. In addition, for mature soot near the flame tips, particles in n-butanol flame has the maximum fringe length and tortuosity while the minimum inter-fringe spacing.

Experimental and modelling investigations of the diesel surrogate fuels in direct injection compression ignition combustion

Experimental investigations on the combustion and emission characteristics of diesel and three potential diesel surrogate fuels have been performed, including the 85% (vol.) n-heptane blended with 15% toluene (T15), 81% n-heptane blended with 14% toluene and 5% c-hexane (T15+CH5), and 80% (vol.) n-heptane blended with 20% toluene (T20). The experimental results showed that due to the lower reactivity of the three diesel surrogate fuels, the combustion phases were more retarded and the indicated thermal efficiencies were lower compared to diesel. For the diesel surrogate fuels with higher volatility, the soot emissions were lower than those of diesel due to more premixed combustion. Moreover, a reduced n-dodecane-toluene reference fuel-c-hexane-polycyclic aromatic hydrocarbon (PAH) mechanism composed of 167 species and 671 reactions was formulated and was extensively validated against the experimental results. To clarify the experimental results, the reduced mechanism was then used for the three-dimensional (3-D) modelling investigations. The modelling results showed that the reduced mechanism can reasonably capture the combustion characteristics of T15+CH5 in the direct injection compression ignition combustion. The NOx and soot emissions were both reasonably predicted. From the modelling investigations, it was inferred that the physical effects on the soot emission were larger than the chemical effects of the different fuel carbon-chain structures. According to the 0-D modelling investigations, the soot tendency of the four pure diesel surrogate constituents can be sequenced as toluene>c-hexane>n-dodecane>n-heptane. Given that toluene is the dominant factor affecting the soot formation than the other three components, the soot tendency of the four diesel surrogate fuels can be sequenced as T20>T15+CH5 (n-dodecane)>T15+CH5 (n-heptane)≈T15.

Correction to Diesel Surrogate Fuels for Engine Testing and Chemical-Kinetic Modeling: Compositions and Properties

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Diesel Surrogate Fuels for Engine Testing and Chemical-Kinetic Modeling: Compositions and PropertiesCharles J. Mueller*, William J. Cannella, J. Timothy Bays, Thomas J. Bruno, Kathy DeFabio, Heather D. Dettman, Rafal M. Gieleciak, Marcia L. Huber, Chol-Bum Kweon, Steven S. McConnell, William J. Pitz, and Matthew A. RatcliffCite this: Energy Fuels 2016, 30, 10, 8790Publication Date (Web):October 12, 2016Publication History Published online12 October 2016Published inissue 20 October 2016https://doi.org/10.1021/acs.energyfuels.6b02499Copyright © 2016 American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceArticle Views624Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (177 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Large eddy simulations of complex multicomponent diesel fuels in high temperature and pressure turbulent flows

A multicomponent droplet evaporation model, which discretizes the one-dimensional species and temperature profiles inside a droplet with a finite volume method and treats the liquid phase as thermodynamically real, has been developed and used for large-eddy simulations of high speed diesel sprays in high temperature and pressure closed chambers. Single drop evaporation results obtained by the variable property multicomponent model are shown to match with the constant property model in the limiting conditions. The multicomponent liquid model used together with the Kelvin–Helmholtz – Rayleigh–Taylor droplet breakup model is found to reasonably well predict the experimentally observed non-linear behavior of spray penetration with changing ambient conditions for n-hexadecane and 4 different multicomponent surrogate diesel fuels with 2–8 components. The effects of various modeling assumptions and gas and liquid parameters on the drop and spray evolution and evaporation are investigated in details.

Characterization of Four Diesel Fuel Surrogates by the Advanced Distillation Curve Method

The development of surrogate fuels with measured and predicted thermophysical properties similar to their authentic refinery stream counterparts is critical for the development of alternative fuels and the optimization of engines to increase efficiency and decrease emissions. In this work, four diesel fuel surrogates, formulated according to a reliable and proven procedure, were characterized by the advanced distillation curve (ADC) method to determine the composition and enthalpy of combustion in various distillate volume fractions. Tracking the composition and enthalpy of distillate fractions provides valuable information for determining structure–property relationships and also provides the basis for the development of equations of state that can describe the thermodynamic properties of these complex or simplified mixtures. This comparison showed that the volatility characteristic of the four surrogates is quite similar not only to the target diesel fuel but also to a number of other prototype alternat...

Diesel Surrogate Fuels for Engine Testing and Chemical-Kinetic Modeling: Compositions and Properties.

The primary objectives of this work were to formulate, blend, and characterize a set of four ultralow-sulfur diesel surrogate fuels in quantities sufficient to enable their study in single-cylinder-engine and combustion-vessel experiments. The surrogate fuels feature increasing levels of compositional accuracy (i.e., increasing exactness in matching hydrocarbon structural characteristics) relative to the single target diesel fuel upon which the surrogate fuels are based. This approach was taken to assist in determining the minimum level of surrogate-fuel compositional accuracy that is required to adequately emulate the performance characteristics of the target fuel under different combustion modes. For each of the four surrogate fuels, an approximately 30 L batch was blended, and a number of the physical and chemical properties were measured. This work documents the surrogate-fuel creation process and the results of the property measurements.

A Multicomponent Blend as a Diesel Fuel Surrogate for Compression Ignition Engine Applications

A mixture of n-dodecane and m-xylene is investigated as a diesel fuel surrogate for compression ignition (CI) engine applications. Compared to neat n-dodecane, this binary mixture is more representative of diesel fuel because it contains an alkyl-benzene which represents an important chemical class present in diesel fuels. A detailed multicomponent mechanism for n-dodecane and m-xylene was developed by combining a previously developed n-dodecane mechanism with a recently developed mechanism for xylenes. The xylene mechanism is shown to reproduce experimental ignition data from a rapid compression machine (RCM) and shock tube (ST), speciation data from the jet stirred reactor and flame speed data. This combined mechanism was validated by comparing predictions from the model with experimental data for ignition in STs and for reactivity in a flow reactor. The combined mechanism, consisting of 2885 species and 11,754 reactions, was reduced to a skeletal mechanism consisting 163 species and 887 reactions for 3D diesel engine simulations. The mechanism reduction was performed using directed relation graph (DRG) with expert knowledge (DRG-X) and DRG-aided sensitivity analysis (DRGASA) at a fixed fuel composition of 77% of n-dodecane and 23% m-xylene by volume. The sample space for the reduction covered pressure of 1–80 bar, equivalence ratio of 0.5–2.0, and initial temperature of 700–1600 K for ignition. The skeletal mechanism was compared with the detailed mechanism for ignition and flow reactor predictions. Finally, the skeletal mechanism was validated against a spray flame dataset under diesel engine conditions documented on the engine combustion network (ECN) website. These multidimensional simulations were performed using a representative interactive flame (RIF) turbulent combustion model. Encouraging results were obtained compared to the experiments with regard to the predictions of ignition delay and lift-off length at different ambient temperatures.

A Soot Precursor Formation Embedded Reaction Mechanism of Diesel Surrogate Fuel

A new chemical kinetics model of diesel surrogate fuel including polycyclic aromatic hydrocarbon formation and growth is presented, which consists of 153 species and 697 reactions. Comparisons with various experimental data available in the literature, including shock tube, n-heptane premixed flames, jet stirred reactor and homogeneous charge compression ignition engine, show good performance of this new chemical kinetics model. The presented mechanism can be used as the basis for further reduction and is applied to the combustion and emission simulation by coupling chemical reaction kinetics model with computational fluid dynamics model in internal combustion engines.

Effects of fuel reactivity and injection timing on diesel engine combustion and emissions

ABSTRACTRecent strategies for simultaneously reducing NOx and soot emissions have focused on achieving nearly premixed, low-temperature combustion (LTC) in diesel engines. A promising approach in this regard is to vary fuel reactivity in order to control the ignition delay and optimize the level of premixing and reduce emissions. The present study examines such a strategy by performing 3-D simulations in a single-cylinder of a diesel engine. Simulations employ the state-of-the-art two-phase models and a validated semi-detailed reaction mechanism. The fuel reactivity is varied by using a blend of n-heptane and iso-octane, which represent surrogates for gasoline and diesel fuels, respectively. Results indicate that the fuel reactivity strongly influences ignition delay and combustion phasing, whereas the start of injection (SOI) affects combustion phasing. As fuel reactivity is reduced, the ignition delay is increased and the combustion phasing is retarded. The longer ignition delay provides additional time for mixing, and reduces equivalence ratio stratification. Consequently, the premixed combustion is enhanced relative to diffusion combustion, and thus the soot emission is reduced. NOx emission is also reduced due to reduced diffusion combustion and lower peak temperatures caused by delayed combustion phasing. An operability range is observed in terms of fuel reactivity and SOI, beyond which the mixture may not be sufficiently well mixed, or compression ignited. The study demonstrates the possibility of finding an optimum range of fuel reactivity, SOI, and EGR for significantly reducing engine out emissions for a given load and speed.

Experiments and Computational Fluid Dynamics Modeling Analysis of Large n-Alkane Ignition Kinetics in the Ignition Quality Tester

This paper presents experimental measurements of ignition delays from low- to high-volatility n-alkanes representative of diesel and jet fuel compounds that are supplemented with a computational fluid dynamics (CFD) analysis. The ignition quality tester (IQT) is shown to be effective for studying ignition of low-volatility fuels, such as n-hexadecane, which are typically difficult to measure. Ignition delays, both experimental and modeled, are presented using an eight-point experimental design matrix (1.5 and 3.0 MPa, 823 and 723 K, and 15 and 21% O2). A detailed n-alkane mechanism (C8–C16 with a total of 2115 species) was reduced to a skeletal 237 species n-hexadecane mechanism using a targeted search algorithm. A CFD model of the IQT (developed using KIVA-3V) coupled with skeletal mechanisms predicted ignition delays of n-heptane and n-hexadecane with reasonable accuracy over the eight-point matrix, with the exception of the highest temperature, lowest pressure, and oxygen concentration conditions. Temperature sweeps across a range of pressures (0.1–1.0 MPa) and temperatures (673–973 K) were performed for n-heptane, n-decane, n-dodecane, and n-hexadecane. The negative temperature coefficient (NTC) region was observed experimentally for the first time for n-hexadecane. The NTC region for n-dodecane and n-decane has previously been observed in shock tubes and rapid compression machines and is reported here for the first time in the IQT. The IQT is thus capable of capturing NTC behavior for large alkanes and can serve as an additional experimental validation tool for chemical kinetic mechanisms of low-volatility surrogates for diesel and jet fuels.