Diesel Surrogate Fuels Research Articles

Chemical Kinetic Mechanism Reduction Scheme for Diesel Fuel Surrogate

In this study, performance of the DRG-based chemical kinetic mechanism reduction techniques was evaluated using a diesel fuel surrogate model, which is the n-hexadecane mechanism. Following that, a new mechanism reduction scheme was developed to generate a reduced mechanism which is suitable to be applied in diesel engine applications.As a result, areduced mechanism with 49 species and 97 elementary reactions was successfully derived from the detailed mechanismwithan overall 97% reduction in species number and computational runtime in zero-dimensional closed homogeneous batch reactor simulations. After that, the reduced n-hexadecane mechanism was applied to simulate spray combustion in a constant volume bomb using OpenFOAM software. Results show that n-hexadecane alone is inappropriate to be employed as a single-component diesel surrogate as its high cetane number has resulted in advanced ignition timing. This agrees with recent study andthus fuel blending is suggested in order to match the diesel fuel kinetics and compositions.

Evaluation and Development of Chemical Kinetic Mechanism Reduction Scheme for Biodiesel and Diesel Fuel Surrogates

Evaluation and Development of Chemical Kinetic Mechanism Reduction Scheme for Biodiesel and Diesel Fuel Surrogates

Thermal Decomposition Kinetics of 1,3,5-Triisopropylcyclohexane

Recent surrogate diesel fuel mixture development identified the need for a multiply substituted, low cetane number, high molecular mass monocycloalkane component. On the basis of a thermophysical property evaluation and prediction, 1,3,5-triisopropylcyclohexane was chosen to serve this need. This fluid is not commercially available; therefore, very few thermophysical property measurements exist, and the thermal decomposition kinetics have not yet been investigated. In this work, we study the thermal decomposition kinetics of 1,3,5-triisopropylcyclohexane between 350 and 425 °C. The decomposition reactions were performed in stainless-steel ampule reactors. At each temperature, the extent of decomposition as a function of time was determined by analyzing the thermally stressed liquid phase by use of gas chromatography. These data were used to derive pseudo-first-order rate constants that ranged from 2.38 × 10–7 s–1 at 350 °C to 7.28 × 10–5 s–1 at 425 °C. The Arrhenius parameters of the thermal decomposition of 1,3,5-triisopropylcyclohexane were measured to be A = 5.67 × 1016 s–1 and activation energy Ea = 279 kJ/mol. These parameters can be used to estimate decomposition rates at other temperatures and are critical to the successful application of 1,3,5-triisopropylcyclohexane in experimental and modeling studies of surrogate diesel fuels.

Experimental studies of autoignition and soot formation of diesel surrogate fuels

Computational simulation has undergone vast development for internal-combustion engine research as a time- and cost-saving tool. Yet combustion simulation for conventional hydrocarbon petroleum fuels faces difficult challenges since such fuels have very complex compositions, consisting of many different molecular species, for which data are sparse. The use of surrogate fuels for combustion simulation could provide a solution to this problem. In this investigation, n-heptane and mixtures of n-heptane and toluene were studied within a broad range of potential surrogate diesel fuels, and the ignition delay and soot formation trends were compared with those of diesel fuel. Ignition delays show good agreement with those for diesel fuel and it was also possible to replicate partially the soot formation behaviour for certain engine conditions. Further investigation is needed to find a surrogate fuel that closely matches over the range of operating conditions of a diesel engine.

Thermophysical properties needed for the development of the supercritical diesel combustion technology: Evaluation of diesel fuel surrogate models

Development of supercritical fuel combustion technology requires reliable data on fuel properties. In this paper, twenty diesel fuel surrogates (DFSs) have been evaluated for representing real diesel fuel (DF) properties including critical point, density, heat capacity, viscosity and thermal conductivity. The critical temperatures of DF were estimated to be 717–745K largely depending on DF distillation profiles, while those of DFSs varied significantly from 540 to 734K and only those of DFSs #5(n-hexadecane), #17 and #19 were within the range for DF. The best predictions of density, heat capacity, viscosity and thermal conductivity of DF were achieved by DFSs #8 (AAD=0.3%), #4 (1.5%), #20 (13%) and #14 (1.7%), respectively, and DFS #4 (n-tetradecane) had the best overall performance with an AAD of 8%. Finally, a simple methodology has been demonstrated for the evaluation of DFSs, and the current results lead to the best predictions of DF thermophysical properties.

A method to determine ignition delay times for Diesel surrogate fuels from combustion in a constant volume bomb: Inverse Livengood–Wu method

In this work a method to determine the ignition delay of Diesel surrogate fuels using data from a constant volume combustion bomb is presented. The studied fuels are n-heptane (a common PRF) and a mixture of 50% of n-heptane and 50% of toluene (in mass) because both fuels have been proposed as Diesel fuel surrogates under HCCI. There are different concepts of spontaneous ignition times in engines or other devices. Auto-ignition times are experimentally obtained in a constant volume combustion bomb or in compression ignition engines, for variable conditions of pressure and temperature. In this work they are obtained in a combustion bomb using four different criteria (pressure, mechanical vibrations, OH* and CH* chemiluminescence emissions). The paper describes an original approach based on an inverse Livengood–Wu method to obtain the ignition delays (as a function of pressure and temperature) from the auto-ignition times. The obtained expressions for the fuels and their mixtures are compared with those of other authors with a reasonable agreement.

Chemical and Thermophysical Characterization of 1,3,5-Triisopropylcyclohexane

The complex nature of finished fuels makes definitive studies on composition and combustion properties very difficult and uncertain. This has led to the adoption of fuel surrogate mixtures in such studies. The development of a surrogate mixture is itself a nontrivial process, and a surrogate mixture is often developed specifically for a given purpose. Often, thermophysical property surrogate mixtures cannot be used for examination of combustion properties, and vice versa. Surrogates range in complexity from a single component to complex mixtures containing 20 or more components. A recent study on surrogate mixture development for diesel fuel used state-of-the-art techniques of 13C and 1H nuclear magnetic resonance (NMR) spectroscopy and the advanced distillation curve to characterize fuel composition and volatility, respectively. This work indicated the need for a multiply substituted, low cetane number, high molecular mass monocycloalkane surrogate mixture component. The addition of 1,3,5-triisopropylcyclohexane as a palette component was chosen to serve this need. Before this component can be used in any modeling or experimental effort, we first require some basic chemical and thermophysical properties. In this paper, we present chemical characterization results from gas chromatography with mass spectrometry, 13C NMR spectrometry, isothermal Kovats' retention indices at (150 to 225) °C (on 5 % phenyl-95 %-dimethyl polysiloxane), and refractive indices at (20, 25, and 30) °C. We also present ambient pressure thermophysical property measurements: density, speed of sound, and derived adiabatic compressibility from (5 to 70) °C and kinematic viscosity from (20 to 100) °C. These properties and characterization parameters are critical to the successful application of 1,3,5-triisopropylcyclohexane in experimental and modeling studies of surrogate diesel fuels.

Methodology for Formulating Diesel Surrogate Fuels with Accurate Compositional, Ignition-Quality, and Volatility Characteristics

In this study, a novel approach was developed to formulate surrogate fuels having characteristics that are representative of diesel fuels produced from real-world refinery streams. Because diesel fuels typically consist of hundreds of compounds, it is difficult to conclusively determine the effects of fuel composition on combustion properties. Surrogate fuels, being simpler representations of these practical fuels, are of interest because they can provide a better understanding of fundamental fuel-composition and property effects on combustion and emissions-formation processes in internal-combustion engines. In addition, the application of surrogate fuels in numerical simulations with accurate vaporization, mixing, and combustion models could revolutionize future engine designs by enabling computational optimization for evolving real fuels. Dependable computational design would not only improve engine function, it would do so at significant cost savings relative to current optimization strategies that rely on physical testing of hardware prototypes. The approach in this study utilized the state-of-the-art techniques of 13C and 1H nuclear magnetic resonance spectroscopy and the advanced distillation curve to characterize fuel composition and volatility, respectively. The ignition quality was quantified by the derived cetane number. Two well-characterized, ultra-low-sulfur #2 diesel reference fuels produced from refinery streams were used as target fuels: a 2007 emissions certification fuel and a Coordinating Research Council (CRC) Fuels for Advanced Combustion Engines (FACE) diesel fuel. A surrogate was created for each target fuel by blending eight pure compounds. The known carbon bond types within the pure compounds, as well as models for the ignition qualities and volatilities of their mixtures, were used in a multiproperty regression algorithm to determine optimal surrogate formulations. The predicted and measured surrogate-fuel properties were quantitatively compared to the measured target-fuel properties, and good agreement was found.

Reduced Polycyclic Aromatic Hydrocarbon Formation Chemical Kinetic Model of Diesel Surrogate Fuel for Homogeneous Charge Compression Ignition Combustion

A reduced mechanism, which could couple with a multi-dimensional computational fluid dynamics code, was developed for the chemical kinetics of diesel surrogate fuel oxidation in modeling polycyclic aromatic hydrocarbon (PAH) formation under homogeneous charge compression ignition (HCCI) diesel engine conditions. The complete kinetic mechanism, which comprised 697 reactions and 153 species, was reduced to a minor mechanism that included only 141 reactions and 75 species using the sensitivity and reaction path analyses. Validation of the present mechanism was also performed with experiments from the shock tube available in the literature, and good agreement between modeling results of the detailed mechanism in the shock tube and HCCI engine was obtained. The results showed that this reduced mechanism gave reliable performance for HCCI combustion predictions. Numerical results also displayed that those PAH concentrations decreased with the increase of the inlet air temperature and equivalence ratio.

Laminar burning speed measurement of premixed n-decane/air mixtures using spherically expanding flames at high temperatures and pressures

Normal-decane (n-C10H22) is regarded as a major component of possible surrogates for jet fuels and diesel fuels. The structure of spherically expanding premixed n-decane/air flames has been studied at high temperatures and pressures. The laminar burning speeds of n-decane/air mixtures have been measured for the temperatures of 350–610K and pressures of 0.5–8atm. The experiments were performed in lean conditions (0.7⩽ϕ⩽1). Laminar burning speed was measured using a thermodynamic model based on the pressure rise during the flame propagation in constant volume vessels. A cylindrical vessel equipped with a high speed CMOS camera was employed to investigate the flame structure and a spherical vessel was used for the burning speed measurements. The results are in good agreement with other experimental data available in the published literature.

MS2-1 Simulation of Diesel surrogate fuels performance under engine conditions using 0D engine - fuel test bench(MS: Modeling and Simulation,General Session Papers)

This paper reports on the application of a simulation based Engine - Fuel Test Bench (EFTB) for studying performance of Diesel engine running on different fuels. The test bench is built around a zero-dimensional (0D) direct injection stochastic reactor model (DI-SRM) for engine in-cylinder processes simulation. Detailed kinetic models of fuel oxidation are used for emissions prediction. A general purpose optimizer supports the overall simulation process. To demonstrate capabilities of the test bench four different fuels have been simulated and compared to each other under Diesel conditions. Pure n-decane, pure n-heptane and blends of n-heptane with iso-octane and with toluene have been considered as of relevance to diesel fuel. The in-cylinder pressure, heat release rate, and exhaust emissions were the primary tracked engine parameters. Thanks to the low CPU costs, detailed description of fuel oxidation and high level of automation, the presented test-bench is well suited to investigate various aspects of engine-fuel interaction. In an efficient manner it allows comparing engine output performance and emissions depending on the applied fuel.

Lipids Profiles of Free Fatty Acids from Olive Oil Triglycerides - The Development of a New Method for Profiling Lipids from Photosynthetic Micro-organisms, a Potential Candidate for the Production of Biofuel

Abstract Currently intensive global research efforts are being made to increase and modify the accumulation of lipids, alcohols, hydrocarbons, polysaccharides, and other energy storage compounds in photosynthetic organisms, such as yeast, and bacteria. Qatar is in a unique position in the world because it has a rich biodiversity of photosynthetic micro-organisms and the climate and space to lead the world in the research and use of photosynthetic micro-organisms as a biofuel source. Photosynthetic micro-organisms are remarkable in that they have a high photosynthetic conversion efficiency, rapid growth rate, diverse metabolic capabilities, accumulate relatively little recalcitrant biomass and are able to synthesise a variety of biological energy carriers, such as starch and lipids, that are relevant to renewable-bioenergy studies. Lipids and starch, can be converted into diesel-fuel surrogates and metabolised into a variety of biofuels. For the study of photosynthetic micro-organism production of lipids, understanding the chemical profile of the lipids and starch in the organism's biomass is important. Triglycerides are a common lipid found in these organisms and are formed by combining glycerol with three molecules of free fatty acid (FFA). FFA profiling is valuable for large-scale production of biofuel as it provides information about the variety of FFA produced by cyanobacteria in different environments and growth conditions. Analytical techniques such as ultra-high pressure liquid chromatography (UPLC), matrix -assisted laser desorption ionisation (MALDI) and quadrupole - time of flight mass spectrometry (Q-TOF) are employed in this study for the profiling of FFA from olive oil. The results have shown that triglycerides and FFA can be detected, identified and quantified with great accuracy and precision using olive oil as a sample. This work has achieved a successful profiling method to extract and separate FFA from triglycerides in olive oil. The work will be applied to the study of biofuels and measuring FFA in order to understand the lipid profiles of photosynthetic micro-organisms.

Numerical Study Comparing the Combustion and Emission Characteristics of Biodiesel to Petrodiesel

Combustion and emission characteristics of compression ignition engines strongly depend upon inner-nozzle flow and spray behavior. These processes control the fuel−air mixing, which in turn is critical for the combustion process. Previous studies by us highlighted the differences in the physical and chemical properties of petrodiesel and biodiesel, which significantly altered the inner-nozzle flow and spray structure. The current study is another step in this direction to gain a fundamental understanding on the influence of fuel properties on the combustion and emission characteristics of the compression ignition engine. n-Heptane and methyl butanoate were selected as surrogates for diesel and biodiesel fuels, respectively, because the chemical kinetic pathways were well-understood. Liquid length and flame lift-off length for diesel and biodiesel fuels were validated against data available in the literature. Liquid lengths were always higher for biodiesel because of its higher heat of vaporization, which ...

PM Characteristics from Pool Diffusion Flame with Surrogate Diesel Fuel

Reduction of nanometer size particulate matter (Nano-PM) in diesel exhaust is important for its harmful potential to health. Therefore it is necessary to understand effect of fuel compositions on PM characteristics in terms of fuel side reduction of PM. However, it is not easy to understand mechanism of diesel PM formation by investigating diesel combustion due to its complicated fuel composition. Purpose of the study is to develop surrogate diesel fuel. A laboratory scale PM generator was applied to generation of nano-PM with diesel and surrogate diesel fuel. In order to evaluate similarity of PM characteristics with diesel and surrogate diesel fuel, Scanning Mobility Particle Sizer (SMPS3034) was used to measure the size distribution of PM. Three kinds of surrogate diesel fuel containing n-decane and α-methylnaphthalene were made with changing their mixing ratio. Flame length for fuel consumption rate and PM number distribution of PM with surrogate diesel fuels were compared with those of fuel.

Binary Mixtures of Branched and Aromatic Pure Component Fuels as Surrogates for Future Diesel Fuels

Binary Mixtures of Branched and Aromatic Pure Component Fuels as Surrogates for Future Diesel Fuels

Kinetics of Oxidation of Commercial and Surrogate Diesel Fuels in a Jet-Stirred Reactor: Experimental and Modeling Studies

The oxidation of a commercial diesel fuel and a diesel surrogate fuel (70% n-decane/30% 1-methylnaphthalene in moles) was performed using a fused-silica jet-stirred reactor under the same initial experimental conditions (560−1030 K, 6 and 10 atm, equivalence ratios of 0.25−1.5, and 10 300 ppm of carbon). The results of this series of experiments consisting of concentration profiles of reactants, stable intermediates, and products as a function of the temperature were compared to each other, confirming that the 70/30% mixture n-decane/1-methylnaphthalene in moles is an excellent simple diesel fuel surrogate. A chemical kinetic model consisting of 4762 reactions involving 1124 species was proposed on the basis of previous chemical mechanisms for the oxidation of n-decane and 1-methylnaphthalene in similar conditions. The kinetic modeling showed reasonable agreement between the present data and computations over the entire range of conditions considered in this study.

Experimental study of the oxidation of large surrogates for diesel and biodiesel fuels

The experimental study of the oxidation of two blend surrogates for diesel and biodiesel fuels, n-decane/ n-hexadecane and n-decane/methyl palmitate (74/26 mol/mol), has been performed in a jet-stirred reactor over a wide range of temperatures covering both low, and high-temperature regions (550–1100 K), at a residence time of 1.5 s, at quasi atmospheric pressure with high dilution in helium (hydrocarbon inlet mole fraction of 0.002) and at stoichiometric conditions. Numerous reaction products have been identified and quantified. At low and intermediate temperatures (less than 1000 K), the formation of oxygenated species such as cyclic ethers, aldehydes and ketones has been observed for n-decane, n-hexadecane, and methyl palmitate. At higher temperature, the formation of these species was not observed any more, and small amounts of unsaturated species (olefins and unsaturated methyl esters) have been detected. Results obtained with methyl palmitate and n-hexadecane have been compared in order to highlight similarities and differences between large n-alkanes and methyl esters.

Experimental comparison of soot formation in turbulent flames of Diesel and surrogate Diesel fuels

Soot formation is compared in turbulent diffusion flames burning a commercial Diesel and two Diesel surrogates containing n-decane and α-methylnaphthalene. A burner equipped with a high-efficiency atomisation system has been specially designed and allows the stabilisation of liquid fuels flames with similar hydrodynamics conditions. The initial surrogate composition (70% n-decane, 30% α-methylnaphthalene) was previously used in the literature to simulate combustion in Diesel engines. In this work, a direct comparison of Diesel and surrogates soot tendencies is undertaken and relies on soot and fluorescent species mappings obtained respectively by Laser-Induced Incandescence (LII) at 1064nm and Laser-Induced Fluorescence at 532nm. LIF was assigned to soot precursors and mainly to high-number ring Polycyclic Aromatic Hydrocarbons (PAH). The initial surrogate was found to form 40% more soot than the tested Diesel. Consequently, a second surrogate containing a lower α-methylnaphthalene concentration (20%) has been formulated. That composition which presents a Threshold Soot Index (TSI) very close to Diesel one is also consistent with our Diesel composition that indicates a relatively low PAH content. The spatially resolved measurements of soot and fluorescent soot precursors are quite identical (in shape and intensity) in the Diesel and in the second surrogate flames. Furthermore the concordance of the LII temporal decays suggests that a similar growth of the primary soot particles has occurred for Diesel and surrogates. In addition, the comparison of the LII fluence curves indicates that physical/optical properties of soot contained in the different flames might be similar. The chemical composition present at the surface of soot particles collected in Diesel and surrogate flames has been obtained by laser-desorption ionisation time-of-flight mass spectrometry. An important difference is found between Diesel and surrogate samples indicating the influence of the fuel composition on soot content.

Experimental investigation of surrogates for jet and diesel fuels

The low and intermediate temperature reactivities of 2:1:1 n-decane:n-butylcyclohexane:n-butylbenzene and 1:1:1 n-decane:n-butylcyclohexane:n-butylbenzene were examined as possible surrogates for jet and diesel fuel, respectively. The hydrocarbons and the proportions were chosen as they match the average composition of the real fuels. The candidate surrogates and the real fuels were oxidized in a pressurized flow reactor at temperatures of 600–800K, pressure of 0.8MPa, and equivalence ratio of 0.30. The three-component mixtures were significantly more reactive than the real fuels. The difficulties of tuning both properties and behavior of the surrogates to the real fuels are discussed. Surrogate fuels that maintain the molecular weight of the real fuels but with reduced reactivity may require the addition of a heavy iso-paraffin.

Characterization of kilowatt-scale autothermal reformer for production of hydrogen from heavy hydrocarbons

Catalytic autothermal reforming is considered one of the most effective methods of producing hydrogen from heavy hydrocarbon fuels, such as diesel fuel, for fuel cell or emissions reduction applications. This article describes an investigation of the reactor characteristics and catalytic efficiency of a kilowatt-scale catalytic autothermal reformer currently being developed at Argonne National Laboratory. Dodecane and hexadecane were used individually as surrogates for diesel fuels to simply the reaction study and the interpretation of the test results. The reforming of these hydrocarbon fuels was examined at a variety of oxygen-to-carbon and steam-to-carbon ratios at gas hourly space velocities ranging from 10,000 to 100,000 h −1. At steady state, the product composition correlated well with that calculated from thermodynamic equilibrium at a representative equivalent temperature. The oxygen-to-carbon ratio was determined to be the most significant operating parameter that influenced the reforming efficiency; the reforming efficiency (and the selectivity to CO x ) increased with increasing oxygen-to-carbon ratio up to about 0.42, at which value the maximum efficiency was attained.