Wide Range Of Equivalence Ratios Research Articles

Experimental study on the competing effect of ceramic pellets on premixed methane-air flame propagation in a duct

It is urgent to explore effective suppression methods for gas fires and explosions to ensure the safe utilizations of combustible gases in industrial processes. In this work, experiments are performed to study the effect of spherical ceramic pellets on premixed methane-air flame propagation in a closed duct. High-speed schlieren photography and pressure transducers are used to record the flame propagation and pressure transient, respectively. Behaviors of the flame propagating through a section of the duct filled with ceramic pellets in mixtures at different equivalence ratios are scrutinized. Three different diameters of pellets are considered in the experiments. The result shows that the flame can be quenched in the case with a smaller pellet diameter (3 mm) for a wide range of equivalence ratios from fuel-lean to fuel-rich mixture. For larger pellet diameter (5 or 10 mm), flame extinction occurs in fuel-rich mixtures (e.g. Φ = 1.1, 1.2). For the cases of flame surviving through the pellets bed, the pellets show a significant influence on the flame structure and behavior. The flame propagation depends on the porosity and the mean void diameter of the porous media in the pellets bed. Small void diameter is beneficial to flame quenching, while large porosity can accelerate the flame propagation. The pressure dynamics evolution is closely related to the interaction of flame with the pellets, and it depends on whether the flame quenches in the pellets bed. Overall, d = 3 mm ceramic pellets display the best suppression effect on flame propagation and pressure buildup in this study. The results of this study are of great significance to guide the safety design of spherical suppression materials in engineering applications for process safety researchers and engineers.

Investigations on laminar premixed flame characteristics of ethyl acetate

Ethyl acetate (EtOAc) has the potential as an alternative fuel or fuel additive in internal combustion engines (ICEs). Therefore, it is important to have a good understanding of its combustion characteristics. In this regard, this study investigated the burning characteristics of EtOAc at the initial temperature of 358–418 K and the initial pressure of 1–4 bar over a wide range of equivalence ratio (0.8–1.4) using experimental and numerical analysis. The burning velocity of EtOAc was measured using the constant pressure method (CPM) and constant volume method (CVM) of the spherically expanding flame (SEF) method. The linear approximation and analytical two-zone burned mass fraction correlation were used to determine the burning velocity in the CVM analysis. Generally, the linear approximation burning velocity was almost 11% higher than the analytical two-zone burning velocity. The difference between the CVM and CPM burning velocity was nearly 24%. Laminar burning velocity at an elevated pressure of 11.2 bar was obtained using the CVM analysis. Finally, the experimental and theoretical Markstein length and number of EtOAc were also investigated and discussed.

Experimental investigation of equivalence ratio fluctuations in a lean premixed kerosene combustor

In this study a measurement technique for determination of equivalence ratio fluctuations from flame chemiluminescence in a kerosene-fuelled lean premixed combustor under atmospheric conditions is presented. Firstly, fundamental investigations into the relationship between the ratio of different chemiluminescence signals and the equivalence ratio are carried out using an imaging spectrometer. The chemiluminescence intensity is recorded for a wide range of equivalence ratios and fuel mass flows during steady state operation. The spectra show that the CH*/OH* ratio depends linearly on the equivalence ratio and is independent of the mass flow in the investigated range. Moreover, the background radiation has no influence on the monotonous trend of the CH*/OH* ratio for kerosene combustion. This interesting finding opens up new possibilities for passive optical measurement of the equivalence ratio in kerosene flames. Bandpass-filtered phase-correlated images of OH* and CH* chemiluminescence of an acoustically excited flame are taken simultaneously on one camera chip using an image doubler. After distortion correction, the image pair is used to calculate the global equivalence ratio from the CH*/OH* ratio. Based on the calibration chart derived in stationary operation, phase-resolved equivalence ratio perturbations are determined during acoustic excitation. The presented technique allows a quantitative measurement of equivalence ratio fluctuations in spray combustion and can therefore provide a better understanding of the fundamental mechanisms of thermoacoustic instabilities triggered by equivalence ratio fluctuations.Graphic abstract

Different Experimental Approaches for Characterization of Thermo-acoustic Instabilities

The coupling between pressure fluctuations and heat release variations during the combustion process is responsible for occurrence of thermo-acoustic instability. These instabilities will cause many adverse effects in power-producing devices. To control thermo-acoustic instabilities, its characterization is essential for design and implementation of control technique. The characterization of thermo-acoustic instabilities can be done using pressure amplitude and its frequency. In this study, the authors have presented two different approaches for thermo-acoustic instability characterization. In the first approach, the wall pressure measurements were taken at eleven locations, along the longitudinal directions, using differential pressure transducer. In the second approach, acoustic pressure outside the Rijke tube is measured. To check the consistency in the results, measurements are taken at different equivalence ratios and total mass flow rates. The result shows that the sound pressure level is higher in case of wall pressure measurement as compared to acoustic measurement outside the Rijke tube. The peak frequency is similar in both the cases, over a wide range of equivalence ratios and total flow rates. The captured standing wave pattern is similar to third mode of instabilities, but it was affected by the pulling force due to use of suction pump at the other end of Rijke tube. The suggested approaches can be effectively used to design the control techniques for suppression of thermo-acoustic instabilities. The acoustic pressure measured outside the Rijke tube is able to give the exact frequency of thermo-acoustic instabilities and also free from disruptions of flow. The exact prediction of mode of instability is essential, to identify location for mounting the pressure transducer on the wall of combustor, which was the major drawback of wall pressure measurements. The study further concluded that the intensity of thermo-acoustic instability is dependent on equivalence ratio.

Effect of hydrogen addition on the combustion characteristics of premixed biogas/hydrogen-air mixtures

The current work presents computational investigations of biogas-hydrogen blends' combustion characteristics for various thermo-physical conditions relevant for practical combustor applications. The numerical simulations were performed using 0-D SENKIN and 1-D PREMIX codes, whereas chemical kinetics is modelled using the GRI Mech 3.0 mechanism. Biogas composition represented by 60CH4/40CO2% (v/v) is blended with different H2 concentration varying from 0 to 50% (v/v) in the fuel. The effect of initial temperature and pressure on ignition delay, laminar flame speed (Su), flame temperature (Tad), species concentrations (Ci), and heat release rate profiles is investigated. The results showed that GRI-Mech 3.0 predictions are in good agreement with the available experimental ignition delay data for CH4/CO2-air mixture for stoichiometric ambient condition (P = 0.1 MPa and φ = 1). For the high-temperature oxidation, GRI-Mech 3.0 has accurately predicted Su available from literature for pure biogas (RH = 0.0) under a wide range of equivalence ratios (φ = 0.7–1.4) for ambient conditions. The computational analysis was then extended for RH ranging from 0.0 to 0.5 over a wide range of equivalence ratio (φ) = 0.7–1.4, initial temperatures (T) = 300–600 K and initial pressures (P) = 0.1–7.0 MPa. These results obtained were used to develop a new analytical correlation for the laminar flame speed (Su = Suo(φ,RH)TTuα(φ)PPuβ(φ,RH)) in terms of operating conditions. The results show that hydrogen addition to the biogas improves both the flame speed and ignition delay. The extent of reduction in flame speed due to elevation of initial pressure is a linear function of hydrogen addition to biogas. Furthermore, the sensitivity analysis was studied to assess the influence of hydrogen added to the biogas using laminar flame speed sensitivity coefficient (σ). The understanding of these mixtures’ combustion characteristics at given initial conditions leading to feasibility conformity of optimal blends of biogas/hydrogen mixtures for the design improvement of practical combustors is discussed.

Dynamics of premixed hydrogen-air flame propagation in the duct with pellets bed

Hydrogen, as the promising clean alternative energy in the future, is in the spotlight now all over the world. However, its flammable and explosive hazards should be highly considered during its practical application. In this study, the experiments are performed to study premixed hydrogen-air flame propagation in the duct with pellets bed, especially for fuel-rich condition. High-speed schlieren photography is employed to capture flame front development during the experiments. As well as the pressure transducer, is used to track the pressure buildup in the flame propagation process. Different diameters of pellets and different concentrations of gas mixture are considered in this experimental study. The typical evolutions about the tulip flame are similar in all cases, although the tulip flame formation time caused by the laminar flame speed are different. The flame propagation velocity is pretty enhanced in fuel-lean mixture under the effect of large diameter pellets bed, but it is significantly suppressed in fuel-rich conditions. While for the small diameter pellets (d = 3 mm), the suppression effect on flame propagation and pressure is obtained over a wider range of equivalence ratios, especially a better suppression effect is generated near the stoichiometric condition.

Laminar burning velocities, CO, and NOx emissions of premixed polyoxymethylene dimethyl ether flames

Polyoxymethylene dimethyl ethers (OMEn) with the chemical structure of CH3O(CH2O)nCH3 are a promising synthetic e-fuel class that can be produced from renewable electricity and improves the emission characteristics of internal combustion engines. However, knowledge of their fundamental combustion properties, such as the laminar burning velocity, is limited in the literature, preventing the full assessment of their application potential in combustion devices. Thus, a heat flux burner is applied in this study to measure the laminar burning velocities of OME1 and OME2 over a wide range of equivalence ratios of 0.6–1.9 and at initial temperatures of 383–401 K under atmospheric pressure for the first time. The obtained data are compared with computed results using a recently developed reaction mechanism for OME1–4. Good agreement is observed. The experimental results are also discussed in the context of a comparison to literature data of dimethyl ether and OME3, demonstrating the minor impact of chain length of (OMEn) on their burning velocities, which is further analyzed in terms of sensitivity analysis on reaction kinetics. Furthermore, the exhaust gas composition of NOx and CO is determined experimentally for flames of OME1 and OME2 using a probe method and compared to the numerical results, observing mostly good agreement, where the remaining differences could be explained on the basis of combined experimental and model uncertainties. This provides unique knowledge on the emission performance of the combustion of (OMEn).

Flame Transfer Functions and Dynamics of a Closely Confined Premixed Bluff Body Stabilized Flame With Swirl

Abstract The flame transfer function (FTF) and flame dynamics of a highly swirled, closely confined, premixed flame is studied over a wide range of equivalence ratios and bulk velocities at a fixed perturbation level at the dump plane. The operating conditions are varied to examine the ratio of flame height to velocity in scaling the FTF. The enclosure geometry is kept constant, resulting in strong flame-wall interactions for some operating conditions due to varying flame height. The resulting effect on the FTF due to changes in the “effective flame confinement” can therefore be studied. For sufficiently high equivalence ratio, and the resulting sufficiently small effective confinement, modulations of the FTF are observed due to interference of the perturbations created at the swirler and at the dump plane. The small length scales and high velocities result in modulations centered at high frequencies and spanning a wide range of frequencies compared to previous studies of similar phenomena. A critical point was reached for increasing effective confinement, where the modulations are suppressed. This is linked to a temporal shift in the heat release rate where the flame impinges on the combustion chamber walls. The shift reduced the expected level of interference, demonstrating effective confinement is important for the FTF response. Additionally, a distributed time lag (DTL) model with two time lags is successfully applied to the FTFs, providing a simple method to capture the two dominant time scales in the problem, recreate the FTF, and examine the effect of effective confinement.

Transient 3D simulations of turbulent premixed flames of gas-to-liquid (GTL) fuel in a fan-stirred combustion vessel

This work aims to conduct turbulent flame studies of GTL fuel and 50/50 diesel-GTLblend and compare them to diesel under a wide range of equivalence ratio (0.7 < Ф < 1.3) and turbulence intensities (0.5 m/s < u′ < 3.0 m/s). For this purpose, Zimont Turbulent Flame Speed Closure (Zimont TFC) model is adapted and implemented into ANSYS Fluent to study the influence of turbulence on premixed combustion. The model is verified against the experimental results of the turbulent flame speeds for methane-air mixture using a cylindrical fan-stirred combustion vessel. Results show that (i) rich diesel and lean GTL fuels are characterized by a faster flame development and higher turbulent flame speeds; (ii) at the same elapsed time, ReT and Da are found to be greater for stoichiometric GTL fuel compared to diesel and 50/50 diesel GTL blend, which indicates that the flame propagates towards the vessel’s wall at a faster rate and the chemistry has dominated turbulence in a shorter time, and (iii) at low turbulence intensity level (u′=0.5 m/s), the flame morphology is defined by a wrinkled flamelet regime in Borghi diagram. However, at moderate and higher turbulence levels (u′=1.5 m/s and u′=3.0 m/s, respectively), the flame structure is defined by the corrugated flamelets regime. Furthermore, the turbulence homogeneity and isotropy have been investigated throughout the combustion vessel by conducting a study for the turbulent kinetic energy balance.

A Numerical Exploration of Engine Combustion Using Toluene Reference Fuel and Hydrogen Mixtures

Hydrogen-fueled internal combustion engines (H2ICEs) are capable of operating over a wide range of equivalence ratios: from ultra-lean mode to stoichiometric conditions. However, they provide maximum thermal efficiency and minimum NOx emissions if operated lean. Although NOx is produced, H2ICEs generate little or no CO, CO2, SO2, HC, or PM emissions. The main limitation to pure hydrogen fueling is power density. To overcome such an issue, mixtures of gasoline and hydrogen can be exploited, with small modifications to the engine feeding system. Due to the peculiar characteristics of hydrogen (in terms of thermophysical properties, molecular weight and propagating flame characteristics) care must be adopted when trying to address combustion using computational fluid dynamics (CFD) tools. In this work, we simulate the combustion of mixtures of toluene reference fuel (TRF) and hydrogen under largely different ratios. To simplify the problem, liquid and gaseous injections are neglected, and a premixed mixture at the inlet of the CFD domain is imposed. Due to the different laminar flame speeds of the mixture components, mass-fraction weighted in-house correlations based on chemical kinetics simulations are adopted. Outcomes are compared with those obtained using standard correlations and mixing rules available in most commercial CFD packages.

Effects of vessel height and ignition position upon explosion dynamics of hydrogen-air mixtures in vessels with low asymmetry ratios

The explosion characteristics of hydrogen-air mixtures in a wide range of equivalence ratios in closed vessels were investigated experimentally. The maximum explosion pressure, maximum pressure rise rate (along with deflagration index), explosion time and heat loss were evaluated. Three vessels with low asymmetry ratios (H/D) of 0.146, 0.244 and 0.341 were used to study the effect of vessel height on explosion parameters, in which H and D are the height and inner diameter of the vessel, respectively. In the H/D = 0.341 vessel, the effect of ignition position on explosion behaviors was also considered. The results show that, with the increase of the vessel height, the maximum explosion pressure increase correspondingly, and the explosion time decreases orderly. In the lowest height vessel (H/D=0.146), the ignitor-regulating column acts as a ‘turbulence-generator’. Thus, the maximum rate of pressure rise could be increased significantly while the heat loss could be decreased. Compared with the central ignition scenario, both the maximum explosion pressure and maximum pressure rise rate are decreased for the asymmetrical ignition; meanwhile, the explosion time and the heat loss during the explosion are increased.

Experimental and Numerical Study of the Effect of CO2 Replacing Part of N2 present in Air on CH4 Premixed Flame Characteristics Using a Reduced Mechanism.

The effect of CO2, which replaces part of N2 present in air, on flame stability, laminar burning velocities (LBVs), and intermediate radicals (O OH) of CH4/O2/N2/CO2 premixed flames has been analyzed using detailed experiments and numerical studies. The numerical simulations were conducted using the PREMIX code with a detailed chemical reaction mechanism (GRI-Mech 3.0) and a reduced mechanism (39 species and 205 reactions) based on GRI-Mech 3.0 over a wide range of equivalence ratios (Φ = 0.7–1.3) and CO2 substitution ratios (0–30%). The reduced mechanism showed a good agreement with the other detailed mechanisms and experimental data. The experimental and numerical results showed that the substitution of CO2 diminishes the stability of the flame, and the flame blow-out speed is significantly reduced (the substitution ratio is 0–30%, and the corresponding flame blow-out velocity is 5.2–2.5 m/s). In addition, CO2 inhibits the LBV of the flame owing to the decrease of O and OH mole fractions. It not only accelerates the consumption of these two free radicals but also inhibits the generation of these two free radicals. Further analysis concluded that the substituted CO2 has the greatest influence on the LBV sensitivity coefficient of the HO2 + CH3 = OH + CH3O reaction.

Numerical study of the premixed ammonia-hydrogen combustion under engine-relevant conditions

Recently, ammonia is considered to be an energy medium for hydrogen or energy storage and ammonia/hydrogen can be a potential fuel blend for the spark-ignition engine. Nevertheless, the combustion properties of ammonia/hydrogen mixtures could be distinctive under different initial conditions. In this study, several essential combustion properties, including laminar burning velocity, minimum ignition energy, NOx and ammonia emissions, combustion efficiency, and mixture heating values of ammonia/hydrogen/air premixed combustion were extensively studied under a wide range of equivalence ratios (ϕ), hydrogen fractions (α) and different compression ratio using one-dimensional laminar planar flame and compared with stoichiometric methane, methanol, and ethanol combustion. The behavior of NOx generation changing with ϕ and α was analyzed in detail. Results showed that most properties of ammonia/hydrogen combustion could be comparable to that of hydrocarbon fuels under engine-relevant conditions, except for the mixture heating value is slightly lower in all conditions. Besides, the NO mole fraction non-monotonically changes with ϕ and α due to the competition between the effects caused by the reduction of nitrogen-atom species and the enrichment of H/O radicals. The NO mole fraction of stoichiometric ammonia/hydrogen could be even lower than that of hydrocarbons. Considering the properties of hydrocarbon fuels as a reference, promising working conditions for ammonia/hydrogen mixtures are ϕ from 1.0 to 1.05 and α from 40% to 60%. Besides, a high compression ratio is more suitable for ammonia/hydrogen mixtures due to the excellent knock resistance ability of NH3/H2 and better improvement than hydrocarbon fuels under high compression ratio.

Experimental investigation of a Jet-A1 fuelled peripheral vortex reverse flow combustor

Combustion characteristics of a novel peripheral vortex reverse flow (PVRF) combustor are investigated using Jet-A1 fuel. Previously, we have demonstrated the operation of PVRF combustor using LPG and ethanol fuels, and here we demonstrate and investigate the operation of PVRF combustor using Jet-A1 fuel. The combustor was operated at atmospheric pressure with preheated inlet air (300 °C) and high thermal intensity (25 MW/m3-atm at ø = 0.8) relevant to gas turbine combustors. Conventional swirler was not employed and the reactants were injected as jets. Combustion was primarily stabilized due to a dominant peripheral vortex of hot burned gases inside the combustor. In the non-premixed mode, the liquid fuel was injected coaxially w.r.t. the incoming air-jet and it was atomized due to strong shearing from the annular air jet. Shadowgraphy was used to investigate the atomization characteristics of the fuel. Electrochemical gas analyser was used to measure exhaust emissions (NOx, CO). The combustor demonstrated low emissions and stable operation over a wide range of equivalence ratios. CH* chemiluminescence was used to study the location and the dynamic behaviour of the reaction zone. The reaction zone was positioned further downstream in the non-premixed mode as compared to the prevaporized-premixed mode suggesting that atomization, evaporation and mixing of fuel in the non-premixed mode is causing a delay for the onset of the reactions. From shadowgraphy images, it was observed that retraction of the fuel jet considerably improved the fuel atomization.

Accelerating Laminar Flame Speed of Hydrous Ethanol via Oxygen-Rich Combustion

To investigate the laminar flame characteristics of hydrous ethanol, experiments were conducted in a constant volume combustion chamber. The laminar burning velocity and Markstein length of ethanol with water content from 0 to 20% by volume were measured over a wide range of equivalence ratios from 0.7 to 1.4 under the initial condition of 388 K and 0.1 MPa. Calculations of the laminar burning velocity with the constant pressure method (CPM) and constant volume method (CVM) were compared and discussed. Apart from experiments, numerical studies were carried out in CHEMKIN based on the Marinov’s and Olm’s ethanol oxidation mechanism. Moreover, the combustion of hydrous ethanol with 20% water by volume in oxygen-enriched air (O2 = 23% by volume) was also studied. Results indicated that the overall trends of laminar burning velocity versus the equivalent ratio were basically consistent between the experiment and the simulation, but the results obtained by CVM were larger than those obtained by CPM and closer to the simulation results. The peak value of laminar burning velocity decreased from 0.638 to 0.591 m/s when the water content increased from 0 to 20% in CVM calculation, but the peak laminar burning velocity of hydrous ethanol with 20% water in oxygen-enriched air enhanced to 0.771 m/s, meaning that the oxygen-enriched air can effectively offset the negative impacts of water. Moreover, the Markstein length of hydrous ethanol decreases with increasing equivalence ratios.

Performance and Emissions of Drop-In Aviation Biofuels in a Lab-Scale Gas Turbine Combustor

Abstract There is a growing need for drop-in biofuels for gas turbines for enhanced energy security and sustainability. Several fuels are currently being developed and tested to reduce dependency on fossil fuels while maintaining performance, particularly in the aviation industry. The transition from traditional fossil fuels to sustainable biofuels is much desired for reducing the rapidly rising CO2 levels in the environment. This requires biofuels to be drop-in ready, where there are no adverse effects on performance and emissions upon replacement. In this study, the performance and emissions of four different aviation drop-in biofuels were evaluated. They include UOP HEFA-SPK, Gevo ATJ, Amyris Farnesane, and SB-JP-8. These aviation biofuels are currently being produced and tested to be ready for full or partial drop-in fuels as the replacement of traditional jet fuels. The characteristic performance of each fuel from the prevaporized liquid fuels was performed in a high-intensity (20 MW/m3-atm) reverse flow combustor. The NO emissions showed near unity ppm levels for each of the fuels examined with a minimum at an equivalence ratio of ∼0.6, while CO levels were in the range of 1000–1300 ppm depending on the fuel at an equivalence ratio between 0.75 and 0.8. For an equivalence ratio range between 0.4 and 0.6, NO and CO emissions remained very low (between 1–2 ppm NO and 2400–2900 ppm CO) depending on the fuel. The examined biofuels did not show any instability over a wide range of equivalence ratios from lean to near stoichiometric condition. These results provide promising results on the behavior of these drop-in aviation biofuels for use in high-intensity gas turbine combustors providing stability and cleaner performance without any modification to the combustor design.

Structural analysis and regime diagrams of laminar counterflow spray flames with low-temperature chemistry

The understanding of spray combustion is a complex scientific problem, as it involves the interaction between evaporation, convection, diffusion, and chemistry. The focus of this study is to examine the effects of chemistry, in particular the low-temperature chemistry, on the structure of canonical counterflow spray flames at relatively low strain rate conditions. Parametric studies using a Eulerian formulation are carried out for monodisperse n-dodecane counterflow spray flames, in order to analyze the sensitivity of the flame structure to strain rate and droplet diameter over a wide range of equivalence ratios. These results reveal complex and multi-modal spray-flame structures that exhibit collocated, distributed, and cool flames. For the collocated flame, the presence of single and multiple low-temperature reaction zones is identified, which results from the evaporation and low-temperature chemistry interaction. The impact of low-temperature chemistry on the distributed flame is not pronounced. For low strain-rate conditions, the presence of a weak cool flame without high-temperature reaction zones is reported. Regime diagrams with respect to Stokes number and equivalence ratio are constructed, identifying distinctly different flame structures. By independently varying the strain rate and changing the droplet diameter, qualitatively similar but quantitatively different regime diagrams are obtained due to the lack of intrinsic self-similarity of the spray flamelet solution.

Numerical Study of Quenching Distances for Side-Wall Quenching Using Detailed Diffusion and Chemistry

The numerical investigation of quenching distances in laminar flows is mainly concerned with two setups: head-on quenching (HOQ) and side-wall quenching (SWQ). While most of the numerical work has been conducted for HOQ with good agreement between simulation and experiment, far less analysis has been done for SWQ. Most of the SWQ simulations used simplified diffusion models or reduced chemistry and achieved reasonable agreement with experiments. However, it has been found that quenching distances for the SWQ setup differ from experimental results if detailed diffusion models and chemical reaction mechanisms are employed. Side-wall quenching is investigated numerically in this work with steady-state 2D and 3D simulations of an experimental flame setup. The simulations fully resolve the flame and employ detailed reaction mechanisms as well as molecular diffusion models. The goal is to provide data for the sensitivity of numerical quenching distances to different parameters. Quenching distances are determined based on different markers: chemiluminescent species, temperature and OH iso-surface. The quenching distances and heat fluxes at the cold wall from simulations and measurements agree well qualitatively. However, quenching distances from the simulations are lower than those from the experiments by a constant factor, which is the same for both methane and propane flames and also for a wide range of equivalence ratios and different markers. A systematic study of different influencing factors is performed: Changing the reaction mechanism in the simulation has little impact on the quenching distance, which has been tested with over 20 different reaction mechanisms. Detailed diffusion models like the mixture-averaged diffusion model and multi-component diffusion model with and without Soret effect yield the same quenching distances. By assuming a unity Lewis number, however, quenching distances increase significantly and have better agreement with measurements. This was validated by two different numerical codes (OpenFOAM and FASTEST) and also by 1D head-on quenching simulations (HOQ). Superimposing a fluctuation on the inlet velocity in the simulation also increases the quenching distance on average compared to the reference steady-state case. The inlet velocity profile, temperature boundary condition of the rod and radiation have a negligible effect. Finally, three dimensional simulations are necessary in order to obtain the correct velocity field in the SWQ computations. This however has only a negligible effect on quenching distances.

Composition of Reduced Mechanisms for Ignition of Biodiesel Surrogates

Chemical kinetics mechanisms describing Fatty Acid Methyl Ester (FAME) biofuel combustion are quite extensive and cannot be implemented in Computational Fluid Dynamics simulations of real engine systems. Using the reduction methodology Ant Colony Reduction (ACR), skeletal reduction followed by optimization has been performed for the C-11 FAME biodiesel components methyl decanoate (MD), methyl 5-decenoate (MDe5), and methyl 9-decenoate (MDe9), and for the alkane n-decane. The aim of the present study was to produce small reduced mechanisms accurately describing ignition of the fuels over a wide range of conditions, and in addition to compare the size and composition of reduced mechanisms constructed from two parent mechanisms of different complexity. Reduction targets were ignition delay times over a wide range of equivalence ratios and pressures, for separate temperature ranges of 600–1100 K (LT) and 1100–1500 K (HT). One of the complex mechanisms was constructed to be simplified by a lumping approach and this one included MD and was also used to perform reduction for the alkane n-decane. The most detailed parent mechanism was used to create reduced mechanisms for all the three methyl esters. The lumped complex mechanisms resulted in more compact reduced mechanisms, 157 reactions for LT of MD, compared to 810 reactions for the more detailed mechanism. MD required the largest fuel breakdown subsets while the unsaturated methyl esters could be described by smaller subsets. All mechanisms had similar subsets for the smallest hydrocarbons and H/O chemistry, independent of the fuel and the choice of parent mechanism. The ACR approach for mechanism reduction created reduced mechanisms with high accuracy for all conditions included in the present study.

An Experiment Study on the Laminar Burning Velocity and Markstein Length of Chlorella Oil/RP-3 Kerosene Blends.

Experiments have been carried out in a constant volume chamber to investigate the effects of Chlorella oil addition on the laminar burning velocity and Markstein length of Chlorella oil/RP-3 kerosene blends at an initial pressure of 0.1 MPa and temperature of 450 K over a wide equivalence ratio range from 0.8 to 1.4. The result shows that at equivalence ratios of 0.9 and 1.1, with the increase of Chlorella oil addition, no cellular structure is observed in the flame propagation images. It means that the Chlorella oil addition has little effect on the flame stability under these experimental conditions; however, at an equivalence ratio of 1.3, with the increase of Chlorella oil addition from 0 to 0.5, the flame tends to be stable. It is found that the Markstein length of Chlorella oil/RP-3 blend decreases with the increase of the equivalence ratio. The blend with 0.5 Chlorella oil addition has a more rapid decrease in Markstein length compared with that of the RP-3 between the equivalence ratio from 1.1 to 1.3. The peak laminar burning velocity of Chlorella oil/RP-3 kerosene blend is obtained at the equivalence ratio of 1.1, and with the increase of Chlorella oil addition from 0 to 0.5, the laminar burning velocity increases about 20%.