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Abstract: The combustion processes of both gasoline and diesel engines are becoming similar, as a result of the application of direct fuel injection to the former and the reduction of the compression ratio of the latter. A novel time-scale interaction (TI) combustion model has been developed for simulating combustion phenomena with high accuracy, ranging from premixed charge combustion to diffusion combustion. This model is based on reasonable combustion regimes, taking into account the characteristic time scales of the chemical reactions and turbulence eddy break-up. The accuracy of the TI combustion model was validated by applying it to gasoline and diesel IC engines under a wide range of operating conditions. Comparisons of measured and calculated heat release rate patterns and cylinder pressure histories showed good agreement for both gasoline and diesel IC engines. [Copyright &y& Elsevier]

Abstract: Tetra-ol glycidyl azide polymer (GAP) is one of the best candidates for the solid fuel of gas hybrid rocket system because of self-combustibility, better mechanical property and high heat of formation, and comprehensive understanding of combustion phenomena is indispensable for such an application. Combustion model of GAP, which is one-dimensional three-phase mode combustion model, was developed by Beckstead et al. and they applied it to tri-ol GAP successfully. We have applied this model to tetra-ol GAP as an initial attempt, and numerical simulation showed that maximum temperatures in the gas phase exceeded those of experimental results significantly, and calculated burning rates were much higher than strand burner data, thus, modification of the model taking account of combustion incompleteness was found to be necessary. Combustion residues of GAP were investigated, and those were found to be composed of soot (black color), and high viscosity residue (HVR), and yellow powder which was only observed at high pressures. These residues were analyzed by means of SEM and FTIR, and mass balance was also measured. Modifications of combustion model were made taking the residue analysis results into account as Blow Off Mechanism. Simulated final temperature in the gas phase and burning rate are lowered effectively and coincide well with experimental data adjusting kinetic parameters. [Copyright &y& Elsevier]

Abstract: A common technique in computational fluid dynamics (CFD) modeling of fire is to assume single step, infinitely fast combustion, in which case the transport equations of all gas species can be combined into one for a single conserved scalar called the mixture fraction. While this approach is adequate for many engineering applications, for fire scenarios that require predictions of CO formation or flame extinction, this approach is inadequate. This paper describes a method of extending the mixture fraction concept to address two-step chemistry. The two-step chemistry allows for flame extinction and the prediction of CO formation and destruction. The mixture fraction is decomposed into components representing the states of the two-step chemistry. The new model is demonstrated with two test cases: a slot burner using direct numerical simulation (DNS) and a reduced scale enclosure using large eddy simulation (LES). Results of the new model are compared with experimental data and simulations using single-step chemistry. [Copyright &y& Elsevier]

Abstract: The present study is devoted to the analysis of the influence of expansion phenomena on turbulent small scales in premixed reactive flows. It is shown that, under certain conditions, the expansion that takes place across wrinkled laminar flamelets can be sufficient to control the fluctuating velocity gradients and associated dissipation rate functions. These conditions are fixed by the respective values of a set of nondimensional parameters, namely the turbulence Reynolds number , the Bray number, and the ratio between integral length scale of turbulence and thermal flame front thickness. A new criterion is introduced that makes it possible to delineate the influence of expansion phenomena on small-scale turbulent premixed reactive flows. The relevance of this criterion is analyzed in the light of experimental results represented in the classical diagram of combustion regime. The present analysis confirms that special care is required to represent and include the influence of expansion phenomena when using either RANS or LES closures to model turbulent premixed combustion. [Copyright &y& Elsevier]

Abstract: The ever increasing cost of hydrocarbon fuels and more stringent emission standards may resolve challenges in producing hydrogen and using it as an alternative fuel in industries. Internal combustion engines are well-established technology and hydrogen fuel in such engines is considered as an attractive choice in exploiting clean, efficient and renewable hydrogen energy. This work presents an improved thermo-kinetics model for simulation of hydrogen combustion in SI engines. The turbulent propagating flame is modeled using turbulent burning velocity model. During combustion the charge is divided into three zones containing unburned charge, flame and burned gas. The adiabatic flame is assumed to be in thermodynamic equilibrium while the detailed chemical kinetics scheme is considered for burned and unburned zones. The results were first validated against published experiments. Good agreements were obtained between simulation and experiment for varying equivalence ratio, ignition timing and compression ratio. Detailed analysis of engine NO X emission was performed afterward. The lean-burn and EGR strategies'' potentials were examined by the current model. The effects of different amounts of cooled dry EGR and hot wet EGR on the NO X emission, engine power output and indicated thermal efficiency were investigated and compared theoretically. [Copyright &y& Elsevier]

Abstract: Techniques for modeling energetic-material combustion and ignition have evolved tremendously in the last two decades and have been successfully applied to various solid-propellant ingredients. There has been a paradigm shift in the predictive capability of solid-propellant combustion models as the field has advanced from a simple and global-kinetics approach to a detailed approach that employs elementary reaction mechanisms in the gas phase, and accommodates thermal decomposition and subsequent reactions in the condensed phase. The detailed models not only allow calculation of propellant burning-rate characteristics, such as pressure and temperature sensitivities, but also of the surface conditions and entire combustion-wave structure, including the spatial variations in temperature and species concentrations. This paper provides a comprehensive review of recent advances in the modeling and simulation of various solid-propellant ingredients over a wide range of ambient conditions. The specific materials of concern include nitramines (RDX, HMX), azides (GAP), nitrate esters (NG, BTTN, TMETN), ADN, and AP monopropellants, as well as homogeneous mixtures representing binary (RDX/GAP, HMX/GAP, and AP/HTPB) and ternary (RDX/GAP/BTTN) pseudo-propellants. Emphasis is placed on the steady-state combustion and laser-induced ignition of nitramines. The capabilities and deficiencies of existing approaches are addressed. In general, the detailed gas-phase reaction mechanisms developed so far represent the chemistry of monopropellants and associated mixtures consistently well, and help understand the intricate processes of solid-propellant combustion. The reaction mechanisms in the condensed phase, however, still pose an important challenge. Furthermore, the current knowledge of the initial decomposition of molecules emerging from the propellant surface is insufficient to render the models fully predictive. Modeling is thus not yet a predictive tool, but it is a useful guide. In the near future, it is likely that detailed combustion models can assist in the formulation of advanced solid propellants meeting various performance and emission requirements. [Copyright &y& Elsevier]

Abstract: The kinetic characterization of the system is of interest right now due mainly to its role in sustainable combustion processes. The aim of this paper is to revise and validate a detailed kinetic model of hydrogen and carbon monoxide mixture combustion with particular focus not only on formation but also on interactions with nitrogen species. Model predictions and experimental measurements are discussed and compared across a wide range of operating conditions. This study moves from the detailed analysis of species profiles in syngas oxidation in flow reactor and laminar premixed flames to global combustion properties (ignition delay times and laminar flame speeds) by referring to a large set of literature data. According to recent literature, the validation of the kinetic scheme confirmed there was a need to slightly modify the kinetic parameters of two relevant formation reactions ( and ) and of reaction . [Copyright &y& Elsevier]

Abstract: While it is common knowledge that PAH formation can be expected at rich combustion conditions, this paper presents experimental and computational evidence that PAH formation can also be expected under lean, or cool, combustion conditions. Experimental evidence for diesel engine operation at lean conditions, as well as the literature references related to waste tire and coal combustion, are cited as supportive evidence of conclusions drawn here. A computational model based on reaction mechanisms for three surrogate fuels: C2H2, C7H16 and C14H28, was validated against the available diesel engine data, and projected to both lean and rich combustion conditions. The finding was that for the adiabatic case, minimum production of PAHs occurs at equivalence of unity and increases as equivalence becomes either lean or rich; the latter observation being consistent with the common knowledge. [Copyright &y& Elsevier]

Abstract: Traditional Monte Carlo ray-tracing (MCRT) methods for continuous participating media are not applicable in media represented by point masses (or stochastic particles) frequently encountered in combustion modeling. In the authors’ previous work several ray models and particle models have been proposed for radiation simulations in such media. In the present paper an efficient emission scheme is developed for MCRT in highly inhomogeneous media represented by particle fields. Ray energies are limited to a narrow range to reduce statistical error, by having particles emit numbers of photons proportional to their emissive power (including combination of weak particles). A method to evaluate the radiative heat source, required by the overall energy equation, is also developed. A particle field representing the highly inhomogeneous medium in a turbulent jet flame is employed to test the proposed methods. [Copyright &y& Elsevier]

Abstract: Nitromethane was investigated in this study due to the push for higher performance and reduced toxicity monopropellant. A comprehensive detailed model for its flame structure and linear regression rate was developed and validated with experimental data. The model considered one-dimensional behavior with surface vaporization and detailed gas-phase kinetics based on the RDX mechanism of Yetter et al. combined with the nitromethane decomposition mechanism of Glarborg, Bendtsen, and Miller, resulting in a mechanism consisting of 47 species and 250 elementary reactions. The predictive model was implemented using a custom FORTRAN code wrapping the CHEMKIN 4 PREMIX gas-phase solver coupled with the condensed-phase solution. Predicted burning rates using the model showed good agreement with measured rates up to 15MPa. Calculated species and temperature profiles showed three distinct regions based upon the appearance and consumption of certain species. The first region was marked by decomposition of nitromethane, the second region by consumption of all intermediate species except CH4 and NO, and the third region by the rise to final temperature and species concentrations near the equilibrium values. Among the intermediate species, CH4 and NO had higher concentrations than those of CH2O, N2O, HNO, and HONO. CH4 served as fuel species and NO provided a portion of the oxidizer for the third-region reactions to reach equilibrium composition. Sensitivity analysis identified the importance of two elementary reactions involving HNO to the temperature profile, and therefore the burning rate. Although the absolute level of NH and HCO were low, they served as an important intermediate species transporting nitrogen and carbon, respectively, between other higher-concentration species. The calculated flame zone thickness is consistent with that measured by microthermocouples. [Copyright &y& Elsevier]

Abstract: The chemistry of nitrogen species and the formation of in hydrogen combustion are analyzed here on the basis of a large set of experimental measurements. The detailed kinetic scheme of combustion was updated and upgraded using new kinetic and thermodynamic measurements, and was validated over a wide range of temperatures, pressures and equivalence ratios. The mechanism''s performance at high pressures was greatly improved in particular by adopting higher rate parameters for the reaction. The sub-mechanism was further validated and updated. The kinetic parameters of the and reactions were updated in order to improve model predictions in specific conditions. Sensitivity analyses were carried out to determine which reactions dominate the and systems at particular operating conditions. Good overall agreement was observed between the model and the wide range of experiments simulated. [Copyright &y& Elsevier]

Abstract: To improve the prediction accuracy of the spark ignition and combustion processes in spark ignition engines, improved ignition and flame propagation models have been developed and implemented in the CFD code, KIVA-3V. An equation to calculate the spark ignition kernel growth rate is derived that considers the effects of the spark ignition discharge energy and flow turbulence on the ignition kernel growth. In addition, a flamelet combustion model based on the G equation combustion model was developed and implemented. To test the ignition and combustion models, they were applied to a homogeneous charge pancake-shaped-combustion-chamber engine, in which experimental heat flux data from probes in the engine head and cylinder liner were available. By comparing the flame arrival timings with the simulation predictions, the ignition and combustion models were validated. In addition, the models were also applied to a homogeneous charge propane-fueled SI engine. Good agreement with experimental cylinder pressures and NO x data was obtained as a function of ignition timing, engine speed, and EGR levels. [Copyright &y& Elsevier]

Hazardous wastes have complex physical forms and chemical compositions and are normally incinerated in rotary kilns for safe disposal and energy recovery. In the rotary kiln, the multifeed stream and wide variation of thermal, physical, and chemical properties of the wastes cause the incineration system to be highly heterogeneous, with severe temperature fluctuations and unsteady combustion chemistry. Incomplete combustion is often the consequence, and the process is difficult to control. In this article, modeling of the waste combustion is described by using computational fluid dynamics (CFD). Through CFD simulation, gas flow and mixing, turbulent combustion, and heat transfer inside the incinerator were predicted and visualized. As the first step, the waste in various forms was modeled to a hydrocarbon-based virtual fuel mixture. The combustion of the simplified waste was then simulated with a seven-gas combustion model within a CFD framework. Comparison was made with previous global three-gas combustion model with which no chemical behavior can be derived. The distribution of temperature and chemical species has been investigated. The waste combustion model was validated with temperature measurements. Various operating conditions and the influence on the incineration performance were then simulated. Through this research, a better process understanding and potential optimization of the design were attained. [ABSTRACT FROM AUTHOR]

The steady-state combustion of the monopropellant glycidyl azide polymer (GAP) has been modeled using a one-dimensional, three-phase numerical model. Combustion characteristics of four formulations of cured GAP with varying amounts of the curing agent hexamethylene diisocyanate (HMDI) have been modeled. A two-step global decomposition condensed-phase kinetic mechanism has been developed, based on experimental data. A detailed gas-phase kinetic mechanism, with 460 reactions and 74 species, has been assembled and used. The combustion has been modeled over pressures of 5-100 atm and initial temperatures of 298 ±50 K. The calculated combustion characteristics include the burning rate, pressure exponent, temperature sensitivity, surface and flame temperatures, temperature and species profiles, and condensed- and gas-phase heat released. The model calculations have been compared with various experimental data, and most of the calculations and their trends seem to be consistent with experimental data. The GAP content of the GAP-HMDI formulation has been predicted to have a significant influence on the burning rate. The calculated GAP-HMDI burning rates were ∼1.05-1.93 cm/s at 70 atm, increasing with the GAP content of the formulation. The calculated pressure exponents were ∼0.4 and the calculated temperature sensitivities were ∼0.01-0.014 K-1. The condensed phase plays a significant role for GAP combustion. Parametric studies have been performed to study the effect of varying the values of reaction parameters and thermophysical properties such as specific heat and thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Spray-guided spark-ignited direct-injection (SG-SIDI) engines are likely to be the next generation of gasoline engines. Compared to current wall-guided (WG-SIDI) engines, they offer improved fuel economy and substantially reduced hydrocarbon and soot emissions. Two stages of stratified combustion (partially premixed flame propagation and mixing-controlled combustion of rich products left from partial combustion of initially fuel-rich mixtures) are investigated here in an experimental SG-SIDI engine using detailed CFD modeling, high-speed spectrally resolved combustion luminosity imaging, and cylinder pressure analysis. The CFD model reproduces the spatial and temporal distribution of both combustion stages. Correlation of CFD calculations and experimental combustion measurements demonstrates that optimum ignition timing occurs for somewhat rich equivalence ratios (0.9–1.6) and relatively low flow velocities (<15m/s) at the spark location. Both model and experiment show: (1) for fixed injection time, increased rich burning occurs for earlier ignition times and (2) higher in-cylinder swirl leads to asymmetric flame propagation and increased rich burning. Calculated and measured overall heat-release rates agree quite well over a wide range of engine operating conditions. These experiment-model comparisons provide a detailed picture of combustion processes in spray-guided SIDI engines and a sound scientific basis for engine design optimization. [Copyright &y& Elsevier]

In a mass burn waste incinerator, the waste undergoes combustion in the bed on the grate and the products of incomplete combustion are destroyed in the gas plenum above the bed. Thus, it is essential to consider the reaction in both the waste bed and the gas plenum when evaluating the combustion performance using computational fluid dynamics (CFD). However, solving the two-phase reacting bed of waste is not straightforward in CFD simulations. This paper presents the combustion and gas flow of a waste incinerator using a new simulation approach that incorporates two models: FLIC for the reacting bed of solid fuels and FLUENT for the turbulent reacting flow of the gas plenum. The two models were linked through the boundary conditions on the waste bed in such a manner that FLIC provides the gas properties leaving the bed as an inlet condition of the gas flow and FLUENT produces the radiation transferred to the bed. The predicted results were compared with on-site measurements in the plant by a novel instrument that collected the temperature, oxygen concentration, and motion data while tumbling with the waste particles within the bed. The measured data were highly fluctuating, but FLIC satisfactorily predicted the overall trend of temperature and oxygen concentration including the upper and lower boundaries of the violent fluctuations. The FLIC/FLUENT combined simulation provided crucial information on the nature of combustion and flow characteristics such as the ignition and burnout points of waste, the rates of each combustion process, and the subsequent gas flow pattern in the combustion chamber. [ABSTRACT FROM AUTHOR]

This paper describes a method for determining the quasi one-dimensional burning velocity for gas explosion experiments in a smooth tube from pressure records. A one-dimensional random choice method code (RCMLAB) has been written in MATLAB. The combustion model in RCMLAB treats the combustion wave as a discontinuity. For a given burning velocity S(t), we can find the weak deflagration solution and calculate the flow field. This allows us to estimate S(t) from the measured pressures. This was done using a proportional controller with the difference ΔP between estimated and observed pressure as input and the time derivative of S as output. The experimental setup consists of three tubes with a diameter of 22 mm and lengths of 1, 2, and 5m. The tubes were filled with premixed stoichiometric propane/air. The model for determining the burning velocity for a gas explosion in a smooth tube seems to work quite well. [ABSTRACT FROM AUTHOR]

Modeling of the smoldering process in a porous fuel bed consists of two parts: kinetic modeling of pyrolysis and combustion reactions and CFD modeling of the flow and energy equations. A transient axisymmetric two-dimensional (2D) model based on the first principles was developed for the forward and natural smoldering of a porous biomass fuel rod. Heat transfer is represented by two energy equations whereby the solid and gas phases are considered to have separate and distinct temperatures interacting through an interface heat exchange. The starting material first undergoes pyrolysis prior to oxidation of the remaining carbonaceous residue. The pyrolysis is assumed to consist of a set of first-order reactions. Oxidation of the carbonaceous residue is accompanied by the formation of gas-phase combustion products, the concentration of which is also computed. Calculations under unsteady conditions are done for both natural and forward smoldering for a variety of operating and boundary conditions as well as physical properties of the fuel and the packing density. The computation captures the development of a steady combustion region in which it moves at a constant rate. The results for the gas and solid temperature profiles, oxygen concentration profile and pressure distribution are also presented. The effects of surface heat loss, heating value of fuel, airflow rate, porosity of the fuel rod on temperature and smolder velocity are discussed. [Copyright &y& Elsevier]

This paper considers a sandwich layered combustion model (an oxidizer and a fuel) that takes into account condensed- and gas-phase chemical reactions and transverse heat and mass transfer. Under particular simplifications, algebraic expressions are obtained for the burning rates of the components and the temperature and concentration of gaseous reagents on the burning surface. Calculated dependences of the burning rate on the sandwich size agree with experiments. [ABSTRACT FROM AUTHOR]

Investigation of the combustion phenomena in a constant volume microcombustor was carried out on a constant volume microcombustor that is subject to significant heat loss to the wall in order to estimate the effects of combustor dimension on flame propagation. A cylindrical combustor of a variable height that is comparable to quenching limit of the combustible mixture of H 2 and air was built. Flame visualization and measurement of transient pressure during the flame propagation were made. Measurements were made at the chamber height ranging from 0.67 mm to 3 mm. A simple theoretical model that takes into account the heat loss to the wall during flame propagation was used to derive available work of the burnt gas from the pressure measurements. For a chamber depth of less than 1 mm, the pressure increase by combustion was negligible and the sensible heat in the burnt gas was not adequate to be converted to mechanical power. For a chamber height greater than 2 mm, however, the amount of heat generated by combustion was sufficient to produce a few Joules of theoretical work even after experiencing increased heat loss due to the small scale of the chamber. [ABSTRACT FROM AUTHOR]

To control and reduce emissions for combustion devices, numerical simulations are becoming increasingly important. In this study, numerical simulations of a domestic methane burner are performed to predict the temperature profile and the formation of carbon monoxide and nitric oxide. A detailed reaction scheme, as well as a detailed transport model was used in this two-dimensional study. We consider premixed laminar flames at low flow speed. Thenumerical simulations are performed with the object-oriented C++ code Gascoigne (Becker and Braack, 2001), which was developed recently and has the adaptive-gridding capability allowing minimization of the error in the numerical simulation with respect to certain functionals, for example, local values ofspecies mass fraction and mean value of temperature or heat release. Acomparison with experiments as well as a parametric study aimed at the minimization of pollutants were carried out. The optimal parameters to guarantee a good compromise between flame stability and toxic emissions are presented. [ABSTRACT FROM AUTHOR]

Nano-sized aluminum dust is quite attractive in the application scenarios with limited residence time. This study simulated an aluminum nanoparticle-air jet flame in a burner that was proposed to characterize the mixing and burning properties of dust and air in a classical ramjet configuration. The model considers the flow of gas phase by employing three-dimensional multicomponent Navier-Stokes equations, and the aluminum particles via the Lagrange approach. A combustion sub-model was developed to characterize the heat convection, radiation and combustion processes of nano-sized aluminum particles. Thereafter, the model was validated by comparing with experimental results of dust jet flow and aluminum particle combustion. With the present model, the characteristics of flow field, and variations of particle temperature, heat release and statuses etc. were examined in detail, by which the mixing zone and flame structure were defined. The results showed that the nano-aluminum particles in the inner mixing layer were firstly ignited by the hot co-flow air and burned, and these particles in the core jet region were ignited downstream. Once the aluminum particles were ignited, they burned out promptly in this burner. The effects of particle size were evaluated, and the results show that the lengths of mixing layer and reaction zone, as well as the width of reaction zone reduce with decreasing particle size, whereas the width of mixing layer stays the same. [ABSTRACT FROM AUTHOR]

The use of lifted flames presents some very promising advantages in terms of pollutant emissions and flame stability. The focus here is on a specific low-swirl injection system operated with methane and derived from an air-blast atomizer for aero-engine applications, which is responsible for flame lift-off. The key feature of this concept is the interaction between the swirling jet and the confinement walls, leading to a strong outer recirculation zone and thus to an upstream transport of combustion products from the main reaction region to the flame base. Here, the representation of the physics involved is challenging, since finite-rate effects govern the lift-off occurrence, and only a few numerical studies have been carried out on this test case so far. The aim of the present work is therefore to understand the limits of some state-of-the-art combustion models within the context of LES. Considering this context, two different strategies are adopted: the Flamelet-Generated Manifold (FGM) approach and the Thickened Flame (TF) model. A modified version of the FGM model including stretch and heat loss effects is also applied as an improvement of the standard model. Numerical results are compared with the available experimental data in terms of temperature and chemical species concentration maps, showing that the TF model can better reproduce the lift-off than the FGM approach. [ABSTRACT FROM AUTHOR]

• A 2D/3D model was developed to simulate composite propellant burning under wide pressure range. • Flame structure and standoff distance for multiple flame were examined in detail. • Heat flux determined by AP monopropellant, premixed binder and primary diffusion flames controls the burning rate. • Effect of primary diffusion flame on the burning rate alleviates with increasing AP particle size. • Relationship between cone-angle of final diffusion flame and flow velocity was elucidated. This study developed a combustion model for ammonium perchlorate (AP)/hydroxyl–terminated polybutadiene (HTPB) composite propellant to capture the flame structure and elucidate the mechanism governing burning rate at different pressures, AP sizes and surface morphologies. A numerical model was proposed to characterize gas domain by solving Navier-Stokes equations of reacting flow field with 3-step and 12-species global kinetics; and the condensed domain was coupled by considering interfacial energy balance. The present model was validated with experimental results of both pure AP and AP/HTPB combustion, in which the mean absolute percentage error of burning rate for all cases was less than 5%. The standoff distances of AP monopropellant, premixed binder and primary diffusion flames were determined as 14.2, 12.1 and 25.8 μm at 2 MPa, respectively, reducing with pressure. The front and height of final diffusion flame were determined by axially varied radial gradient of temperature and its height was obtained as 152 μm at 2 MPa, which rises as the pressure or AP particle size increases. The increase of burning rate with pressure is attributed to the raise of surface heat flux dominated by standoff distances of AP monopropellant, premixed binder and primary diffusion flames, in which the effect of primary diffusion flame enhances as the AP size decreases resulting from enlarged lateral diffusion of species. Finally, the effects of protrusive, recessive AP surfaces and their combination with planar AP surface on the flow and flame properties were examined. [ABSTRACT FROM AUTHOR]

Laser or flash excitation is an attractive ignition option for many energetic systems because of increased safety and control. Commonly used electrical ignition systems are more likely to cause accidental ignition due to stray currents. Upgrading to laser or flash ignition mitigates this problem as well as allowing the ignition at multiple sites more easily for improved control of the energy release. Carbon nanotubes and nanoscale aluminum have been shown to be flash ignitable in loose powders or very porous low-density materials; however, these previous low-density formulations may not be as useful in practical energetic systems. In this study, nano aluminum particles are combined with a polyvinylidene fluoride binder/oxidizer in order to create a full-density photosensitive material. Using a low energy broadband flash source and an Nd:YAG laser at 1064 and 532 nm, films of nano aluminum and polyvinylidene fluoride were successfully ignited experimentally and ignition response was quantified. Solids loading was found to be the dominating factor controlling minimum ignition energies, with the lowest energies observed at 20 to 25 wt.% nAl. Simulations of the wave and particle interactions were modeled with COMSOL Multiphysics® for both the flash and laser-induced heating. The results show that optimal energy absorption occurs at nAl particle fractions of 20–25 wt.%, consistent with the experimental observation. Additionally, the results show the effect of plasmonic resonant enhancement of the heating, specifically at lower wavelengths near 250 nm. [ABSTRACT FROM AUTHOR]

• Models to predict biodiesel properties for combustion modeling reviewed in detail. • Based on several statistical parameters best models to predict thermophysical properties of biodiesel suggested. • Experimental data base for critical properties of methyl ester constituents of biodiesel need to be developed. • To extend the applicability of property prediction models, there is a need to develop experimental data in the high temperature range. Among the various alternative fuel options for diesel, biodiesel has emerged as the most promising fuel because of its renewable origin, availability, biodegradability, high combustion efficiency and lower emissions. Although, experimental investigations on biodiesel combustion in different engine types are exhaustive, corresponding numerical investigations are sparse. The underlying mechanisms behind the combustion trends with biodiesel can be better understood through numerical modeling of combustion processes. Further, numerical modeling should be an integral part of engine design and development work with alternative fuels like biodiesel that is subjected to composition variability. Arriving at optimal biodiesel composition for engine applications through experimental measurements is time consuming and laborious and thus, the role of computational fluid dynamic investigation (CFD) is imperative. For biodiesel spray and combustion modeling studies, the liquid and vapor phase thermophysical properties of biodiesel at different temperatures ranging from ambient to critical conditions are required which are impossible to measure experimentally. Thus, there are sustained interests in developing numerical models for predicting thermophysical properties of biodiesel from combustion modeling standpoint. There are various approaches and models developed to estimate the thermophysical properties of biodiesel. In the present review, approaches and models available to estimate the important thermophysical properties of biodiesel including density, viscosity, surface tension, latent heat of vaporization and vapor pressure are comprehensively analyzed using various statistical parameters. Further, available approaches to predict the critical properties which are required for predicting the thermophysical properties of biodiesel are also reviewed. Based on several parameters such as reported deviation, method of validation, simplicity, and applicable range, the most suitable approach and the corresponding model for estimating the thermophysical properties of biodiesel are suggested for spray and combustion modeling studies. [ABSTRACT FROM AUTHOR]

The effect of preheating primary air on the co-combustion characteristics of a 50–50% blend of pinewood and corn straw in a fixed bed. The primary air temperatures were assessed from 20 to 130 °C. The co-combustion characteristics were included the co-combustion behaviors and emissions. In order to reveal the features of the combustion process in the porous bed, a two-dimensional unsteady state model was employed to investigate the combustion process in a fixed bed of blended biomass on the combustion process in a fixed bed reactor. Conservation equations of the bed were implemented to describe the combustion process. The gas phase turbulence was modeled using the k-ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. Results showed that by increasing primary air temperature the residual mass on bed decreased, while the average burning rates and ignition front propagation velocity increased At the primary air temperature of 85 °C the smallest unburned carbon was left in the ash, and the emissions of nitrogen-compounds were relatively small. In contrast, the primary air temperature of 85 °C was found to be well-operating condition, which can be suggested for industrial boiler during blend co-combustion. The simulation results were then compared with experimental data for different temperature, which shows that the combustion process in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data. [ABSTRACT FROM AUTHOR]

This paper presents the application of an emission limiting model-based predictive controller for a small-scale biomass grate furnace. The furnace has a nominal power of 100 kW with wood pellets as fuel, but it can be operated with different fuels as well. The model predictive approach extends the existing static feedforward controller of the investigated furnace with a dynamic feedback controller that is able to improve the combustion performance. Simultaneously, the formation of carbon monoxide emissions is minimized within the prediction horizon based on an available emission estimation model for pellets. The results obtained from closed-loop measurements show that the control concept is able to reduce carbon monoxide emissions in partial load operation up to four times while the control error of the supply water temperature for heating is nearly halved during transient operation. This is achieved by incorporating the emission estimation model into the constrained optimization of the predictive controller. Additional results obtained from closed-loop experiments for different fuel types with varying water contents demonstrate the advantages of the proposed model-based approach and its robustness with respect to typical uncertainties of the combustion process. • Applied emission limiting model predictive controller for a small-scale furnace. • Carbon monoxide emission reduction validated with closed-loop measurements. • Presented model predictive controller is robust with respect to different fuels. • Application of an efficient nonlinear biomass model for control purposes. • Integration of a carbon monoxide soft-sensor into the control algorithm. [ABSTRACT FROM AUTHOR]

This study aims to analyze the effects of a novel ternary blend of n-butanol and castor oil methyl ester (COME) with petro-diesel on combustion, engine performance and emission characteristics of four stroke single cylinder diesel engine and to obtain optimum blending proportion which can simultaneously reduce UHC, CO, and NO x without affecting engine performance. A quick and simple approach involving a single zone combustion model coupled with double and triple Wiebe functions has been successfully applied to analyze combustion behavior of binary and ternary fuel blends respectively. Neat diesel was used as a baseline fuel to compare combustion, performance and emission characteristics with binary and ternary fuel blends (B30, B20Bu10, B10Bu20 and B15Bu15). Apparent heat release rate (AHRR) calculated from the model is in good agreement (RMSE ≤ 1.33) with experimental values. Peak AHRR values (J/°CA) for fuel blends B30, B20Bu10, B15Bu15, B10Bu20 and neat diesel were found to be 26.1, 29.4, 32.7, 37.1, and 36.1 respectively. The ignition delay period was not affected for B30 blend however it was observed to be increased by 2.89–3.35°CA for n-butanol blended fuels. Results of B30 fuel blend showed reduction in BTE by 1–3% with increase in greenhouse gas emissions. The results of ternary fuel blend (B15Bu15) showed improvement in engine performance characteristics whereas NO x emission was reduced in the range of 20–60% compared to B30. Detrimental effect on engine performance, emission characteristics and combustion behavior was observed for B10Bu20. Therefore, B15Bu15 was considered as an optimum fuel blend. • First time successfully analyzed 3-stage combustion modeling for ternary fuel blends. • Apparent heat release rate for ternary blends was predicted accurately by triple Wiebe function. • n-butanol as admixture in COME/diesel blends improved engine performance. • Admixture n-butanol in COME/diesel blends significantly reduced NO x emission. • Ternary blends of n-butanol/COME/diesel significantly reduced all engine emissions. [ABSTRACT FROM AUTHOR]

We consider a specific parameter regime in a model for combustion in hydraulically resistant porous media. We prove the existence of the traveling fronts in this regime and investigate their stability. The existence is proved using Geometric Singular Perturbation theory. The stability analysis involves locating the spectrum of the linearization of the underlying system about the front by numerical computation of the Evans function combined with energy-like estimates. Furthermore, a conclusion about nonlinear stability is also obtained. • We consider a model for combustion in hydraulically resistant porous media. • We prove the existence of traveling fronts and investigate their stability. • The existence is proved using Geometric Singular Perturbation theory. • The linear stability involves Evans function computations and energy-like estimates. • The nonlinear stability in an exponentially weighted norm is obtained. [ABSTRACT FROM AUTHOR]