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Currently, thermal power plants operating on hydrocarbon fuels (gas, fuel oil, peat, shale, etc.) are one of the main sources of electricity. An effective and promising method for suppressing harmful emissions (NOx, carbon oxides, soot) from the combustion of fossil fuels is the injection of steam into the combustion chamber. The influence of various mathematical submodels was studied on the accuracy of the numerical simulation of the process of n-heptane combustion in a laboratory burner with steam additive to the reaction zone as a promising chemical engineering method for the disposal of substandard liquid fuels and combustible waste with the production of thermal energy. The problem was solved in a three-dimensional stationary formulation. Systematic verification of these submodels, and a comparison of the results of the calculation with the experimental data obtained were carried out. The comparison with the experimental data was carried out for gas components and temperature distribution at the burner outlet; high agreement of the results was achieved. Optimal submodels of the methodology for calculating the process of fuel combustion in a jet of steam were determined. The best agreement with the experiment data was obtained using the EDC model in combination with a mechanism consisting of 60 components and 305 elementary reactions. More correct simulation results were obtained using the RSM turbulence model and the DO radiation model. [ABSTRACT FROM AUTHOR]

A novel data-intensive methodology to produce a high fidelity, extremely-reduced "compact" kinetic model for a high boiling point complex liquid fuel is proposed and demonstrated. A five-component surrogate definition for the liquid fuel is developed that displays a high accuracy to the experimentally-derived combustion property targets. The calculations of the Lawrence Livermore National Lab diesel surrogate model containing 6476 species are used to serve as gas turbine industry-defined performance targets for this surrogate. Acknowledging that the retention of a multi-component surrogate definition is a limitation on the size of the model, the surrogate fuel is consolidated into a single virtual molecule. Subsequently, the reaction mechanism is simplified by replacing high carbon number chemistry with a virtual scheme. This scheme links the virtual fuel molecule to low carbon number chemistry using four virtual species and forty-four virtual reactions, resulting in a reduction to 429 species in the model. The Machine Learned Optimisation of Chemical Kinetics (MLOCK) algorithm is adapted to "compact" this model. Compaction is the over-reduction and optimisation of a kinetic model. Path flux analysis generates an overly-reduced model with 31 species that has a poor replication of the detailed model calculations. To address this, virtual reaction rate constants of important virtual reactions are numerically optimized to detailed model high temperature calculations. MLOCK systematically perturbs all three virtual Arrhenius reaction rate constant parameters to generate and evaluate numerous model candidates, refining the search space based on prior results, finding better models. A low temperature virtual reaction network, comprising one new virtual species and three new virtual reactions, is appended to the high temperature compact model. MLOCK is employed to reoptimize the model to calculations at low and intermediate temperatures. The application of this methodology results in a 32-species compact model in ChemKin/Cantera format, which retains fidelities in the range of 76 to 92 % across a comprehensive range of gas-turbine relevant performance calculations for low, intermediate and high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, numerical and experimental investigations have been carried out to delineate the effect of various spray parameters on CO and NO x emissions in a combustor operating in flameless combustion mode with kerosene fuel. Thermal input was varied in the range of 20–41 kW (Heat release density ∼5–10 MW/m 3 ) with different fuel injectors and various fuel injection pressures. Spray parameters were varied by employing two separate conditions (i) same fuel flow rate with different solid cone pressure swirl spray nozzles (N1 – N4) and injection pressures (2.5–14 bar) to achieve varying spray parameters at same thermal input (ii) same fuel injection nozzle at different fuel flow rates and injection pressures (5–13 bar) to understand their effect on combustion and emissions. In both the cases, Sauter Mean Diameter (SMD) varied in the range of 34–58 μm with spray cone angle varying from 42° to 56° using different nozzles and fuel injection pressures. Tangential air injection helped achieve higher recirculation of hot combustion products in the primary zone of the combustor for all thermal inputs. The finer sprays obtained at higher injection pressures helped achieve improved recirculation and better mixing, resulting in uniform temperature and hence reduced CO and NO x emissions. The measured CO and NO x emissions were in the range of 28–70 ppm and 2–10 ppm for all heat inputs with global equivalence ratio varying from ϕ = 0.6 to 1, respectively. Measured acoustic emission levels were in the range of 98–101 dB and 104–107 dB for the flameless and transition mode respectively. The measured CO, NO x and acoustic emissions are an order of magnitude smaller those corresponding to conventional combustion mode. It was observed that coarser sprays led to a significant increase in acoustic emissions, relatively non-uniform temperature distribution and higher CO, NO x emissions during flameless combustion mode. [ABSTRACT FROM AUTHOR]

This study presents the design and development of a novel, self-aspirating, liquid fuel, annular, porous medium burner (SLAPMB) with stabilized flame inside a packed bed using liquid ethanol. The SLAPMB is built in an annular shape with an open area at the center for more secondary air ( SA ) entrainment, and a vaporizer for vaporizing the liquid ethanol is embedded inside the burner wall. The transient period of the SLAPMB during the switching period from LPG to ethanol vapor is investigated for understanding the simultaneous combustion phenomena within the porous medium burner and the vaporization process within the vaporizer. Effects of the primary air ( PA ), firing rate ( FR ) on the flame stabilization, temperature profiles within the burner, and emission characteristics are investigated. The PA strongly affects the flame stabilization within the burner. Flame moves upstream as the PA increases and vice versa with the flame moving downstream as the PA decreases. The existence of an SA inlet can significantly reduce CO emission and increase thermal efficiency. The ethanol flame can be successfully stabilized within the burner with a temperature peak occurring at the middle region of the burner with a relatively low emission of CO and NOx of about 900 ppm and 50 ppm, respectively. Thermal efficiency is 33.6%. The SLAPMB can offer a relatively wide turndown ratio with the firing rate ( FR ) ranging from 16 kW to 23 kW without the problem of flame stabilization and emission. [ABSTRACT FROM AUTHOR]

Abstract: In this work we analyze a diffusion flame established in a low-permeability medium. A low-strained impinging jet of oxidant against a pool of low-volatility liquid fuel is the considered geometry. Owing to the differences on the transport properties of gas, liquid and solid, the problem presents physical processes occurring in different length scales. Hence, we perform an asymptotic analysis in order to obtain the profiles of temperature and species concentration in each length scale. As a result of the low-permeability feature of the medium, the velocity field is determined mainly by the gradient pressure (Darcy equation). The viscous effects become confined into small regions near the stagnation-point and the liquid–fuel interface. The effects of porosity, fuel Lewis number, strain-rate and liquid–fuel volatility on the flame temperature, flame position and vaporization rate are discussed. It is shown that the low-permeability medium is necessary in order to sustain the vaporization process of the low-volatility liquid fuel, as it enhances the heat transfer to the fuel reservoir. This model is valid for high rates of interphase heat exchange and low rates of strain. [Copyright &y& Elsevier]

Highlights: [•] Examined distributed combustion for gas turbines applications using HiTAC. [•] Gaseous, liquid, conventional and bio-fuels are examined with ultra-low emissions. [•] Novel design of fuel flexibility without any atomizer for liquid fuel sprays. [•] Demonstrated fuel flexibility with emissions <4.5PPM of NO for different fuels. [•] Demonstrated CO emission <10ppm for methane based fuels, <40PPM for others. [Copyright &y& Elsevier]

Abstract: This paper presents the experimental and numerical results for a two stage combustor capable of achieving flameless combustion mode with 20kW thermal input and heat release density up to 5MW/m3. The fuel and oxidizer are supplied at ambient conditions. The concept of high swirl flows has been adopted to achieve high internal recirculation rates, residence time and increased dilution of the fresh reactants in the primary combustion zone, resulting in flameless combustion mode. Air is injected through four tangential injection ports located near the bottom of the combustor and liquid fuel is injected through a centrally mounted pressure swirl injector. Preliminary computational analysis of the flow features shows that decrease in the exit port diameter of the primary chamber increases the recirculation rate of combustion products and helps in achieving the flameless combustion mode. Based on preliminary computational studies, a 30mm primary chamber exit port diameter is chosen for experimental studies. Detailed experimental investigations show that flameless combustion mode was achieved with evenly distributed combustion reaction zone and uniform temperature distribution in the combustor. The CO and NO x emissions are reduced from 350 to 11ppm and 45 to 12ppm respectively at an equivalence ratio of 0.92, as operation of the combustor changes from conventional to flameless combustion mode. Measurement of CO and NO x emissions show that these emissions are reduced by an order of magnitude when operated in flameless combustion mode. The acoustic emission levels are reduced by 6–8dB as combustion mode shifts from conventional mode to flameless combustion mode. [Copyright &y& Elsevier]

Abstract: Utilization of a porous medium for combustion of liquid fuels is proved to be a promising approach for future applications. The porous medium burner for liquid fuels is more advantageous than the conventional open spray flame burner for several reasons; these include enhanced evaporation of droplet spray owing to regenerative combustion characteristics, low emission of pollutants, high combustion intensity with moderate turn-down ratio and compactness. This article provides a comprehensive picture of the global scenario of research and developments in combustion of liquid fuels within a porous medium that enable a researcher to determine the direction of further investigation. Accordingly, a glossary of the important terminology, the modeling approach, advances in numerical and experimental works and applications are included. The papers published in standard journals are reviewed and summarized with relevant comments and suggestions for future work. [Copyright &y& Elsevier]

• N-heptane combustion in a low emission burner has been investigated numerically. • Effect of steam and air forced supply on the combustion characteristics was analyzed. • Soot and NOx formation are significantly reduced with increasing steam flow rate. Combustion of n-heptane in a laboratory pattern of an original evaporative-type burner with the supply of air or superheated steam to the reaction zone was studied experimentally and numerically. Turbulence was simulated on the basis of the k-ω SST RANS model. Combustion was simulated using the Eddy Dissipation Concept (EDC) model with a detailed kinetic mechanism. The developed mathematical model was verified; a good agreement between calculation results and obtained experimental data is shown. For the first time, a comparative analysis of the effect of forced supply of steam and air on the local and integral characteristics of combustion is carried out. Radical difference in the effect of steam supply in comparison with air supply on reducing emissions of nitrogen oxides and soot from the burner is shown. The burner operating regimes have been studied in detail in a wide range of flow rates of supplied steam and fuel. It has been found that with an increase in steam flow rate, underburning, soot formation and production of nitrogen oxides are significantly reduced. [ABSTRACT FROM AUTHOR]

Abstract: Combustion of kerosene inside porous inert medium (PIM) has been investigated with the goal of reducing the emissions of nitric oxides (NO x ), carbon monoxide (CO) and soot. Silicon-carbide (SiC) coated carbon foam is used as PIM to attain high structural strength. The two-zone porous burner design consists of preheat and combustion sections. Different PIM configurations were tested by stacking together square porous pieces of 2.5cm thickness. Two types of fuel injectors are considered: (i) in the air-assist injector, approximately 5% of the combustion air is used for atomization and the remaining air enters as the primary co-flow around the injector, and (ii) in the swirling-air injector, all of the combustion air enters the injector to create a swirling flow around the fuel jet to enhance atomization and fuel–air premixing. The distance between the injector and PIM inlet is a key operational parameter, which was varied in experiments with both injectors over a range of equivalence ratios and heat release rates. The NO x and CO emissions were measured to optimize the PIM configuration with minimum emissions. Results show stable combustion over a wide operating range. Three combustor operational regimes are identified depending upon the injector location. [Copyright &y& Elsevier]

Abstract: To avoid the complexities associated with the droplet/vapor transport and nonuniform evaporation processes, a fundamental investigation of liquid fuel combustion in idealized configurations is very useful. An experimental–computational investigation of prevaporized n-heptane nonpremixed and partially premixed flames established in a counterflow burner is described. There is a general agreement between various facets of our nonpremixed flame measurements and the literature data. The partially premixed flames are characterized by a double flame structure. This becomes more distinct as the strain rate decreases and partial premixing increases, which also increases the separation distance between the two reaction zones. The peak partially premixed flame temperature increases with increasing premixing of the fuel stream. The peak CO2 and H2O concentrations are relatively insensitive to partial premixing. The CO and H2 peak concentrations on the premixed side increase as the fuel-side equivalence ratio decreases. These species are transported to the nonpremixed reaction zone where they oxidize. The C2 species have peaks in the premixed reaction zone. The concentrations of olefins are ten times larger than those of the corresponding paraffins. The oxidizer is present in partially premixed flames throughout the combustion system and there are no regions characterized by simultaneous high temperature and high fuel concentration. As a result, pyrolysis reactions leading to soot formation are greatly diminished. [Copyright &y& Elsevier]