Pulse Combustor Research Articles

INCREASING THE STABILITY OF COMBUSTION PROCESSES IN THE COMBUSTION CHAMBER OF GAS-TURBINE ENGINE THROUGH THE IMPROVEMENT OF THE AIRGAS CHANNEL

A possibility of carrying out the numerical experiment using the up-to-date tools of computational hydrodynamics to predict pulsating combustion modes at the stage of engine development has been discussed. It will allow us to considerably reduce the expenditures required for the engine design and its development increasing simultaneously the operating efficiency of power systems. The purpose of this investigation is to increase the stability of combustion processes of gaseous fuel in the low-emission combustion chambers of gas turbine engines due to the gas-dynamic improvement of the air-gas channel. Theoretical studies showed that the gas-dynamic improvement of the air-gas channel in the low-emission combustion chambers of gas turbine engines allows us to enlarge the range of the stable operation of fuel-combustion system, to reduce pressure pulsations in the air-fuel mixture, and consequently reduce the vibrations of elements in the combustion chamber and in the engine on the whole. Theoretical investigations of the pulsation characteristics of the low emission combustion chamber with the preliminary mixing of air-fuel mixture for the gas turbine engine of 25 MW allowed us to establish that amplitude maximum pressure pulsations are observed in the paraxial recirculation zone, in the region of secondary air inlets; inside the flame tube in the region of the third and fourth cowlings; on inlet diffuser walls, in the output cross-section of flame tube before the turbine blades; on peripheral swirler blades, in the region of fuel outflow orifices and in swirler channels. The most efficient reduction of pulsations is observed in the primary combustion zone and the pulsations produced by the central vortex in the mixing zone closer to the chamber output are less efficient.

Thrust generation by pulse combustion of gas in a submerged chamber

This paper presents the results of experimental and theoretical studies of the hydrodynamic processes occurring during gas combustion in a vertical cylindrical chamber submerged in water. It is shown that combustion of a single portion of a stoichiometric propane–oxygen mixture leads to cyclic generation of force impulses on the thrust wall: the first impulse is generated due to the combustion of gas, and the subsequent impulses are generated due to hydrodynamic oscillations of the gas cavity. A total specific impulse of 104–105s (105–106m/s) was experimentally obtained.Expressions for the adiabatic oscillation period of the gas cavity and the maximum impulse of the force acting on the thrust wall during expansion of the cavity were obtained by approximate calculations. It is shown that the period is proportional to the length of the chamber to a power of 0.65, and the maximal force impulse is proportional to the square root of the length of the chamber. The oscillation periods calculated from the maximum size of the cavity are in good agreement with experimentally measured period of the first pulsation. Calculated force impulses are larger than experimental ones, which is attributed to thermal and hydrodynamic losses.The results of the study are applicable to water propellers, devices for regenerating filters, generating acoustic waves, and cleaning underwater bodies.

Fast Pulse Combustion Process for Producing Lithium-Ion Cathode Materials

With the use of a fast pulse combustion process in a reactor we are able to produce LiFePO4, albeit with the use of an additional annealing step[1]. The role of latter is to introduce appropriate ordering into the structure. Disorder in the crystal structure of LiFePO4 has been identified by many groups[2–4], especially for materials synthesized via reactions without a high-temperature sintering step in an inert or reducing atmosphere, or using fast reactions on the order of minutes[5,6]. The most favorable intrinsic defect is the Li-Fe ‘anti-site’ pair in which the Li ion (on the M1 site) and the Fe ion (on the M2 site) are interchanged[2]. In this report we show that such a disordered structure can be obtained even with synthesis times shorter than 2 seconds; at such short times one usually obtains amorphous materials[7]. The disorder will be observed through Mossbauer analysis and Rietveld refinement of XRD data. The galvanostatic cycling behavior of such disordered LiFePO4 is shown together with the annealed version on the attached graph. We were able to cycle the former up to a current density of 340 mA/g (corresponds to 2C). Another group of interesting cathode materials is the lithium nickel manganese cobalt oxides. Using different ratios between the three transition metals different compositions can be obtained, some showing a very high capacity of 220 mAh/g when charged to 4.7 V[8,9]. With our method we are able to produce a wide range of compositions, also lithium rich ones. This is possible because of the very fast reaction from solutions of metal salts, where the mixing proceeds on the molecular level. The fast reaction is the reason that no phase separation or grouping of an element can occur, leading to a uniform composition across the whole material. Simultaneously the method also allows decoration of the particles with a carbon coating, which could help improve the capacity retention[9]. The synthesis of present cathode materials was carried out in a pulse combustion reactor[1], which uses the pulsating flow of flue gases from the combustion chamber to supply the necessary energy for the reaction. The pulsating flow is a result of pulsating fuel and air ignition. It has been shown previously that this kind of burning has a better heat transfer rate than similar turbulent flows[10]. The flue gases enter the reactor pipe that has a two fluid nozzle at the point of flue gas entry. The nozzle is used to produce droplets of precursor in the hot zone of the reactor. The solvent from the droplets evaporates at a very high rate causing formation of agglomerated nano powders, which are then fully or partly crystallized after passing through the heated reactor pipe. The desired temperature in the reactor depends on the product. The dried precursor undergoes a reaction, similar to that in the solution combustion synthesis[11] (SCS), because the precursor can be composed of nitrates and a carbohydrate, acting as a fuel. Another possible precursor type are flammable precursors, such as those used in liquid feed flame spray pyrolysis[7,12](LF-FSP), however, they are usually not used in production of cathode materials with this reactor.

External high-frequency control of combustion instability

The article presents the results of experimental studies of combustion instability in the pulse combustor. Propane-air mixture is burned in the chamber with the flame holder. It was experimentally found that feeding high-frequency sound vibrations into the combustion chamber causes the suppression of pulsating combustion. The oscillation frequency ranges in 870 to 1400 Hz. This corresponds to 9-12 resonance frequencies of oscillations in the combustor. The physical mechanism of the observed phenomenon consists in changing the conditions of formation and destruction of fuel jets in the vortex zone behind the flame holder.

Battery properties of lithium iron phosphate nano-particles synthesized by pulse combustion spray pyrolysis

Battery properties of lithium iron phosphate nano-particles synthesized by pulse combustion spray pyrolysis

Ignition delay times of single kerosene droplets based on formaldehyde LIF detection

Single droplet ignition experiments were performed with GTL kerosene, Jet A-1, and Exxsol D80 (reduced aromatics) in the temperature range from 550 to 900K in air at 3bar. The laser-induced fluorescence (LIF) intensities of liquid GTL kerosene and Exxsol D80 are on a lower level than that of Jet A-1. Formaldehyde LIF and background emission were measured with pulse-to-pulse wavelength switching at closely spaced excitation wavelengths (353.373 and 353.386nm). Typically, formaldehyde LIF and background emission were observed simultaneously. However, in some droplet ignition sequences background emission was observed first followed by formaldehyde LIF after a time delay. Therefore, in the case of kerosene background subtraction has to be performed carefully to derive correct ignition delay times based on formaldehyde LIF (cool flame). A pulsating combustion was observed in several kerosene droplet ignition experiments. The cool flame ignition was found to appear significantly earlier for the synthetic GTL kerosene compared to Exxsol D80 and conventional Jet A-1 kerosenes. For GTL kerosene we found a cool flame ignition delay time of 624ms, while corresponding values for Exxsol D80 and Jet A-1 amount to 1467 and 1699ms, respectively. The differences for the starting time of hot ignition (around 1050ms) and ignition temperatures (near 700K) are comparatively small under the conditions of our experiments.

Valorisation of food waste to produce new raw materials for animal feed

This study assesses the suitability of vegetable waste produced by food industry for use as a raw material for animal feed. It includes safety and nutritional viability, technical feasibility and environmental evaluation. Vegetable by-products were found to be nutritionally and sanitarily appropriate for use in animal feed. The drying technologies tested for making vegetable waste suitable for use in the animal feed market were pulse combustion drying, oven and microwave. The different meal prototypes obtained were found to comply with all the requirements of the animal feed market. An action plan that takes into account all the stages of the valorisation process was subsequently defined in agreement with local stakeholders. This plan was validated in a pilot-scale demonstration trial. Finally, the technical feasibility was studied and environmental improvement was performed. This project was funded by the European LIFE+ program (LIFE09 ENV/ES/000473).

Heat transfer in valveless Helmholtz pulse combustor straight and elbow tailpipes

A heat transfer correlation is proposed for the pulsating flow in the tailpipe of a valveless Helmholtz pulse combustor. The correlation is developed based on the experimental data of the heat transfer in the straight tailpipe. The constants in the correlation are determined by least-squares fitting of experimental data. The regression model is assessed, and its significance is tested. The correlations of the 45°, 90°, and 135° elbow tailpipes are revised by multiplying factors to that of the straight tailpipe. The maximum error of the correlations is no more than 20%.

A Low Cost and High Capacity Synthesis of Lithium Iron Phosphate Using a Pulse Combustion Reactor System

We have developed a reactor for continuous synthesis of various metal oxide materials in oxidizing or reducing atmosphere. The capacity of the current pilot reactor version is 2 L of precursor per hour. In the case of synthesis of lithium iron phosphate this corresponds to 100 grams per hour and the procedure is scalable to 100 kilograms per hour. The apparatus is comprised of a pulse combustion type burner, which operates at a frequency of 150 – 240 Hz and a temperature above 1000 °C, a two fluid nozzle for spraying the precursors, and a reactor pipe, where the reaction takes place. The oxidizing and reducing atmosphere is controlled by setting a fuel rich or fuel lean burning. When working with reducing atmosphere the spraying gas is nitrogen, otherwise air or oxygen can be used. The particles are cooled down with air to about 150 °C and collected with an electrostatic precipitator. Here we demonstrate the functioning of the reactor on the example of lithium iron phosphate. The two precursors used consisted of iron nitrate and lithium carbonate, dissolved in nitric acid. The phosphorus source in one case was ammonium dihydrogen phosphate and triethyl phosphate in the other. As the fuel we used either urea combined with sucrose or glycine. All compounds were dissolved in deionized water. When the precursor is heated up, the water evaporates, and the remaining nitrates and organics react. This process is equivalent to solution combustion synthesis. However, changing the composition of the precursor strongly affects the morphology of the produced materials, which means that the reaction in the precursor is as important as the conditions in the reactor. By spraying such precursors into the hot zone of the reactor, which is held at about 800 °C, the formed droplets are each its own microreactor. The water from the droplets evaporates very fast because of the high temperature and good heat transfer in pulse combustion burners; the temperature in the reactor drops to about 700 °C. This leads to a precipitation of precursor salts and hinders the coalescence of droplets. After the salts reach a high enough temperature, the reaction starts so that a lot of gaseous products are produced. In the case of urea precursor, porous spheres with a diameter of 3 – 15 μm are formed; in the case of glycine precursor agglomerates of particles from 50 to 300 nm are formed. The particles in both cases are carbon coated, either due to carbonization of sucrose or an excess of glycine fuel. As synthesized lithium iron phosphate is partly amorphous, mainly because of the very short residence time at a temperature above 500 °C. Heat treatment in an Ar atmosphere at 700 °C for 3 hours yielded phase pure lithium iron phosphate. The as prepared and heat treated materials have been investigated using XRD, SEM, CHNS elemental analysis and ICP. The electrochemical behavior of as prepared and thermally treated materials has been investigated in a lithium half cell.

Effect of Mechanical Activation on Ti3AlC2 Max Phase Formation under Self-Propagating High-Temperature Synthesis

<p>In this study, we have investigated the effect of various mechanical activation (MA) modes on phase and structure formation in powder mixtures made up to produce Ti<sub>3</sub>AlC<sub>2</sub> MAX phase. The optimal MA duration has been established which results in the maximum heat release under SHS due to accumulation of structural defects leading to the growth of internal energy. The effect of MA on the character and kinetics of combustion front propagation has been investigated. It was shown that following pretreatment of a powder mixture in a planetary ball mill, the combustion mode changes from stationary to a pulsating combustion and, consequently, the combustion rate decreases. The burning-out of the sample is partial and with interruptions (depressions). Force SHS-pressing technology was used for obtaining of compacted samples with homogeneous structure based on Ti<sub>3</sub>AlC<sub>2</sub>.</p>

Non-linear dynamics in pulse combustor: A review

The state of the art of non-linear dynamics applied to pulse combustor theoretically and experimentally is reviewed. Pulse combustors are a class of air-breathing engines in which pulsations in combustion are utilized to improve the performance. As no analytical solution can be obtained for most of the nonlinear systems, the whole set of solutions can be investigated with the help of dynamical system theory. Many studies have been carried out on pulse combustors whose dynamics include limit cycle behaviour, Hopf bifurcation and period-doubling bifurcation. The dynamic signature has also been used for early prediction of extinction.

The acoustic model of oscillations of gas combustion in coaxial pipes

Organization of pulse combustion mode is one of the possible solutions to the problem of energy efficiency installations using hydrocarbon fuel. For grate combustion of solid fuels, in particular, solid industrial wastes are considered to be promising coaxial system, allowing the admission of secondary air to the combustion zone. In this paper we proposed an acoustic model of oscillations of gas when burning solid fuel in the system is coaxially arranged pipes with natural air supply. The description of the motion of the gas in the system during one period of oscillation.

Operating Mode Analysis of Pulse Combustor with Exhaust Decoupler

The operating mode of the pulse combustor with the exhaust decoupler was summarized and discussed. Based on the earlier study of the nonlinear analysis of the system, the basic three modes were explained in detail. Furthermore, two limited modes were addressed. The analysis of the modes distribution and mode transition show that the high-frequency and antiphase (HA) mode was the better mode for the pulse combustor.

CFD Simulation of Heat Transfer of Pulsating Gas in a Pipe

Numerical Simulation of pulsating flow in a pulse combustor tailpipe was performed using computational fluid dynamics (CFD) method. The flow in the pipe was characterized by periodic pulsating. The influence of this pulsating includes incomplete flow development and high level of convective heat transfer rate, and both were considered and investigated by the CFD model. Compared with the steady flow condition, results showed that the heat transfer coefficient and Nusselt number were 2.35 times higher.

Математическая модель процессов тепломассобмена в аппаратах пульсирующего горения

Математическая модель процессов тепломассобмена в аппаратах пульсирующего горения

Pulse Combustion Spray Drying of Egg White: Energy Efficiency and Product Quality

A new technique for spray drying of egg white was developed and termed as pulse combustion spray drying (PCSD) which uses high-temperature pulsating jets generated by the pulse combustor to atomize and dry the liquid feed simultaneously. The pilot-scale PCSD testing of egg white was conducted and the drying energy efficiency was evaluated. Selected product properties of the PCSD egg white powders were measured. It was found that compared with traditional spray drying, the PCSD process achieved a higher energy efficiency of 2,604 kJ/kg water evaporated and the PCSD powders had a superior surface characteristics, smaller mean particle diameter, and more homogeneous size distribution. Additionally, the egg white proteins and their foaming and gelling properties were protected well in the PCSD process. Experimental results showed that the PCSD technique is promising for drying of egg white and even other heat-sensitive food feeds.

Nanocomposite and mechanically alloyed reactive materials as energetic additives in chemical oxygen generators

Chemical oxygen generators are widely used for aircraft, spacecraft, submarines, and mine rescue. Oxygen-generating compositions typically include alkali metal chlorate or perchlorate that decomposes at increased temperatures, a transition-metal oxide as a decomposition catalyst, and a metal fuel that reacts with part of the produced oxygen to provide heat for a self-sustained propagation of the decomposition/combustion wave. To increase the oxygen yield per unit mass, it is of interest to minimize the amount of metal fuel, but decreasing its content leads to pulsating combustion and undesired fluctuations of the oxygen flow rate. The present paper explores the feasibility of replacing iron and tin, currently used in oxygen generators, with reactive materials, produced by arrested reactive milling and by mechanical alloying. Because of their high energy density, easy ignition, and good storability, these materials have the potential to improve the performance characteristics of oxygen generators. Thermodynamic calculations for combustion of sodium chlorate mixed with various reactive materials identified the most attractive additives providing high temperatures and high oxygen yield. Experiments on combustion of sodium chlorate-based mixtures with nanoscale cobalt oxide catalyst and the most promising energetic additives were conducted in an argon environment, using laser ignition. Infrared video recording was used to investigate the thermal wave propagation over the mixture pellet. The experiments have shown that mechanically alloyed Al/Mg (1:1 mass ratio) material is a promising alternative to iron and tin, because significantly smaller amounts of this additive are needed for a steady propagation of the combustion wave.

Influence of turbulent flow on the deflagration-to-detonation transition in hydrogen-oxygen-air mixtures in a pulse combustor

The effect of turbulization of a hydrogen-oxygen-air mixture flow on the deflagration-to-detonation transition in a pulse combustor (PC) is studied. The parameters of operation of the PC with flame front propagation in a quiescent and strongly turbulized mixtures (Re ≫ 104) are compared. It is shown that, in case of a quiescent mixture no detonation occurs because of a small length of the PC. The presence of intense pulsations (Re > 2 · 104) created by elements of special configuration in the mixing chamber promotes the formation of a detonation wave, the velocity of which depends on the fuel-to-oxidizer equivalence ratio.

Frequency Characteristics of the Valveless Self-Excited Pulse Combustor of Bend Tailpipe Helmholtz Type

The frequency characteristics of the valveless self-excited pulse combustor of bend tailpipe Helmholtz type with continuous supply of gas and air were investigated by experiment in this paper. The effects of bend tailpipe structure, heat load and the excess air ratio on the frequency of operation were studied. The results show that the frequency of operation decreases with the increase of tailpipe bent angle and the frequency is relatively low with the bent position at tailpipe entrance. The frequency is increased with the increase of heat load, and decreased with the excess air ratio.

Dynamic Characterization of a Laboratory-Scale Pulse Combustor

Pulse combustion is a self-sustained and self-oscillating process driven by combustion, coupled with resonant oscillation of the flow in the tailpipe. This article describes the investigation of the effects of different parameters in a laboratory-scale pulse combustor and analyzes them using concepts of nonlinear dynamics. Two orientations of the fuel injection holes were used. In one orientation, the fuel comes in vertically in parallel and counter-flow with the air stream, while in the other orientation the fuel is injected horizontally at cross-flow with the air stream. For the vertical orientation, the frequency slightly decreased with decrease of global equivalence ratio and inlet flow rate. With change of lean to rich air/fuel mixture, the dynamics changes from non-pulsating to pulsating combustion. The transition from noise-dominated to periodic oscillation has also been verified by evaluating the correlation dimension. In the horizontal orientation of the fuel inlet, the pulsating behavior has been obtained even under fuel-lean conditions due to better mixing of air and fuel, and phase and fast Fourier transform plots indicate quasi-periodic behavior.