Combustion Vibration Research Articles

Thermoelectric coupling effect of secondary injection on gasoline fuel spray and mixing of a free vibration combustion alternator

This article focuses an unconventional energy transducer called free vibration combustion alternator that directly utilizes mechanical vibration to convert fuel combustion heat energy into electrical energy, while studying the impact of secondary injection strategy on fuel spray and mixing in a free vibration combustion alternator. A thermoelectric-mechanical coupling model is developed to take into account the interaction effect between vibration, generation, combustion on fuel spray and mixing in free vibration combustion alternator. Meanwhile, an algorithm method is proposed to iterate the calculation results of vibration and combustion for simulating the effect of the secondary injection strategy on the mixture formation characteristic. The results indicate that the fluctuation of secondary injection ratio affects the free vibration combustion alternator vibration, and then changes the compression ratio and the initial conditions for fuel injection and mixture formation. The free vibration combustion alternator operating in secondary injection proportion of 9:1 condition shows equivalent speed of 2061 r/min, compression ratio of 8.75, fuel evaporation rate of 91.4%, mixing uniformity index of 86.4%, and they are adjusted to 1855 r/min, 7.96, 99.9%, 32.2% respectively when the secondary injection proportion is 1:9. Moreover, a larger secondary injection proportion causes stronger turbulent motion, significantly improving the mixing quality.

SEMI-EMPIRICAL MATHEMATICAL MODEL OF NITROGEN OXIDES EMISSION FROM LOW-EMISSION COMBUSTION CHAMBER AS A PART OF AUTOMATIC CONTROL SYSTEM OF AN AERO ENGINE

The article is devoted to the problem of automatic control of nitrogen oxide emissions from a low-emission combustion chamber (LECC) of a gas turbine engines' (GTE) new generation. Since the measurement technologies have not reached the required level of availability today, and the reliability of the automatic control system (ACS) depends on the validity of input information about the engine state, it is proposed to use the built - in predictive mathematical model of the LECC. The model equations are functions of the measured parameters. The compact design requirements and significant nonlinearity of combustion determine the stochastic nature of the LECC. Taking into account the strict ICAO standards for the emission of harmful substances, all this leads to a narrow range of stable operating modes, limited, on the one hand, by the normalized level of nitrogen oxide emissions, and, on the other hand, by unacceptable modes of flame blowout or vibration combustion (thermoacoustic vibrations). It is proposed to build into the ACS a hybrid model of the processes of generating harmful emissions in the MEKS GTE, consisting two parts. The first semi-empirical submodel combines the physical equation of Zeldovich and the generalized empirical coefficient calculating as a function of several critical variables. This submodel allows generating training samples for the second submodel in case of insufficient experimental data. The second submodel is based on a neural network. The article discusses the development and testing of the first submodel, which identification algorithm is based on the accepted hypothesis of the possibility of applying the principle of superposition in describing the interaction of diffusion and homogeneous flames. The algorithm is based on the Zeldovich equation, which makes it possible to determine the dependence of the generation of nitrogen oxides on the composition of the air-fuel mixture using the distribution function of the probability density of its pulsations depending on the value of the integral equivalent ratio φ, which characterizes the concentration of fuel in the mixture. A feature of the LECC is the presence in the flame tube of longitudinal acoustic waves, excited by the release of heat during combustion, having a frequency equal to natural frequency of the gas-air column. These acoustic waves are leading to fluctuations of φ and causing the harmonic fluctuations in the mathematical expectation of the mixture composition. In this work the numerical modeling of the distribution of the inhomogeneity and pulsation of the fuel-air mixture concentration over the area of the flames in the CFX package allowed to obtain the characteristics of the mathematical expectations and dispersion, as well as the natural frequencies of the object. The distribution functions of the probability density of pulsations of the mixture concentration for diffusion and homogeneous circuits are calculated analytically, taking into account the acoustics of the combustion chamber. The analysis of the effect of dispersion of acoustic waves on the form of the resulting probability density curves in diffusion and homogeneous plumes is carried out.

Vibratory Combustion, Problems and Investigation Methods

Vibratory Combustion, Problems and Investigation Methods

MECHANISM OF DETONATION FORMATION IN THE PROCESS OF VIBRATION COMBUSTION

Based on thermodynamic analysis of combustion processes, we build a new model of laminar combustion process of vibration combustion. If the passive component velocity for the two-component mixture is controlled at the inlet (the interior energy is pumped at the inlet of the combustion chamber), high-frequency resonance oscillations of vibration combustion are shown to develop depending on the structure of the standard chemical potential. The resonance is driven by hydrodynamic instability. Numerical experiment models the regimes of resonance with pumped internal energy, the nature of their nucleation depending on the structure of the standard chemical potential is revealed. For low temperatures, the appearance of detonation combustion with substantial pressure increase is established near resonance.

The emergence of pressure self-oscillations in the flow of heat carriers and the development of mechanisms for reducing the amplitude of these oscillations

Self-oscillations of pressure arising in the elements of power equipment with an internal heat supply can, in some cases, impair the operation of this equipment. At high amplitudes of self-oscillations, conditions for its damage can be created. Thermoacoustic self-oscillations are a consequence of flow instability. A well-known example of processes accompanied by the generation of thermoacoustic self-oscillations is vibration combustion, which is observed in rocket engines, in air heaters for blast furnaces, etc. In order to determine the characteristics of pressure self-oscillations, numerical studies of natural convection in a vertical channel with internal local heat release are carried out. Heat release from internal sources occurs in a limited section of the channel, which is closer to the inlet cross section of the channel. At the outlet cross section of the channel, there is a system of coaxial cylindrical bodies that constitute additional local hydraulic resistance to air flow. The characteristics of the air flow in the channel, which are accompanied by self-oscillations of velocity and pressure, are determined from the numerical solution of the system of equations of dynamics and heat transfer for a compressible medium, taking into account the dependence of the thermophysical properties of air on temperature. Based on the results of this solution, the velocity, pressure and temperature fields in the flow are determined. It is shown that changes in flow velocity and pressure with time have the character of oscillations with variable amplitude. Velocity oscillations at the channel outlet are in antiphase with velocity oscillations at the channel inlet. The amplitudes and frequencies of these oscillations are found. The measures were determined to reduce the amplitude of pressure fluctuations in the flow. Among them - the dispersal of sources of internal heat release and a decrease in local hydraulic resistance. These measures can be applied to reduce the negative impact of self-oscillations on power equipment.

Simulation of Vibration Combustion

We consider a mathematical model of the laminar process of vibration combustion proposed recently. It allows us to simulate detonation and deflagration modes, the occurrence of which occurs depending on the structure of the standard chemical potential. For simplicity of presentation and analysis, we consider a one-dimensional mathematical model formulated for the reduced dimensionless variables for the case of a two-component mixture. The obtained numerical results are presented and discussed.

Physical Mechanisms and Conditions of Excitation of Vibratory Combustion of Solid Fuels

The authors have obtained experimental characteristics of the self-oscillating process of vibratory combustion of a solid fuel. As a result of the analysis of the obtained diagrams of amplitude and frequency characteristics of the self-oscillating process of vibratory combustion of a solid fuel depending on the position of the combustion zone in a Riecke tube, the fuel structure, and methods of charging, the authors have made the following assumption. Two types of processes coexist during the vibratory combustion of a solid fuel: for the fundamental harmonics of the oscillating process of low frequency, the energy approach known in the literature, and for harmonics of higher frequency, the vortex mechanism. Methods of experimental verification of this assumption have been developed and used. Experimental results confirm the proposed model of vibratory combustion of a solid fuel. A theoretical computational procedure for the development of vibratory combustion has been worked out. A theoretical study of the motion of a combustion wave at stochastic parameters of the process of heat release has been made.

CREATION OF AFTERBURNING TURBOFAN ENGINE – HISTORY AND PRESENT

The main problems of the creation of afterburning turbofan engines, among which the irremovable surge of the compressor, is disclosed by historical analysis. According to the published models, such surge is a hydrodynamic instability in the form of rotating stall mutual transitions to surge with the primary cause of instability in the form of stall or vibration combustion in the afterburner. The Pratt & Whitney F100 serial engine, which based on TF30 is one of the first in which the irremovable surge was detected. As a result, several planes F-15 crashed, so far as the compressor could not be restored to a stable state without stopping and restarting the engine. Dissection of the problem with this phenomenon led to the conclusion that this irremovable surge problem was generated by the engine design. To eliminate it, the company had to refine several systems, such as an electronic engine control system, fuel supply of the afterburner along with the nozzle locations, firing belt, combustion stabilization, an extension of flow separation along the contours, etc. According to the analysis of publications, particular difficulties arose with the recoverable unsurge operation of such engines. It is noteworthy that today, the F-135-PW100 engines have been installed on the F-35 aircraft, the predecessors of which are the F-100 engines with the same problems. The results of experimental studies of a fan are presented in the article to deepen in the stall flow mechanism and the occurrence of rotating stall of the fan blades. The perturbations from vibrational combustion in the afterburner combustion chamber to the fan stall boundary in the afterburning turbofan engine system at bench conditions were simulated by independent throttling of the duct over a wide range of the bypass ratio. Numerous monographs and publications according to vibrational combustion, in particular in afterburner combustion chambers TRDF AL-21F and TRDDF AL-31F, of A. M. Lulka, confirm the possibility of the propagation of perturbations against the flow in the bypass duct and the impossibility of their propagation through the turbines. The propagation of surge perturbations in the afterburning turbofan engine to the compressor of the internal duct behind the fan occurs through the interaction of the duct. The more reliable way to prevent emergencies is to provide stability margin area of compressors. Estimation of the pre-stall state of the flow traditionally is carried out by the diffusivity factor of Lieblein FD, which is applicable in 2D calculations. The integral variational principle of nonequilibrium thermodynamics of the “maximum flow of mechanical energy” of V. N. Yershov was applied.

QUESTIONS AND PROBLEMS OF MATHEMATICAL MODELING QUA NONEQUILIBRIUM OF COMBUSTION PROCESSES

On the basis of thermodynamic analysis, new mathematical models of the combus- tion process (thermal theory) and vibrational combustion are constructed. A global inhomo- geneity of the system can be described as an inhomogeneous distribution of the enthalpy over a two-component mixture. In this case, for the combustion process in the phase space of the variables (%, P, T, n, S, E), an increase in the enthalpy is not a total differential. An increase in the enthalpy is a total differential on the local equilibrium manifold (a laminar combustion process). These two assertions, which allow one to single out in the phase space the corre- sponding adiabatic of the combustion process (the Hugoniot adiabatic) and the equation for the entropy, close the classical mathematical model of the combustion process. The above numerical experiments show that two regimes of the combustion process (deflagration and detonation) depend on the structure of the standard chemical potential Moreover, a control of the passive component velocity at the inlet results in (depending on the structure of the standard chemical potential) high-frequency oscillations, which are responsible for a blow-up.

About the Danger of Vibration Combustion in Gas Explosions in the Room

In recent years, in experimental gas explosions in open volumes, such a phenomenon as vibration combustion has been recorded or, as they sometimes say, flame-acoustic combustion, or simply combustion, but accompanied by acoustic gas oscillations. Generally speaking, this type of combustion was known for a long time in the 19th century, from the time of Higgins and Rijke, and acquired the poetic name “singing flame”. However, at the onset of gas turbine and rocket engines, this phenomenon manifested itself in their combustion chambers and was designated as a whip, as it resulted in structural damage. But the vibration combustion is known not only for the destructive force, but also for the intensification of fuel combustion process in high-duty furnaces.

X All-Russian Conference with international participation “Fuel combustion: theory, experiment, applications”

X All-Russian Conference with international participation “Fuel combustion: theory, experiment, applications”This Conference was firstly organized in the 70s of the XX century. In recent decades, the Conference has been held regularly every three years and it is a unique scientific event in Russia that attracts a lot of attention of Russian and foreign scientists and specialists in the field of energy, chemistry and mechanics of reacting media. The present Conference covers the following topics:• Theory and numerical modeling of combustion• Heat and mass transfer in combustion systems• Combustion kinetics, catalysts• Combustion in gas-liquid media• Combustion of solid fuel• Combustion in near-and supersonic flows, detonation• Thermoacoustic instability and vibrational combustion• Combustion processes control• Combustion diagnostic methods and instruments• Advanced technologies of fuel combustion• Deep coal processing, including gasification• Combustion of unconventional fuels• Issues of creating engines of a new generation• Environmental problems of burning fuels• Fire spreads• Economic issues of fuel power engineeringThe Scientific Committee appreciates the enormous work of the editorial board and reviewers in the preparation of this volume. We would like to express our sincere thanks to all authors for their research contributions, and also to organizers of the conference for their valuable spadework.

Intense Regime of Vibratory Combustion of Biofuel

Experimental investigation of the vibratory combustion of a solid biofuel (wood pellets) has been conducted. In some experiments, a significant enhancement of acoustic radiation with vibratory combustion of the pellets was observed which was accompanied by the increase in their burnup rate. In the event of such a regime the flame temperature decreased, whereas the density of the heat flux on the combustion-chamber wall increased due to the turbulization of the boundary layer. An empirical-theoretical dependence to calculate heat transfer in intense regimes of vibratory combustion of the solid biofuel has been obtained.

Actions of explosive loads of the protecting designs taking into account vibration combustion

Emergency explosions inside room (EIR) cause significant damage. The public increasingly reacts to them. The resident and industrial buildings are not counted on the action EIR in Russia despite the fact that industrial buildings can be recognized explosive. The use of safety structures (SS) is the only way to reduce the impact EIR. The action of SS is studied experimentally and theoretically exclusively for case of a quasistationary explosion and constant burning rate . In presented article the influence of the acceleration of burning and wave effects on the formation of explosive loads on the enclosing structures at EIR is studied. In particular, vibrational combustion is studied that generates standing waves and case of acceleration of combustion with the formation of blast wave. Standing nonlinear acoustic waves are generated against the back-ground of excess pressure and the outflow of gases at vibrational combustion. The pressure in standing waves is approximated by the sine. The frequency of oscillations corresponds to the basic mode of oscillation of the volume of hot explosive products. The amplitude of the oscillations depends on the geometric shape of the volume and the rate of explosive combustion at the onset of vibration combustion. Pressure perturbation from vibrational combustion are superimposed on the pressure profile of a triangular shape at the moment of maximum pressure. Profile is characterized by rise time and pressure drop time. So the formed lead acts on a system with elastic deformation with a concentrated mass. The maximum deformation and the coefficient of dynamism of the system are determined depending on the ratio of the frequency of the pressure oscillations in the acoustic oscillations of the rise and fail time of pressure, and frequency of natural oscillations of the system. The obtained results make it possible to clarify the calculation of the bearing capacity of buildings.

Study on optimization method of GDI engine combustion noise based on noise-performance map

An optimization of GDI engine combustion noise was evaluated through experimental and simulation methods. First, finite element model of engine was established; the vibration response and combustion noise caused by combustion incentives were calculated by the direct frequency response method and the acoustic transfer vector method. Above of this, the pure combustion noise attenuation curve was defined. According to the combustion spectrum calculated, the optimized frequency range was determined. Then, combining with the analysis result of the combustion noise attenuation curve, the frequency position of cylinder pressure spectrum to be optimized was obtained. Besides this, the combustion parameters were measured through test and its relationship to cylinder pressure spectrum and engine power performance was studied, the noise-performance map was established. Based on optimized cylinder pressure spectrum and noise-performance map, the optimum values of combustion parameter were marked very quickly. The results show that, when the fuel injection timing optimization value was used, combustion noise was reduced most by 6.4 dB in the range of 0â–“1000 Hz, while torque reduced only by 3.8 Nm, which achieved the goals of the favoring NVH performance and engine power performance.

Millisecond detonator with high delay precision

ABSTRACTWe identify the most important factor affecting the delay precision detonators by orthogonal experiments, thus optimize formulations to expect to get a better precision detonator recipe. Ultrafine ms delay due to the small particle size drug, the distance between the particles is small, a small gap, in the natural body of air the air is delayed relatively small, although the moisture absorption, but the overall water was reduced, and therefore can effectively avoid vibration combustion and second volume drift, therefore burning more stable, so the delay time stability, high delay precision, good storage performance.

Research on Vibration Combustion Mechanism of Rijke Tube

Research on Vibration Combustion Mechanism of Rijke Tube

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ АВТОКОЛИВАНЬ В РРД, ЩО ЗУМОВЛЕНІ НЕСТАЦІОНАРНИМ ВИТІКАННЯМ ГАЗІВ З РЕАКТИВНОГО СОПЛА

The mathematical model of general system instability in a liquid jet engine is obtained, taking into account the nonstationarity of the outflow of combustion products from the jet nozzle. The peculiarity of the variation of self-oscillations of vibration combustion is established depending on the geometric structure of the hydraulic characteristic of the jet nozzle. The possibility of decreasing the amplitude or complete suppression of the considered oscillations is justified. The theoretical description of vibrational combustion is represented by a system of equations for the mechanics of gases, in which the energy equation is reduced to the pressure characteristic of the heat supply. This made it possible to establish previously unknown mechanisms of this phenomenon caused by the formation of an ascending (unstable) branch on the pressure characteristic of the heat supply. Using the numerical integration of the obtained equations of the mathematical model of the self-oscillations under consideration, the nature of their dependence on the delay in combustion of fuel for various geometric types as a pressure characteristic of the heat supply as well as the hydraulic characteristics of the jet nozzle is established. The nature of the deformation of the limiting cycles of self-oscillations in the combustion chamber of LPRE is established, when mechanisms of both intra-chamber instability and flow from the jet nozzle are manifested. Using numerical simulation, an increase in the limiting cycle of self-oscillations is established with an increase in the delay time of combustion of fuel when the stationary regime is on a stable monotonically decreasing branch of the pressure characteristic of the heat supply. The expression for the critical delay time of fuel combustion is analytically obtained as a function of the acoustic parameters of the combustion chamber, its pressure characteristic and the hydraulic characteristic of the reactive nozzle. The obtained expression makes it possible to quantify the influence of these parameters on the boundary of the stability region of the stationary regime.

О возможности вибрационного горения при внутренних взрывах

Проанализированы условия возбуждения вибрационного горения в помещениях и аппаратах. Установлено, что главной причиной возбуждения является формирование волны разрежения в результате сокращения площади горения при взаимодействии пламени с ограждающими стенками. Показано, что волна разрежения возмущает горение таким образом, что скорость тепловыделения вызывает рост давления. Определено, что в объеме генерируются и усиливаются акустические волны, амплитудное давление в колебаниях которых в разы превышает давление квазистатического взрыва. Установлено также, что необходимыми условиями для вибрационного горения является способность стен отражать колебания и способность зоны горения возбуждаться под действием акустических колебаний, так что горение в углах стабилизируется и пламя не уносится через сбросное отверстие истекающими газами.

The consideration of the turbulence influence on the gas explosion expansion in non-closed areas

In the gas explosions simulation practice in non-closed areas there is a common opinion of burning rate increase at turbulization of initial gas mixture stream. The article shows that in conditions of turbulization there is no increase of the burn rate, but of the flame front area. A wording change of pressure rise reason does not lead to a change of the calculation results, but gives the opportunity to look at the problem differently and interpret a physical process correctly. In order to prove it there are results of the vibrational combustion modeling in terms of gas explosion in the cylinder with an opening on the side. The results show that along with the pressure fluctuation there is burning area size fluctuation that occur synchronous and with the same amplitude. The modeling basis is the system of differential equations, that describe the adopted in gas dynamics fundamental conservation laws, the equation of state, written in the so-called Euler’s form. The system is supplemented with flame spread conditions. The system solution is based on the Russian method of the numerical approximation of this system-the large-particle method.

Energy Loss and the Choice of Damper of Torsional Vibration Combustion Engines

The crankshaft is exposed to numerous external extortions which generate bending, axial and torsional vibrations. Torsional vibrations are especially dangerous for a safe operation. They are generated by strongly dynamic loads, which come from the combustion processes of fuel-air mixture in cylinders and from the elements of drive system, and engine accessories. Until recently this problem concerned mainly the engines of high power, where dynamic effects generated the vibrations with amplitudes exceeding the limit values, which in effect led to failure of the engine. Crankshafts also significantly increased their torsional elasticity because of the common trend of reducing the engine mass. It resulted in the necessity of using the elements reducing the amplitude of torsional vibrations of the shaft. Rubber torsional vibration dampers are commonly used for this purpose. The author observed that while choosing torsional vibration dampers, the producers concentrated only on the criterion of reducing the amplitude of torsional vibrations below limit values. They forgot that the optimization criterion can be expanded in such a way so that a better effect can be obtained. What is more, safe and economical operation of the engine could be provided.