Pulse Combustor Research Articles

Pulsating combustion of propane-butane fuel mixture with air in a vortex combustion chamber

In this paper pulsating combustion of a pre-mixed propane-butane fuel with air in a vortex combustion chamber is considered. In view of the insufficiency of information about the reasons of self-oscillations, it is necessary to determine the gas-dynamic, physical and chemical parameters that cause oscillations of the heat release rate in the vortex combustion chambers.

An effectiveness analysis of the pulsed resonant fuel combustion in the processes of steel­casting ladle drying and warming

This paper reports a technique of the pulsed resonant fuel combustion in the processes of drying and heating steel-casting ladles, devised to save fuel. The research method is based on the initiation of pulsations when burning fuel at a frequency equal to the frequency of natural fluctuations within the working volume of the ladle, which leads to the resonance of pulsations. This study aimed to define a technique to effectively burn fuel and to confirm a decrease in fuel consumption in the process of the pulsed resonant combustion. The experimental and industrial studies involving 8 drying operations and 5 ladle heating operations have established the possibility to comply with the normative requirements in line with the technological instructions at the level of 80‒100 %. The possibility to search for the pulsed resonance frequencies under industrial conditions has been confirmed, despite the negative impact of high temperatures, acoustic interference, and inertia of the equipment. The feasibility of a pulsation unit has been determined, as well as the possibility to steadily maintain, during the drying process, the required resonance frequencies of gas pulsations. A more intensive course of the drying process has been observed, which makes it possible to shorten the process duration and, accordingly, to reduce fuel consumption. The high excitability of resonance frequencies in the ladle during heating has been detected, due to the short length and volume of the section of a gas pipeline between the pulsation unit and burner compared to the drying bench. The warm-up intensity was noticeably higher than that of drying due to the lower end temperature of the lining (777‒910 °C instead of 900‒1,120 °C) and the lack of moisture evaporation. Using the pulsed resonant fuel combustion mode at the posts of intensive heating of ladles for melting makes it possible to force the heating by the resonant pulsation of the torch. During pulsed resonant combustion, the usable utilization of fuel heat increases markedly, which leads to an increase in the drying and heating processes efficiency and corresponding fuel economy. The decrease in the consumption of natural gas when drying the ladles amounted to 2.7÷26.1 %; at the warm-up ‒ 19.5÷37.8 %. These data indicate the energy efficiency of the pulsed resonant combustion and the feasibility of implementing a burning technique in the processes of ladle drying and warming

Mathematical Analysis and Simulation of Ahrens Model in Pulse Combustor

Ahrens model accepted large data of Kilicarslan but with some real differences. In Kilicarslan model, released heat in combustion having more I2R that is released under Ahrens. As per Ahrens if any specific object divides reaction and cool zone then heat release / cycle is very less compare with Kilicarslan. But with one condition of one object that is, it should be pressure independent otherwise density of reactants remains constant (or not enough increased); as a result, more heat released with less satisfied output. Mathematical model of Ahrens brief about object zones and its separation. This paper also brief about dynamic work function of tailpipe with adjustment of frequency which will proceed for system stability and its accuracy.

Characterizing nonlinear dynamic features of self-sustained thermoacoustic oscillations in a premixed swirling combustor

To meet stringent NOx emission requirements, lean premixed swirling combustion technology is widely applied in power generation and propulsion systems. However, such combustion systems are more susceptible to nonlinear combustion instability due to the fluid flow-acoustics-combustion interaction. It is typically self-exited and characterized by large-amplitude pulsating oscillations. By applying experimental measurements and theoretical modelling, we explore the rich physics of how a methane-burnt swirling flame sustains periodic pulsating combustion oscillations, and its nonlinear dynamics features via recurrence plots (RP) and 0–1 chaotic test. The effects of (1) the equivalence ratio Φ, (2) the volume flow rate Va of inlet air and (3) the swirling number SN are examined. Hopf Supercritical and period-doubling bifurcation behaviours are experimentally observed with increased Φ from lean to rich combustion. Same nonlinear features are theoretically modelled by using ‘kick-oscillator’ model representing combustion pulses and to capture periodic limit cycle behaviours followed by period-doubling bifurcation and transition to chaos. The deterministic or chaotic nature of the swirling combustor could be experimentally identified using classical approaches such as probability density functions (PDFs) and acoustics power spectrum in presence of combustion-sustained periodic fluctuations and 0–1 chaotic test method. When the combustor is experimentally operated under either lean (Φ ≤ 0.6) or rich (Φ ≥ 1.1) conditions, no self-sustained periodic acoustic fluctuations are generated. Furthermore the combustor is found to be more chaotic. The flame shapes (M- or V-shaped), colour, brightness and volumes are found to depend on SN strongly. The present findings are physically insightful on understanding nonlinear features of swirling flow-acoustics-flame interaction.

Practical applicability of the method for measuring pressure of controlled medium on the example of a pulsating combustion boiler

This paper proposes a new way to study the nature of vibration component of pressure change over time for an energy device. This method makes it possible to record and process measurement results, compare frequency characteristics at various points of the device working space, and evaluate the presence of defects in its work. The authors have identified the main problems of developing a measuring complex to study the nature of vibration component of the pressure change over time for an energy device, and numerical and field tests have been carried out.

Kerosene combustion in a supersonic flow

A new approach is proposed to the initiation of kerosene combustion in a supersonic airflow with the stagnation temperature below 2000 K, which consists of a pulsed-periodic gas-dynamic action on the flow. The experiments have shown that it is possible to implement a quasi-steady pulsed combustion mode by choosing the parameters of pulses: energy, duration, and frequency.

Pulsating combustion of solid particles in Helmholtz resonator type device

There are a number of works in which pulsating combustion of the wood particles in Helmholtz resonator type device was studied. The dependences of the frequency and amplitude of oscillations on the geometry of the device were determined. The aim of this work is to study the thermodynamic properties of pulsating combustion. P-V diagrams of pulsating combustion and the amplitude of oscillations of the heat release rate are determined. It is proved that the acoustic power generated in the combustion zone is the result of work performed on the gas during one oscillation cycle.

Characterization of LiFePO4 samples obtained by pulse combustion under various conditions of synthesis

Lithium iron phosphate (LiFePO4, LFP) is one of the widely used cathode materials for rechargeable lithium ion batteries. LFP batteries are widely used for electric vehicles and backup power due to their important advantages such as low cost, lifetime, efficiency, and reliability. There are still several technical challenges that need to be addressed: the increase of energy density or further reduction of their final cost. This paper concerned with the characterization of carbon coated LiFePO4 nanopowder cathode materials produced under different conditions by pulse combustion for providing energy to the reactor for the synthesis. The reactor was built according to the principles of the thermoacoustic burner on the basis of the Helmholtz resonator. The investigated nanopowders are synthesized by complete and incomplete combustion and calcined at 700 °C. The obtained samples were characterized by X-ray diffraction, Fourier transform infrared, Raman, and Mössbauer spectroscopy. Observed low-temperature magnetic phase transitions definitively identified the crystal phases. The morphology of samples was controlled by scanning electron microscopy. The aim of this work is to show that it is possible to achieve a desired crystal phase by pulse combustion in a relatively cheap and fast way. The extremely rapid synthesis of almost pure phase material is possible due to the reduction in size of interacting particles and to an enormous number of collisions between them as a result of strong turbulent flow associated with explosive combustion.

Experimental evaluation of CO, NO[formula omitted], formaldehyde and acetaldehyde emission rates in a combustion chamber with OEC under acoustic excitation

This study experimentally evaluates the interaction of the oxygen enhanced combustion (OEC) technique with the pulsating combustion technique by the acoustic excitation of flames, the effects of these techniques on atmospheric emissions of CO, NOx, formaldehyde and acetaldehyde, and the temperature of exhaust gases in diffusive and confined natural gas flames. The results showed a general trend of reductions in the emissions of CO and NOx with the enrichment of the oxidant with O2 and also under some conditions with an acoustically excited flame. The results showed that the acetaldehyde emissions decreased with the ratio of equivalence but increased in the presence of acoustic excitation. Formaldehyde emissions showed no significant trend. The results show that the simultaneous application of the OEC and acoustic excitation techniques in a controlled manner can reduce pollutant emissions and increase the efficiency of thermal combustion equipment.

A model of pulse combustion drying and breakup of colloidal suspension droplets

Pulsation of gas flow created in pulse combustion drying has been shown to increase the overall heat and mass transfer coefficients during the drying process, resulting in process intensification. Some studies reported that pulse combustion drying could produce particles that are much smaller, even down to nanoscale, than those produced with normal spray drying. It is still unclear when and why pulse combustion drying might produce so small particles. It was argued in previous studies that the droplets undergo breakup during the drying process, and the difference in balance between two pressures, namely osmotic pressure and Laplace pressure, is responsible for droplet fragmentation. A droplet will breakup when the osmotic pressure due to interaction of nanoparticles becomes greater than the Laplace pressure that keeps the droplet as a unit. In the more classical theory, breakup of a spherical droplet situated in a fluid flow is determined by whether the force exerted by the fluid flow on the droplet surface can overcome the surface tension force. In the current study, breakup of a nano-suspension droplet during pulse combustion drying is modelled. From the difference between Laplace pressure and osmotic pressure, a new variable named modified surface tension is introduced. The results of simulation show how the key parameters in pulse combustion drying as well as the colloidal droplet properties influence the droplet breakup. For easier colloidal droplet breakup, a large droplet, small nanoparticles, high surface charge, higher gas temperature, stronger gas oscillation, and relatively high frequency are favorable. It is shown that while droplet breakup can result from pulse combustion drying conditions, it cannot be the main mechanism that makes nanoparticle production possible.

Facile and rapid synthesis of Mo5SiB2-based ceramics from solid-phase combustion reaction with reducing stages

Thermite-based combustion reaction combining MoO3 and B2O3 as the oxidants, Al as the reductant, with Mo, Si, and B powders was conducted to fabricate Mo5SiB2–Al2O3 composites. Combustion synthesis involving co-reduction of MoO3 and B2O3 is less exothermic than that adopting MoO3 as the sole oxidizing agent. The resulting products with Mo5SiB2/Al2O3 ratios between 0.8 and 1.3 were synthesized from the MoO3/B2O3-based samples and those between 1.25 and 2.5 from the MoO3-based samples. These two combustion reactions were shown to have low activation energies of Ea = 60.7 and 86.5 kJ/mol, indicating that the SHS reactions involving aluminothermic reduction of either MoO3/B2O3 or MoO3 significantly reduce the kinetic barrier of forming Mo5SiB2. In particular, it was found that prolonged reaction times contributed to the improvement in evolution of Mo5SiB2 from intermediate phases (Mo3Si and MoB) for the samples with a reaction front speed slower than 4 mm/s or a pulsating combustion wave. The as-synthesized composites exhibit a dense morphology with connecting plate-like Mo5SiB2 grains.

About the intensification of convective heat transfer from combustion products to the walls of a cylindrical shaped pulsing combustion chamber

Franke’s critical dependence determines the theoretical relationship for the numbers Nu for pulsating and stationary flow regimes. It is based on the heat exchange intensification hypothesis due to the interaction of the pulsating velocity profile and the boundary layer near the heating surface. The article presents the results of studies to test the efficiency of the Franke’s ratio for a given range of pulsed combustion chamber diameters, as well as to determine the influence of the geometric parameters of the chamber on the convective heat transfer from the combustion products to the walls of the chamber

Recommendations for creating a noise silencer for the aerodynamic valve of the pulsating combustion chamber

At present, researches in the field of designing and introducing into thermal processes power plants based on pulsating combustion are actively carried out in many countries. The absence of a burner and the considerable pressure of the exhaust flue gas, which does not require a high chimney, remain operational even at excess pressure close to zero in the supply pipeline, which are additional advantages of the pulsating combustion chamber, which ensures its attractiveness in the heat and power sector of the market [1].

Characterizing hydrogen-fuelled pulsating combustion on thermodynamic properties of a combustor

Unlike hydrocarbon fuel, hydrogen is ‘green’ and attracting more and more attentions in energy and propulsion sectors due to the zero emission of CO and CO2. By applying numerical simulations, we explore the physics of how a hydrogen-burnt flame can sustain pulsating combustion and its impact on the thermodynamic properties of a standing-wave combustor. We also explain how implementing a heat exchanger can mitigate such pulsating combustion. The dynamic interactions of the unsteady flow-flame-acoustics-heater are examined by varying the mass flow rate ṁH2 and the heating bands’ surface temperature TH. The frequency and amplitude of the pulsating combustion are shown to depend strongly on ṁH2. In addition, varying TH is shown to lead to not only the molar fraction of the combustion species being changed but also the flame-sustained pulsating oscillations being mitigated somehow. Finally, nonlinearity is observed and identified in the unsteady flow velocity and the two heat sources.

Experimental study on the pre-evaporation pulse combustion of liquid fuel within a porous medium burner

Experimental studies are conducted to investigate the behaviors of pre-evaporation pulse combustion of liquid fuel within a porous medium burner. A controllable electric preheating system is developed to enhance the evaporation of droplet spray and auto-ignite the flammable vapor without second ignition. Base on the stability analysis of the preheating temperature and the calibration of the fuel flow, the characteristics of the pulse flame in a single injection duration are observed in detail. The thermal characters in terms of the temperature distribution are investigated, and the influences of equivalenceratio and the air flow on the temperature are discussed in the present work. Experimental results show that the pulse flame propagates in the manner of four-phases,i.e., the quasi-steady flame, the transient flame, the free flame and the preheating flame. While the quasi-steady flame keepsin a moving state with speed around 0.1 mm/s magnitude order, the propagation of transient flame is similarto a deflagration process with a significant speed of 1.2 m/s magnitude order. The minimum preheating temperature for full evaporation and sustainable combustion is necessary about 1023 K, and the maximum flame temperature achieves up to around 1300 K. As the equivalence ratio increases, an evident temperature improvement and a larger high temperature zone appear, however the propagation speed of the quasi-steady flame almost keeps constant. An increasing air flow plays a limited effect on the maximum temperature while it actually leads toa faster speed of the high temperature zone.

Dynamic Characterization of Pulse Combustion by Image Series Processing

This paper proposed a flame image processing method to characterize the dynamic progress of pulse combustion at different operation conditions. Experiments were carried out using a Helmholtz pulse combustor with a range of gas supply pressures that determine the operation conditions of the combustor. The spatial distribution, time-domain, and frequency-domain characteristics were proposed to characterize the dynamic behaviors of pulse combustion. Image segmentation was first adopted to divide the original image into the flame region and background. The center of gravity, non-uniformity, dispersity, and normalized flame area were then extracted to quantify the spatial distribution characteristics of the flame. Variations of the center of gravity, non-uniformity, dispersity, and normalized flame area with time were also obtained to describe the temporal features of the flame. The fast Fourier transform-based analysis was implemented to attain the frequency-domain features of the flame from the time series of the normalized flame area. Results show that the proposed method is effective in characterizing the spatial, temporal, and spectral features of the dynamic process in a pulse combustor. The promising results indicate that the proposed method can be used to monitor the operation conditions of the combustor, including its safety and stability, and provide comprehensive reference data for in-depth understanding of pulse combustion.

Fabrication of Mo5SiB2-based composites by combustion synthesis involving aluminothermic reduction of MoO3

Fabrication of Mo5SiB2–Al2O3 composites with a broad range of the Mo5SiB2/Al2O3 ratio was conducted by thermite-based combustion synthesis in the SHS mode. Thermite reagents of MoO3 + 2Al were introduced into two Mo‒Si–B ternary systems adopting amorphous boron and MoB as their respective boron source. The boron-containing samples were more energetic and were applied to produce composites with Mo5SiB2/Al2O3 from 1.25 to 2.5, beyond which combustion was extinct. The composites with Mo5SiB2/Al2O3 from 0.8 to 1.3 were prepared from less exothermic MoB-based samples. Besides causing a decrease in combustion velocity and reaction temperature, the increase of the Mo5SiB2/Al2O3 proportion led to a transformation in combustion wave propagation from a steady to pulsating mode. For the samples featuring a pulsating combustion wave, the reaction time at peak combustion temperatures was extended and then the evolution of Mo5SiB2 from intermediate phases (Mo3Si and MoB) was significantly improved. The deduced activation energy suggests a lower kinetic barrier for thermite-based combustion synthesis to fabricate Mo5SiB2-based composites. The microstructure of synthesized composites indicates that quadrangular Mo5SiB2 grains with an average size of 10–15 µm are tightly packed and irregular Al2O3 grains are randomly dispersed.

Detonation of a hydrogen-oxygen gas mixture in a plane-radial combustor with exhaustion toward the periphery in the regime of oxygen ejection

The results of experimental study concerning a continuous spin detonation of hydrogen-oxygen mixture in a flow-through plane-radial combustor with a diameter of 10 cm and with exhaustion toward the periphery in the regime of oxygen ejection are presented. In the experiment, the regimes of continuous spin detonation with one and two transverse detonation waves rotating with velocity D = 1.3÷1.43 and 1.45÷1.54 km/s, measured relative to the inner cylindrical surface of the combustor, respectively, and two near-sonic waves rotating with velocities of about 0.7 km/s have been observed. The waves of pulse combustion with frequencies of 4.4 – 3.6 kHz have been found for the first time. The structure of waves and flow in their vicinity has been studied.

Implementation of heterogeneous detonation in a pulsed combustor – PDE model

ABSTRACTThis work is devoted to the use of detonative combustion of a liquid fuel in technical devices to obtain a jet thrust. The experimental and theoretical aspects of the organization of detonation in heptane/air/oxygen mixtures are considered. The pulsed regime of detonation at a frequency of 50 Hz has been implemented for the first time in a small-size tube (25 mm in diameter and 740 mm in length). The physical and technical methods that could accelerate the deflagration-to-detonation transition have been studied. The influence of thermal activation of a combustible mixture prior to its ignition and of the special form of a porous obstacle on the magnitude of the predetonation distance is established. The degree of this influence depends on the component composition, equivalence ratio, and the degree of filling the tube with a mixture.

ACOUSTİC SİGNATURE OF TWO CUTTERS AND FOUR CUTTERS EV SWİRL STABİLİZED GASEOUS BURNERS

ABSTRACTToday’s gas turbine technology is established in a wide range of applications, including (i) the production of electrical power, (ii) thrust generation in turbojets and (iii) driving large size pumps and compressors. The greatest advantages of gas turbines against other prime mover systems e.g. steam turbine systems and piston engine systems, lie in its higher specific power, compact design and low initial costs based on power output.A major problem in gas turbine combustors is combustion instabilities which may cause many undesirable effects including; (a) increased noise levels, (b) oscillating thrust, (c) mechanical vibration that may lead to serious damage and even total loss of the system. These instabilities are characterized by large oscillations of the flow parameters, which in many circumstances may result in the inability of the combustion process to sustain these large oscillations; leading to partial or total flame blow-off. These combustion oscillations could, however be desirable as in pulsed combustors; as it enhance combustion intensity, increase thermal efficiency and reduce the emission of pollutants like NOx, CO and soot. In light of the above mentioned concepts, the present study is directed towards extending the previous studies on the recently introduced turbojet EV burner having two-circumferential swirling entry air passages by a four-circumferential swirling air entries configuration.This burner design concept appears to offer many advantages, including: The replacement of the traditional fixed vane swirler by circumferential swirling air passages; and hence not only minimizes blockage and allows prior premixing of fuel and air within the conically shaped entry section to the combustor but also eliminates possible risk in case of swirler blade damage.The study is an experimental investigations of the acoustic signature of a newly designed 4-slot EV burner. All the results are to be compared with those obtained by the previously developed 2-slot configuration. This allows the identification of the merits and/or drawbacks of both designs.