scholarly journals Experimental Study on Dynamic Combustion Characteristics in Swirl-Stabilized Combustors

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1609
Author(s):  
Donghyun Hwang ◽  
Kyubok Ahn
Keyword(s):  
Experimental Study ◽  
Heat Release ◽  
Dynamic Pressure ◽  
Combustion Instability ◽  
Flame Structure ◽  
Pressure Sensors ◽  
Necessary Condition ◽  
Rayleigh Criterion ◽  
Pressure Oscillations ◽  
Geometric Conditions

An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.

scholarly journals Measuring the phase between fluctuating pressure and flame radiation intensity in a cylindrical combustion chamber

2019 ◽  
Author(s):  
S. Gröning ◽  
J.S. Hardi ◽  
D. Suslov ◽  
M. Oschwald
Keyword(s):  
Energy Transfer ◽  
Phase Shift ◽  
Heat Release ◽  
Acoustic Pressure ◽  
Dynamic Pressure ◽  
Rocket Engine ◽  
Pressure Sensors ◽  
Pressure Oscillations ◽  
Flame Radiation ◽  
Rate Oscillations

The energy transfer from the heat release of the combustion to the acoustic pressure oscillations is the driving element of combustion instabilities. This energy transfer is described by the Rayleigh criterion and depends on the phase shift between the pressure and heat release rate oscillations. A research rocket engine combustor, operated with the propellant combination hydrogen/oxygen, was equipped with dynamic pressure sensors and fibre optical probes to measure the flame radiation. This setup has been used for a phase shift analysis study which showed that unstable operation is characterized by a phase shift leading to an energy transfer from the heat release to the acoustic pressure oscillations.

The Histogram of Pressure Oscillations Amplitudes, in Lean Premixed Combustions, Caused by Thermo-Acoustic Instabilities

2010 ◽  
Author(s):  
Nasser Seraj Mehdizadeh ◽  
Nozar Akbari
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Combustion Instability ◽  
Premixed Combustion ◽  
Space Distribution ◽  
Rayleigh Criterion ◽  
Pressure Oscillations ◽  
Lean Premixed

Lean premixed combustion is widely used in recent years as a method to achieve the environmental standards with regard to NOx emission. In spite of the mentioned advantage, premixed combustion systems, with equivalence ratios less than one, are susceptible to the combustion instability. To study the lean combustion instability, by experiments, one premixed combustion setup, equipped with reactant supplying system, is designed and manufactured in Amirkabir University of Technology. In this research, gaseous propane is introduced as fuel and several experiments are performed at nearly atmospheric pressure, with equivalence ratios within the range of 0.7 to 1.5. In this experiments fuel mass flow rate is varied between 2 and 4 gr/s. Unstable operating condition has been observed in combustion chamber when equivalence ratio is less than one. To distinguish the combustion instability for various operating conditions, probability density functions, spectral diagrams, and space distribution of pressure oscillations, along with Rayleigh Criterion, are utilized. Accordingly, effect of equivalence ratio on stabilizing the unstable combustion system is investigated. Moreover, convective delay time is calculated for all experiments and the results are compared with Rayleigh Criterion. This comparison has shown good agreement the experimental results and Rayleigh Criterion. Finally, stability limits are identified based on inlet mass flow rate and equivalence ratio.

Vortex-driven acoustically coupled combustion instabilities

1987 ◽  
Vol 177 ◽  
pp. 265-292 ◽  
Author(s):  
Thierry J. Poinsot ◽  
Arnaud C. Trouve ◽  
Denis P. Veynante ◽  
Sebastien M. Candel ◽  
Emile J. Esposito
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
Combustion Instability ◽  
Low Frequency ◽  
Combustion Instabilities ◽  
Rayleigh Criterion ◽  
Phase Average ◽  
Steady Heat

Combustion instability is investigated in the case of a multiple inlet combustor with dump. It is shown that low-frequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system. Using spark-schlieren and a special phase-average imaging of the C2-radical emission, the fluid-mechanical processes involved in a vortex-driven mode of instability are investigated. The phase-average images provide maps of the local non-steady heat release. From the data collected on the combustor the processes of vortex shedding, growth, interactions and burning are described. The phases between the pressure, velocity and heat-release fluctuations are determined. The implications of the global Rayleigh criterion are verified and a mechanism for low-frequency vortex-driven instabilities is proposed.

Control of Combustion Driven Oscillations by Equivalence Ratio Modulations

1999 ◽  
Author(s):  
Christian Oliver Paschereit ◽  
Ephraim Gutmark ◽  
Wolfgang Weisenstein
Keyword(s):  
Control System ◽  
Heat Release ◽  
Fuel Injection ◽  
Combustion Instability ◽  
Combustion Process ◽  
Sudden Expansion ◽  
Pressure Oscillations ◽  
Reduced Pressure ◽  
Axisymmetric Mode ◽  
Recirculating Flow

Unstable thermoacoustic modes were investigated and controlled in an experimental low-emission swirl stabilized combustor, in which the acoustic boundary conditions were modified to obtain combustion instability. Several axisymmetric and helical unstable modes were identified for fully premixed conditions. The combustion structure associated with the different unstable modes was visualized by phase locked images of OH chemiluminescence. The axisymmetric mode showed large variation of the heat release during one cycle, while the helical mode showed variation in the radial location of maximal heat release. The helical and axisymmetric unstable modes were associated with flow instabilities related to the recirculating flow in the wakelike legion on the combustor axis and shear layer instabilities at the sudden expansion (dump plane), respectively. A closed loop active control system was employed to suppress the thermoacoustic pressure oscillations and to reduce undesired emissions of pollutants during premixed combustion. Microphone and OH emission detection sensors were utilized to monitor the combustion process and provide input to the control system. High frequency valves were employed to modulate the fuel injection. The specific design of the investigated experimental burner allowed testing the effect of different modulated fuel injection concepts on the different combustion instability modes. Symmetric and antisymmetric fuel injection schemes were tested. Suppression levels of up to 12 dB in the pressure oscillations were observed. In some cases a concomitant reductions of NOx and CO emissions were obtained, however, in other instances increased emissions were recorded at reduced pressure oscillations. The effect of the various pulsed fuel injection methods on the combustion structure was investigated.

Experimental Study of a Jet-Driven Helmholtz Oscillator

1979 ◽  
Vol 101 (3) ◽  
pp. 383-390 ◽  
Author(s):  
Thomas Morel
Keyword(s):  
Experimental Study ◽  
Dynamic Pressure ◽  
Helmholtz Resonator ◽  
Chamber Pressure ◽  
Geometrical Parameters ◽  
Pressure Oscillations ◽  
Loud Sound ◽  
Optimum Range ◽  
Round Jet ◽  
Jet Velocities

This paper describes an experimental study of a Helmholtz resonator driven by a round jet passing through it. This device, dubbed the jet-driven Helmholtz oscillator (JDHO), is a rigid chamber with two round openings located coaxially in two opposite walls, through which a jet is allowed to pass across the chamber. At certain jet velocities, jet instabilities couple with the Helmholtz resonance to produce very powerful chamber-pressure oscillations at a frequency slightly higher than the chamber Helmholtz frequency. The amplitude of these pressure oscillations may reach values of up to 5.6 times the jet dynamic pressure. Simultaneously, the exiting flow pulsates at the same frequency with an amplitude of up to 60 percent of the exit jet velocity, and a loud sound is emitted. The thrust of the present study was twofold: to determine the optimum range of geometrical parameters producing the maximum magnitudes, and to identify the mechanisms underlying the oscillator operation.

Combustion instability characteristics in a dump combustor using different hydrocarbon fuels

2019 ◽  
Vol 123 (1263) ◽  
pp. 586-599
Author(s):  
D. Hwang ◽  
Y. Song ◽  
K. Ahn
Keyword(s):  
Dynamic Pressure ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Hydrocarbon Fuels ◽  
Chamber Length ◽  
Dump Combustor ◽  
Geometric Conditions ◽  
Power Spectral ◽  
Dynamic Combustion

ABSTRACTThe combustion instability characteristics in a model dump combustor with an exhaust nozzle were experimentally investigated. The first objective was to understand the effects of operating conditions and geometric conditions on combustion instability. The second objective was to examine more generalised parameters that affect the onset of combustion instability. Three different premixed gases consisting of air and hydrocarbon fuels (C2H4, C2H6, C3H8) were burnt in the dump combustor at various inlet velocity, equivalence ratio and combustion chamber length. Dynamic pressure transducer and photomultiplier tube with a bandpass filter were used to measure pressure fluctuation and CH* chemiluminescence data. Peak frequencies and their maximum power spectral densities of pressure fluctuations at same equivalence ratios showed different trends for each fuel. However, the dynamic combustion characteristics of pressure fluctuations displayed consistent results under similar characteristics chemistry times regardless of the used hydrocarbon fuels. The results showed that characteristic chemistry time and characteristic convection time influenced combustion instabilities. It was found that the convective-acoustic combustion instability could be prevented by increasing the characteristic chemistry time and characteristic convection time.

Statistical study on engine knock oscillation and heat release using multiple spark plugs and pressure sensors

Fuel ◽  
2021 ◽  
Vol 297 ◽  
pp. 120746
Author(s):  
Hao Shi ◽  
Kalim Uddeen ◽  
Yanzhao An ◽  
Yiqiang Pei ◽  
Bengt Johansson
Keyword(s):  
Heat Release ◽  
Statistical Study ◽  
Pressure Sensors ◽  
Engine Knock

Active Control of Combustion Instability Using Symmetric and Asymmetric Premix Fuel Modulation

2007 ◽  
Author(s):  
Daniel Guyot ◽  
Christian Oliver Paschereit
Keyword(s):  
Heat Release ◽  
Closed Loop ◽  
Modulation Frequency ◽  
Combustion Instability ◽  
Open Loop ◽  
Closed Loop Control ◽  
Nox Emissions ◽  
Loop Control ◽  
Asymmetric Modulation ◽  
Control Schemes

Active instability control was applied to an atmospheric swirl-stabilized premixed combustor using open loop and closed loop control schemes. Actuation was realised by two on-off valves allowing for symmetric and asymmetric modulation of the premix fuel flow while maintaining constant time averaged overall fuel mass flow. Pressure and heat release fluctuations in the combustor as well as NOx, CO and CO2 emissions in the exhaust were recorded. In the open loop circuit the heat release response of the flame was first investigated during stable combustion. For symmetric fuel modulation the dominant frequency in the heat release response was the modulation frequency, while for asymmetric modulation it was its first harmonic. In stable open loop control a reduction of NOx emissions due to fuel modulation of up to 19% was recorded. In the closed loop mode phase-shift control was applied while triggering the valves at the dominant oscillation frequency as well as at its second subharmonic. Both, open and closed loop control schemes were able to successfully control a low-frequency combustion instability, while showing only a small increase in NOx emissions compared to, for example, secondary fuel modulation. Using premixed open loop fuel modulation, attenuation was best when modulating the fuel at frequencies different from the dominant instability frequency and its subharmonic. The performance of asymmetric fuel modulation was generally slightly better than for symmetric modulation in terms of suppression levels as well as emissions. Suppression of the instability’s pressure rms level of up to 15.7 dB was recorded.

scholarly journals Manufacturing of Microfluidic Devices with Interchangeable Commercial Fiber Optic Sensors

Sensors ◽  
2021 ◽  
Vol 21 (22) ◽  
pp. 7493
Author(s):  
Krystian L. Wlodarczyk ◽  
William N. MacPherson ◽  
Duncan P. Hand ◽  
M. Mercedes Maroto-Valer
Keyword(s):  
Porous Structure ◽  
Steady Flow ◽  
Microfluidic Device ◽  
Fiber Optic ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Microfluidic Devices ◽  
Fiber Optic Sensors ◽  
Valuable Insight ◽  
Local Pressure

In situ measurements are highly desirable in many microfluidic applications because they enable real-time, local monitoring of physical and chemical parameters, providing valuable insight into microscopic events and processes that occur in microfluidic devices. Unfortunately, the manufacturing of microfluidic devices with integrated sensors can be time-consuming, expensive, and “know-how” demanding. In this article, we describe an easy-to-implement method developed to integrate various “off-the-shelf” fiber optic sensors within microfluidic devices. To demonstrate this, we used commercial pH and pressure sensors (“pH SensorPlugs” and “FOP-MIV”, respectively), which were “reversibly” attached to a glass microfluidic device using custom 3D-printed connectors. The microfluidic device, which serves here as a demonstrator, incorporates a uniform porous structure and was manufactured using a picosecond pulsed laser. The sensors were attached to the inlet and outlet channels of the microfluidic pattern to perform simple experiments, the aim of which was to evaluate the performance of both the connectors and the sensors in a practical microfluidic environment. The bespoke connectors ensured robust and watertight connection, allowing the sensors to be safely disconnected if necessary, without damaging the microfluidic device. The pH SensorPlugs were tested with a pH 7.01 buffer solution. They measured the correct pH values with an accuracy of ±0.05 pH once sufficient contact between the injected fluid and the measuring element (optode) was established. In turn, the FOP-MIV sensors were used to measure local pressure in the inlet and outlet channels during injection and the steady flow of deionized water at different rates. These sensors were calibrated up to 140 mbar and provided pressure measurements with an uncertainty that was less than ±1.5 mbar. Readouts at a rate of 4 Hz allowed us to observe dynamic pressure changes in the device during the displacement of air by water. In the case of steady flow of water, the pressure difference between the two measuring points increased linearly with increasing flow rate, complying with Darcy’s law for incompressible fluids. These data can be used to determine the permeability of the porous structure within the device.

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