Active Combustion Control Research Articles

Development and testing of a discrete coil magnetostrictive actuator

Active combustion control (ACC) technology is an effective measure for suppressing the combustion oscillation of aero-engines. The magnetostrictive actuator is the most suitable choice for the ACC actuator due to its excellent high-frequency characteristics and high-temperature resistance. In order for the magnetostrictive actuator to produce high-frequency displacement, the constant current driver must have sufficient power, which results in a larger mass of the driver. A solution is to use multi-channel and low-power constant current driver. Therefore, the coil of the magnetostrictive actuator is axially dispersed and driven by two four-channel servo amplifiers. The driver’s mass is significantly reduced while maintaining the same electromagnetic conversion effect. In addition, an analytical model of a discrete coil magnetostrictive actuator is established, and a series of experiments are conducted. The maximum hysteresis error of output displacement at 200 Hz is reduced by 15.2%. Furthermore, under PID closed-loop control, the root mean square (RMS) error is less than 2% when tracking a 10 Hz sinusoidal displacement with coil switching drive.

Detection of Precursors of Thermoacoustic Instability in a Swirled Combustor Using Chaotic Analysis and Deep Learning Models

This paper investigates the role of chaotic analysis and deep learning models in combustion instability predictions. To detect the precursors of impending thermoacoustic instability (TAI) in a swirled combustor with various fuel injection strategies, a data-driven framework is proposed in this study. Based on chaotic analysis, a recurrence matrix derived from combustion system is used in deep learning models, which are able to detect precursors of TAI. More specifically, the ResNet-18 network model is trained to predict the proximity of unstable operation conditions when the combustion system is still stable. The proposed framework achieved state-of-the-art 91.06% accuracy in prediction performance. The framework has potential for practical applications to avoid an unstable operation domain in active combustion control systems and, thus, can offer on-line information on the margin of the combustion instability.

The Effects of Solvent Extraction on the Functional Group Structure of Long-Flame Coal

The functional group structures of coal molecules are one of the most important factors affecting spontaneous combustion. However, it is difficult to determine the exact effects of such structures. Extraction technology is able to modify the functional groups in coal as a means of inhibiting spontaneous combustion reactions. The present work extracted coal from the Caojiatan mine in northern Shaanxi, China, with various solvents. The extraction effectiveness of these solvents was found to decrease in the order of dioctyl sulfosuccinate (AOT) > water > n-hexane > cyclohexane + AOT + ethanol > cyclohexane > ethanol > methanol. With the exception of the AOT, the concentration of functional groups in the extracted coal was decreased compared with that in a control specimen extracted using only water. Ethanol, n-hexane, and methanol provided the optimal extraction efficiencies in terms of capturing coal molecules with aromatic structures, aliphatic structures, and oxygen-containing groups, respectively. The results of this work are expected to assist in future research concerning the extraction of coal molecules with specific functional groups. This work also suggests new approaches to the active prevention and control of spontaneous combustion during the mining, storage, and transportation of coal.

Temperature dependence modeling and experimental evaluation of a multidimensional discrete magnetostrictive actuator

Active combustion control has shown a bright prospect for suppressing aero-engine combustion oscillations but also puts forward higher requirements for the actuator on the high bandwidth, large stroke, and high weight-power ratio. A multidimensional discrete magnetostrictive actuator proposed in our previous work can meet these requirements simultaneously. However, the temperature of the working environment around the aero-engine is high, so it is essential to further investigate the temperature-dependent characteristics of the actuator. In this paper, a multi-physics coupled temperature-dependent analytical model is developed, and the influence mechanism of temperature on the actuator is analyzed from the perspective of physics with a wide field of view from the material level to the actuator system level. Experiments based on a fabricated prototype were conducted and the results indicate that both the stroke, hysteresis, and closed-loop tracking performance of the actuator decrease with the increase in temperature, but the temperature has little effect on the frequency response; the proposed analytical model can accurately describe the temperature-dependent output characteristics of the multidimensional discrete magnetostrictive actuator, the root mean square error of which is less than 3% within 200 Hz.

Meticulous Graded and Early Warning System of Coal Spontaneous Combustion Based on Index Gases and Characteristic Temperature.

The accurate prediction of coal spontaneous combustion (CSC) in the goaf areas of coal mines is a vital aspect of the migration from passive to active fire prevention and control. However, CSC is highly complicated and existing technologies cannot accurately monitor coal temperatures over wide expanses. Thus, it may be beneficial to assess CSC based on various index gases produced by the reactions of coal. In the present study, the CSC process was simulated by temperature-programmed experiments, and the relationships between index gas concentrations with the coal temperature were determined using logistic fitting functions. CSC was divided into seven stages, and a coal seam spontaneous ignition early warning system involving six criteria was established. Field trials demonstrated that this system is a viable approach to predicting coal seam fires and meets the requirements for the active prevention and control of coal combustion. This work establishes an early warning system based on specific theoretical guidelines that permits the identification of CSC and the implementation of active fire prevention and extinguishing measures.

Ozone-assisted low temperature oxidation of methanol and ethanol

Ozone-assisted combustion is an advanced combustion technology that is considered a promising means for the active control of combustion. Ozone addition can enhance combustion processes and extend the experimental parameters to extreme conditions. In this work, ozone-assisted low temperature oxidation of methanol and ethanol in a jet-stirred reactor (JSR) was carried out at atmospheric pressure, with a fuel initial mole fraction of 0.005, an equivalence ratio of 0.28, and in the temperature range of 330–800 K. Significant conversions of methanol and ethanol were observed in the low temperature region when ozone was added. Numerous intermediate species were analyzed and quantified by synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography, which are crucially important for unraveling the low temperature oxidation reaction network. The kinetic model of NUIGMech1.1 is tentatively updated to better explain the measured results, although the improvements of the C1–C2 core mechanisms are difficult. Ozone addition enhances the action of the reaction channel of related radicals. Model analysis shows that the kinetics of Ö/ȮH/HȮ2 atoms/radicals are crucial for the overall reaction progress, as well as the reaction of HȮ2 radicals with ozone, which mainly contributes to the formation of ȮH radicals during the initial reaction stage. Inconsistency between measurements and model predictions highlights the considerable uncertainty in the C1-C2 alcohols subchemistry at lower temperatures. The experimental results obtained in this work and model development will motivate further study of the low temperature oxidation chemistry of methanol and ethanol.

Flame temperature and heat release rate sensor for active combustion control

Accurate and real-time measurement of combustion chamber flame temperature and heat release rate (HRR) is critical for active control of combustion instability. This paper developed a flame temperature and HRR sensor based on radical emission spectroscopy. The sensor contains two optical acquisition channels with different responses to detect the spectral intensities of two different bands of hydroxyl (OH*). Optical acquisition channels contain optical filters, photodiodes, and photocurrent amplifier circuits. The single band spectral intensity can reflect the fluctuation of the HRR. The flame temperature can be calculated by the ratio of the spectral intensities of the two bands. The optimal detection bands are determined as 310.2–320.1 nm and 303.7–309.0 nm based on the genetic algorithm. In the temperature range of 1700–1900 K, the sensor achieved a precision of ±10 K, and the sensor successfully detects the HRR oscillation with a main frequency of 326 Hz.

Development and Characteristic Investigation of a Multidimensional Discrete Magnetostrictive Actuator

Active combustion control (ACC) has been proved to be an effective method for the suppression of pressure oscillation in aero engine combustion chambers, which will seriously endanger flight safety of aircrafts. However, the actuators for ACC need to work with a bandwidth of 1000 Hz, a stroke up to submillimeter level and a high power density simultaneously. Existing electromagnetic actuators, or smart material actuators, are still unable to meet these requirements at the same time. To address this issue, in this article, a multidimensional discrete magnetostrictive actuator (MDMA) was developed by adopting the multidimensional discrete configuration. In order to obtain large output displacement while maintaining the characteristics of high bandwidth and high power density of magnetostrictive materials, tubular and cylindrical magnetostrictive rods are nested axially and radially through sleeves to form a discrete magnetostrictive stack; independent excitation coils and permanent magnet rings are integrated axially to form a discrete electromagnetic excitation system. Then, a magnetic equivalent circuit (MEC) model was developed to analyze the magnetic field distribution characteristic of MDMA components. Next, a multiphysics comprehensive dynamic model was established to describe the complex dynamic properties of multidimensional discrete structures. Subsequently, a prototype of the MDMA was fabricated, which is only 56 mm in diameter and only 71.5 mm high. Experimental results indicate that, the proposed MDMA reaches a stoke of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m, and the working bandwidth can exceed 1000 Hz. Furthermore, closed-loop control tests were conducted and the results showed that the MDMA can effectively track sinusoidal references of different amplitudes under low frequency with a feedback PID controller.

Characterisation and comparison of unsteady actuators: a fluidic oscillator and a sweeping jet

PurposeThe purpose of this study is to compare two unsteady actuators: an oscillator and a sweeping jet. Both actuators can produce an oscillating jet of different amplitudes and frequencies without any moving parts, making them an attractive actuator concept. The Coanda effect phenomenon can explain the operating principles of these two unsteady actuators.Design/methodology/approachA numerical study was conducted to compare the amplitudes and frequencies of fluidic and sweeping jet (SJ) oscillators to obtain an efficient actuator to control separated flows at high Reynolds numbers. For this goal, two-dimensional unsteady Reynolds-averaged Navier-Stokes simulations were carried out using computational fluid dynamics (CFD) fluent code to evaluate the actuator performances. The discrete fast Fourier transform method determined the oscillation frequencies.FindingsThe oscillation frequencies gradually increase as the inlet pressure increases. The characteristics and dimensions of the vortices produced in the mixing chamber and feedback loops vary overtime when the injected fluid is swept sideways. The frequencies supplied by the SJ are stronger than those obtained by the fluidic oscillator, which may contribute to improving the aerodynamic performance at a lower power supply cost.Originality/valueThe existence of the splitter in the fluidic oscillator led to the production of separate pulses, which would be useful in various industrial applications, including active control of combustion and mixing processes while other applications such as flow separation control require SJs. With the latter actuator higher and interesting frequencies can be obtained, leading to efficient flow control.

The Possibility of Active Attitude Control for Fuel Spray

Abstract The internal combustion engine (ICE) is an attractive power source for automobiles, with its superior storability, transportability, and suppliability of liquid fuel with high energy density. Compact ICEs with high performance and a low environmental load are greatly needed. In the future, smart active control of combustion by means of fuel spray injection must be considered as a breakthrough technology to address serious issues related to conventional ICEs, such as emissions. A designed fuel injection rate and spray pattern during the injection period have been technically developed, and combustion can be partially controlled in the conventional ICE. However, spatial fuel distribution is not progressing as desired in the field of combustion; thus, new and effective active control technologies for fuel spray are very necessary for the smart control of combustion. Cavitation, flash boiling, spray-to-spray interaction, spray-to-wall interaction, and air flow have potential as a basis for active attitude control of fuel spray. This article uses evidence from the literature to discuss the possibility of active spray attitude control for future fuel spray combustion technology in a smart compact ICE.

Active Control of Coaxial Jet Mixing and Combustion with Axisymmetric and Non-axisymmetric Mode Excitations

Coaxial jet mixing and combustion are actively controlled through manipulation of the vortical structures and the associated mixing with twelve micro jet actuators installed on the annular nozzle. The different azimuthal mode examined here are the fundamental axisymmetric mode and the alternative mode. In the alternative mode, six adjacent micro jets are driven out-of-phase with the other six. The alternative mode provides a phase difference in the generation of the left and right side vortices and avoids interference between these vortices, so that larger vortices are developed if compared to the axisymmetric mode. The effect of the different azimuthal modes on the mixing and the exhaust gas characteristics are discussed.

Manipulation of Large-Scale Vortical Structures and Mixing in a Coaxial Jet with Miniature Jet Actuators Toward Active Combustion Control

Manipulation of large-scale vortical structures and associated mixing in a methane-air coaxial jet is carried out by using miniature jet actuators installed on the inner surface of the annular nozzle. The periodic radial miniature jet injections are achieved with a rapid-response servo-valve. The spatio-temporal primary jet structures are investigated through phase-locked 2C-PIV (2 Component Particle Image Velocimetry) and stereoscopic-PIV. It is found that intense ring-like vortices are produced perfectly in phase with the periodic miniature jet injections regardless of the valve-driven frequency fv examined. When the Strouhal number Stv, which is defined with fv, is larger than unity, the ring-like vortices are densely formed and thus methane/air mixing is prompted with low periodic fluctuation. The diameter of the vortices becomes small as Stv is increased, so that the transport range of the inner methane and outer air fluids can be controlled by changing Stv. In addition, the evolution of counter-rotating vortex pair is also observed in the cross-sectional plane. These streamwise vortices are directly formed as a result of the radial miniature jet injection, which leads to entrainment of the ambient fluid near the primary jet shear layer, and they also contribute to the mixing enhancement. Moreover, it is demonstrated that coaxial jet flame characteristics such as carbon monoxide (CO) emission and flame holding can be drastically improved under different equivalence ratios by the present jet control scheme.

Inverse diffusion and partially premixed flames with elliptical/swirling- and cross-flows

The combustion performance of inverse diffusion and partially premixed flames was optimized by employing concentric elliptical ports with variable relative angular orientation, co-swirling, and cross-flow opposing jets of different inclination angles. The flexible and favorably active control of combustion was pronounced by changing the nozzle relative angular orientation. The optimum angular shift was found to be 20° where the flame length was shortened by 39% from the case of 0° and the NOx levels were reduced to about 0.51 g/kg of fuel for the inverse partially premixed flames. At such optimum angular shift, the minimum CO and NOx emissions respectively decreased to 17.1 and 1.52 g/kg of fuel for the inverse diffusion flames. The elliptical jets increased the size of the swirling flow recirculation zone by about 28%. Increasing the inner aspect ratio consistently increased the combustion efficiency, where the CO emissions reach minimum values of 12.3 and 6.22 g/kg of fuel respectively for the inverse diffusion and partially premixed flames. The correspondingly minimum NOx emissions were thus 0.89 and 0.51 g/kg of fuel at a cross-flow momentum flux ratio of 2.0. Splitting the opposing cross-flow air jets by increasing their inclination angle above 0° duplicated the stagnation zone vortical impact to enrich the average turbulent energy at the major axis tips. The inclination angle of 15° was the optimum at no swirl while increasing the outer swirl angle shifted the optimum inclination angle to 25°. The inner/outer co-swirl of 45°/60° thus provided a minimum CO emission of 11.1 g/kg of fuel for the inverse diffusion flame and 2.65 g/kg of fuel for the inverse partially premixed flame.

Active Control of Methane-Air Coaxial Jet Mixing and Combustion with Arrayed Miniature Jet Actuators

Large-scale vortical structures and associated mixing in a methane-air coaxial jet are actively controlled by manipulating the initial jet shear layer with miniature jet actuators installed on the inner surface of the annular nozzle. The periodic radial miniature jet injections are realized by using a rapid-response pneumatic servovalve, and sinusoidal/pulsed flowing are employed in the present study. The spatio-temporal primary jet structures are investigated through phase-locked 2C-PIV (2 Component Particle Image Velocimetry) and Stereoscopic-PIV. In the pulsed configuration, it is found that intense vortex rings are produced in phase with the periodic control input regardless of the valve-driven frequency fv examined. When the Strouhal number Stv, which is defined with fv, is larger than unity, the vortex rings are densely-shed and thus methane/air mixing is prompted with low periodic fluctuation. The diameter of the vortices becomes small as Stv is increased, so that the transport range of the inner methane and outer air fluids can be controlled by changing Stv. In addition, the evolution of counter-rotating streamwise vortex pair is also confirmed. These streamwise vortices are formed as a result of the radial injection of the miniature jet, which leads to entrainment of the ambient fluid near the primary jet shear layer. They contribute the mixing enhancement in the downstream, where the vortex rings are broken down. Moreover, it is demonstrated that the coaxial jet flame characteristics such as flame holding are drastically improved by the present jet control scheme.

Ni-based microvalves for flow modulation: Toward active combustion control

We report on the development of nickel-based micro diaphragms for fuel flow modulation during jet engine combustion. The micro diaphragms were fabricated and assembled, after which they were tested in a prototype mesoscale fuel injector. A combination of deep reactive etching, silicon loss molding, electroplating, and conventional machining techniques were utilized to implement the mesoscale fuel injector and the nickel diaphragms. Modulation of fluid flow through the fuel injector was demonstrated with the nickel diaphragm functioning as a valve. The diaphragms were characterized and the measured results were compared with results from finite element analysis. The fuel injector was characterized for flow rate versus applied fluid pressure and these results were compared with computational fluid dynamics results. The primary goal of this work is to demonstrate the concept of flow modulation using a nickel-based diaphragm, with future generations planned to be implemented in silicon carbide. Future application of this technology will be in active combustion control to mitigate combustion instabilities in jet engines when they occur.

Behavior of a small diffusion flame as an electrically active component in a high-voltage circuit

Active control of combustion is challenging because there are few actuators with sufficient power to overcome the effects associated with the significant energy release associated with flames. The control leverage afforded by adjusting the fuel stream has so far been the most effective for this purpose. Naturally occurring flame ions allow an alternative control option via external electric fields, and this mechanism has been investigated, in experimental analysis of small non-premixed flame acted on by a high-voltage grid. During the course of these studies, the voltage–current characteristics of air–methane flames has been identified. This article describes how electric fields acting on flame ions affect the local convective environment and produce a very characteristic electrical behavior that can be analyzed as part of an electrical circuit for control in order to produce a desired flame response, using the ion production as a sensor for overall reaction intensity and a fairly simple PID control algorithm to effect the desired flame response.

Combustion measurement of thermoacoustic oscillating flames by diode-laser absorption spectroscopy sensors

Diode-laser absorption spectroscopy has been applied to a swirl-stabilized turbulent combustor to detect high frequency combustion oscillation and combustion state related to combustion noise. Two diode-laser absorption spectroscopy techniques of scanned-wavelength method and fixed-wavelength method are adopted. In the scanned-wavelength method, fluctuations of temperature and H 2O mole fraction up to 1 kHz are detected. Two dominant peak frequencies of power spectra of these fluctuations, which are about 125 Hz and 140 Hz, coincide with those of pressure fluctuation in the combustor. In the case of control by secondary fuel injection, the energy at peak frequency of temperature and H 2O mole fraction decreases in accordance with noise reduction. Similar to the combustion noise, temperature fluctuation shows a minimal value at the appropriate frequency of secondary fuel injection. By analysing transmitted signals, the fixed-wavelength method provides power spectra similar to those obtained by the scanned-wavelength method. The advantage of the fixed-wavelength method is capability of detection of high frequency combustion oscillation more than 1 kHz. These results prove that the diode-laser absorption spectroscopy has great applicability as sensors for the combustion measurement of thermoacoustic oscillating flames and active control of turbulent combustion.

Active Combustion Control Using a Fluidic Oscillator for Asymmetric Fuel Flow Modulation

Fluidic oscillators are of special interest for fuel-based active control schemes featuring high frequency fuel flow modulation, as they are much more durable then conventional valves due to the absence of fast moving parts. In this work the performance of a fluidic oscillator in an active combustion control scheme is demonstrated. The oscillation frequency was controlled by varying the inlet mass flow of the oscillator. High speed camera recordings and hot wire measurements were performed to investigate the fluidics' oscillation characteristics. The oscillator was then incorporated into a bluff body burner, where it modulated parts of the fuel flow blended with nitrogen. Pressure and heat release fluctuations in the combustor were recorded and images of the flame were taken. At stable combustion the spectra of the heat release signals showed a clear peak corresponding to the fluidics' oscillation frequency, thus validating the ability of the oscillator to influence the combustion process. When operating ...

179 急速圧縮装置を用いた高温・高圧下での炭化水素-空気混合気の燃焼特性の能動的燃焼制御(熱工学I)

179 急速圧縮装置を用いた高温・高圧下での炭化水素-空気混合気の燃焼特性の能動的燃焼制御(熱工学I)

Homogeneous charge compression ignition: the future of IC engines?

The Homogeneous Charge Compression Ignition Engine, HCCI, has the potential to combine the best of the Spark Ignition and Compression Ignition Engines. With high octane number fuel, the engine operates with high compression ratio and lean mixtures giving CI engine equivalent fuel consumption or better. Owing to pre-mixed charge without rich or stoichiometric zones, the production of soot and NOx can be avoided. This paper presents some results from advanced laser diagnostics showing the fundamental behaviour of the process from a close to homogeneous combustion onset towards a very stratified process at around 20–50% heat released. The need for active combustion control is shown and possible means of control are discussed. Results with multi-cylinder engines using negative valve overlap, variable compression ratio, fast inlet temperature control as well as dual fuel are given.