Lean Blowout Performance Research Articles

Assessment of a hydrogen-fueled swirling trapped-vortex combustor using large-eddy simulation

In recent years, the study of hydrogen combustion has gained significant interest due to its exceptional lean blow-out (LBO) performance, high efficiencies, and almost negligible greenhouse gas emissions. The present study combines the advantages of hydrogen combustion with the beneficial characteristics of trapped-vortex combustion (TVC) and swirling flows. Large-eddy simulation (LES) is conducted to evaluate the performance of a swirling trapped-vortex combustor. LES sub-gird terms are described using k-equation subgrid model, while, turbulence-combustion interaction is modelled employing the PaSR (Partially Stirred Reactor) closure with a detailed 23-step chemical reaction mechanism for hydrogen/air. A radial vane swirler is incorporated to supply an annular mainstream and generate a wake region in front of the cavity leading edge to enhance cavity flow entrainment. To evaluate the performance of a hydrogen-fueled TVC under non-swirl and swirling conditions with varying swirl numbers (0.1–0.6), several flow and combustion characteristics are analyzed. These includes temperature distribution, vortical structure, combustion efficiency, NO emission, and flame shape. The results show that a large recirculation zone dominates the cavity for the all swirl numbers resulting in a strong fuel–air mixing and high combustion efficiency. It is demonstrated that the swirling motion effectively mitigates the negative impacts of pressure fluctuations arising from the interaction of combustion with cavity oscillations. A stable flame is observed inside the cavity and in the shear layer at the cavity lip in all cases, merging to form a distinctive C-shaped flame. Increasing the swirl number causes the second part of the flame to move to the wake region before the leading edge, enhancing combustion stability and efficiency. Combustion efficiency exceeds 98.5% for all cases, reaching 99.8% for a swirl number of 0.6. The temperature distribution is nearly uniform inside the cavity, with an improved distribution at the TVC’s outlet for higher swirl numbers. Under non-swirling conditions, the corrected NO concentration is below 5 ppm. Increasing the swirl number escalates the outlet NO emission, nevertheless, a maximum NO concentration of 19 ppm is observed for the swirling cases. Comparing these findings with existing data suggests that the swirling TVC offers advantages over other hydrogen-fired TVC’s.

Experimental study on the effect of liquid loading on n-heptane spray jet flame stability

Flame stability significantly influences the performance of a practical combustor. The mechanisms governing the stability limits of spray jet flames are examined here using an annular co-flow spray burner. This study focuses on investigating the impact of liquid loading on spray jet flame stability, represented by flame lift-off height (LOH) and lean blow-out (LBO) limit. This is achieved by utilizing a parametric experimental study in which co-flow temperatures (Tco-flow = 298 K, 350 K, 400 K, and 450 K), spray nozzle sizes (dorifice = 0.209 mm, 0.219 mm, 0.232 mm, and 0.237 mm), fuel/air flow rates, and velocities are independently varied. A single liquid fuel, n-heptane, is used so that the vapor/liquid fractions (droplet lifetime) can be easily predicted via simple vapor–liquid equilibrium calculations to assist in the explanation of the stability mechanisms involved. The results show that the spray flame LOH mechanisms are affected by both chemical flame speed and, to a lesser extent, vaporization. On the other hand, the LBO limit is found to be controlled by the amount of liquid fuel in the presence/entering the flame. When the co-flow temperature is increased, while keeping constant co-flow velocity, the flame stabilizes near the burner lip. However, an opposite trend is noticed for flame blow-out limits, with the flame being more difficult to blow out when lower co-flow temperatures are applied. The variation of nozzle sizes leads to similar conclusions, i.e., when larger nozzle sizes are used, leading to the formation of larger droplets, the flame stabilizes further downstream and becomes more difficult to reach blow-out. The interpretation of the results indicates that delaying the vaporization and generating local enrichment regions near the flame edge enhances the flame LBO performance. Such an approach may be used as an efficient passive control mean to enhance flame stabilization; however, secondary impacts on emissions must be considered.

Experimental and numerical prediction of LBO performance in a centrally staged combustor

A new type of centrally staged combustor was proposed for an aeroengine combustor with a fuel–air ratio of 0.037. The combustor dome comprised a three-stage swirler, which included a pilot stage and main stage. The pilot stage was composed of Stage 1 and Stage 2 swirlers, and all swirlers were radial. The effects of different inlet Reynolds numbers and swirler structural parameters, including the installation angle of the first radial swirler, installation angle of the second radial swirler, installation angle of the main stage, and co– and counter-rotation of Stage 1 and Stage 2 swirlers on the lean blow-out (LBO) performance of the centrally staged combustor were examined at an atmospheric pressure and inlet temperature of 473 K. Experiments with single-dome rectangular test pieces and numerical methods were used. The results showed that the fuel–air ratio decreases with an increase in the inlet Reynolds number, indicating that the increase in inlet Reynolds number plays an important role with respect to the LBO. When the rotation directions of Stage 1 and Stage 2 swirlers were opposite, the fuel–air ratio of the LBO was smaller than that of Stage 1 and Stage 2 swirlers in the same rotation direction, indicating that the rotation directions of Stage 1 and Stage 2 swirlers significantly affect the LBO performance. Stage 1 and Stage 2 swirlers exhibited the best LBO performance when they rotated in opposite directions, and the rotation direction of the main stage slightly affected the LBO performance. The best combination of rotation directions is that the rotation directions of Stage 1 and Stage 2 swirlers should be opposite and rotation direction of Stage 2 swirler should be the same as that of the main stage. With the increase in the installation angle of Stage 1 and Stage 2 swirlers, the LBO fuel–air ratio decreased by nearly 4% and 9%, respectively, and the LBO performance improved. The prediction of the LBO limit of 0.00553, using the fuel steady-state successive approximation method, was less than 0.0066, which was measured in the test, indicating that the method should be improved. The flow field characteristics of the LBO process, which could not be obtained in the test process, were obtained via numerical simulation.

Experimental investigation on lean blowout dynamics of spray flame in a multi-swirl staged combustor

• Continuous lean blowout process of spray flames with linear reduction of fuel-to-air ratio. • Evolution of LBO performance under simulated flight-idle conditions inside a staged combustor. • LBO flame dynamics identified by proper orthogonal decomposition method. • Peak frequency transitions can be used as precursors to blowout events. Lean combustion has been widely applied in gas turbine combustors due to its superiority in reducing NOx emissions. However, it poses a significant risk of blowout for aero-engines especially when operating under low power conditions. In this paper, the LBO (lean blowout) process of spray flame was experimentally investigated and the flame was visualized by high-speed imaging of CH* chemiluminescence. A stratified partially premixed injector was applied and fueled with aviation kerosene at simulated flight-idle conditions. During the experiments, LBO was induced through linear reduction of pilot fuel flow rate. It was found that the LBO performances deteriorated as the altitude increases and the relationship between LBO FAR (fuel to air ratio) and altitude conformed to an exponential function. Evolution of flame macrostructures during LBO process showed that the flame changed from a double V-shape to a single V-shape with the decrease of FAR . FFT (fast Fourier transform) and POD (proper orthogonal decomposition) methods were introduced to post-process the high-speed imaging data in different periods before flame extinction. At the last second before LBO, POD modal distributions presented typical axial oscillation, circumferential rotation and high-order radial oscillations successively. The spectral analysis showed that the peak frequencies in the spectra of global CH* chemiluminiscence intensity and the spectra of POD modal time coefficients both changed prominently within 3∼7 seconds before flame complete extinction, which was of good repeatability during repeated tests and was considered to be a precursor for blowout event.

Effect of a passive control strategy on lean ignition and blowout performance of a gas turbine combustor

In this study, a radial strut is designed in the mainstream channel of a trapped vortex combustor (TVC) to improve the mixing between cavity products and mainstream air. This improves combustion efficiency and uniformity of outlet temperature distribution. However, a certain amount of mainstream flow is entrained into the cavity owing to the blockage of the radial strut; this entrainment deteriorates the ignition and blowout performance. To resolve this problem, a passive control strategy using a vertical jet is proposed to restrain the entrainment of mainstream flow into the cavity. Experimental results indicate that compared with the conventional TVC, the proposed strategy significantly improves the ignition and blowout performance. To gain insight into the experimental results, Reynolds-averaged Navier-Stokes-based simulations with a validation methodology were conducted to simulate the flow field and fuel distribution characteristics of the cavity. The simulation results demonstrate that the passive control strategy can effectively restrain the mainstream air entrained in the cavity. The improved ignition and blowout performance provided by passive control strategy can be attributed to the formation of a desirable flow structure with two vortices and high local fuel equivalence ratio inside the cavity.

Experimental study on effects of prefilming and non-prefilming atomization on the combustion characteristics in a realistic full annular combustor

The interaction between liquid fuel and the walls poses a major challenge to using the airblast atomizer in the combustor of an advanced aero-engine because the mechanism of this interaction is not fully understood. In this study, the authors experimentally examine the influence of the interaction between liquid particles and the walls on the performance of a full annular combustor in terms of fuel atomization, the characteristics of the flow field, ignition and lean blowout (LBO), the combustion efficiency, and the distributions of temperature at the outlet corresponding to prefilming and non-prefilming methods of atomization. The results show that the Sauter mean diameter (SMD) of the prefilming airblast atomizer was smaller than that of the non-prefilming airblast atomizer when the fuel pressure difference was small. As the fuel pressure difference was continuously increased, the SMD of the prefilming airblast atomizer gradually became larger than that of the non-prefilming airblast atomizer. The morphology of the flow field downstream of the airblast atomizer could be changed by adjusting between the prefilming and non-prefilming modes, i.e., the flow field downstream of the prefilming mode was a typical swirling recirculation zone while that downstream of the non-prefilming mode had a recirculation zone on both sides of the forward jet at the center. When the inlet air flow is small, the ignition and LBO performance of the non-prefilming scheme were better than those of the prefilming scheme. As the inlet air flow was continuously increased, however, the ignition and LBO performance of the prefilming scheme became better than those of the non-prefilming scheme, and it had a higher combustion efficiency under the ground idle condition for different fuel–air ratios. The quality of temperature distribution at the outlet corresponding to the non-prefilming scheme was better than that of the prefilming scheme as well.

Experimental study on ignition and lean blowout characteristics of high temperature rise combustor

Ignition and lean blowout characteristics are an important performance index of the Aeroengine combustor, which is directly related to the reliability of the whole engine. The ignition process of the combustor was filmed by a CCD camera, and three stages of successful ignition were obtained. By changing the intake conditions, the variation of the minimum ignition energy in the fuel-air ratio (FAR) is tested. With the decrease of the FAR, the minimum ignition energy increases and there is a sudden increase process. As the room temperature and pressure conditions, the lean blowout (LBO) FAR is roughly 0.014, and Increasing kerosene temperature can improve the LBO performance in the combustor.

Ignition, lean blowout, and flame propagation in a combustor using flameholder with a trapped vortex cavity

In this study, experiments are carried out to investigate a combustor based on the trapped vortex flame stabilization concept. The combustor involves a pilot trapped vortex cavity and a radial V-shaped flameholder. Multiple tests are conducted to measure the ignition and lean blowout performance (LBO) under a wide range, especially under sub-atmospheric pressures. High-speed photography methods are applied to capture the ignition process. The results showed that in sub-atmospheric pressure conditions, the ignition and LBO performance, flame area, and flame radial penetration length are all experiencing a significant decrease, while increasing inlet Mach number and temperature have both positive and negative impacts. Different periods of the ignition process are sorted by post-processing the images; during the ignition, the pilot flame rotates with the main vortex and propagates along the cavity; the flameholder entrains the flame into the mainstream zone. The study would establish a fundamental overview of the performance of this structure under sub-atmospheric pressure, further promoting the optimization and application of the cavity-based flame stabilization conception.

Experimental study on the impact of alternative jet fuel properties and derived cetane number on lean blowout limit

AbstractThe impact of alternative aviation jet fuels and their properties on lean blowout (LBO) limits has recently raised several questions in the jet fuel area. There is a need for a detailed investigation of the impact of fuel properties on the LBO limit involving actual engine hardware. This study investigates the impact of a range of alternative aviation jet fuels with notable differences in physical and chemical properties and derived cetane number (DCN) on the LBO limit and their effects on key performance indicators. LBO performance results for ten different alternative fuels using a Rolls-Royce single-can Tay combustor are presented in this study. The study also assesses impact of different equivalence ratios and flow rates on LBO, with the aim of determining the impact of a certain range of operating conditions. The results are further analysed to determine the influence of fuel chemical and physical properties on the LBO limit. Finally, based on results in the above experiments, individual fuel properties are adjusted for subsequent experimental analysis of blended fuels. With this approach, 25 additional fuel blends are evaluated and presented, with an emphasis on varying the DCN. This study provides effective data and results to facilitate future fuel optimisation and reduce the risk of a negative performance of new fuels in gas turbines.

Experimental and numerical study of flow and ignition and lean blowout characteristics of jet-cooled wall flameholder in a dual-mode combustor

The wall flameholder is one of the credible alternatives to realize pilot ignition in augmented/ramjet combustors. To overcome the ablation for a long-term operation, two types of jet cooling, external-inhaled air and pressure-driven jet cooling, are proposed for the wall flameholder. In this work, the flow and combustion process in a laboratory scale rig is studied for different cooling schemes and cooling conditions using experimental and numerical methods. Flow analysis in pressure-driven jet cooling scheme shows that the flow field of flameholder is influenced significantly by the cooling hole angle on the oblique plate α and on the rear plate β. In particular, the cooling jet angle combinations (α=30o, β=30o) and (α=90o, β=150o) are the two schemes with the most different characteristics. To investigate the effects of jet cooling type and cooling jet angle on the flow, ignition, and lean blowout (LBO) characteristics, the two distinctively different angle combinations are applied to form two kinds of jet cooling schemes mentioned above. Results suggest that the jet cooling type has less impact on the flow field but more influence on the flow loss than the cooling jet angle. The ignition performance of cooling schemes with α=30o and β=30o is better than that of those with α=90o and β=150o, but it has a more significant flow loss. The LBO limits of external-inhaled air cooling are lower than that of pressure-driven jet cooling. Moreover, the ignition and LBO limits decrease gradually with the increased mainstream temperature and they are only slightly affected by the mainstream velocity. Notably, the pressure-driven jet cooling scheme can slightly reduce the flow loss but it leads to a deteriorated ignition and LBO performance. The external-inhaled air cooling scheme with α=30o and β=30o has an excellent ignition and LBO performance, and the ignition and LBO limits increase with the increasing cooling air flow rate and the decreasing cooling air temperature.

Prediction of lean blowout performance on variation of combustor inlet area ratio for micro gas turbine combustor

PurposeThis paper aims to predict the effect of combustor inlet area ratio (CIAR) on the lean blowout limit (LBO) of a swirl stabilized can-type micro gas turbine combustor having a thermal capacity of 3 kW.Design/methodology/approachThe blowout limits of the combustor were predicted predominantly from numerical simulations by using the average exit gas temperature (AEGT) method. In this method, the blowout limit is determined from characteristics of the average exit gas temperature of the combustion products for varying equivalence. The CIAR value considered in this study ranges from 0.2 to 0.4 and combustor inlet velocities range from 1.70 to 6.80 m/s.FindingsThe LBO equivalence ratio decreases gradually with an increase in inlet velocity. On the other hand, the LBO equivalence ratio decreases significantly especially at low inlet velocities with a decrease in CIAR. These results were backed by experimental results for a case of CIAR equal to 0.2.Practical implicationsGas turbine combustors are vulnerable to operate on lean equivalence ratios at cruise flight to avoid high thermal stresses. A flame blowout is the main issue faced in lean operations. Based on literature and studies, the combustor lean blowout performance significantly depends on the primary zone mass flow rate. By incorporating variable area snout in the combustor will alter the primary zone mass flow rates by which the combustor will experience extended lean blowout limit characteristics.Originality/valueThis is a first effort to predict the lean blowout performance on the variation of combustor inlet area ratio on gas turbine combustor. This would help to extend the flame stability region for the gas turbine combustor.

Rotating gliding arc discharge plasma-assisted combustion from ignition hole

Plasma-assisted combustion (PAC) is a potential method to improve the performances of aero-engine combustion chambers. A plasma-assisted combustion actuator (PACA) that operates without an additional air supply device was designed to improve the performance of the combustion chamber. To validate the feasibility of using the PACA to enhance the annular combustor performance, a plasma-assisted combustion test platform was established. It was found that the PACA could improve combustion performance in many aspects. Experimental results showed that the average outlet temperature of the combustion chamber increased from 1386 to 1652 K when the excess air coefficient (α) was 0.8 after PAC. Compared with the normal conditions, the uniformity of the outlet temperature field was improved. The combustion efficiency of the PAC could be increased by up to 10.98% under fuel-rich conditions. In addition, the lean blowout performance was improved, which meant the flame could continue burning under leaner fuel conditions. In other words, PAC greatly improved the stability of combustion.

Effect of different turbulence model on prediction of lean blowout limit for micro gas turbine combustor

ABSTRACT This paper aims to present turbulence modelling results of methane/air combustion in a micro gas turbine combustor. Modelling studies were carried out with different turbulence models to evaluate Lean Blowout (LBO) performance on the micro gas turbine combustion chamber by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are k-epsilon standard, k-epsilon RNG, K-epsilon realisable, k-omega standard, and k-omega SST. A two-dimensional axisymmetric 3 kW swirl stabilised micro gas turbine combustor model was built to investigate the impact of various turbulence models on the prediction of LBO behaviour of the combustor fuelled with methane. Performance evaluation of these models was executed by calculating the average exit gas temperature (AEGT) that have been used for predicting the blowout conditions. Results obtained from this study were validated with experimental results. Numerical results showed that two-equation turbulence models give consistent simulation results with experimental results employing trend and value. Standard k-epsilon was found to give consistent simulation results with experimental data.

Liquid Jet Fuel Property Impacts on Combustion Performance

This paper investigates the influence of liquid jet fuel properties on flame lean blowout (LBO) using an annular coflow spray burner. This behavior has been studied before; however, inconsistent conclusions have been reached regarding the dependency of LBO performance on the properties that influence fuel atomization and mixture formation. LBO limits are measured at three different fuel flow rates to evaluate the influence of the atomization quality/regimes on LBO. It was found that the laboratory spray burner provides similar trends in LBO as a realistic gas turbine combustor but with less time and fuel consumption. Furthermore, the approach used in this work differs from traditional LBO measurements in that the fuel flow rate is kept constant while altering the air flow rate to allow for greater control of the atomization process, which is strongly affected by the fuel flow rate. The results suggest that, to an extent, higher amounts of liquid fuel entering the flame can enhance flame stability. They also suggest that testing at different fuel flow conditions and/or with variable injection hardware, coupled with testing of jet fuels exhibiting variations in key physical properties important in their atomization, is most likely the cause of discrepancy observed in previous works.

Effect of mainstream forced entrainment on the combustion performance of a gas turbine combustor

In trapped vortex combustors, a radial strut is designed to improve the combustion efficiency and achieve uniform temperature distribution. However, under the action of the strut, a mainstream forced entrainment phenomenon may take place in the cavity, which would extinguish the local flame there. In this study, to achieve high combustion efficiency with robust stability, a strategy to optimize the radial strut was proposed to control the mainstream forced entrainment phenomenon. Then, an experimental study was conducted to investigate the effects of mainstream forced entrainment on the combustion efficiency, ignition, and lean blowout performance in a workable trapped vortex combustor. Additionally, numerical simulations on the flow field were performed to obtain insights into the experimental results. It was found that the mainstream entrained into the cavity is helpful for improving the combustion efficiency and inner-cavity ignition performance. This occurs because the entrained mainstream changes the flow field behind the strut, which provides many more shield regions for fuel combustion and flame propagation. However, the mainstream entrained into the cavity is harmful to the ignition of the outer cavity and lean blowout performance, because the entrained mainstream can not only decrease the size of the main vortex of the cavity, but also reduce the local fuel to air ratio inside the cavity. Additionally, it was found that a change in the strut dimensionless parameter L/D can effectively control the flow fields, and thus the combustion performance. Furthermore, a critical value of 0.50 was obtained for the strut dimensionless parameter L/D.

Chemical and physical effects on lean blowout in a swirl-stabilized single-cup combustor

Understanding the lower stability limit of gas turbine combustors is imperative for safe operation as well as for the approval of novel sustainable aviation fuels. Previous results have indicated that at relatively low temperatures and pressures (Tair = Tfuel = 238 and 258 K, P = 101 kPa, ΔP/P = 2%), the lean blowout (LBO) limits correlated to fuel physical properties, while at relatively high temperatures and pressures (Tair = 394 K, Tfuel = 322 K, P = 207 kPa, ΔP/P = 3%) chemical properties were highly correlated. This suggests that a transition occurs between physical and chemical property dependency. In the present effort, a single nozzle swirl-stabilized combustor was used to study the LBO for fuels with varying chemical and physical properties as well as operating conditions to study a transition from physical property dependence at low pressures and temperatures to chemical property dependence at higher temperatures and pressures. Four fuels with a wide range of physical and chemical properties were tested at combustor inlet conditions of Tair = Tfuel = 305–355 K, P = 107 kPa, and ΔP/P = 2–6%. It was found that the transition of LBO dependence from fuel physical to chemical properties does not happen at a single point. Rather, a transition range of conditions was observed for changes made to the pressure drop across the combustor dome (ΔP) as well as changes made to air and fuel temperature. Changes in ΔP/P were found to change the relative LBO performance across fuels and demonstrated a change in physical to chemical property dependence as ΔP/P increased. Analysis via random forest regression using dimensionless parameters such as an approximate Weber number and Ohnesorge number further highlighted the transition from physical to chemical property dependency with increasing ΔP/P.

Effect of the Swirl Intensity of Pilot Inner Swirler on the Combustion Stability of a Lean Staged Injector With a Prefilm Atomizer

Abstract Lean staged combustion can reduce the NOx emissions by prevaporizing and premixing fuel with air, which is considered the state-of-the-art solution strategy in achieving low emission in aeronautical combustors. However, lean premixed combustion is subjected to combustion stability problems, which restrict the ground and altitude operation limits of the commercial engine. In this work, the effect of the swirl intensity of pilot inner swirler on combustion stability of a lean staged injector is experimentally and numerically studied. The lean staged injector is piloted by a dual swirler prefilm atomizer. The swirl intensity of the pilot inner swirler is varied by parameterizing the vane angle as +20 deg, −20 deg, and −35 deg, with −20 deg selected as the baseline with a counterswirling design. A single sector model combustor is designed, and the nonreacting flow field and fuel concentration distributions are measured by particle image velocimetry (PIV) and kerosene planar laser induced fluorescence (kerosene-PLIF) techniques. The alteration of swirl direction from counterswirling to coswirling induces a negligible effect on flow structures, but the spray distribution changes from a solid pattern to a hollow pattern. The increase in the pilot inner swirl intensity causes a shrunk cyclone recirculation zone (CRZ) and a reduction of kerosene concentration in the central region. The influences of the pilot inner swirler angle on combustion stability are evaluated. The ignition and lean blow-out (LBO) results show that the baseline injector exhibits excellent combustion stability, while the coswirling design holds the highest ignition and LBO fuel–air ratio (FAR). In order to find out the physical mechanisms dominating the ignition and LBO processes, nonreacting numerical simulations are conducted to provide information regarding the flow structures and kerosene concentrations at ignition limits. Moreover, the ignition sequences are redefined as the radial flame propagation phase, the axial flame propagation phase, and the flame stabilization phase. The comparison of kerosene concentration along the radial and axial propagation routes concludes that the fuel enrichment in the two processes improves the ignition performance. On the other hand, the Karlovitz number of flame anchoring points in the flame rooting region is calculated to evaluate the flame stabilization characteristics. The results indicate that promoting the number of flame anchoring points and their radial range benefits the LBO performance.

Experimental study of dielectric barrier discharge plasma-assisted combustion in an aero-engine combustor

A plasma-assisted combustion test platform was established to validate the feasibility of enhancement on the performances of aero-engine combustion chamber by plasma-assisted combustion technology. The plasma-assisted combustion actuator using dielectric barrier discharge to produce plasma was designed to assemble in front of the combustor diffuser. Comparative experiments between conventional and plasma-assisted combustion were carried out to analyze the combustion enhancement effect on the combustor performances, such as average outlet temperature, combustion efficiency, pattern factor and lean blowout performance. The experimental results show that the combustion efficiency is improved by plasma, especially in fuel-rich condition (α=0.8), the increment reaches 2.31%, when α are 1 and 2, the increments are 1.21% and 0.94% respectively when voltage is 40 kV, and the increment is only 0.39% in too lean conditions (α=4). On the other hand, the higher the voltage, the more obvious increase of the combustion efficiency. The uniformity of the outlet temperature field and lean blowout performance is also improved by plasma-assisted combustion. Under the fuel-rich condition, patten factor is reduced by more than 5%. And the expansion of lean blowout limit is about 4.2%, 9.1%, 12.2% and 23.7% when the inlet velocity is range from 60 m/s to 120 m/s.

Ignition and blow-off process assisted by the rotating gliding arc plasma in a swirl combustor

A rotating gliding arc (RGA) in three different discharge powers (from 35 W to 250 W) was designed to enhance ignition and combustion in a swirl model combustor with a flow speed from 15 m/s to 60 m/s. The flame development process was recorded using the 10 kHz high-speed CH⁎ imaging. It was concluded that the repeatable ignition in the presence of the RGA can be observed in the combustor. The RGA method is capable of gaining a greater probability to inject energy into the appropriate local equivalence ratio and instantaneous air velocity. The ignition process by the RGA can be divided into three stages: sliding stage; flame spread stage and flame fluctuation stage. The RGA method can also increase the probability of re-ignition in a lean blow-off process than the auto re-ignition. The uniformity of the lean blowout performance was improved after the RGA-assisted combustion. The lean blowout limit can be extended by 62.2% in the presence of the RGA in the swirl combustor. The lower frequency and higher averaged power of the RGA is more capable of igniting the fuel and maintaining the swirl flame in the lean equivalence ratios.

Study on the Effects of Dome Fuel Distribution Ratio on Lean Blowout of a Model Combustor

The experimental studies and numerical simulation were conducted on the effects of the dome fuel distribution ratio on the lean blowout of a model combustor. The experimental results indicate that as the key parameter, the dome fuel distribution ratio, increases from 2.06% to 16.67%, the lean blowout equivalence ratio declines obviously at the beginning, and then the decrease slows down, in addition, the amplitude of the pressure fluctuation in the combustor reduces significantly while the dominant frequency keeps basically constant. In order to analyze the experimental results, the numerical simulation is adopted. The temperature and local equivalence ratio distributions are employed to explain the reason why the lean blowout performance improves with the increase of the dome fuel distribution ratio.