Trapped Vortex Combustor Research Articles

Quantitative OH Planar Laser Induced Fluorescence Diagnostics of Syngas and Methane Combustion in a Cavity Combustor

The current work reports quantitative OH species concentration in the cavity of a trapped vortex combustor (TVC) in the context of mixing and flame stabilization studies using both syngas and methane fuels. Planar laser induced fluorescence (PLIF) measurements of OH radical obtained using a Nd:YAG pumped dye laser are quantified using a flat flame McKenna burner. The momentum flux ratio (MFR), defined as the ratio of the cavity fuel jet momentum to that of the guide vane air stream, is observed to be a key governing parameter. At high MFRs ~4.5, the flame front is observed to form at the interface of the fuel jet and the air jet stream. This is substantiated by velocity vector field measurements. For syngas, as the MFR is lowered to ~0.3, the fuel-air mixing increases and a flame front is formed at the bottom and downstream edge of the cavity where a stratified charge is present. This trend is observed for different velocities at similar equivalence ratios. In case of methane combustion in the cavity, where the MFRs employed are extremely low at ~0.01, a different mechanism is observed. A fuel-rich mixture is now observed at the center of the cavity and this mixture undergoes combustion. On further increase of the cavity equivalence ratio, the rich mixture exceeds the flammability limit and forms a thin reaction zone at the interface with air stream. As a consequence, a shear layer flame at the top of the cavity interface with the mainstream is also observed. The equivalence ratio in the cavity also determines the combustion characteristics in the case of fuel-air mixtures that are formed as a result of the mixing. Overall, flame stabilization mechanisms have been proposed, which account for the wide range of MFRs and premixing in the mainstream as well.

Numerical Investigation of a Trapped Vortex Miniature Ramjet Combustor

The design of a miniature ramjet combustor using gaseous methane fuel for Mach 2.5 has been conducted. The main challenges stem mainly from the insufficient space for mixing and burning, short residence time, and the flame stabilization. Impossible utilization of relatively large air-blast fuel injectors provides more difficulties for the design. The trapped vortex combustor, as a novel way of flameholding by trapping the pilot flame inside a cavity instead of exposing it to the mainstream, is selected. Three main parts are studied numerically, which include the cold flowfield characteristics, the fuel-injection schemes, and the overall combustion performance. The results show that the drag coefficient can help to determine the optimum cavity size for trapping a stable vortex. Injecting all the fuel in the cavity always leads to an overly fuel-rich condition, whereas injecting in front of the cavity with a momentum flux ratio between 0.61 and 1.0 can successfully achieve stoichiometric mixing in the cavity. However, compared to nonreacting fuel mixing, the combustion performance is found to be more sensitive to the value of . Among the cases studied, the one with a small of about 0.61 has more intense pilot flames and shorter main combustor flames. The effects of angled injection, upstream injection location, and the combustor length based on the found are also investigated.

Combustion noise characteristics of an experimental 2D trapped vortex combustor

The objective of present investigation is to understand the effects of various operating parameters on the combustion noise characteristics of a 2D trapped vortex combustor (TVC). Spectral analysis of the microphone signal indicates that the power spectral density (PSD) magnitude increases with primary air velocity (Vp) for both mainstream Reynolds number (Rems) 20 000 and 40 000 cases considered in this study. Combustion noise measurements reveal that the spectral amplitude of the combustor increases with cavity equivalence ratio (ϕc). Moreover, for a particular Vp case, the PSD magnitude is observed to be higher for Rems=20000 as compared to that of Rems=40000 case due to the quenching of mainstream flame in the latter case. For a particular mainstream Reynolds number, the noise level increases with the momentum flux ratio between cavity and mainstream flow. Analysis of results reveals that the noise level varies between 80 dB for non-merged flame and 100 dB for merged flame cases. An attempt has also been made to correlate the overall sound pressure level (OASPL) with the non-dimensional operating variables.

Experimental and numerical investigations on liner cooling characteristics of a trapped vortex combustor

Experimental and numerical investigations have been carried out to examine the cooling effect of the liner wall of the cavity zone and the dilution zone in a trapped vortex combustor. The flow field and heat transfer characteristics of three cooling schemes are examined by numerical simulations. Experimental efforts focus on two of the three schemes investigated by numerical simulation, the effects of the inlet temperature, the inlet Mach number and the excess air ratio on the dilution wall temperature are obtained. The results show that, the numerical data agree well with the experimental results. The lowest wall temperature, the highest surface heat transfer coefficient, the highest cooling efficiency are achieved with the impingement/effusion cooling scheme.

Wall pressure fluctuations in rectangular partial enclosures

Wall pressure fluctuations generated within rectangular partial enclosures (RPEs) have been studied experimentally for a broad range of geometrical parameters. The geometry represents a simplified version of a new generation trapped vortex combustor and consisted of a rectangular cavity connected to a neck of smaller size. Wall pressure fluctuations have been measured through wall mounted microphones providing single and multi-variate pressure statistics both in the physical space and in the Fourier domain. In order to interpret the pressure signals, aerodynamic and acoustic investigations have been carried out as well for several cavity–neck ratios. The analysis of the acoustic response of the cavity has been conducted both numerically and experimentally and a simple theoretical model has been proposed to predict the frequency of the acoustic resonances. The aerodynamic study has been carried out through PIV measurements that provided characterization in terms of the geometrical parameters of both the large-scale vortex generated within the cavity and the recirculation zone formed upstream of the neck. The use of the POD decomposition permitted us to correlate the dynamics of the recirculation with the observed pressure statistics. The aerodynamic and acoustic investigations allowed us to interpret exhaustively the wall pressure cross-statistics and to separate contributions induced by hydrodynamic and purely acoustic pressure fluctuations.

Computational Study on flow Structures of Quench Zone in a Rich-quench-lean Trapped-vortex Combustor

Abstract The quench zone is one of key issues for a rich-quench-lean(RQL)/trapped-vortex combustor(TVC). The characteristics of flow structures of quench zone were investigated computationally with the correction by the particle image velocimetry(PIV) results. RQL/TVC combines the potential advantages of the low emission staged combustion technology of RQL with TVC. TVC has been a very promising novel combustor concept offering improvements in lean blow-out, altitude relight, and operating range. Besides, compared to conventional combustors, TVC has a potential to decrease nitrogen oxides emissions. By utilizing quench devices with different sizes of holes under the same blockage ratio in mainstream position, this paper describes the characteristics of flow structures of quench zone in a RQL/TVC. The results show that, through the quench devices, the mainstream flow quickly mixes with the flow from the cavity zone under variable mixing levels which are related to the changing of different sizes of holes. The effects of turbulent intensity and unmixedness level were examined and discussed.

Optical diagnostics of fuel–air mixing and vortex formation in a cavity combustor

The current work reports optical diagnostic measurements of fuel–air mixing and vortex structure in a single cavity trapped vortex combustor (TVC). Specifically, the mixture fraction using acetone PLIF technique in the non-reacting flow, and PIV measurements in the reacting flow are reported for the first time in trapped vortex combustors. The fuel–air momentum flux ratio, where the air momentum corresponds to that entering the cavity through a specially-incorporated flow guide vane, is used to characterize the mixing. The acetone PLIF experiments show that at high momentum flux ratios, the fuel–air mixing in the cavity is very minimal and is enhanced as the momentum flux ratio reduces, due to a favourable vortex formation in the cavity. Stoichiometric mixture fraction surfaces show that the mixing causes the reaction surfaces to shift from non-premixed to partially-premixed stratified mixtures. PIV measurements conducted in the non-reacting flow in the cavity further reinforce this observation. The scalar dissipation rates of mixture fraction were compared with the contours of RMS of fluctuating velocity and showed very good agreement. The regions of maximum mixing are observed to be along the fuel air interface. Reacting flow PIV measurements which differ substantially from the non-reacting cases primarily because of the heat release from combustion and the resulting gas expansion show that the vortex is displaced from the centre of the cavity towards the guide vane. Overall, the measurements show interesting features of the flow including the presence of the dual cavity structure and lead to a clear understanding of the underlying physics of the cavity flow highlighting the importance of the fuel–air momentum ratio parameter.

Structural design and performance experiment of a single vortex combustor with single-cavity and air blast atomisers

The adoption of vortex combustion technology is a relatively recent phenomenon. Among such technology is the trapped vortex combustor, which demonstrates a wide range of stable combustion and low pollutant emissions and accordingly has good application prospects in the field of aeroengines. A new type of single-cavity vortex combustor with air blast atomisers is introduced in this paper. This study conducted a combustion experiment that detailed the influence of the mainstream parameters, fuel parameters and combustion organisation on the combustion characteristics of the liquid-fuelled combustor. The results of this experiment suggest that this new type of vortex combustor has a reasonably designed structure and demonstrates good combustion performance. In addition, pollutant emissions under a low power state are predicted using a semi-empirical formula in which the effects of flow parameters, fuel parameters and atomisation characteristics of the fuel supply equipment are considered. Furthermore, the predicted value obtained is consistent with the experimental value. The results of this study provide a reference for the structural design and engineering application of the vortex combustor.

Experimental investigations on flow field and combustion characteristics of a model trapped vortex combustor

Experimental studies are carried out to investigate cold flow field and combustion performance of a workable liquid-fueled trapped vortex combustor (TVC). A remarkable design of the model is that all the air flows through the combustor is supplied from a single source, which makes it distinct from most of the models mentioned in open literatures. Planar particle image velocimetry (PIV) is used to measure the cold flow field, with particular emphasis placed on vortical flow pattern within cavities, turbulence intensity distribution and interaction between cavity stream and mainstream. The aim of the PIV measurement is to better understand the underlying flow physics in a TVC, as well as to provide a benchmark for validation and improvement of computational models. Combustion experiments are carried out with preheated air (473K) at atmospheric pressure using liquid kerosene. Flame images at different operating conditions are obtained and the effects of fuel to air ratio (FAR) and inlet Mach number on the physical appearance of flames are clearly revealed. The fuel to air ratio at lean blow out (LBO) is in the range from 0.0043 to 0.0056 as the inlet Mach number varies from 0.15 to 0.30, which indicates good flame stability. The combustion efficiency falls reasonably in the range of 92–100%. The improvement of the radial profile of outlet temperatures indicates the effectiveness of dilution holes.

Reacting Flows in Ultra-Compact Combustors with Combined-Diffuser Flameholder

In ultra-compact combustors, the length of the system is reduced by integrating the turbine turning vanes within the combustor and the primary zone is in a cavity recessed from the core flow. To understand the combustion characteristics of an ultra-compact combustor, the turning vanes were removed and a combined-diffuser flameholder was integrated upstream of a trapped-vortex combustor cavity. Two variants of the combined-diffuser flameholder are compared. In configuration , the row of passages nearest the trapped-vortex combustor is opened, whereas for configuration , an additional row of flow passages vertically adjacent is also open. Grid-independent three-dimensional simulations of these geometries are performed following a steady, multiphase, Reynolds-averaged Navier–Stokes, -progress variable/flamelet approach with source terms to model effusion cooling. Nondispersive infrared analyzers were used to measure the concentrations of , , and CO at the exit of the test section using three sets of emission rakes, with each having five vertically aligned, quick quenching sampling probes. Reasonable comparison was obtained between predictions and measurements of and mass fraction profiles. Besides comparison between the two configurations, the effect of combustion on the flowfield/flamelet/flame structure is provided. Recommendations on further improvement of the design and numerical model are also discussed.

Numerical investigation on flow structures of a laboratory-scale trapped vortex combustor

Flow fields of combustors have been commonly used to help understand combustion characteristics. In this paper, numerical simulations with validated methodology are employed to provide insight of the flow structures of a laboratory-scale trapped vortex combustor (TVC). Turbulence model determination and numerical method validation are accomplished with the help of experimental data from particle image velocimetry (PIV) measurements. A comparison of numerical and experimental results suggests that the standard k–ε turbulence model is able to provide a satisfactory prediction of the flow structures. Both of the two typical cavity flow patterns mentioned are observed: in a plane between two radial struts, the cavity flow features the dual-vortex pattern, however, in a plane along a radial strut, the cavity flow is dominated by the single-vortex pattern. This difference in flow patterns of different planes indicates the difference in cavity stream–mainstream mixing mechanism, which further, is believed to lead to enhanced mixing in spanwise direction.

Numerical study of flame/vortex interactions in 2-D Trapped Vortex Combustor

The interactions between flame and vortex in a 2-D Trapped Vortex Combustor are investigated by simulating the Reynolds Averaged Navier Stokes (RANS) equations, for the following five cases namely (i) non-reacting (base) case, (ii) post-vortex ignition without premixing, (iii) post-vortex ignition with premixing, (iv) pre-vortex ignition without premixing and (v) pre-vortex ignition with premixing. For the post-vortex ignition without premixing case, the reactants are mixed well in the cavity resulting in a stable ?C? shaped flame along the vortex edge. Further, there is insignificant change in the vorticity due to chemical reactions. In contrast, for the pre-vortex ignition case (no premixing); the flame gets stabilized at the interface of two counter rotating vortices resulting in reduced reaction rates. There is a noticeable change in the location and size of the primary vortex as compared to case (ii). When the mainstream air is premixed with fuel, there is a further reduction in the reaction rates and thus structure of cavity flame gets altered significantly for case (v). Pilot flame established for cases (ii) and (iii) are well shielded from main flow and hence the flame structure and reaction rates do not change appreciably. Hence, it is expected that cases (ii) and (iii) can perform well over a wide range of operating conditions.

Effect of cavity-injector/radial-strut relative position on performance of a trapped vortex combustor

Previous works have put forward the key role of radial strut in a trapped vortex combustor (TVC), however, few researches focusing on radial strut can be found in the existing literature so far. The present study is carried out to investigate the effect of the cavity-injector/radial-strut relative position on the performance of a trapped vortex combustor. This effect is directly explored by TVC combustion experiments that are run at atmospheric pressure using RP-3 liquid aircraft fuel. The specific positions include: the inline arrangement, the intermediate arrangement and the staggered arrangement. The staggered arrangement shows remarkable advantages in terms of ignition, lean blow out (LBO) and combustor temperature rise, whereas the inline arrangement performs rather poorly. Numerical simulations with validated methodology of non-reacting flows are then conducted for the purpose to explain the experimental results. The good performance of the staggered arrangement is mainly attributed to the counter-rotating streamwise vortex pair, the high turbulent kinetic energy and turbulent dissipation rate.

Trapped Vortex Combustion Chamber: Design and Experimental Investigations Using Hydrogen as Fuel

The design of trapped vortex combustion chamber was undertaken as a part of ongoing research on micro combustion chamber using hydrogen as fuel. The reacting experimental studies were then carried out on the designed chamber. The fuel was injected directly into the cavity. The combustion was first initiated in the cavity with 3 % of the main flow air supplied in reverse direction to the fuel flow. The combustion in cavity was of rich type. Temperature levels in the range of 900 K were encountered in the cavity. Thereafter, diffusion combustion was initiated using the flame generated in the cavity. The temperature levels in this stage were in the range of 1,800 K. The overall pressure drop for a trapped vortex combustor was less than 5 % at all operating parameters.

A comparative study between combustion performances of turbine inter-guide-vane burner and trapped vortex combustor

To improve the performance of aero gas turbine engines, more and more interests have been shown on turbine inter-guide-vane burner based on the ultra-compact combustion concept. To make a universal turbine inter-guide-vane burner, a new concept is proposed using a trapped vortex cavity to replace the high swirling circumferential cavity combustor to address the need to scale the configuration for a larger turbine spool. Three models, including trapped vortex combustor, transition model, and turbine inter-guide-vane burner, are designed. Comparative analysis between combustion performances of three models by using numerical simulation method is carried out. The scale-adaptive simulation turbulence model is used in the simulation process, aiming to reduce the deviation between numerical simulation value and actual value. Finally, the turbine inter-guide-vane burner model is found to be the superior design proposal for turbine inter-guide-vane combustion technology, compared with the other two models.

Study of Turbulence Characteristics in Different Advanced Vortex Combustor Structure

Based on the idea of single cavity trapped vortex combustor, a advanced vortex combustor which is constitute by three blunt bodies and double concave cavity is proposed. And the interior combustor flow characteristics are analyzed. The results shows that the flow field characteristics changed a lot before and after combustor modification, and D2=20mm, D3=4mm are respectively the best modification scheme on the second and third blunt body.

Mixing Enhancement in a Compact Trapped Vortex Combustor

Previous studies on a single-cavity, compact trapped vortex combustor concept showed good flame stability for a wide range of flow conditions. However, achieving good mixing between cavity products and mainstream flow was still a major challenge. In the present study, a passive mixing enhancement strategy of using inclined struts along with a flow guide vane is presented and experimentally tested at atmospheric pressure conditions. Results show excellent mixing and consequently low values of the combustor exit pattern factor in the range of 0.1 and small flame lengths (5–7 times the main-duct depth). The pressure drop is small in the range of 0.35%, and NOx levels of the order of 1–2 ppm are achieved. The flame stability is excellent, and combustion efficiency is reasonable in the range of 96%. The effectiveness of the proposed strategy is explained on the basis of in-situ OH chemiluminescence images and prior numerical simulations of the resulting complex flow field. The flow guide vane is observed to lead to a counterclockwise cavity vortex, which is conducive to the rise of cavity combustion products along the inclined struts and subsequent mixing with the mainstream flow.

Experimental Investigation of Airflow Distribution for a Novel Combustor Mode

This paper investigated the airflow distribution performance of the combustor which utilized trapped vortex in the cavity to improve the flame stability. Hole-filling method was used to study trapped vortex combustor airflow distribution at normal temperature and pressure condition. The influence of inlet velocity and mainstream flow-passage height were investigated. The results show that, inlet velocity hardly impacts the airflow distribution of trapped vortex combustor, but chamber height is a key parameter for airflow distribution. The size, number and opening area of the holes in trapped vortex combustor are important to airflow distribution, and increasing cavity back body air flow could bring well lean blowout limit. The research results may serve as a useful reference in further development and engineering application of trapped vortex combustor.

Experimental study of entrainment phenomenon in a trapped vortex combustor

Trapped vortex combustor (TVC) is an advanced low-pollution gas turbine combustor, with the adoption of staged combustion technique. To achieve low-pollutant emission and better combustion performance, the proportion of the air flow in each combustion zone should be precisely determined in the design of the combustor. Due to the presence of entrainment phenomenon, the total air flow in the cavity zone is difficult to estimate. To overcome the measurement difficulty, this study adopts the indirect measurement approach in the experimental research of entrainment phenomenon in the cavity. In accordance with the measurement principle, a TVC model fueled by methane is designed. Under two experimental conditions, i.e. with and without direct air intake in the cavity, the influence of the mainstream air flow velocity, the air intake velocity in the cavity, the height of inlet channel, the structure of holder and the structural proportion of the cavity on entrainment in the cavity is studied, respectively, through experiment at atmospheric temperature and pressure. The results suggest that the air flow velocity of mainstream, the air intake velocity of the cavity and the structure of the holder exert significant influence on the air entrainment, while the influence of structural proportion of the cavity is comparatively insignificant. The square root of momentum ratio of cavity air to mainstream air could be used to analyze the correlation of the entrainment data.

Design and Performance of an Improved Trapped Vortex Combustor

A trapped vortex combustor (TVC) has been a very promising novel concept for it offers improvements in lean blow out, altitude relight, operating range, as well as a potential to decrease NOx emissions compared to conventional combustors. The present paper discusses the improved designs of the new combustor over the prior ones of our research group, including that: a) the overall dimensions, both axial and radial, are reduced to those of an actual aero-engine combustor; b) the air flow distribution is optimized, and especially 15 (of the air is fed into the liner as cooling air; c) a straight-wall diffuser with divergence angle 9°is added. A series of experiments (cavity-fueled only, under atmospheric pressure) has been conducted to investigate the performance of the improved TVC. Experimental results show that at the inlet temperature of 523 K, the inlet pressure of 0.1 MPa, stable operation of the TVC test rig is observed for the Mach number 0.15–0.34, indicating good flame stability; the combustion efficiency obtained in this paper falls into the range of 60%−96% as the total excess air ratio increases, the combustion efficiency decreases, while the increase of the inlet temperature is beneficial to high combustion efficiency; besides, the optimal Mach numbers for high combustion efficiency under different inlet conditions are confirmed. The outlet temperature profiles feature a bottom in the mid-height of the exit. This paper demonstrates the feasibility for the TVC to be applied to a realistic aero-engine preliminarily and provides reference for TVC design.