Lean Blowout Performance Research Articles

Correlation of combustor lean blowout performance to supercritical pyrolysis products

Studies to assess correlations between fuel pyrolysis products and fuel-to-air equivalence ratio at combustor lean blowout (LBO) were conducted. Eighteen fuels, including conventional and alternative fuel formulations and blends, single compounds and binary surrogates of hydrocarbon compounds, were studied. The pyrolysis tests consisted of thermally cracking the fuels in a flow reactor at supercritical conditions of 4.14 MPa and up to 625 °C, at varying residence times. The liquid and gaseous pyrolysis products were analyzed via gas chromatography to correlate yields to the fuel LBO data acquired in a previous study on a single-nozzle swirl-stabilized combustor. Focus was given to correlate LBO with primary decomposition products, since it is hypothesized that fuel combustion characteristics, particularly ignition and flame extinction, are related to the rate and type of products formed upon initial thermal decomposition of the parent fuel. Therefore, only the range of conversions for which low molecular weight products had a near-constant formation rate was considered. Results show that the highly branched fuels primarily decomposed to branched C4 and methane, while fuels with high concentration of linear alkanes show greater yields of C2-C4 alkanes and 1-alkenes. Regression analyses of the pyrolysis gas and LBO data show very strong correlations (R2 > 0.90) for several pyrolysis products for the conventional and alternative fuels, with ethane, ethylene and iso-butylene yields providing the best correlations to LBO. The calculated LBOs based on regression parameters and concentrations of the pyrolysis gases were within 2% of the measured LBO for most fuels tested. These initial results suggest that despite the vast differences in fuel reaction timescales in the flow reactor (∼0.2–11 s) and combustor environments (<0.5 ms), fuel pyrolysis species in a flow reactor environment are relevant and may be used to predict fuel combustion behavior. If further validated, this method provides a capability to identify fuel components that can improve combustion performance via their primary pyrolytic product slates, potentially providing a more cost-effective alternative to combustion testing for determination of fuel combustion performance metrics. Results of the pyrolysis tests of all fuels, and future efforts are discussed.

Experimental investigation on alternative fuel combustion performance using a gas turbine combustor

In order to ensure reliable combustion performance and low emissions profiles for prospective alternative fuels, this study was conducted in order to evaluate the impact of fuel properties and their composition on lean blowout performance and emission characteristics of various fuels. Significant contributions to knowledge have been achieved using visual images of the flames at the occurrence of lean blowout (LBO) that were captured by a high-speed camera and analysed to develop a new model for the evaluation of the LBO of current and future alternative fuels.The results show that high-density and high aromatic content fuel has the potential to produce higher soot formation. In addition, a low lean blowout equivalence ratio and low soot propensity is unlikely to be achieved at the same time by simply altering the value of fuel properties. It was discovered that the Derived Cetane number was observed to have a considerable effect on improving the LBO performance without inducing heavier soot emissions. An analysis of the impact of the fuel aromatic content (type and proportion) presents a hypothesis that not all aromatics species produce the same levels of particulate matter emissions.This work provides a comprehensive data foundation, analytical concepts and potential research techniques for the application of expeditious fuel screening tools to assess the combustion behaviour of current fuels, and also facilitates the potential for further operational fuel development. The visualisation method used in this work could contribute towards developing applications for flame detection in fuel performance assessment.

Experimental study of rotating gliding arc discharge plasma-assisted combustion in an aero-engine combustion chamber

The combustion chamber is the core component of an aero-engine, and affects its reliability and security operation, even the performance of the aircraft. In this work, a Plasma-Assisted Combustion (PAC) test platform was developed to validate the feasibility of using PAC actuators to enhance annular combustor performance. Two plans of PAC (rotating gliding arc discharge plasma) were designed, Assisted Combustion from Primary Holes (ACPH) and Assisted Combustion from Dilution Holes (ACDH). Comparative experiments and analysis between conventional combustion and PAC were conducted to study the effects of ACPH and ACDH on the performances including average outlet temperature, combustion efficiency, pattern factor under four different excessive air coefficients (0.8, 1, 2, and 4), and lean blowout performance at different inlet airflow velocities. Experimental results show that the combustion efficiency is improved after PAC compared with that in normal conditions, and the combustion efficiency of ACPH increases 2.45%, 1.49%, 1.04%, and 0.47%, while it increases 2.75%, 1.67%, 1.36%, and 0.36% under ACDH conditions. The uniformity of the outlet temperature field and the lean blowout performance are improved after PAC. Especially for ACPH, the widening of the lean blowout limit is 8.3%, 12.4%, 12.8%, and 25% respectively when the inlet velocity ranges from 60 m/s to 120 m/s. These results offer new perspectives for using PAC devices to enhance aero-engine combustors’ performances.

Effect of swirl number of pilot stage on TeLESS II combustor's lean blow-out performance

Effect of swirl number of pilot stage on TeLESS II combustor's lean blow-out performance

Experimental and numerical study of the effect of main stage stratifier length on lean blow-out performance for a stratified partially premixed injector

The lean blow-out performance of the pilot flame in a stratified partially premixed injector is studied in this work considering the influence of the main stage stratifier length. Particle image velocimetry and kerosene planar laser-induced fluorescence experiments at nonreacting conditions were carried out to give an explanation of the combustion performance. The evolutions of spray and velocity in space are discussed in detail to find out the inherent correlations of combustion stability, spray distribution, and flow structures. Moreover, special attentions are paid to the variation of primary recirculation zone with the increase of the stratifier length and its driving factors. Specifically, by lengthening the stratifier of the main stage, the primary recirculation zone is enlarged both axially and radially, and this creates an advantageous flow topology for the anchoring of the pilot flame. Finally, the dominating mechanisms for the primary recirculation zone that are responsible for the alteration of the primary recirculation zone size are pointed out with the assistance of computational fluid dynamics.

Prediction of lean blowout performance of gas turbine combustor based on flow structures

ABSTRACTThe insufficient depth of modelling to capture the flow physics within primary combustion zone is the prime reason behind limited accuracy of semi-empirical correlations. Flame volume concept establishes a better connection between LBO performance and flame parameters, which improves the modelling depth and hence the prediction accuracy. Nonetheless, estimation of flame parameters is a challenging task. In addition, the iterative loop to approach convergence for a single geometry demands several numerical simulation runs. In this study, the association of LBO performance has been extended to flow structures, they are uniquely associated with the geometric features and can efficiently relate global LBO performance with primary zone geometry. The lean blowout phenomenon was presented as a contest between igniting and extinction forces within Reverse Flow Zone. These forces were quantified by four performance parameters including area, minimum axial velocity, average temperature, and average velocity. Selected parameters provide valuable information regarding the size of recirculation bubble, the intensity of flow reversal and the amount of entrained hot gases. For the purpose of validation, 11 combustor geometries were selected. The RANS simulation was carried out to estimate performance parameters, and predicted performance was compared against experimental data. The excellent agreement highlights the efficiency and promising future for the proposed methodology. Moreover, the association of prediction process with flow structure, instead of geometric features/dimension, makes it universal prediction methodology for wide range of combustor configurations.

Hybrid Lean Blowout Prediction Methodology with Reactive Flow Simulation

ABSTRACTRobust and accurate prediction tools are required at a component design stage in order to choose the most suitable geometry. Semi-empirical correlations are sufficiently robust to predict lean blowout (LBO) performance of combustors; however, their accuracy is limited due to insufficient modeling depth, which can relate geometric variation with LBO performance. The flame volume concept, which is dynamically linked to the flow structures, spatial interaction of mixing jets, heat evolution, and dissipation in the primary zone, has brought improvements. Nevertheless, its estimation is a challenging task. Previously, it was evaluated from the flammable volume estimation within a cold flow simulation that it needed a correction step. This work extends the hybrid LBO prediction to reactive flow simulations with Reynolds Averaged Navier–Stokes simulations in Fluent platform. In this study, 10 geometric configurations were investigated and their experimental data was presented. Relationship between the flow structures in a primary zone and the global LBO stability was successfully described by defining a ‘heat content’ parameter. Flame identification criterion was also established and effectively utilized for the flame-volume estimation within reactive flow simulations. As a result, the correction step was eliminated and led to reduction of the iteration loop. Comparison of the simulated and experimental flame volume reported maximum and average errors of ±15% and ±5%, respectively. The improvement was mainly attributed to the inclusion of reactive flow simulations and the flame identification criterion.

Experimental study of lean ignition and lean blowout performance improvement using an evaporation flameholder

The hyperburner of a turbine-based combined cycle (TBCC) works at a relatively low temperature and high local velocity flow conditions compared with an afterburner or a ramjet combustor. Therefore, wider lean ignition and blowout limits are required in a TBCC. Both a circular and crescent-shaped evaporation tube flameholders were designed and numerically simulated. Moreover, experiments were performed to measure the lean ignition and blowout performance for the two flameholder types under conditions of T=450–650K and Ma=0.1–0.4. The results indicate that a crescent-shaped evaporation tube provides steady high temperature wake flow, thereby increasing the fuel evaporation rate, and that a crescent-shaped evaporation tube flameholder is superior to a circular evaporation tube flameholder; this is because the wake flow of a crescent-shaped evaporation tube is not affected by the Mach number of the flow. This is beneficial for both reliable lean ignition and wide lean blowout limits. For flows with high Mach numbers, when compared with a circular evaporation tube flameholder, the lean ignition and blowout performance is strongly enhanced for a crescent-shaped evaporation tube flameholder. The experimental results show that a crescent-shaped evaporation tube flameholder exhibits much better performance under flow conditions where T=450K and Ma=0.4. The lean ignition and lean blowout equivalence ratios of a crescent-shaped evaporation tube flameholder were only 31% and 47% that of a circular evaporation tube flameholder, respectively.

Emission Characteristics Through Rich–Lean Combustor Development Process for Small Aircraft Engine

Following increasing awareness of aircraft emissions and demand for technologies to reduce NOx emissions, experimental research has been conducted to develop a combustor for a small aircraft engine in the TechCLEAN of Japan Aerospace Exploration Agency project. The combustor was tuned to produce rich–lean combustion behavior through combustion tests, including full annular combustion experiments, under atmospheric and actual operating conditions of the target engine. Excellent combustion performance was observed. The final, optimized full annular combustor achieved a reduction of NOx emissions below 40% of the standard regulated by Committee on Aviation Environmental Protection/4 of International Civil Aviation Organization while maintaining low CO and total hydrocarbon emissions and showing superior exit temperature profiles and lean blow-out performance. Through the combustor development process, the dependence of combustion characteristics on combustor configuration was also clarified.

Investigations of the effects of spray characteristics on the flame pattern and combustion stability of a swirl-cup combustor

An experimental study on both spray and combustion were carried out in order to investigate the effects of gap of nozzle shroud on combustion stability and correlate the spray characteristics with some of combustion performances in a swirl-cup combustor, such as flame pattern, ignition and lean blow-out performances. The performances of ignition and lean blow-out were evaluated in a three-sector combustor in which only the middle dome is operated. Spray analyses were conducted on test sets in a quiescent open-air environment, with measurements of spray pattern by kerosene planar laser induced fluorescence (Kerosene-PLIF) and droplet size by Fraunhofer diffraction techniques. The optimum gap of nozzle shroud for ignition performance is obtained. Based on the droplets spatial distribution in the combustor with recognition of multi-phase nature of the ignition process, the phenomenon that the gap of nozzle shroud has a great impact on the ignition performance was analyzed. Meanwhile, one also analyzed the lean blow-out performance associated with the droplets spatial distribution. By tuning the fuel mixture from ignition condition to the near lean blow-out condition, one found that the lean blow-out performance is less sensitive to the gap of nozzle shroud. Furthermore, CFD simulation results of the flow field under the typical combustor operation conditions were presented and discussed to provide insight into the interaction between air streams from anti-carbon apertures and primary swirler.

Experimental investigation on ignition and lean blow-out performance of a multi-sector centrally staged combustor

Improvement on extinction and pollution emission have become one of the most prominent research topics in gas turbine. It is widely recognized that the fuel/air mixture distribution in the recirculation zone is a critical factor in improving lean blow-out (LBO) and ignition. This paper proposed a new low emission scheme with fuel staged centrally and hybrid injector to improve flameout and emission. A relative small amount of fuel enters into central pilot airblast atomizer burner and then atomized by inner swirl air. The remaining majority of fuel is directly injected into vane channels of the primary swirler through a series of holes located on the sidewall of the main stage. Only pilot stage is fueled under ignition and lean flameout condition. The uniformity of fuel/air mixture distribution in the primary zone of the new design decreases NOX emission, meanwhile the fuel air mixture in pilot recirculation zone is locally rich to improve flameout and ignition.

A Preliminary Study on Lean Blowout of One Combustion Stability Device

The lean blowout experiments of the combustion stability device A (multi-vortexes-dome combustor model) have been carried out at atmospheric pressure. In contrast with the experimental data of device B, and the result shows that the lean blowout performance of the device A is superior to the device B at low operating condition. Furthermore, both the devices A and B were modeled, and the combustion numerical simulations were performed with the steady Flamelet model of non-premixed combustion and the simplified mechanism of methane-air reaction with 14 species and 26 step elementary reactions. The numerical results are in agreement with the experimental phenomena.

A study on lean blowout of multi-vortexes-dome model combustor

The lean blowout experiments of the combustion stability device A (multi-vortexes-dome model combustor) have been carried out at atmospheric pressure. Compared with the device B (single-vortex-dome model combustor), the experimental results show that the device A has a superior lean blowout performance when the combustor reference velocity is within the range from 3.50m/s to 5.59m/s ( while the liner reference velocity is between 3.84 and 6.13m/s), and this superiority will remain stable after the inlet air flow rate reaches a certain value. In order to analyze the phenomena and experimental results, the numerical simulation method is used, and the strain rate and the cold reflux impact are employed to further explain the reason that causes the difference between the two devices’ lean blowout characteristics.

Experiment and simulation study on lean blow-out of trapped vortex combustor with various aspect ratios

This paper investigated the lean blow-out (LBO) performance of several combustors which utilized trapped vortex in the cavity to improve the flame stability. Experiments and simulation study had been performed for various height to length (Hf/L) ratios of the cavity. The experiment results showed that the minimum pressure drop across the combustor occurred when the Hf/L ratio was 0.8; and that very low overall LBO equivalence ratios were observed over a wide range of primary air flows at the same H/L ratio. In the simulations, the large eddy simulation (LES) was used to predicate the transient flow field in the cavity. Simulation results showed that the core of the trapped vortex was in the middle of the cavity at Hf/L=0.8, and the velocity profile of the vortex was better organized than those of other combustors with different Hf/L ratios. Moreover, the simulated period of vortex swirling was the shortest at Hf/L=0.8. Therefore, the experimental observations on the LBO performance of several combustors with different Hf/L ratios were well explained by the present simulation results. Based on the experimental data, a preliminary study of the empirical correlation of LBO was conducted on trapped vortex combustor (TVC). Compared with Lefebvreʼs empirical correlation, the proposed new empirical correlation has better agreement with the experimental data.

Combustion of hydrogen in an experimental trapped vortex combustor

Combustion performances of pure hydrogen in an experimental trapped vortex combustor have been tested under different operating conditions. Pressure fluctuations, NOx emissions, OH distributions, and LBO (Lean Blow Out) were measured in the tests. Results indicate that the TVC test rig has successfully realized a double vortex construction in the cavity zone in a wide range of flow conditions. Hydrogen combustion in the test rig has achieved an excellent LBO performance and relatively low NOx emissions. Through comparison of dynamic pressure data, OH fluctuation images, and NOx emissions, the optimal operating condition has been found out to be Φp =0.4, fuel split =0.4, and primary air/fuel premixed.

Emissions Performance of the Parker Macrolaminate Premixer Tested Under Simulated Engine Conditions

Single-injector high-pressure rig evaluation of the prototype Parker macrolaminate dual fuel premixer (previously tested at NETL, Mansour et al., 2001) with pressure swirl macrolaminate atomizers was conducted under simulated engine operating conditions running on No. 2 diesel fuel (DF2). Emissions, oscillations and lean blowout (LBO) performance on liquid fuel at high, part and no load operating points (pressures of 160, 100, 120 psig, and inlet temperatures of 690, 570, 590°F, respectively) and various pressure drops (ΔP/P) and air fuel ratio conditions were investigated. The results indicate that the Parker premixer design has the potential to reduce the DF2 NOX emission to below 15 ppmv, 15% O2. At simulated high load conditions with a nominal flame temperature TPZ of 2700°F, the NOX and CO emissions are approximately 10 and 2.5 ppmv at 15% O2, respectively. These NOX results have not been corrected for fuel bound nitrogen (FBN). From the studies of Lee (2000), small amounts of FBN in the liquid fuel generally are completely converted over to fuel NOX under lean premixed conditions. The fuel tested has a nominal 60 ppmw of FBN which converts to an estimated fuel NOX of 4 ppmv at 15% O2. These results compare extremely favorable to existing commercially available premixer technologies tested under similar rig operating conditions. More importantly, the NOX yield for the Parker Macrolaminate premixer appears to be independent of operating conditions (from high to no load and various pressure drop conditions). Variations in combustor pressure, inlet temperature T2 and residence time (τ) or pressure drop (ΔP/P) does not seem to have an effect on the formation of NOX. According to Leonard and Stegmaier (1993), insensitivity of NOX formation to operating conditions is a good indication of high degree of premixing. Additionally, the premixer NOX data is only 1 to 2 ppmv higher than the jet stirred reactor (JSR) results (ran at T2=661°F,PCD=1 atm and TPZ=2762°F with similar DF2) of Lee et al. (2001) further confirming the quality of premixing achieved. Combustion driven oscillations was not investigated by tuning the rig so that oscillations would not be a factor.