Combustor Lean Blowout Research Articles

Experimental and numerical study on flow/flame interactions and pollutant emissions of premixed methane-air flames with enhanced lean blowout hydrogen injection

This study investigates experimentally and numerically the stability, combustion, and emissions characteristics of premixed swirl-stabilized methane/air flames with enhanced lean blowout (ELBO) injection of hydrogen in the non-premixed mode for higher turndown ratio gas turbines. The study analyzed the effects of hydrogen fraction (HF: volumetric percentage of H2 in the total fuel) ranging from 0 to 25% and equivalence ratio (φ) ranging from 0.5 to 0.893 on flow/flame interactions and flame stability, structure, and emissions. The introduction of non-premixed H2 yields two conflicting outcomes, with enhancements in reaction kinetics and flame speed yet counteracted by increased hydrogen jet momentum dispersing the flame. The combustor lean blowout (LBO) limit remains relatively unaffected (φoverall≈ 0.5) by H2 injection. Flame temperature is primarily influenced by φ and minorly by HF. Increasing HF resulted in localized temperature rises around H2 jets without an overall increase in flame temperature, offering a promising strategy for reduction of NOx emissions. Nevertheless, using H2 as a pilot fuel leads to an increase in intermediate species like OH, H, and O, contributing to flame stabilization. However, this practice also results in higher CO and unburned hydrocarbons emissions due to the inherent characteristics and heightened reactivity of H2.

Advanced fuel limit design to improve dynamic performance of marine three-shaft gas turbine

Gas turbine powered integrated power system can effectively supply for shipboard weaponry, representing an obvious developing trend of world naval ship power. However, in the large pulsed power load environment, system stable operation still suffers from insufficient gas turbine power response. In order to improve the dynamic performance and transient stability of three-shaft gas turbine, in this paper, fuel limit design is focused to a novel perspective. As a basis, a high accuracy model of three-shaft gas turbine is established, the model accuracy is validated against actual test data. By decoupling and analyzing multi-inertia coupling structure of three-shaft gas turbine, a transient performance prediction method is proposed, and the advanced fuel limit design considering multiple factors such as compressor surge, turbine overtemperature and combustor lean blowout is suggested. MATLAB/Simulink simulations are carried out to present the performance of advanced fuel limit design under different operating conditions. The simulation results indicate that, in a set large pulsed power load environment, the upgraded fuel limit could increase fuel flow rate and power response by a multiple of approximately 3.1 while satisfying safe indicators, reducing the transient speed regulation from 21.7 % to 7.2 %, meeting the stability capability to adapt for load impact.

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.

Experimental and numerical investigation of stability and emissions of hydrogen-assisted oxy-methane flames in a multi-hole model gas-turbine burner

This paper reports experimental and numerical study of stability and combustion characteristics of premixed oxy-methane flames with hydrogen-enrichment (CH4–H2/O2–CO2 flames) in a model multi-hole burner for clean energy production in gas turbines. The combustor lean blow-out (LBO) limit was presented on an equivalence ratio (Ø) - hydrogen fraction (HF: volumetric fraction of H2 in a mixture of H2+CH4) map spanning over Ø-values of 0.1–1 and HF-values of 0–70% at fixed hole jet velocity and oxygen fraction (OF: volumetric fraction of O2 in a mixture of O2+CO2) of 5.2 m/s and 30%, respectively. The condition of the combustion chamber is assumed to be depicted by the corrugated premixed flame regime. The premixed turbulent flame was modeled using the reaction progress variable flame front topology approach with the Large Eddy Simulation (LES) technique. The recorded combustor stability maps showed great resistance of the micromixer burner technology to flashback, recommending its use for stable gas turbine operation. The results show that H2-enrichment widens the combustor operability limits (higher turndown ratio) by extending the LBO from Ø = 0.45 at HF = 0% down to Ø = 0.15 at HF = 70% with a slight reduction in the heat release factor by 0.1. The high reactivity and higher flame speed of H2 ensures the sustenance of flame at lower equivalence ratios. At high equivalence ratios, H2 addition enhances the reaction rates and makes both the primary and secondary reaction zones shorter and more intense. Increasing HF leads to increase in the Damköhler number (Da) and decrease in both the Karlovitz number (Ka) and flame thickness. The CO emission at the combustor outlet reduced significantly from 241 ppm at HF = 0% to 33.1 ppm at HF = 10%, then it increased back to 364 ppm at HF = 50%.

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.

Prevention of lean flame blowout using a predictive chemical reactor network control

Optimization of efficiency and pollution control for gaseous species and particulate matter are common to any combustion system. Combustor lean blowout (LBO) is a concern for aircraft safety and for land-based gas turbines designed to operate at lean equivalence ratios to achieve better fuel efficiency and to limit NOx emissions. This paper provides an experimental demonstration of model-based control applied to a laboratory jet-stirred reactor (JSR) approaching LBO. The approach uses (1) combustor temperature measurements, coupled with (2) the calculation of free radical concentrations in the reactor using a real-time chemical reactor network (RT-CRN) model as the reactor approaches LBO, which in turn (3) are used by a predictive control algorithm to achieve stable combustion. The RT-CRN represents the combustor as three perfectly stirred reactors (PSRs) in series with a recirculation pathway; the model inputs include real-time measurements of temperature and mass flow rates of fuel and air. In a series of experiments, the combustor is operated on a premixed methane-air mixture; after achieving stable combustion, the air flow rate is increased beyond the stable air-fuel ratio either as a step function or by ramping up linearly. The predictive RT-CRN control algorithm calculates the distribution of hydroxyl (OH) radicals in the free jet, impinging jet, and recirculation regions of the JSR in near real-time (∼1 s delay), and determines the leanest stable state based on the OH uniformity in the combustor. As the OH shifts towards the recirculation region, the reactor approaches LBO, if this condition is detected the control algorithm injects additional fuel; reactor stabilization is achieved within a 5–15 s time frame. Although this proof-of-concept demonstration is performed for LBO control in a JSR with ceramic walls, the control methodology is applicable to other types of high-intensity recirculation stabilized combustors.

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

Characterization of Gas Turbine Lean Blowout During Frequency Excursions in Power Networks

While gas turbines are popular in power networks due to reduced emissions and economical operation, their frequency response characteristics are substantially different from other conventional generation technologies; hence, gas turbine dynamics may influence system stability during significant frequency excursions. This study characterizes the impact of gas turbine combustor lean blowout (LBO) while considering large frequency excursions and, in particular, during short-circuit faults. Studies have shown that combined-cycle gas turbines are more vulnerable to an LBO condition during short-circuit events when they operate at rated power output. A sensitivity analysis was also carried out against a number of factors influencing the LBO, revealing that generator loading and rate-of-change-of-frequency are the main contributing factors for the LBO. Furthermore, mitigation strategies are also proposed to alleviate the LBO condition during large frequency excursions.

Ignition and Emission Characteristics of Surrogate and Practical Jet Fuels

Aircrafts have been identified as a significant source of particulate matter (PM) emissions, which have been associated with adverse health effects and decreased ambient air quality. Recent published studies have shown that synthetic fuels, such as iso-paraffinic Fischer−Tropsch (F−T) fuels, can significantly reduce PM emissions compared to operation with petroleum-derived fuels. It is believed that the absence of aromatics in synthetic fuels slows the molecular growth to higher ringed polycyclic aromatic hydrocarbons (PAHs), which ultimately leads to lower soot emissions. However, it is not known if differences in chemical composition between synthetic and conventional (JP-8) fuel also change the ignition and combustion characteristics, which likely impact high altitude relight and combustor lean blowout (LBO) limits. This study was conducted to investigate how differences in fuel composition can impact the chemical ignition and emissions characteristics of a fuel and to help deconvolute the effect of physical and chemical processes on combustion efficiency. Only the chemical ignition delay was considered as the fuels were prevaporized and premixed prior to ignition. The fuels investigated in this study were a F−T processed synthetic jet fuel (synjet), a conventional JP-8, 2-methylheptane (surrogate synjet fuel), and a mixture of 80% heptane and 20% toluene (surrogate JP-8). The experiments were conducted using a modified single-pulse reflected shock tube instrumented to measure fuel ignition delay times and PAH and soot yields. The shock tube results show that both the actual and surrogate synjet fuels produced lower soot and PAH emissions than the actual and surrogate JP-8 fuels at temperatures of interest. These results are consistent with previous turbine engine test results with the actual fuels. It was observed, however, that, for the conditions tested, both surrogate and actual synjet and JP-8 fuels evaluated had similar ignition delays, which may imply that there is no correlation between soot emissions and chemical ignition delay. However, these results may be controlled by the test conditions, and accordingly, future tests at different conditions (e.g., higher equivalence ratios, pressures, lower pre-ignition temperatures) are warranted.