Low Emission Combustion System Research Articles

Characterization of diesel spray combustion under micro-hole and ultra-high injection pressure conditions-analyses of diffused back-illumination imaging and OH* chemiluminescence imaging

This study investigated the spray combustion characteristics of diesel fuel using the Diffuse Back-illumination Imaging (DBI), Direct Photographic, and OH* chemiluminescence methods under different injection pressures (100–300 MPa) and different hole diameters (0.07–0.133 mm). The results indicated that at a certain point, the downstream of the spray, which holds a strong turbulent mixing, starts to disappear gradually without bright flames due to the cool flame combustion process. Based on this process, the ignition timing was determined using the space integral of intensity and optical thickness through the DBI method, which was validated by the OH* chemiluminescence method. The utilization of a micro-hole diameter injector and ultra-high injection pressure can effectively reduce ignition delay. Significant oxidation processes were observed both downstream and upstream for the micro-hole injector under ultra-high injection pressure. A parameter utilizing spatially integrated natural luminosity to OH* chemiluminescence ratio showed that increasing injection pressure and reducing hole diameter effectively reduced soot under unit fuel oxidation conditions. And predicted model results of droplet diameter and equivalence ratio (Siebers' and Hiroyasu's model) were used to analyze the experimental results. These findings contribute to the understanding of spray combustion characteristics and inform the development of efficient and low-emission combustion systems.

Investigations on Emission Characteristics of Methane in Small Scale a Swirl Flameless Combustor: Using Preheating Air Diluted CO2 and N2 Gas at Various Temperatures

In order to reduce the damage to the environmental, it is desirable to have low emission combustion and high-efficiency system of operation. In achieving this, the multi-stages and exhaust gas recirculation (EGR) were adopted to reduce NOx formation during combustion. In this paper, a numerical study of the impact of diluted preheated oxidizer variables on NOx emissions from methane combustion was performed. This study utilizes Computational Fluid Dynamics (CFD) analysis to determine the influence of preheating fuel and air on the combustion efficiency when asymmetric vortex flameless was applied on different supply tangential air location at different oxygen concentrations. The design parameters utilized are diluted N2 and CO2, oxygen concentrations of 10%, 7% and 5%, and air temperatures that were set at 300 K, 500 K, 700 K and 900 K, respectively. The exhaust gas recirculation (EGR) was simulated using CO2 gas and N2 gas. The results show that by oxygen concentration has direct relationship with NOx emission for all equivalence ratios. Apart from that, CO2 dilution air offers better results than N2 dilution in reducing NOx emissions. In terms of preheating air, higher NOx emission was observed with the increase of air temperature. However, the effect of preheating air on the NOx emission is greater than the effect of preheating of fuel. Based on these results, numerous ports were considered important to achieve a good mix of air and fuel. The analysis outcome shows that more inlet tangential air has a significant influence on combustion temperature and NOx emission.

A Stochastic and Bayesian Inference Toolchain for Uncertainty and Risk Quantification of Rare Autoignition Events in Dry Low-Emission Premixers

Abstract Quantification of aleatoric uncertainties due to the inherent variabilities in operating conditions and fuel composition is essential for designing and improving premixers in dry low-emissions (DLE) combustion systems. Advanced stochastic simulation tools require a large number of evaluations in order to perform this type of uncertainty quantification (UQ) analysis. This task is computationally prohibitive using high-fidelity computational fluid dynamic (CFD) approaches such as large eddy simulation (LES). In this paper, we describe a novel and computationally efficient toolchain for stochastic modeling using minimal input from LES, to perform uncertainty and risk quantification of a DLE system. More specially, high-fidelity LES, chemical reactor network (CRN) model, beta mixture model, Bayesian inference and sequential Monte Carlo (SMC) are integrated into the toolchain. The methodology is applied to a practical premixer of low-emission combustion system with dimethyl ether (DME)/methane–air mixtures to simulate auto-ignition events at different engine conditions. First, the benchmark premixer is simulated using a set of LESs for a methane/air mixture at elevated pressure and temperature conditions. A partitioning approach is employed to generate a set of deterministic chemical reactor network (CRN) models from LES results. These CRN models are then solved at the volume-average conditions and validated by LES results. A mixture modeling approach using the expectation-method of moment (E-MM) is carried out to generate a set of beta mixture models and characterize uncertainties for LES-predicted temperature distributions. These beta mixture models and a normal distribution for DME volume fraction are used to simulate a set of stochastic CRN models. The Bayesian inference approach through SMC method is then implemented on the results of temperature distributions from stochastic CRN models to simulate the probability of auto-ignition in the benchmark premixer. The results present a very satisfactory performance for the stochastic toolchain to compute the auto-ignition propensity for a few events with a particular combination of inlet temperature and DME volume fraction. Characterization of these rare events is computationally prohibitive in the conventional deterministic methods such as high-fidelity LES.

Influence of Hole-to-Hole Interaction on the Acoustic Behavior of Multi-Orifice Perforated Plates

Abstract A key factor for developing low-emission combustion systems in modern gas turbines and aero-engines is the acoustic liner's optimized design. Several models are available in the literature for the acoustic impedance of perforated acoustic liners. Most of these impedance models neglect the interaction effect between the orifices. In practice, the orifices are generally closely distributed such that the interactions between acoustic radiation from neighboring orifices can affect their acoustical behavior. The hole-to-hole interaction effect may change the resonance frequency of the resonator due to the nonplanar wave propagation in the cavity, the orifices in the perforated plate, and the near-wall region in the combustor. Considering this effect may help to predict the resonance frequency of the resonator accurately. In this work, a three-dimensional (3D) analytical approach is developed to account for the nonplanar wave propagation in the cavity and orifices on the perforated plate. The present study employs the proposed 3D analytical method to determine the hole-to-hole interaction end correction of multi-orifice perforated plates. Additionally, the hole-to-hole interaction end correction from a series of perforated plates with different orifice radii and spacings is obtained via the finite element method. Perforated plate specimens with different center-to-center hole spacing are tested using an impedance tube. Experimental results show that the resonance frequency is shifted toward a lower frequency with decreasing holes' spacing. The resulting model is compared with the experiments and the end-correction models available in the literature. The comparison shows that the available end-correction models cannot capture the hole-to-hole interaction effect, which is observed in experiments. In contrast, the proposed model can reproduce measurements with high quality. The resulting model demonstrates that the acoustic end-correction length for orifices is closely related to the perforated plate's porosity ratio and orifice radius. The proposed model is readily applicable in the design of multi-orifice perforated plates.

Reducing Uncertainty in the Onset of Combustion Instabilities Using Dynamic Pressure Information and Bayesian Neural Networks

Abstract Modern low-emission combustion systems with improved fuel-air mixing are more prone to combustion instabilities and, therefore, use advanced control methods to balance minimum NOx emissions and the presence of thermoacoustic combustion instabilities. The exact operating conditions at which the system encounters an instability are uncertain because of sources of stochasticity, such as turbulent combustion, and the influence of hidden variables, such as unmeasured wall temperatures or differences in machine geometry within manufacturing tolerances. Practical systems tend to be more elaborate than laboratory systems and tend to have less instrumentation, meaning that they suffer more from uncertainty induced by hidden variables. In many commercial systems, the only direct measurement of the combustor comes from a dynamic pressure sensor. In this study, we train a Bayesain Neural Network to predict the probability of onset of thermoacoustic instability at various times in the future, using only dynamic pressure measurements and the current operating condition. We show that on a practical system, the error in the onset time predicted by the Bayesain Neural Networks is 45% lower than the error when using the operating condition alone and more informative than the warning provided by commonly used precursor detection methods. This is demonstrated on two systems: (i) a premixed hydrogen/methane annular combustor, where the hidden variables are wall temperatures that depend on the rate of change of operating condition, and (ii) full-scale prototype combustion system, where the hidden variables arise from differences between the systems.

Multi-bifurcation behaviors of stability regimes in a centrally staged swirl burner

Multi-bifurcation behaviors of staged swirl flames fueled with methane at atmospheric pressure are experimentally investigated by varying the global equivalence ratio (ϕglo). Based on the characteristics of measured pressure oscillations and the associated results of phase space reconstruction, recurrence plots, and synchrosqueezing-transform-based time-frequency analysis, the multi-bifurcation behaviors of this thermoacoustic system with four different stability regimes have been identified. With incremental increase in ϕglo from 0.55 to 0.79, these four stability regimes follow the sequence of a quiet mode (Regime I), the first limit cycle with moderate oscillations (Regime II), an intermediate state with intermittent bursts of multi-modes (Regime III), and the second limit cycle with much stronger oscillations (Regime IV). The flame dynamics in Regimes II and IV undergoing limit cycle oscillations are compared. The flame structure in Regime II displays an attached twin-flame structure, the same as that observed in Regime I. However, a large-scale periodic convective motion is found in Regime IV, which is identified to be the main thermoacoustic driving factor in the local Rayleigh index maps. Further experiments are carried out by continuously increasing ϕglo to examine the synchrosqueezing-transform spectra of transient processes during the two bifurcations. The present investigation is instrumental in obtaining a fundamental understanding of nonlinearity and multi-bifurcation of thermoacoustic instabilities in centrally staged swirl combustors, which is vital in guiding the early stage design and developing detection/control strategies in practical low-emission combustion systems.

Efficient emission modelling in lean premixed flames with pre-tabulated formation characteristics

It is practically important to accurately predict NOx and CO emissions in lean premixed flames for the development of fuel-efficient and low-emission combustion systems. In this study, the efficient modelling with pre-tabulated formation characteristics of NOx and CO is systemically investigated. Their formation characteristics for turbulent flames in the flamelet and thin reaction zone regimes are first quantified with one-dimensional adiabatic premixed flames through the incorporation of turbulence induced diffusion. Results show that the formation of NOx and CO can be characterized by two different stages, i.e., a rapid increase of both in flame front and the linear growth for NOx and exponential decay for CO in post-flame zone. An efficient NOx and CO modelling approach is formulated and demonstrated in a full-scale methane gas turbine combustor, in which species NOx and CO are transported and solved, with the source terms being modelled by pre-tabulated formation characteristics from one-dimensional premixed flames with detailed chemical kinetics. Realizable k-epsilon model and finite rate/eddy dissipation model in conjunction with a two-step global mechanism are employed to primarily predict the flow and flame characteristics. Results show that the predicted NOx and CO agree with experimental measurements over a wide range of equivalence ratios. The discrepancy in NOx emission can be accounted by fuel/air unmixedness. For CO, the rapid increase due to the incomplete CO oxidation resulting from its increasing characteristic oxidation time near lean blow-out (LBO) is correctly captured. It is further shown that the predicted CO emission is sensitive to combustion/kinetics model parameters and the accurate prediction of flame shape and dynamics is crucial to capture the trend of CO formation near LBO.

Bayesian inference and uncertainty quantification for hydrogen-enriched and lean-premixed combustion systems

Development of probabilistic modelling tools to perform Bayesian inference and uncertainty quantification (UQ) is a challenging task for practical hydrogen-enriched and low-emission combustion systems due to the need to take into account simultaneously simulated fluid dynamics and detailed combustion chemistry. A large number of evaluations is required to calibrate models and estimate parameters using experimental data within the framework of Bayesian inference. This task is computationally prohibitive in high-fidelity and deterministic approaches such as large eddy simulation (LES) to design and optimize combustion systems. Therefore, there is a need to develop methods that: (a) are suitable for Bayesian inference studies and (b) characterize a range of solutions based on the uncertainty of modelling parameters and input conditions. This paper aims to develop a computationally-efficient toolchain to address these issues for probabilistic modelling of NOx emission in hydrogen-enriched and lean-premixed combustion systems. A novel method is implemented into the toolchain using a chemical reactor network (CRN) model, non-intrusive polynomial chaos expansion based on the point collocation method (NIPCE-PCM), and the Markov Chain Monte Carlo (MCMC) method. First, a CRN model is generated for a combustion system burning hydrogen-enriched methane/air mixtures at high-pressure lean-premixed conditions to compute NOx emission. A set of metamodels is then developed using NIPCE-PCM as a computationally efficient alternative to the physics-based CRN model. These surrogate models and experimental data are then implemented in the MCMC method to perform a two-step Bayesian calibration to maximize the agreement between model predictions and measurements. The average standard deviations for the prediction of exit temperature and NOx emission are reduced by almost 90% using this method. The calibrated model then used with confidence for global sensitivity and reliability analysis studies, which show that the volume of the main-flame zone is the most important parameter for NOx emission. The results show satisfactory performance for the developed toolchain to perform Bayesian inference and UQ studies, enabling a robust and consistent process for designing and optimising low-emission combustion systems.

An alternative approach to evaluate fuel/air mixing quality

ABSTRACTA practical method to evaluate quantitatively the uniformity of fuel/air mixing is essential for research and development of advanced low-emission combustion systems. Typically, this is characterised by measuring an unmixedness parameter or a uniformity index. An alternative approach, based on the fuel/air equivalence ratio distribution, is proposed and demonstrated in a simple methane/air venturi mixer. This approach has two main advantages: it is correlated with the fuel/air mixture combustion temperature, and the maximum temperature variation caused by fuel/air non-uniformity can be estimated. Because of these, it can be used as a criterion to check fuel/air mixing quality, or as a target for fuel/air mixer design with acceptable maximum temperature variation. For the situations where the fuel/air distribution non-uniqueness issue becomes important for fuel/air mixing check or mixer design, an additional statistical supplementary criterion should also be used.

Features of commissioning a gas turbine unit with a low-emission combustion chamber

Environmental safety issues are a priority in the modernization development of aviation or ground-based combustion chambers of gas turbine engines. In order to reduce the emission of harmful substances from combustion products, a low-emission combustion system, which is based on the concept of LPP (Lean-premixed and prevaporised), is being used today. This concept implements the principle of burning “ultra-poor” premixed air-fuel mixtures. The operational experience of combustion chambers developed in accordance with the indicated concept shows that one of the implementation problems is the difficulty in ensuring a good start. This paper presents the results of adjusting the operating process of a modern combustion chamber, launching a gas turbine unit, including drawing up a fuel supply control algorithm, experiments with igniting ignition devices and setting the gas turbine on idle mode. A feature of the commissioning work is the debugging of the operating process of the combustion chamber directly as part of the gas turbine unit, bypassing the traditional pilot-testing on the rig.

Numerical Investigation of a High Momentum Jet Flame at Elevated Pressure: A Quantitative Validation with Detailed Experimental Data

The development of efficient low emission combustion systems requires methods for an accurate and reliable prediction of combustion processes. Computational Fluid Dynamics (CFD) in combination with combustion modelling is an important tool to achieve this goal. For an accurate computation adequate boundary conditions are crucial. Especially data for the temperature distribution on the walls of the combustion chamber are usually not available. The present work focuses on numerical simulations of a high momentum jet flame in a single nozzle FLOX® type model combustion chamber at elevated pressure. Alongside the balance equations for the fluid the energy equation for the solid combustor walls is solved. To assess the accuracy of this approach, the temperature distribution on the inner combustion chamber wall resulting from this Conjugate Heat Transfer (CHT) simulation is compared to measured wall temperatures. The simulation results within the combustion chamber are compared to detailed experimental data. This includes a comparison of the flow velocities, temperatures as well as species concentrations. To further assess the benefit of including the solid domain in a CFD simulation the results of the CHT simulation are compared to results of a CFD computation where constant temperatures are assumed for all walls of the combustion chamber.

Development and prospects for the introduction of a low-emission combustion system for ground-based gas turbine engines and gas turbine units

Today, more and more “stringent” requirements are established in the world for the emission of harmful substances in the combustion products of gas turbines operated and newly developed, which is why the issue of ensuring environmental safety is relevant. The article presents the basic principles of organizing low - emission fuel combustion based on a generalization of experience in the successful operation of gas turbines of the NK family, which ensured that modern requirements for reliability and environmental safety are met. An example is given of the modernization of the gas turbine combustion chamber in order to reduce the levels of emissions of harmful substances. The experience of introducing into serial production of additive technology for the manufacture of basic elements of low-emission combustion chamber using selective laser melting technology is described.

Technology of low-emission fuel combustion and conceptual structure of the combustion chamber of a gas-turbine power plant

Currently, the priority for improvement of the combustion chambers of aircraft gas turbine engines and ground-based gas turbine plants is associated with a decrease in the concentration of harmful substances in the exhaust gases while ensuring fuel economy and operational efficiency. Pride of place in the design of a gas turbine power plant goes to solving the problem of organizing the combustion process, i.e. the development of a low-emission combustion system that provides high efficiency and environmental safety. Thus, ecology today determines not only the appearance of a combustion chamber, but also that of a gas turbine power plant as a whole. Below, an attempt is made to summarize the results of developing a low-emission combustion system for various types of combustion chambers of convertible gas turbine power plants and to present a unified approach to the problem of designing a conceptual structure of a low-emission combustion chamber.

Development of a Highly Flexible Variable Valvetrain System for Combustion System Investigations

<div class="section abstract"><div class="htmlview paragraph">For the optimization and extension of operating range of future combustion systems aiming at ultra-low emissions and high efficiency, the control of gas exchange plays a major role. Important parameters for optimization are e.g. volumetric efficiency, residual gas control, in-cylinder charge motion and precise control of the level of homogeneity or inhomogeneity of the charge as required by the particular combustion mode. In addition, advanced operating modes such as Miller or Atkinson cycle or gasoline compression ignition demand a high degree of variability in cam timing. A highly flexible variable valvetrain has been designed for the investigation and development of such new combustion processes. This novel valvetrain is based on a mechanically fully variable actuation concept using two independently rotating cam disks per valve. By this arrangement, new degrees of freedom in the design of the valve opening curve arise. For a single cylinder research engine using a four-valve cylinder head, this valvetrain has been designed in a way so that all four valves can be controlled independently, offering the possibility of e.g. inlet valve phasing combined with a second event on the exhaust. The new valvetrain has been manufactured and tested on a mechanical component test bench. In a “backward” design approach, the valve lift curves and the timing variation range required for the generation of particular variations of in-cylinder charge motion were defined by 3D CFD simulation. On this basis, the layout of the valvetrain components for realization in the research engine was defined. The new valvetrain will be employed for the development of highly efficient low-emission combustion systems on the test bench.</div></div>

Extension of Fuel Flexibility by Combining Intelligent Control Methods for Siemens SGT-400 Dry Low Emission Combustion System

Extension of gas fuel flexibility of a current production SGT-400 industrial gas turbine combustor system is reported in this paper. A SGT-400 engine with hybrid combustion system configuration to meet a customer's specific requirements was string tested. This engine was tested with the gas turbine package driver unit and the gas compressor-driven unit to operate on and switch between three different fuels with temperature-corrected Wobbe index (TCWI) varying between 45 MJ/m3, 38 MJ/m3, and 30 MJ/m3. The alteration of fuel heating value was achieved by injection or withdrawal of N2 into or from the fuel system. The results show that the engine can maintain stable operation on and switching between these three different fuels with fast changeover rate of the heating value greater than 10% per minute without shutdown or change in load condition. High-pressure rig tests were carried out to demonstrate the capabilities of the combustion system at engine operating conditions across a wide range of ambient conditions. Variations of the fuel heating value, with Wobbe index (WI) of 30 MJ/Sm3, 33 MJ/Sm3, 35 MJ/Sm3, and 45 MJ/Sm3 (natural gas, NG) at standard conditions, were achieved by blending NG with CO2 as diluent. Emissions, combustion dynamics, fuel pressure, and flashback monitoring via measurement of burner metal temperatures, were the main parameters used to evaluate the impact of fuel flexibility on combustor performance. Test results show that NOx emissions decrease as the fuel heating value is reduced. Also note that a decreasing fuel heating value leads to a requirement to increase the fuel supply pressure. Effect of fuel heating value on combustion was investigated, and the reduction in adiabatic flame temperature and laminar flame speed was observed for lower heating value fuels. The successful development program has increased the capability of the SGT-400 standard production dry low emissions (DLE) burner configuration to operate with a range of fuels covering a WI corrected to the normal conditions from 30 MJ/N·m3 to 49 MJ/N·m3. The tests results obtained on the Siemens SGT-400 combustion system provide significant experience for industrial gas turbine burner design for fuel flexibility.

Experimental and Numerical Investigation of Fuel–Air Mixing in a Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustor

This paper presents the results of an investigation in which the fuel/air mixing process in a single slot within the radial swirler of a dry low emission (DLE) combustion system is explored using air/air mixing. Experimental studies have been carried out on an atmospheric test facility in which the test domain is a large-scale representation of a swirler slot from a Siemens proprietary DLE combustion system. Hot air with a temperature of 300 °C is supplied to the slot, while the injected fuel gas is simulated using air jets with temperatures of about 25 °C. Temperature has been used as a scalar to measure the mixing of the jets with the cross-flow. The mixture temperatures were measured using thermocouples while Pitot probes were used to obtain local velocity measurements. The experimental data have been used to validate a computational fluid dynamics (CFD) mixing model. Numerical simulations were carried out using CFD software ansys-cfx. Due to the complex three-dimensional flow structure inside the swirler slot, different Reynolds-averaged Navier–Stokes (RANS) turbulence models were tested. The shear stress transport (SST) turbulence model was observed to give best agreement with the experimental data. The momentum flux ratio between the main air flow and the injected fuel jet, and the aerodynamics inside the slot were both identified by this study as major factors in determining the mixing characteristics. It has been shown that mixing in the swirler can be significantly improved by exploiting the aerodynamic characteristics of the flow inside the slot. The validated CFD model provides a tool which will be used in future studies to explore fuel/air mixing at engine conditions.

Investigation of Flow Aerodynamics for Optimal Fuel Placement and Mixing in the Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustion Chamber

This paper is concerned with optimizing the fuel–air mixing processes that take place within the radial swirler slot of a dry low emission (DLE) combustion system. The aerodynamics of the flow within the slot is complex and this, together with the placement of the fuel holes with cross injection, controls the mixing of the fuel and air. Computational fluid dynamics (CFD) with the shear stress transport (SST) (k–ω) turbulence model was used for flow and mixing predictions within the radial swirler slot and for conducting a CFD-based design of experiments (DOE) optimization study, in which different parameters related to the fuel injection holes were varied. The optimization study was comprised of 25 orthogonal design configurations in the Taguchi L25 orthogonal array (OA). The test domain for the CFD, and its experimental validation, was a large-scale representation of a swirler slot from the Siemens proprietary DLE combustion system. The DOE study showed that the number of fuel holes, injection hole diameter, and interhole distance are the most influential parameters for determining optimal fuel mixing. Consequently, the optimized mixing configuration obtained from the above study was experimentally tested on an atmospheric test facility. The mixing patterns from experiments at various axial locations across the slot are in good agreement with the mixing predictions from the optimal CFD model. The optimized fuel injection design improved mixing compared with the baseline design by about 60%.

PERFORMANCE EVALUATION AND FLAME STABILIZATION OF STAGNATION POINT REVERSE FLOW COMBUSTOR

The conventional gas turbine engines use straight flow combustors. The reverse-flow layout effectively uses the air flow to cool down the combustor liner and the transition piece as a counter flow heat exchanging process. The absorbed heat by the air is returned back to the system. The reverse flow configuration causes the flow to stagnate and hot products to reverse and leave the combustor. One of the major challenges facing designers of low NOx emission combustion systems is flame stability, as the weaker combustion process is more vulnerable to small perturbations in combustor operating conditions. Since further reduction of NOx will likely require even leaner mixtures, schemes for lean stability extension must be considered. Stability can be dependent on the balance between flow and flame propagation velocities. In combustors where combustion is limited by reaction rates, however practical combustors do not operate in either limit. To stabilize a flame in the desired region of interest, various stabilization methodologies are adopted that either enhance the flame propagation speeds or create zones with low velocities where a flame can be sustained for inspection of premixed flame stability in Stagnation Point Reverse Flow combustor model, using Computational Fluid dynamics(CFD). The CFD analysis yielded the results which go with actual experimental results.

Determination of laminar burning velocities for lean low calorific H2/N2 and H2/CO/N2 gas mixtures

Combustion of lean and ultra-lean synthetic H2/CO mixtures that are highly diluted in inert gases is of great importance in several fields of technology, particularly in the field of post combustion for combined heat and power (CHP) systems based on fuel cell technology. In this case H2/CO mixtures occur via hydrocarbon reforming and their complete conversion requires efficient, compact and low emission combustion systems. In order to design such systems, knowledge of global flame properties like the laminar burning velocity, is essential. Using the heat flux burner method, laminar burning velocities were experimentally determined for highly N2 diluted synthetic H2 and H2/CO mixtures with low calorific value, burning with air, at ambient temperature and atmospheric pressure. Furthermore, numerical 1-D simulations were performed, using a series of different chemical reaction mechanisms. These numerical predictions are analysed and compared with the experimental data.

Effect of Change in Fuel Compositions and Heating Value on Ignition and Performance for Siemens SGT-400 Dry Low Emission Combustion System

The influence of changes in fuel composition and heating value on the performance of an industrial gas turbine combustor was investigated. The combustor tested was a single cannular combustor for Siemens SGT-400 13.4 MW dry low emission engine. Ignition, engine starting, emissions, combustion dynamics, and flash back through burner metal temperature monitoring were among the parameters investigated to evaluate the impact of fuel flexibility on combustor performance. Lean ignition and extinction limits were measured for three fuels with different heat values in term of Wobbe Index (WI): 25, 28.9, and 45 MJ/Sm3 (natural gas). The test results show that the air fuel ratio at lean ignition/extinction limits decreases and the margin between the two limits tends to be smaller as fuel heat value decreases. Engine start tests were also performed with a lower heating value fuel and results were found to be comparable to those for engine starting with natural gas. The combustor was further tested in a high pressure air facility at real engine operating conditions with different fuels covering WIs from 17.5 to 70 MJ/Sm3. The variation in fuel composition and heating value was achieved in a gas mixing plant by blending natural gas with CO2, CO, N2, and H2 (for the fuel with WI lower than natural gas) and C3H8 (for the fuel with WI higher than natural gas). Test results show that a benefit in NOx reduction can be seen for the lower WI fuels without H2 presence in the fuel and there are no adverse impacts on combustor performance except for the requirement of higher fuel supply pressure, however, this can be easily resolved by minor modification through the fuel injection design. Test results for the H2 enriched and higher WI fuels show that NOx, combustion dynamics and flash back have been adversely affected and major change in burner design is required. For the H2 enriched fuel, the effect of CO and H2 on combustor performance was also investigated for the fuels having a fixed WI of 29 MJ/Sm3. It is found that H2 dominates the adverse impact on combustor performance. The chemical kinetic study shows that H2 has significant effect on flame speed change and CO has significant effect on flame temperature change. Although the tests were performed on the Siemens SGT-400 combustion system, the results provide general guidance for the challenge of industrial gas turbine burner design for fuel flexibility.