Energy and climate change policies associated with the continuous increase in natural gas costs pushed governments to invest in renewable energy and alternative fuels. In this perspective, the idea to convert gas turbines from natural gas to syngas from biomass gasification could be a suitable choice. Biogas is a valid alternative to natural gas because of its low costs, high availability and low environmental impact. Syngas is produced with the gasification of plant and animal wastes and then burnt in gas turbine combustor. Although synfuels are cleaned and filtered before entering the turbine combustor, impurities are not completely removed. Therefore, the high temperature reached in the turbine nozzle can lead to the deposition of contaminants onto internal surfaces. This phenomenon leads to the degradation of the hot parts of the gas turbine and consequently to the loss of performance. The amount of the deposited particles depends on mass flow rate, composition and ash content of the fuel and on turbine inlet temperature (TIT). Furthermore, compressor fouling plays a major role in the degradation of the gas turbine. In fact, particles that pass through the inlet filters, enter the compressor and could deposit on the airfoil. In this paper, the comparison between five (5) heavy-duty gas turbines is presented. The five machines cover an electrical power range from 1 MW to 10 MW. Every model has been simulated in six different climate zones and with four different synfuels. The combination of turbine fouling, compressor fouling, and environmental conditions is presented to show how these parameters can affect the performance and degradation of the machines. The results related to environmental influence are shown quantitatively, while those connected to turbine and compressor fouling are reported in a more qualitative manner. Particular attention is given also to part-load conditions. The power units are simulated in two different operating conditions: 100 % and 80 % of power rate. The influence of this variation on the intensity of fouling is also reported.

New laminar flame speed experiments have been collected for multiple alternative liquid fuels. Understanding the combustion characteristics of these synthetic fuels is an important step in developing new chemical kinetics mechanisms that can be applied to real fuels. Included in this study are two synthetic Jet fuels: Syntroleum S-8 and Shell GTL. The precise composition of these fuels is known to change from sample to sample. Since these are low vapor pressure fuels, there are additional uncertainties in their introduction into gas-phase mixtures, leading to uncertainty in the mixture equivalence ratio. An in-situ laser absorption technique was implemented to verify the procedure for filling the vessel and to minimize and quantify the uncertainty in the experimental equivalence ratio. The diagnostic utilized a 3.39-μm HeNe laser in conjunction with Beer’s Law. The resulting spherically expanding flame experiments were conducted over a range of equivalence ratios from φ = 0.7 to φ = 1.5 at initial conditions of 1 atm and 403 K in the high-temperature, high-pressure constant-volume vessel at Texas A&M University. The experimental results show that both fuels have similar flame speeds with a peak value just under 60 cm/s. However, it is shown that when comparing the results from different data sets for these real fuels, equivalence ratio is not necessarily the best parameter to use. Fuel mole fraction may be a better parameter to use as it is independent of the average fuel molecule or fuel surrogate used to calculate equivalence ratio in these real fuel/air mixtures.

Over recent decades, the variability and high costs of the traditional gas turbine fuels (e.g. natural gas), have pushed operators to consider low-grade fuels for running heavy-duty frames. Synfuels, obtained from coal, petroleum or biomass gasification, could represent valid alternatives in this sense. Although these alternatives match the reduction of costs and, in the case of biomass sources, would potentially provide a CO 2 emission benefit (reduction of the CO 2 capture and sequestration costs), these low-grade fuels have a higher content of contaminants. Synfuels are filtered before the combustor stage, but the contaminants are not removed completely. This fact leads to a considerable amount of deposition on the nozzle vanes due to the high temperature value. In addition to this, the continuous demand for increasing gas turbine efficiency, determines a higher combustor outlet temperature. Current advanced gas turbine engines operate at a turbine inlet temperature of (1400–1500) °C which is high enough to melt a high proportion of the contaminants introduced by low-grade fuels. Particle deposition can increase surface roughness, modify the airfoil shape and clog the coolant passages. At the same time, land based power units experience compressor fouling, due to the air contaminants able to pass through the filtration barriers. Hot sections and compressor fouling work together to determine performance degradation. This paper proposes an analysis of the contaminant deposition on hot gas turbine sections based on machine nameplate data. Hot section and compressor fouling are estimated using a fouling susceptibility criterion. The combination of gas turbine net power, efficiency and turbine inlet temperature (TIT) with different types of synfuel contaminants highlights how each gas turbine is subjected to particle deposition. The simulation of particle deposition on one hundred (100) gas turbines ranging from 1.2 MW to 420 MW was conducted following the fouling susceptibility criterion. Using a simplified particle deposition calculation based on TIT and contaminant viscosity estimation, the analysis shows how the correlation between type of contaminant and gas turbine performance plays a key role. The results allow the choice of the best heavy-duty frame as a function of the fuel. Low-efficiency frames (characterized by lower values of TIT) show the best compromise in order to reduce the effects of particle deposition in the presence of high-temperature melting contaminants. A high-efficiency frame is suitable when the contaminants are characterized by a low-melting point thanks to their lower fuel consumption.

In the last years, the development of synthetic aviation jet fuels has attracted much interest, to provide alternatives to crude-oil based kerosene. Synthetic jet fuels can be produced from a variety of feedstocks and processes. To limit possible harmful effects on the environment when burning a jet fuel, discussions are attributed to the effects of the specific composition of a synthetic fuel on its performance and its emission pattern. A numerical tool, if available, would also be helpful within the specification process any aviation jet fuel must pass. The present work contributes to the studies and efforts how to design a synthetic jet fuel to match predefined properties, e.g. the energy content or a less harmful emission characteristics compared to Jet A-1. The approach of a generic fuel will be followed in order to design a synthetic jet fuel with pre-defined chemical properties: A chemical kinetic reaction mechanism will be elaborated capable predicting the fundamental combustion properties of the generic fuel for each possible mixing ratio of the components included. In this work, a generic mixture serving as an innovative synthetic jet fuel was studied, with n -dodecane, cyclohexane, and iso -octane chosen as single fuel components; no aromatics were added to reduce the concentration of soot precursors. Then, their fundamental combustion properties, i.e. laminar burning velocity and ignition delay time, were measured in a burner test rig and applying the shock tube technique, respectively. These experimental data were used for the validation of the reaction mechanisms developed for each single fuel component, which were then combined to the reaction mechanism for the generic fuel under consideration. To allow a comparison of the combustion behavior of the synthetic jet fuel directly, with the same reaction mechanism, to Jet A-1, toluene was added as a model component for aromatics. A reduced surrogate reaction model was produced, too. All the reaction mechanisms elaborated are shown to reasonably predict the fundamental combustion properties within the parameter range considered. The compact reduced surrogate model can serve as a virtual jet fuel within numerical simulations. Thus, ultimately, an estimation of the suitability of an innovative synthetic jet fuel as a blending component to crude-oil kerosene is enabled. As a result, CFD simulations can be run efficiently tackling the combustion of a synthetic fuel in a jet engine under practical conditions and by taking into account the interaction between turbulence and chemistry.

In this paper the use of alternative fuels — synthetic kerosene based — were investigated in a small aircraft gas turbine engine to determine their sound and vibrations signature at Georgia Southern University’s Aerospace Engine Laboratory. Three types of fuels were used: a natural gas, a coal derived synthetic kerosene and Jet-A as a reference fuel. The alternative fuels are Fischer-Tropsch process fuels. Synthetic fuels are attractive in the aviation industry because of their potential for reducing energy dependence and the growing need for higher efficiencies, while reducing emissions. The research SR-30 gas turbine was used to evaluate combustion noise from the selected fuels. The turbine can operate at a maximum speed of 80,000 rpm, produce a maximum thrust of 40 lb f , has a pressure ratio of 3.4 to 1, and a specific fuel consumption of 1.22 lb fuel /th rust per hour. The measurement transducers were state of the art Brüel & Kjaer ¼ inch microphone and a triaxial accelerometer which were interfaced with the analysis software, Brüel & Kjaer Pulse 21. Data was taken at 70,000 rpm for a time span of five minutes at stabilized conditions. One-third octave analysis indicated highest sound difference between the fuels at 400 Hz, and a more pure sound level was obtained. The difference for Jet A was as much as 6 dBA higher for exhaust measurement at 400 Hz, and for FT-NG the exhaust had a higher decibel reading from the exhaust side by as much as 4.4 dBA at the 400 Hz frequency, and FT-CG had as much as 7.3 dBA difference at 315 Hz. The sound from the combustion of these fuels produced the differences of sound when the positions of the microphones changed. However, with this new introduction of sound measurement locations and angles, the combustion differences are still distinct and show a more in depth view of the sound quality that is being received by the microphone.

Current elevated turbine inlet temperatures were made possible by the development of blade thermal barrier coatings (TBCs). However the effectiveness of these coatings could be compromised by erosive particles ingested into the engine with the incoming air or generated by the combustion of heavy and synthetic fuels. Reliable test facilities are essential to characterize their erosion resistance in increased test temperatures. This paper provides a detailed description of an advanced high temperature erosion tunnel capable of testing at temperature of 1370 °C (2500 °F) that has been recently constructed and installed in the University of Cincinnati Gas Turbine Erosion Lab. The paper also presents an overview of both theoretical and experimental investigations dealing with the new high temperature erosion tunnel design optimization and validation with comparisons to our legacy erosion tunnels. Results are presented for tested standard plasma sprayed 7 wt% Yttria stabilized Zirconia (7YSZ) TBC coated samples’ erosion rates at different temperatures, particle impact velocities and impingement angles.

Currently, the aviation sector is seeking for alternatives to kerosene from crude oil, as part of the efforts combating climate change by reducing greenhouse gas (GHG) emissions, in particular carbon dioxide (CO 2 ), and ensuring security of supply at affordable prices. Several synthetic jet fuels have been developed including sustainable bio-kerosene, a low-carbon fuel. Over the last years, the technical feasibility as well as the compatibility of alternative jet fuels with today’s planes has been proven However, when burning a jet fuel, the exhaust gases are a mixture of many species, going beyond CO 2 and water (H 2 O) emissions, with nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC) including aromatic species and further precursors of particles and soot among them. These emissions have an impact on the local air quality as well as on the climate (particles, soot, contrails). Therefore, a detailed knowledge and understanding of the emission patterns when burning synthetic aviation fuels is inevitable. In the present paper, these issues are addressed by studying numerically the combustion of four synthetic jet fuels (Fischer-Tropsch fuels). For reference, two types of crude-oil based kerosenes (Jet A-1 and Jet A) are considered, too. Plug flow calculations were performed by using a detailed chemical-kinetic model validated previously. The composition of the multi-component jet fuels were imaged by using the surrogate approach. Calculations were done for relevant temperatures, pressures, residence times, and fuel equivalence ratios φ . Results are discussed for NOx, CO as well as benzene and acetylene as major soot precursors. According to the predictions, the NOx and CO emissions are within about ± 10% for all fuels considered, within the parameter range studied: T = 1800 K, T = 2200 K; 0.25 ≤ φ ≤ 1.8; p = 40 bar; t = 3 ms. The aromatics free GtL (Gas to Liquid) fuel displayed higher NOx values compared to Jet A-1/A. In addition, synthetic fuels show slightly lower (better) CO emission data than Jet A-1/A. The antagonist role of CO and NO x is apparent. Major differences were predicted for benzene emissions, depending strongly on the aromatics content in the specific fuel, with lower levels predicted for the synthetic aviation fuels. Acetylene levels show a similar, but less pronounced, effect.

A number of pathways for producing new alternative fuels are emerging. One such fuel is Hydrodeoxygenated Synthesized Aromatic Kerosene (HDO-SAK) which is composed of approximately 95% mono-aromatic compounds. This fuel is intended as a blending component to increase the aromatic content of other synthetic fuels that do not contain aromatic compounds and can be used to create either semi-synthetic or fully-synthetic jet fuel for use in aviation. This paper presents the results of engine tests using the HDO-SAK blended with Synthesized Paraffinic Kerosene from Hydroprocessed Esters and Fatty Acids (HEFA-SPK) to create a fully-synthetic fuel with aromatic content that matched that of a comparison conventional jet fuel. Both the HDO-SAK blended fuel and conventional Jet A were tested in a Microturbo TRS-18 turbojet engine at a range of engine conditions and simulated altitudes up to 8,600 m in the National Research Council Canada (NRC) Research Altitude Test Facility (RATFac). This paper details the engine performance results from this testing which represents the first time this particular alternative fuel has been tested in an engine.

Research on synthetic jet fuels production and combustion has recently gained importance because they could help addressing security of supply and sustainable air transportation challenges. The combustion of a 100% Gas to Liquid from Shell (C 10.45 H 23.06 ; M=148.44 g.mol −1 ; H/C=2.20; density=737.7 g L −1 ), a 100% vol. Coal to Liquid from Sasol (C 11.06 H 21.6 ; M=154.32 g mol −1 ; H/C=1.95; density= 815.7 g L −1 ) and surrogates composed of various concentrations of n-decane iso-octane, n-propylcyclohexane, n-propylbenzene, and decalin, were studied in a jet-stirred reactor under the same conditions (temperature, 550–1150 K; pressure, 10 bar; equivalence ratio, 0.5–2). Comparison of these results helped designing optimum surrogate model fuels for the chemical kinetic computations. For simulating the kinetics of oxidation of the synthetic fuels we used new surrogates consisting of mixtures of n-decane, iso-octane, 2-methylheptane, 3-methylheptane, decalin, n-propylcyclohexane, n-propylbenzene, and tetralin. The detailed chemical kinetic reaction mechanism proposed here consisted of 2430 species reacting in 10962 reversible reactions. It was validated using the entire experimental database obtained previously in our laboratory and in the present work. The current chemical kinetic model was also tested for the auto-ignition under shock tubes using data from the literature. Kinetic computations involving reaction paths analyses and sensitivity analyses were used to interpret the results.

The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of flame stabilization envelopes relative to the behavior of conventional fuels. Previous studies using the Toroidal Well Stirred Reactor (TWSR) found that synthetic alternatives to JP8 behave similarly in terms of lean flameout, but there is significant difference in the flameout behavior of a highly aliphatic fuel versus that of a highly aromatic fuel. Detailed computational fluid dynamics (CFD) and chemical reactor modeling (CRM) is necessary to understand differences in flame stabilization. The first portion of this study employs CFD models of the TWSR with reduced methane combustion chemistry. The models provide insight into the mechanism of flame stabilization inside the reactor as equivalence ratio is decreased to flameout. The CFD domain is expanded over earlier published TWSR CFD studies to capture previously unknown asymmetrical flame behavior. The Reynolds Stress Model (RSM) is used for turbulence closure, and the Eddy Dissipation Concept (EDC) model is used to include turbulence-chemistry interaction. The CFD results show that radical species (specifically OH) are transported around the reactor to interact with the incoming premixed fuel-air jet and initiate chain branching reactions. As the equivalence ratio decreases, and flameout is approached, the species concentration in the reactor becomes less homogenous. Radical production is delayed and eventually insufficient radical concentrations are available to ignite the incoming jet. The production and transport of radical species throughout the reactor are, thus, responsible for stabilizing the flame. CFD and PSR studies with methane agree that the radical behavior dictates blowout. The second portion of this study focuses on the importance of radical species in flame stabilization, but now employs a single perfectly stirred reactor (PSR) model, which allows the study of detailed chemistry for individual components of jet fuel. An aliphatic compound (iso-octane) and an aromatic compound (toluene) are used as investigative fuels to compare the differences in the chemical kinetic behavior of blowout for aliphatic versus aromatic fuel classes. The models show that the rates at which radical species (O, H, and OH) destroy the original fuel molecule are significantly different for iso-octane and toluene. During combustion, the radical destruction of toluene is much slower than for iso-octane at a constant temperature. In PSR systems, the toluene flame blows out at a higher temperature because a higher temperature is needed to provide sufficient radical concentrations and reaction rates to maintain a stable flame.

Ten fuels were burned in a GT-225 diffusion-flame combustor and the performance, durability, and emissions evaluated. These fuels were: reference kerosene, three petroleum distillales, two alcohols, one coal-derived fuel, a fuel made from far sands, and two fuels made from oil shale. All of the fuels were burned without modifying either combustor or fuel nozzle. The more volatile petroleum distillates burned more efficiently than kerosene. The alcohols and the more viscous synthetic fuels exhibited combustion efficiencies slightly lower than that of kerosene, possibly as a result of pooper initial atomization. The synthetic fuels having high aromatic contents produced higher flame-tube-wall temperatures than did kerosene, but not sufficiently high to reduce durability. The emissions from the combustion of all petroleum distillates were comparable to those of kerosene. The alcohols gave 60 to 80 percent lower oxides of nitrogen emissions, up to 650 percent higher carbon monoxide emissions and up to 300 percent higher total hydrocarbon emissions than kerosene, but these emissions were considerably reduced by increasing atomizing-air differental pressure to the injector. Some of the synthetic fuels contained large amounts of nitrogen and substantial oxidation of it was evidenced. The most viscous synthetic fuels exhibited carbon monixide and total hydrocarbon emissions 100 percent higher than kerosene.

Two combustor rigs have been used to study the sensitivities of combustor operation to the physical and chemical properties of fuels. Nineteen fuels including synfuels were used to accentuate the properties of concern: composition, viscosity, and boiling-point distribution. Flame radiation and smoke were best correlated by hydrogen content rather than hydrocarbon structure; the soot formation was due to gas-phase reactions. Lean-blowout conditions were about the same for all fuels except that gasoline could be burned leaner at idle conditions. Ignition limits were more sensitive to volatility than viscosity. Gaseous emissions and combustion efficiency were not significantly affected by fuel properties although some sensitivity to boiling point distribution was evident. In all performance areas, the syncrude fuels correlated in the same ways as the petroleum-derived fuels except for the NO x emissions from the nitrogen containing shale oil fuel.

Liquid synthetic fuels derived from non-petroleum resources will play a major role in meeting future national energy demands. In the case of gas turbine applications, it is known that the different properties of these fuels can rusult in substantially altered combustion performance. Most importantly, decreased fuel hydrogen content resulting from an increased aromatic content has been observed to result in increased exhaust smoke and particulates as well as greater flame luminosity. This paper contributes empirical information and insight which allows the greater soot formation tendencies of low hydrogen content fuels to be better understood. A small scale laboratory device which simulates the strongly backmixed conditions present in the primary zone of a gas turbine combustor is utilized. The Jet Stirred Combustor provides for very rapid mixing between a premixture of vaporized fuel and air and the combustion products within a 5.08-cm-dia hemispherical reactor. Results to be presented are gaseous combustion product distributions, incipient soot limits, and soot production (mg) for a variety of fuels. The influences of combustor inlet temperature and reactor mass loading have been evaluated and the sooting characteristics of fuel blends have been studied. These results have been analyzed to develop useful correlation which are in general agreement with existing mechanistic concepts of the soot formation process.

A brief review of BBC gas turbine experience in operation on low Btu gas is presented. The applicability of this experience to combustion technology associated with current generation Turbodyne/BBC turbines is discussed. The integration of a currently available turbine design into possible synthetic fuel systems is presented as an available alternative in generation system planning.

Rapid changes in the fuel availability and cost picture, coupled with environmental concerns, emphasize the need to consider new concepts for power generation by industrial plants and electrical utilities. A number of processes are now being developed to produce clean gaseous and liquid fuels from coal and low-grade petroleum products which offer potential for use in gas turbine-based power generating systems. This paper reviews several of the processes and considers the economic and environmental factors affecting their application to power generation systems.

This paper presents a summary of work which is being conducted in the United States in the area of synthetic fuels derived from coal for marine applications, and also gives an overview of the current supply and demand for oil fuels and defines the impact of this picture on the future fuel needs of the maritime and naval communities.

Combustion tests on over twelve types of coal derived liquid fuels from the EDS, H-coal, SRC-I and SRC-II processes and three shale oil fuels have been conducted in gas turbine type combustors. Emission measurements wre made of NO x , smoke, CO, and unburned hydrocarbons. Combustor wall temperature profiles were measured. The results are correlated with the fuel properties — percent nitrogen, hydrogen and aromaticity. This paper (Part II) describes the results of full scale combustor testing and of a long-term corrosion/deposition test. A companion paper by Cohn, et al. Part I discusses the fuels used in the program and the subscale combustor test results.

The “Low NOx Heavy Fuel Combustor Program” is a part of the DOE/LeRC “Advanced Conversion Technology Project” (ACT). The program is a multiple contract effort with funding provided by the Department of Energy, and technical program management provided by NASA LeRC. Main program objectives are to generate and demonstrate the technology required to develop durable gas turbine combustors for utility and industrial applications, which are capable of sustained, environmentally acceptable operation with minimally processed petroleum residual fuels. The program will focus on “dry” reductions of oxides of nitrogen (NOx), improved combustor durability and satisfactory combustion of minimally processed petroleum residual fuels. Other technology advancements sought include: fuel flexibility for operation with petroleum distillates, blends of petroleum distillates and residual fuels, and synfuels (fuel oils derived from coal or shale); acceptable exhaust emissions of carbon monoxide, unburned hydrocarbons, sulfur oxides and smoke; and retrofit capability to existing engines.

Combustion tests on over twelve types of coal derived liquid fuels from the EDS, H-coal, SRC-I and SRC-II processes and three shale oil fuels have been conducted in gas turbine type combustors. Emission measurements were made of No x , smoke, CO, and unburned hydrocarbons. Combustor wall temperature profiles were measured. The results are correlated with the fuel properties-percent nitrogen, hydrogen and aromaticity. This part of the paper discusses the fuels used in subscale combustion tests along with the test results. A companion paper (Part II) describes the results of full-scale combustor tests and a long term corrosion/deposition test.

The work described herein was conducted under an Electric Power Research Institute contract, Evaluation of Synthetic Fuel Character Effects on Rich-Lean Stationary Gas Turbine Combustion Systems. The purpose of this program was to determine the effect of synthetic fuel properties on combustor emissions, performance, and durability. Four synthetic fuels and No. 2 petroleum distillate fuel were tested in a subscale combustor over a wide range of conditions with the purpose of expanding the fuels property base and range of conditions beyond that of preceding programs. No x emissions were very low and insensitive to combustor pressure and fuel-bound nitrogen. Rich-lean results show some indication of increased smoke and liner heating with reduced fuel hydrogen content, although not as consistent as the trends for lean combustors.