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A promising avenue for development in the aerospace industry involves relocation of engines from conventional locations beneath the wings, to within the aircraft fuselage. Aircraft with these so-called embedded engines have the potential to increase engine efficiency, but necessitate the use of a serpentine engine inlet duct (S-duct) to provide the propulsion system with air. The optimal shape of an aircraft S-duct varies with flight condition, incentivizing the use of morphing systems to vary inlet parameters during flight: allowing for continual supply of the optimal airflow level. Design of a morphing system therefore requires collaboration across multiple disciplines, including aerodynamic analysis and structural analysis. This work presents a methodology for the structural optimization of morphing systems utilizing aerodynamic shape optimization results as inputs, in order to assess the relationship between morphing performance and structural stiffness. The methodology is implemented on a baseline morphing S-duct model for which shape optimization has been previously conducted. Structural optimization is conducted using a gradient-based multi-material topology optimization software with multi-phase penalization. While the conclusions of this work indicate that the impact of multiple material optimization in the S-duct case study is minimal, the methodology does provide non-intuitive designs capable of supporting morphing. At the expense of structural stiffness, the methodology is shown to increase morphing performance through the generation of compliant mechanisms. A parameter study conducted on the S-duct model successfully proves the ability of the methodology to assess the trade-offs between structural and morphing performance. By emphasizing morphing performance, mass reductions from 1.75 kg to 0.201 kg were observed at the expense of a 94% reduction in fatigue lifecycle.

LIF/Mie ratio-metric imaging was used to characterize sprays produced by a simple hollow-cone pressure atomizer, operating under elevated ambient pressures up to 10 atm. A structured laser sheet was used as the source of illumination to suppress the multiple scattered light, generating images that are free of the artefacts typically found in conventional laser sheet images. The resulting LIF/Mie ratio-metric images were calibrated using Phase Doppler anemometry to generate axial planar maps of the spray’s Sauter-mean diameter (SMD). This calibration methodology was applied over a range of ambient pressures and liquid flows to assess the robustness of the structured LIF/Mie ratio-metric imaging as a droplet sizing technique. The test fluids consisted of conventional and alternative jet fuels as well as nozzle calibration fluid. Results presented in the paper indicate both the effectiveness and certain limitations of the technique.

The applicability of morphing structures for airframe design is well documented, as aircraft surfaces are sensitive to flight conditions and environmental factors. This becomes a critical factor in the design of airframes with internally mounted propulsion systems. Such designs necessitate the use of a serpentine inlet, the optimal shape of which is dependent on flight conditions. This work focusses on the structural optimization of a section of a serpentine aircraft inlet capable of morphing. The trade-offs between morphing ability and structural performance are of key interest, and are explored in this study. As a structure becomes more compliant to accommodate a change of shape, it loses structural stiffness. A topology optimization algorithm was written to generate a Pareto Frontier of optimal designs for this problem. The scope of this work is limited to a small section of a specific serpentine inlet design for which aerodynamic shape optimization for different flight conditions has already been conducted., AIAA Scitech 2021 Forum, January 11–15 & 19–21, 2021, Virtual Event

Morphing materials and structures capable of assuming specific shapes under precise conditions have become increasingly relevant for numerous industries, including aerospace. However, a significant limitation of many proposed morphing materials and structures is their manufacturability. Furthermore, many morphing materials are not capable of supporting significant loads independently. It is therefore of interest to develop a methodology to generate support structures for morphing materials that can support specific desired shapes, and can be manufactured easily. This work proposes a methodology for optimizing compliant mechanisms that can be 3D printed using commercially available materials. These mechanisms are designed to lie behind traditional morphing materials such as shape-memory alloys, and assume a specific displacement profile when subjected to certain loading conditions. The methodology is tested on two separate displacement profiles and is compared with respect to buckling constraint severity., AIAA Scitech 2020 Forum, January 6-10, 2020, Orlando, FL

An experimental study was conducted to study the internal and external two-phase flow in an effervescent atomizer using high-speed imaging. The impact of the aerator tube configuration and mixing zone length on the size of bubbles inside the mixing zone and the spray droplet characteristics at different gas-to-liquid flow rates ratios were studied. An aerator tube with the conical end base was manufactured and tested. It is observed that the separation bubble at the trailing edge is suppressed by this configuration, which resulted in more uniform and smaller bubbles compared to the standard aerator tube with a flat base. The length of the mixing zone was found to have an impact on the bubble size distribution inside the mixing zone; more uniform and smaller bubbles are generated in the shorter mixing zone. The mixing zone length, however, does not show a distinct impact on the droplet velocity and size. It is concluded that a conical base aerator tube and a shorter mixing zone could significantly improve the spray steadiness and the atomization process.

The National Jet Fuel Combustion Program (NJFCP) is an initiative, currently being led by the Office of Environment & Energy at the FAA, to streamline the ASTM jet fuels certification process for alternative aviation fuels. In order to accomplish this objective, the program has identified specific applied research tasks in several areas. The National Research Council of Canada (NRC) is contributing to the NJFCP in the areas of sprays and atomization and high altitude engine performance. This paper describes work pertaining to atomization tests using a reference injection system. The work involves characterization of the injection nozzle, comparison of sprays and atomization quality of various conventional and alternative fuels, as well as use of the experimental data to validate spray correlations. The paper also briefly explores the application viability of a new spray diagnostic system that has potential to reduce test time in characterizing sprays. Measurements were made from ambient up to 10 bar pressures in NRC’s High Pressure Spray Facility using optical diagnostics including laser diffraction, phase Doppler anemometry (PDA), LIF/Mie Imaging and laser sheet imaging to assess differences in the atomization characteristics of the test fuels. A total of nine test fluids including six NJFCP fuels and three calibration fluids were used. The experimental data was then used to validate semi-empirical models, developed through years of experience by engine OEMs and modified under NJFCP, for predicting droplet size and distribution. The work offers effective tools for developing advanced fuel injectors, and generating data that can be used to significantly enhance multi-dimensional combustor simulation capabilities., ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Monday 11 June 2018, Oslo, Norway

An experimental study is reported that investigated the bubble formation from a novel nozzle design in a liquid cross-flow using high speed imaging. Different configurations and orientations of the novel nozzle design were considered over a range of gas-to-liquid flow rate ratios (GLR) from 0.00031 to 0.00204. The results show that for all cases, the novel nozzle generated smaller bubbles at higher detachment frequency compared to the standard nozzle. At low liquid velocities, the novel nozzle generated bubbles that were 30% smaller in size at a detachment frequency 2–3 times higher than that for the standard nozzle. It was also found that the bubble diameter and the detachment frequency are almost independent of the liquid velocity. The underlying physical process of bubble formation and detachment in the novel nozzle under liquid cross-flow was also investigated. It was observed that the process comprised of three phases: expansion, collapse and pinch off. It was also found that the rebound force of the bubble from a side-hole under the influence of liquid drag force and hydrostatic pressure plays a key role in the early bubble detachment. The results demonstrated that the novel nozzle design performs better than the standard nozzle in the liquid cross-flow, especially at high GLRs.

Effervescent atomization technique is used in many industrial applications such as gas turbines, internal combustion engines, furnaces and burners, and pharmaceutical sprays. The present study is focused on investigating the influence of a new type of bubble breaker on the two-phase flows inside and outside an effervescent atomizer. Different configurations (size and number of holes) of the new bubble breaker were considered over a range of gas to liquid flow rates ratios (GLRs) from 0.001 to 0.022. High-speed imaging was used to visualize and quantify bubble and spray characteristics. The results showed that the two-phase flow regime and bubbles' size inside the effervescent atomizer, and the spray droplets' size and velocity outside the atomizer are strongly influenced by the bubble breaker. The results demonstrated that the bubble breaker effectively fragments large bubbles into smaller ones. Furthermore, the results illustrate that the diameter and numbers of holes of the bubble breaker affect the bubble size inside the mixing zone as well as the droplet size and velocity.

2018 AIAA Aerospace Sciences Meeting, 8–12 January 2018, Gaylord Palms, Kissimmee, Florida, USA

This study reports gaseous and particle (ultrafine and black carbon (BC)) emissions from a turbofan engine core on standard Jet A-1 and three alternative fuels, including 100% hydrothermolysis synthetic kerosene with aromatics (CH-SKA), 50% Hydro-processed Esters and Fatty Acid paraffinic kerosene (HEFA-SPK), and 100% Fischer Tropsch (FT-SPK). Gaseous emissions from this engine for various fuels were similar but significant differences in particle emissions were observed. During the idle condition, it was observed that the non-refractory mass fraction in the emitted particles were higher than during higher engine load condition. This observation is consistent for all test fuels. The 100% CH-SKA fuel was found to have noticeable reductions in BC emissions when compared to Jet A-1 by 28-38% by different BC instruments (and 7% in refractory particle number (PN) emissions) at take-off condition. BC emissions from this fuel were lower than from Jet A-1 by 45-50% (and 25-26% in refractory PN) at idle or cruise condition. The 100% CH-SKA fuel was observed to have a minimum influence on non-refractory PN emissions. A lower volume in naphthalene in the 100% CH-SKA fuel was hypothesized to be one of the factors attributing to the reduced BC emissions when compared to Jet A-1 emissions. For the 50% HEFA-SPK fuel, BC emissions were lower than the BC emissions from Jet A-1 by 58-86% for various engine load conditions. BC emissions from the 100% FT-SPK fuel were lower than from the Jet A-1 by 70-98%. Both the refractory and non-refractory PN emissions from these fuels were lower by comparable magnitude when compared to that from Jet A-1.

The effects of altitude and fuel composition on gaseous and particle emissions from a turbojet engine were investigated as part of the National Jet Fuels Combustion Program (NJFCP) effort. Two conventional petroleum based jet fuels (a “nominal” and a “worst-case” jet fuel) and two test fuels with unique characteristics were selected for this study. The “worst-case” conventional jet fuel with high flash point and viscosity resulted in reduced combustion efficiency supported by the reduced CO2 emissions and corresponding increased CO and THC emissions. In addition, increased particle number (PN), particle mass (PM), and black carbon (BC) emissions were observed. Operating the engine on a bimodal fuel, composed of heavily branched C12 and C16 iso-paraffinic hydrocarbons with an extremely low cetane number did not significantly impact the engine performance or gaseous emissions but significantly reduced PN, PM, and BC emissions when compared to other fuels. The higher aromatic content and lower hydrogen content in the C-5 fuel were observed to increase PN, PM, and BC emissions. It is also evident that the type of aromatic hydrocarbons has a large impact on BC emissions. Reduction in combustion efficiency resulted in reduced CO2 emissions and increased CO and THC emissions from this engine with increasing altitudes. PN emissions were moderately influenced by altitude but PM and BC emissions were significantly reduced with increasing altitude. The reduced BC emissions with increasing altitude could be a result of reduced combustion temperature which lowered the rate of pyrolysis for BC formation, which is supported by the NOx reduction trend., ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, 26-30 June 2017, Charlotte, North Carolina, USA

The National Research Council Canada (NRC) is an allied partner in the National Jet Fuels Combustion Program (NJFCP), which is a US multi-agency program led by the Federal Aviation Administration (FAA). NJFCP aims to accelerate the ASTM International fuel approval process for alternative jet fuels (AJF) by conducting combustion-related testing and modelling to gain a better understanding of the effect of AJF on engine combustion. In support of NJFCP, NRC has undertaken studies on a turbojet engine to investigate the effect of various fuels on engine ignition at simulated altitude conditions. One baseline conventional petroleum derived jet fuel with “average” physical properties and three test fuels meant to represent AJF with unique characteristics were tested. Significant differences were observed in the ignition performance of the fuels. Despite the test fuel having very different chemical compositions, the fuel physical properties appear to have the predominant influence on the ignition performance., 55th AIAA Aerospace Sciences Meeting, 9-13 January 2017, Grapevine, Texas, USA

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.

The use of alternative fuels has the potential to enhance energy independence and reduce environmental impact of air travel. It is important to characterize gas turbine operation using such fuels under controlled conditions before implementing them in flight. The performance of a CF-700 engine core was examined in a sea level test facility. The following fuels were tested and will be reported on: 1. Jet A-1 - baseline fuel 2. 100% unblended Hydroprocessed Esters and Fatty Acids (HEFA) synthetic kerosene fuel with aromatics (SKA) 3. 100% unblended Fischer-Tropsch (FT) synthetic paraffinic kerosene (SPK) 4. Blended 50% HEFA-SPK and 50% Jet A-1 Fuel 2 above is an alternative fuel that can potentially be used without blending with conventional fuel. One purpose of the static engine testing was to determine if this fuel was suitable for use on subsequent test flights in a Dassault Falcon 20 aircraft. Engine performance testing was conducted at various power settings for each fuel. Relevant plots of performance are presented, compared and discussed. Transient tests were also performed including slams and chops. Observations of the effects of the different fuels on the engine fuel system are presented as some alternative fuels have the potential to cause seals to shrink and leaks to occur. The leaks observed are noted as are the steps taken to mitigate the problem., ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, GT 2015, 15 June 2015 through 19 June 2015

The development and testing of a liquid-fuel modulation system for active combustion control applications is presented. This article focuses primarily on the actuator selection process, discussing the tradeoffs between high-bandwidth electromagnetic actuators, piezoelectric stacks, and magnetostrictive actuators. The comparison shows that a piezoelectric stack is the best candidate for our combustion control system due to its compact size, bandwidth capabilities, and relatively low cost. Using a piezoelectric stack, the fuel modulation system was capable of modulating more than 75% of the mean flow rate and successfully stabilized a single-nozzle kerosene combustor.

Alternative fuel for aviation has been the centre of serious focus for the last decade, owing mostly to the challenges posed by the price of conventional petroleum fuel, energy security and environmental concerns. The downslide in the oil prices in the recent months and the fact that energy security is not considered a major threat in commercial aviation, these factors have worked negatively for the promotion of alternative fuels. However, the continuous commitment to environmental stewardship by Governments and the industry have kept the momentum going towards the transparent integration of renewable alternatives in the aviation market. On the regulatory side, much progress have been made in the same timeframe with five alternative fuels being certified as synthetic blending components for aviation turbine fuels for use in civil aircraft and engines. Another seven alternative fuels are in the various stages of certification protocol. This progress has been made possible because of the extensive performance testing, both at full engine conditions and at engine components level. This article presents the results of engine performance and air pollutant emissions measurements gathered from the alternative fuels qualification testing conducted at the National Research Council Canada over the last seven years. This benchmarking data was collected on various engine platforms at full engine operation at sea level and/or altitude conditions using a variety of aviation alternative fuels and their blends. In order to provide a reference comparison basis, the results collected using the alternative fuels are compared with baseline Jet-A1 or JP-8 conventional fuels.

Aerated-liquid atomization, also called "effervescent atomization", is a technique that has a wide range of applications such as gas turbine combustors, internal combustion engines, furnaces and burners, and pharmaceutical sprays. We report on an experimental study conducted to investigate the two-phase flow in an Effervescent atomizer. A novel aerator tube base was implemented and tested. It is observed that the novel configuration suppresses the separation bubble at the trailing edge and results in more uniform and smaller bubbles compared to the standard flat base aerator. It has been found that the more uniform and smaller bubbles are generated as the mixing chamber length is reduced. It is concluded that by using a conical base aerator and by reducing the mixing chamber length, the spray steadiness and the atomization process can be significantly improved., ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2014, Collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels, 3 August 2014 through 7 August 2014

The motivation for the work comes from the requirement to assess the feasibility of using alternative fuels in lean-premixed land-based stationary gas turbine combustion systems. Lean-premixed systems are prone to combustion instability issues and the need is to determine how the use of alternative fuels would affect such instabilities. The paper presents the results of an acoustically-forced laminar flat flame study that was conducted to measure the influence of flow velocity oscillations on the response of syngas flames under various operating conditions and in comparison to natural gas flames. The results indicate that syngas concentration in a methane-syngas-air mixture significantly affects the flame response. On the other hand, the ratio of hydrogen-to-carbon monoxide in the syngas was found to have a negligible effect on the flame response for a fuel blend made up of 50% methane and 50% syngas. Flame liftoff distance and flame speed were found to be important parameters that govern the flame transfer function magnitude and resonant frequency for a thermally stabilized flat flame. The paper also presents insights into flame transfer function scaling based on a refined Strouhal definition., ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, June 16-20, 2014, Düsseldorf, Germany

Injection of bubbly gas flow into a liquid stream has wide application in chemical and biochemical industries. In these applications, generation of smaller bubble at higher frequency is desirable to achieve better reaction efficiency. We report on an experimental study conducted to investigate the bubble formation in liquid cross-flow using a novel nozzle design developed by Gadallah and Siddiqui [1]. This design is based on the creation of two side holes in the standard nozzle near the main nozzle hole. The experiments were performed in an acrylic square flow channel and high speed imaging was used to capture bubble dynamics. An image processing algorithm was used to quantify the size and frequency of detached bubbles and to track each individual bubble at different gas flow rates and liquid velocities. The results show that the new design of nozzle generates more bubbles of smaller size compared to the standard nozzle with no side hole at low liquid flow rates. It was observed that while the liquid velocity has crucial affect on the bubble size and detachment frequency from a standard nozzle, these parameters are weakly dependent on the liquid flow rate in the novel nozzle. The results show that at low liquid flow rates or in the stagnant liquid, the novel nozzle generates bubbles that are more than 20% smaller in size and more than two times faster compared to the standard nozzle. Copyright © 2013 by ASME and Her Majesty the Queen in Right of Canada., ASME 2013 Fluids Engineering Division Summer Meeting, FEDSM 2013, July 7-11, 2013, Incline Village, Nevada, USA, Series: FED

Adoption of hydro-processed esters and fatty acid biojet fuels is a critical component for the sustainability of the aviation industry. Aviation biofuels reduce pollution and provide alternatives to conventional fossil fuels. A study of the impacts of biofuels on emissions from a T56 turbo-prop engine was undertaken as a joint effort among several departments of the Government of Canada. In this study, particulate (including particle number and black carbon (BC) mass) and regulated gaseous emissions (CO2, CO, NO, NO 2, THC) were characterized with the engine operating on conventional F-34 jet fuel and jet fuel blended with camelina-based hydro-processed biojet fuel (C-HEFA) by 50% in volume. Emissions characterization, conducted after 20-hour ground engine durability tests, showed immediate significant reductions in particle number and BC mass when the engine was operated on the C-HEFA blend. Operating at high speed ground idle (HSGI) using the C-HEFA blend reduced particle number and BC mass emissions by 31% and 50%, respectively. At Take-off engine mode, particle number and BC mass reductions were 22% and 32%, respectively. In addition, particles generated from the C-HEFA blend were also observed to be slightly smaller than those generated from the conventional jet fuel by 2-4 nanometer (nm). CO emissions from the C-HEFA blend were lower by 4-6%. CO2 emissions from the C-HEFA blend were lower by approximately 1%, consistent with the difference in hydrocarbon ratios in the C-HEFA blend., SAE 2013 AeroTech Congress and Exhibition, AEROTECH 2013, 24 September 2013 through 26 September 2013, Montreal, QC

Alternative fuel sources are becoming an operational reality; these fuels have the potential to reduce emissions, improve combustion characteristics and to increase fuel supply security. A test with a T56 turboprop engine was performed to demonstrate that a CHEFA/JP8 (Camelina Hydroprocessed Ester and Fatty Acids and standard JP8) fuel blend would meet operational requirements. The primary test objective was to assess whether a fuel change had an immediate impact on the engine condition, performance, emissions or vibration characteristics. This paper presents test results comparing engine performance with JP8 and a 50/50 blend of JP8 and CHEFA. Comparison runs were conducted before and after a 20 hour ground durability test with the CHEFA fuel blend. A nearly time-expired, nacelle-dressed T56 on an outdoor test stand was tested. The engine was equipped with minimallyintrusive non-standard pressure, temperature and emissions monitoring equipment, and a field vibration assessment suite in addition to the standard flight instrumentation. This paper discusses the test plan, data acquisition methods, results and data repeatability. The performance and emissions results are compared to the changes predicted theoretically from the fuel properties. Observations from the borescope inspections before, during and after the 20 hour durability test are also presented. The lessons learned in this test could be applied to future fuel or process-change tests, and the results provide a performance baseline for engine health assessment. Copyright © 2012 by Her Majesty the Queen in Right of Canada, ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, GT 2012, June 11-15, 2012, Copenhagen, Denmark

To enhance energy security and reduce the environmental impact of aviation, alternate fuels derived from various nonpetroleum based sources are being developed. Currently alternate fuels are produced to match the properties of existing jet fuels allowing the new fuels to be used in current fleets concurrently with traditional jet fuel. The alternate fuels must, therefore, perform as well as the traditional fuels through the entire operating envelope. This paper provides the results of performance testing in an altitude chamber up to 11,300 m (35,000 feet) with a simulated forward speed up to Mach 0.75. The test engine was an instrumented 1.15 kN thrust turbojet burning conventional Jet A-1 as a baseline; a semi-synthetic blend of camelina based hydro processed renewable jet and JP8; a blend of 50% Fischer-Tropsch synthetic paraffinic kerosene and 50% JP8; and a 100% Fischer-Tropsch synthetic paraffinic kerosene. Both steady state and transient performance are presented. The theoretical effect of the alternate fuels for a simple idealized Brayton cycle is also presented. The work was conducted as part of on-going efforts by departments within the Government of Canada to systematically assess alternative aviation fuels., ASME TurboExpo 2011: Power for Land, Sea, and Air, 6-10 June 2011, Vancouver, Canada

Gas injection into a liquid cross flow from a nozzle causes bubble formations which have potential applications in industry such as chemical plants, waste water treatment and bio- and nuclear-reactors. The purpose of this study is to experimentally investigate the effects of nozzle shape and configuration with respect to the liquid cross-flow direction, on the bubbly flow characteristics such as bubble formation, detached bubble size and frequency at different gas and liquid flow rates. The experiments were conducted in a Plexiglas two-dimensional rig using a high speed camera. High speed imaging and an image processing algorithm were used to track each individual bubble and to quantify the bubble growth as well as the detachment frequency and the bubble velocity. Back light shadowgraphy which utilizes a low intensity diffuse light source to illuminate the background was used to image bubbles. Nozzles were mounted in the test section which was designed such that the flow in this section has a two-dimensional profile. The results showed that the bubble size increases with an increase in GLR (gas to liquid flow rates ratio). Furthermore, the bubble formations and detached bubble size were strongly influenced by the nozzle shape and configuration. Copyright © 2012 by ASME., ASME 2012 Fluids Engineering Division Summer Meeting, FEDSM 2012 Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and M, FEDSM 2012, 8 July 2012 through 12 July 2012, Rio Grande

Dry low emissions premixed combustion systems have the ability to give larger NOx emissions reduction in comparison to diffusion type of combustors. However, these systems are prone to flashback because the fuel and oxidizers are mixed upstream of the combustion chamber. This is particularly true for premixed systems burning high-reactivity fuels due to their higher flame speed. Flashback is undesirable in gas turbines because it leads to overheating and failure of fuel nozzles and premixing sections. Recently, a novel application of Plasma Actuation through non-thermal Dielectric Barrier Discharge has been shown to significantly delay flashback in the core flow along the axis of the premixer. Building on this successful endeavour, efforts were directed to prove the effectiveness of the control method in situations where flashback was triggered in the boundary layer. Results show that the current application delays the occurrence of flashback in the boundary layer of the premixer to higher equivalence ratios. Improvements in the combustor operability margin of 10 to 14% when burning natural gas-air mixtures, and of about 3.5% when replacing the fuel by an equimolar mixture of natural gas and hydrogen, were achieved. It was found that the proposed application of plasma actuation is even more efficient in preventing flashback in the boundary layer than in the core flow., ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, GT 2012, June 11-15, 2012, Copenhagen, Denmark

Thermoacoustic instabilities in combustors have remained a topic of investigation for over a few decades due to the challenges it posses to the operation of low emission gas turbines. For combustors burning liquid fuel, understanding the cause-andeffect relationship between spray combustion dynamics and thermoacoustic oscillations is imperative for the successful development of any control methodology for its mitigation. The paper presents some very unique operating characteristics of a kerosene-fueled diffusion type combustor undergoing limit-cycle oscillations. Combustor stability limits were mapped using three different-sized injectors. The results show that combustor instability depends on the characteristics of the fuel spray. A simple analytic analysis is also reported in support of a plausible explanation for the unique combustor behavior. The study indicates that high amplitude acoustic pressure in the combustor may cause secondary breakdown of fuel droplets resulting in premixed pre-vaporized type burning of the diffusion type combustor., {"references":["J. C. Solt, J. Tuzson, Proceedings of 1993 ASME IGTI Conference\nPaper 93-GT-270, 1993.","T. Lieuwen, B. T. Zinn, AIAA 36th Aerospace Sciences Meeting &\nExhibit Paper 98-0641, 1998.","A. Y. Tong, W. A. Sirignano, Journal of Propulsion and Power 5(3)\n(1989) 257-261.","W. A. Chishty, Effects of Thermoacoustic Oscillations on Spray\nCombustion Dynamics with Implications for Lean Direct Injection\nSystems, PhD thesis, Virginia Polytechnic Institute and State University,\nBlacksburg, VA, USA, 2005.","A. M. Mellor, Design of Modern Turbine Combustors, Academic Press\nLimited, 1990.","C. Clanet, G. Searby, P. Clavin, Journal of Fluid Mechanics 385 (1999)\n157-197.","S. Dowson, J. Fitzpatrick, Journal of Sound and Vibration 230(3) (2000)\n649-660.","A. V. Anilkumar, C. P. Lee, T. G. Wang, NASA Conference Publication\n3338, (1996) 559-564.","R. Schmehl, G. Klose, G. Maier, S. Wittig, S., NATO RTO Gas Turbine\nEngine Combustion, Emissions and Alternate Fuels, 1999.\n[10] P. J. O-Rourke, A. A. Amsden, SAE Technical Report 872089, 1987.\n[11] J.-H. Park, Y. Yoon, Atomization and Sprays 12 (2002) 387- 401."]}

To address the global fuel challenges of energy security, economic sustainability and climate change the stakeholders of aviation industry are actively pursuing the development and qualification of alternative 'drop-in' fuels. New standards will be required to regulate the use of these new fuels, which requires not only fuel specification and rig/engine and flight testing but also an emission life cycle impact assessment of these fuels. This paper reports on emission data measured at various simulated altitudes and engine speeds from a jet engine operated on conventional and alternative aviation fuels. The work was conducted as part of on-going efforts by departments within the Government of Canada to systematically assess regulated as well as non-regulated emissions from the use of alternative aviation fuels. The measurements were performed on an instrumented 1000 N-thrust turbojet engine using a baseline conventional Jet A-1 fuel and a semisynthetic (50/50) blend with Camelina based Hydroprocessed Renewable Jet (JP8-HRJ8) fuel. Emission results reported here include carbon dioxide, carbon monoxide, nitrogen oxides and particulate matter measured at several simulated altitudes and power settings. In order to ensure that the assessments have a common baseline, relevant engine performance and operability data were also recorded. Copyright © 2011 by ASME., ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition, GT2011, 6 June 2011 through 10 June 2011, Vancouver, BC

In recent years, lean-premixed (LP) combustors have been widely studied due to their potential to reduce NOx emissions in comparison to diffusion type combustors. However, the fact that the fuels and oxidizers are mixed upstream of the combustion zone makes LP type of combustors a candidate for upstream flame propagation (i.e., flashback) in the premixer that is typically not designed to sustain high temperatures. Moreover, there has been a recent demand for fuel-flexible gas turbines that can operate on hydrogen-enriched fuels like Syngas. Combustors originally designed for slower kinetics fuels like natural gas can potentially encounter flashback if operated with faster burning fuels like those containing hydrogen as a constituent. There exists a clear need in fuel-flexible lean-premixed combustors to control flashback that will not only prevent costly component damage but will also enhance the operability margin of engines. A successful attempt has been made to control flashback in an atmospheric LP combustor, burning natural gas-air mixtures, via the application of Dielectric Barrier Discharge (DBD). A low-power DBD actuator was designed, fabricated and integrated into a premixer made out of quartz. The actuator was tuned to produce a low magnitude ionic wind with an intention to modify the velocity profile in the premixer. Flashback conditions were created by decreasing the air flow rate while keeping the fuel flow rate constant. Within this experimental setup, flashback happened in the core flow along the axis of the cylindrical premixer. Results show that the utilization of the DBD delays the occurrence of flashback to higher equivalence ratios. Improvements as high as about 5% of the flashback limit have been obtained without compromising the blowout limit. It is anticipated that this novel application of DBD will lead to future demonstrations of the concept under realistic gas turbine operating conditions. Copyright © 2011 by Her Majesty the Queen in Right of Canada., ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition, GT2011, 6 June 2011 through 10 June 2011, Vancouver, BC

Gaseous and particle emission assessments on a 1.15 kN-thrust turbojet engine were conducted at five altitudes in an altitude chamber with Jet A-1 fuel, pure Fischer Tropsch (FT), and two mixed fuels of JP-8 with FT or Camelina based hydro-processed jet fuels. In general, lower emissions in CO2, NOx, and particle number as well as higher emissions in CO and THC were observed at higher altitudes compared to lower altitudes. These observations, which were similar for all test fuels, were attributed to the reduced combustion efficiency and temperature at higher altitudes. The use of alternative fuels resulted in lower CO2 emissions, ranging from 0.7% to 1.7% for 50% to 100% synthetic fuel in the fuel mixture at various altitudes. In terms of CO, the use of 100% FT fuel resulted in CO reduction up to 9.7% at 1525 m altitude and up to 5.9% at 9145 m altitude. Significant reduction in particle diameter, number and mass emission rates were observed with the use of alternative fuels due to the low aromatic and sulfur content in the fuels. Higher reductions were observed for increasing percentage of the alternative synthetic fuel in the fuel mixture. With the use of pure FT fuel, up to 80% and 96% reductions in particle number emissions were observed at 1525 m and 9145 m altitudes, respectively. In comparison, a larger particle reduction benefit was observed for the Camelina based hydro-processed jet fuel than for the FT fuel., SAE 2011 AeroTech Congress and Exhibition, AEROTECH 2011, 18 October 2011 through 21 October 2011, Toulouse

The paper reports on an experimental study conducted to investigate the dynamics of gas bubbles when injected from an orifice that is subjected to a liquid cross-flow. The experiments were conducted over a range of gas and liquid flow rates and at various orientations of the liquid channel. An image processing algorithm was developed for the detection and characterization of the bubbles in both temporal and spatial coordinates. The transient behaviour of bubble dynamics at different channel orientations under different liquid and gas flow conditions are presented in the paper. Results show that the equivalent bubble diameter in the vertical plane decreased with increase in time as well as with increase in the gas-to-liquid velocity ratio. The channel inclination has no appreciable effect on the bubble diameter. The streamwise bubble velocity showed significant transient fluctuations, which diminished with an increase in the channel inclination angle. The fluctuations of the bubble vertical velocity were found to be unaffected by the channel inclination angle. The magnitudes of both streamwise and vertical velocities were influenced by the channel inclination, however, the trends were found to be opposite. Copyright © 2011 by ASME., ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011, 24 July 2011 through 29 July 2011, Hamamatsu

The purpose of this project was to compare the performance and operability of 50% Fischer-Tropsch Synthetic Paraffinic Kerosene (SPK) and 50% NATO F-34 (JP-8) blend and 100% Jet A-1 in a General Electric F404-400 augmented turbofan engine in the configuration currently in use with the Canadian Forces (CF). The paper describes the main test elements to simulate several aspects of CF use of the engine like acceptance testing, post-overhaul tests, performance (steady state and transient), operability, and durability. An abbreviated endurance test is described as is the special condition monitoring instrumentation. In addition, limited combustor and augmentor combustion stability tests were conducted and some results are described. Fuel properties are documented for reference. The linkage with and support of members of The Technical Cooperation Program (TTCP) is highlighted in terms of joint development of the test plans and sharing the results. Discussions of needs for future limited alternative fuel qualification tests are also presented.Copyright © 2010 by Her Majesty the Queen in Right of Canada

The results are presented from a 3-D simulation of the bubble formation from a submerged orifice in liquid cross-flow. VOF model is used for the simulations. The VOF equation is solved using an explicit time-marching scheme. A second order upwind differencing scheme is applied for the solution of momentum equation. The pressure-implicit with splitting of operators (PISO) scheme is used for the pressure-velocity-coupling scheme. Pressure is discretized with a PRESTO scheme. The computational domain has the dimensions of 100 mm length, 50 mm width and 16 mm height with an orifice of 0.25 mm radius, placed at the bottom of the channel and 10 cm from the water inlet. The water inlet velocity of 0.05 and 0.136 m/s and air inlet mass flow rate of 10−6 and 10−5 kg/s are considered. The simulation results are compared with the experimentally acquired images of the bubbles in the cross-flow stream using a high speed camera (3000 fps). A good agreement with respect to bubble shape and bubble terminal velocity is observed between the experimental and simulation results for both cases. The 3-D numerical model is compared with the 2-D model in order to highlight and emphasize the need for 3-D model to correctly simulate the dynamics of such flow configurations.

In lean premixed combustors of gas turbine engines, fuel-air mixing is considered vital for controlling pollutant emissions as well as combustion instability. Enhancement in mixing may be obtained by modulating the fuel flow rate. Modulation of fuel flow is also a useful technique to actively control combustion instabilities arising from the pressure oscillations in the combustor and thrust augmenters. Effectiveness of the forced oscillations depends on the level of dispersion present in the system. Knowledge of dispersion levels is also important in determining the degree of mixing and therefore, the effectiveness of a premixer. This paper presents the experimental efforts undertaken to study the spatial and temporal dispersion of fuel flow rate oscillation introduced at the premixer inlet. Effects of oscillation amplitude and frequency are investigated at different bulk flow rates and at various locations in the premixer. Also presented is a review of the in-house numerical work done towards this end, using three computational methods. Results show that the degree of dispersion in fuel flow rate oscillations depends on modulation amplitude and frequency as well as advective velocity of the bulk flow.Copyright © 2009 by Crown Copyright in Right of Canada

An analytical model based on advection-diffusion volume is analyzed with the objective to investigate the limits of achievable damping in fuel-air ratio oscillations over the range of frequencies at which combustor thermoacoustic instabilities are normally encountered. Results show that there exists an optimum degree of diffusion that will allow maximum damping in fuel-air ratio fluctuations. The upper bound on damping is found to be dependent on a constant value of a new non-dimensional number, defined as a ratio between Peclet Number and Strouhal Number. The analysis presented here is considered useful to evaluate the extent of damping that is inherently obtainable in practical premixers. Also presented are the results of experimental investigations, which were conducted to verify the analytically predicted behavior of premixers. The measurements were performed over a selected range of frequencies using a premixer configuration with square cross section and with fuel jet issuing in a co-flowing bulk air stream. The effects of modulation amplitude and frequency, and pressure drop across the premixer on the damping effectiveness of the premixer were examined. Results show that for the test conditions considered, the modulation amplitude has a profound effect on the premixer performance, whereas pressure drop effects are insignificant.Copyright © 2008 by ASME

This paper presents the theoretical and experimental framework used to characterize the capability of premixers used in Dry Low Emission (DLE) gas turbines to dampen fuel-to-air ratio (FAR) oscillations and thus serve as a passive control device for combustion noise. Based on a convection-diffusion volume model, transfer function analysis in the frequency-domain was used to describe the interaction between convection and turbulent diffusion mechanisms. The study showed that the best achievable damping was obtained when the ratio of convection to turbulent diffusion effects (expressed in terms of Peclet number) was unity. For this particular condition, the spreading of Residence Time Distribution (RTD) is optimal hence decreasing the coherence between incoming and outgoing perturbations. For large Peclet numbers, mixing mechanisms are not sufficient to dampen incoming FAR fluctuations and for very small Peclet numbers FAR perturbations can be communicated almost instantaneously to the premixer outlet, without attenuation.Copyright © 2007 by ASME

Unsteady heat release and pressure oscillations are inherent in many gas turbine combustors, at least for some operating conditions. It is the in-phase coupling of these quantities that leads to thermoacoustic instabilities. Combustors burning liquid fuel sprays with high-energy release rate are susceptible to this kind of instability because of the inherent unstable processes associated with spray combustion. Any effort towards development of effective active fuel modulation methodologies for control of thermoacoustic instabilities is therefore, dependent upon the understanding of the possible coupling between the spray dynamics and the combustor acoustic field. In this paper, we present some aspect of the ongoing efforts in our laboratory to gain knowledge of this interaction. Experimental and modeling results from both reacting and non-reacting flow studies are presented. Observations made on a kerosene fuelled LDI combustor suggest that the onset of the thermoacoustic instability is a function of the energy gain of the system, while the sustenance of instability is due to the in-phase relationship between combustor acoustics and unsteady heat release driven by acoustic oscillations. The presence of a two distinct unstable operating combustor regimes is observed and discussed as well. It is also shown that the intensity of the acoustic field in comparison to other flow field phenomena in the combustor is the dominant factor in influencing the combustor operation i.e., reacting flow field and spray characteristics.

This effort presents the application of an experimental high frequency and time-resolved global optical flow diagnostics for the characterization of pulsed spray flows. Such flows are encountered during active control of thermoacoustic instabilities, where high-bandwidth fuel modulation is often utilized to disrupt the combustor acoustic and unsteady heat release coupling. The understanding of spray dynamics is thus of paramount importance for these active control methodologies in order to achieve optimum control authority. A novel time-resolved Digital Particle Image Velocimetry (TRDPIV) implementation is employed for the dynamic investigation of the modulated spray. The method can measure both the droplet velocities as well as the droplet size distribution, from the same recorded images. The method provides planar image based droplet sizing using Mie scattering from DPIV measurements, with >5KHz sampling rate. Thus, eliminating complicated experimental approaches based on interferometer or fluorescence-Mie ratio. This paper presents the results of drop size characterization. Data processing is performed using different particle size evaluation schemes. The results are compared with measurements acquired from Phase Doppler Anemometry (PDA), conducted under same the experimental conditions. Experiments are conducted in non-reacting quiescent conditions, using an industrial simplex nozzle. The proportional spray modulation is obtained using a throttle valve-piezoelectric stack actuation system. The measurements for the current DPIV work are obtained under different pulsing amplitudes and frequencies. The results indicate that time-resolved DPIV can be a valuable tool in investigating dynamic response of modulated sprays.Copyright © 2004 by ASME

An experimental liquid fuel LDI combustor, developed to study thermoacoustic instability processes and to test active combustion control systems, was found to demonstrate three distinct stability regimes, with system characteristics not reported in earlier literature. These observations led to a series of further investigations, both in reactive and non-reactive conditions, to gain an insight into effects of combustor acoustics on fuel spray dynamics. This paper presents only the non-reacting flow results, from both experimental and modeling investigations. The experimental setup and construction details of an isothermal acoustic rig are presented. Phase-locked PDA measurements of droplet velocities and diameters from a simplex atomizer spray were acquired, with and without combustor swirl co-airflow, under varying acoustic forcing conditions and spray feed pressures. Measurements made at four locations in the spray are related, in the paper, to these variations in mean and unsteady inputs. The dynamic behavior of the spray is then presented in terms of frequency response characteristics related to acoustic fields imposed on the spray. Finally, results from non-reacting spray modeling, predicting droplet trajectories, are reported. The modeling was done using the deterministic separated flow approach. These trajectories are compared to the reported experimental results to support preliminary explanations for the unique experimental observations of the swirl-stabilized kerosene flame in a single can combustor geometry.Copyright © 2004 by ASME