Liquid Fuel Composition Effects on Forced, Non-Premixed Ignition

2016 ◽  
Author(s):  
Brandon Sforzo ◽  
Hoang Dao ◽  
Sheng Wei ◽  
Jerry Seitzman
Keyword(s):  
High Speed ◽  
Chemical Kinetic ◽  
Optical Measurements ◽  
Liquid Fuels ◽  
Kinetic Properties ◽  
Fuel Composition ◽  
Ignition Process ◽  
Oxidation Reactions ◽  
High Speed Imaging ◽  
Ignition Probability

The effects of jet fuel composition on ignition probability have been studied in a flowfield that is relevant to turbine engine combustors, but also fundamental and conducive to modeling. In the experiments, a spark kernel is ejected from a wall and propagates transversely into a crossflow. The kernel first encounters an air-only stream before transiting into a second, flammable (premixed) stream. The two streams have matched velocities, as verified by hot-wire measurements. The liquid fuels span a range of physical and chemical kinetic properties. To focus on their chemical differences, the fuels are prevaporized in a carrier air flow before being injected into the experimental facility. Ignition probabilities at atmospheric pressure and elevated crossflow temperature were determined from optical measurements of a large number of spark events, and high speed imaging was used to characterize the kernel evolution. Eight fuel blends were tested experimentally; all exhibited increasing ignition probability as equivalence ratio increased, at least up to 1.5. Statistically significant differences between fuels were measured that have some correlation with fuel properties. To elucidate these trends, the forced ignition process was also studied with a reduced order numerical model of an entraining kernel. The simulations suggest ignition is successful if sufficient heat release occurs before entrainment of colder crossflow fluid quenches the exothermic oxidation reactions. As the kernel is initialized in air, it remains lean during the initial entrainment of the fuel-air mixture; thus richer crossflows lead to quicker and higher exothermicity.

scholarly journals Liquid Fuel Composition Effects on Forced, Nonpremixed Ignition

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Brandon Sforzo ◽  
Hoang Dao ◽  
Sheng Wei ◽  
Jerry Seitzman
Keyword(s):  
High Speed ◽  
Chemical Kinetic ◽  
Optical Measurements ◽  
Liquid Fuels ◽  
Kinetic Properties ◽  
Fuel Composition ◽  
Ignition Process ◽  
Oxidation Reactions ◽  
High Speed Imaging ◽  
Ignition Probability

The effects of jet fuel composition on ignition probability have been studied in a flowfield that is relevant to turbine engine combustors, but also fundamental and conducive to modeling. In the experiments, a spark kernel is ejected from a wall and propagates transversely into a crossflow. The kernel first encounters an air-only stream before transiting into a second, flammable (premixed) stream. The two streams have matched velocities, as verified by hot-wire measurements. The liquid fuels span a range of physical and chemical kinetic properties. To focus on their chemical differences, the fuels are prevaporized in a carrier air flow before being injected into the experimental facility. Ignition probabilities at atmospheric pressure and elevated crossflow temperature were determined from optical measurements of a large number of spark events, and high-speed imaging was used to characterize the kernel evolution. Eight fuel blends were tested experimentally; all exhibited increasing ignition probability as equivalence ratio increased, at least up to the maximum value studied (∼0.8). Statistically significant differences between fuels were measured that have some correlation with fuel properties. To elucidate these trends, the forced ignition process was also studied with a reduced-order numerical model of an entraining kernel. The simulations suggest ignition is successful if sufficient heat release occurs before entrainment of colder crossflow fluid quenches the exothermic oxidation reactions. As the kernel is initialized in air, it remains extremely lean during the initial entrainment of the fuel–air mixture; thus, richer crossflows lead to quicker and higher exothermicity.

High Speed Imaging of Forced Ignition Kernels in Non-Uniform Jet Fuel/Air Mixtures

2017 ◽  
Author(s):  
Sheng Wei ◽  
Brandon Sforzo ◽  
Jerry Seitzman
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Air Flow ◽  
Cetane Number ◽  
High Energy ◽  
Liquid Fuels ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Turbine Engine ◽  
Planar Laser

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates non-uniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel-air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three, synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel-air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low aromatic/low cetane number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high aromatic, more easily ignited fuel, shows the largest reaction region at early times.

scholarly journals High-Speed Imaging of Forced Ignition Kernels in Nonuniform Jet Fuel/Air Mixtures

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Sheng Wei ◽  
Brandon Sforzo ◽  
Jerry Seitzman
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Air Flow ◽  
Cetane Number ◽  
High Energy ◽  
Liquid Fuels ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Turbine Engine ◽  
Planar Laser

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates nonuniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel–air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel–air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low-aromatic/low-cetane-number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high-aromatic, more easily ignited fuel, shows the largest reaction region at early times.

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit S. Pathania ◽  
Patton M. Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Annular Combustor ◽  
Initial Flame ◽  
Limiting Condition

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff-Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit Pathania ◽  
Patton Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Design And Optimization ◽  
Annular Combustor ◽  
Favorable Conditions

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess ignition probability and provide insights into the mechanisms of failure and of successful flame propagation. Two configurations were employed, with 12 and 18 burners, mixture velocity was varied between 10 and 30 m/s, and equivalence ratio between 0.58 and 0.68. Ignition was initiated by a sequence of sparks and "ignition" is defined as successful ignition of the whole annular combustor. Mechanism of success and failure of the ignition process was investigated via high-speed imaging of OH*chemiluminescence. Lean ignition limits were evaluated and compared to the lean blow-off limits. It was found that failure is linked to the trapping of the flame kernel inside the inner recirculation zone (IRZ) of a single burner, followed by localised quenching on the bluff body due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner. Finally, the ignition probability(Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign~0 for most conditions, while Pign increased moving the spark away from the bluff body or placing it between two burners and peaked to Pign~1 when the spark was located downstream in the combustion chamber. The results provide information on the most favorable conditions for achieving ignition and could help design and optimization of realistic gas turbine combustors.

Fuel Influence on Targeted Gas Turbine Combustion Properties: Part I — Detailed Diagnostics

2014 ◽  
Author(s):  
Thomas Mosbach ◽  
Victor Burger ◽  
Barani Gunasekaran
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Leading Edge ◽  
Operating Conditions ◽  
Optical Measurements ◽  
Test Facility ◽  
Research Centre ◽  
High Speed Imaging ◽  
Combustion Properties ◽  
First Results

The threshold combustion performance of different fuel formulations under simulated altitude relight conditions were investigated in the altitude relight test facility located at the Rolls-Royce plc. Strategic Research Centre in Derby, UK. The combustor employed was a twin-sector representation of an RQL gas turbine combustor. Eight fuels including conventional crude-derived Jet A-1 kerosene, synthetic paraffinic kerosenes (SPKs), linear paraffinic solvents, aromatic solvents and pure compounds were tested. The combustor was operated at sub-atmospheric air pressure of 41 kPa and air temperature of 265 K. The temperature of all fuels was regulated to 288 K. The combustor operating conditions corresponded to a low stratospheric flight altitude near 9 kilometres. The experimental work at the Rolls-Royce (RR) test-rig consisted of classical relight envelope ignition and extinction tests, and ancillary optical measurements: Simultaneous high-speed imaging of the OH* chemiluminescence and of the soot luminosity was used to visualize both the transient combustion phenomena and the combustion behaviour of the steady burning flames. Flame luminosity spectra were also simultaneously recorded with a spectrometer to obtain information about the different combustion intermediates and about the thermal soot radiation curve. This paper presents first results from the analysis of the weak extinction measurements. Further detailed test fuel results are the subject of a separate complementary paper [1]. It was found in general that the determined weak extinction parameters were not strongly dependent on the fuels investigated, however at the leading edge of the OH* chemiluminescence intensity development in the pre-flame region fuel-related differences were observed.

Visualizing an ignition process of hydrogen jets containing sodium mist by high-speed imaging

2019 ◽  
Vol 56 (6) ◽  
pp. 521-532
Author(s):  
Daisuke Doi ◽  
Hiroshi Seino ◽  
Shinya Miyahara ◽  
Masayoshi Uno
Keyword(s):  
High Speed ◽  
Ignition Process ◽  
High Speed Imaging

Low NOX Combustion for Liquid Fuels: Atmospheric Pressure Experiments Using a Staged Prevaporizer-Premixer

2001 ◽  
Author(s):  
John C. Y. Lee ◽  
Philip C. Malte ◽  
Michael A. Benjamin
Keyword(s):  
Diesel Fuel ◽  
Atmospheric Pressure ◽  
Small Variation ◽  
Chemical Kinetic ◽  
Optical Measurements ◽  
Liquid Fuels ◽  
Stirred Reactor ◽  
Wide Range ◽  
Outlet Stream ◽  
Low Nox Combustion

Low emissions of NOx are obtained for a wide range of liquid fuels by using a staged prevaporizing-premixing injector. The injector relies on two stages of air temperature and fires into a laboratory jet-stirred reactor operated at atmospheric pressure and nominal ϕ of 0.6. The liquid fuels burned are methanol, normal alkanes from pentane to hexadecane, benzene, toluene, two grades of light naphtha and four grades of No. 2 diesel fuel. Additionally, natural gas, ethane and industrial propane are burned. For experiments conducted for 1790 K combustion temperature and 2.3±0.1 ms combustion residence time, the NOx (adjusted to 15% O2 dry) varies from a low of 3.5 ppmv for methanol to a high of 11.5 ppmv for No. 2 diesel fuel. For the most part, the NOx and CO are positively correlated with the fuel carbon to hydrogen ratio (C/H). Chemical kinetic modeling suggests the increase in NOx with C/H ratio is caused in significant part by the increasing super-equilibrium concentrations of O-atom created by the increasing levels of CO burning in the jet-stirred reactor. Fuel bound nitrogen also contributes NOx for the burning of the diesel fuel. This paper describes the staged prevaporizing-premixing injector, the examination of the injector and the NOx and CO measurements and their interpretation. Optical measurements, using beams of He-Ne laser radiation passed across the outlet stream of the injector, indicate complete vaporization and a small variation in the cross-stream averaged fuel/air ratio. The later is determined by measuring the standard deviation and mean of the transmission of the laser beam passed through the stream. Additional measurements and inspections indicate no pressure oscillations within the injector and no gum and carbon deposition. Thus, the NOx and CO measurements are obtained for fully vaporized, well premixed conditions devoid of preflame reactions within the injector.

Simulations of flame propagation during the ignition process in an annular multiple-injector combustor

2019 ◽  
Vol 29 (6) ◽  
pp. 1947-1964 ◽  
Author(s):  
Dongmei Zhao ◽  
Yifan Xia ◽  
Haiwen Ge ◽  
Qizhao Lin ◽  
Jianfeng Zou ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Adaptive Mesh Refinement ◽  
High Speed ◽  
Early Stage ◽  
Adaptive Mesh ◽  
Critical Issue ◽  
Experimental Investigations ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Content Type

Purpose Ignition process is a critical issue in combustion systems. It is particularly important for reliability and safety prospects of aero-engine. This paper aims to numerically investigate the burner-to-burner propagation during ignition process in a full annular multiple-injector combustor and then validate it by comparing with experimental results. Design/methodology/approach The annular multiple-injector experimental setup features 16 swirling injectors and two quartz tubes providing optical accesses to high-speed imaging of flames. A Reynolds averaged Navier–Stokes model, adaptive mesh refinement (AMR) and complete San Diego chemistry are used to predict the ignition process. Findings The ignition process shows an overall agreement with experiment. The integrated heat release rate of simulation and the integrated light intensity of experiment is also within reasonable agreement. The flow structure and flame propagation dynamics are carefully analyzed. It is found that the flame fronts propagate symmetrically at an early stage and asymmetrically near merging stage. The flame speed slows down before flame merging. Overall, the numerical results show that the present numerical model can reliably predict the flame propagation during the ignition process. Originality/value The dedicated AMR method together with detailed chemistry is used for predicting the unsteady ignition procedure in a laboratory-scale annular combustor for the first time. The validation shows satisfying agreements with the experimental investigations. Some details of flow structures are revealed to explain the characteristics of unsteady flame propagations.

Blowout Sensitivities in a Liquid Fueled Combustor: Fuel Composition and Preheat Temperature Effects

2017 ◽  
Author(s):  
Nicholas Rock ◽  
Ianko Chterev ◽  
Benjamin Emerson ◽  
Jerry Seitzman ◽  
Tim Lieuwen
Keyword(s):  
Cetane Number ◽  
Reaction Rates ◽  
Smoke Point ◽  
Liquid Fuels ◽  
Inlet Temperature ◽  
Kinetic Properties ◽  
Fuel Composition ◽  
Fuel Droplets ◽  
Air Inlet ◽  
Radiation Losses

The objective of this paper is to identify the influence of fuel composition on blowoff limits in a liquid fueled combustor. In premixed, gaseous systems, blowoff is a kinetically limited phenomenon, possibly with additional heat loss effects. In liquid fueled systems, the situation is far more complex, as a variety of processes can influence blowoff, including kinetics, atomization, vaporization, mixing, and heat transfer. Which one of these processes is controlling is a function of fuel and air preparation and premixing, approach flow temperature and pressure, and fuel physical and kinetic properties. This paper extends our prior work on this problem by presenting blowoff results from ten liquid fuels at two air inlet temperatures, 450 K and 300 K. At 450 K, blowoff appears to be limited by kinetics and/or radiation losses, while it seems vaporization limited at 300 K. Specifically, strong negative correlations were observed between blowoff limits and the cetane number of the fuel at the 450 K conditions. Similarly good correlations are observed with the fuel smoke point, and its percentage of aromatics. This supports two different hypotheses: (1) it is the fuels with the shortest ignition delay, and therefore the fastest reaction rates, that are the most resistant to blowoff, or (2) it is the fuels with the greatest radiation losses (presumably vaporizing/preheating the approach flow fuel droplets) that are the most blowoff resistant. Additional measurements with other fuels that decouple ignition and radiative characteristics are needed to differentiate these effects. At air inlet temperatures of 300 K, the governing physics seem quite clear from the data. Strong positive correlations were observed with LBO and boiling point temperature across the entire distillation range. As long as the air inlet temperature is above the fuel flash point, the easiest to vaporize fuels are the hardest to blowoff. It is suspected that difficult to vaporize fuels blowoff easily due to locally non-flammable regions in this low temperature regime.

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