Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Part II — Effects of Venturi Angle

2018 ◽  
Author(s):  
Cunxi Liu ◽  
Fuqiang Liu ◽  
Jinhu Yang ◽  
Yong Mu ◽  
Gang Xu
Keyword(s):  
Flow Field ◽  
High Altitude ◽  
Gas Turbines ◽  
Fuel Injection ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Main Stage ◽  
Fuel Injector ◽  
Lean Burn ◽  
Low Emission

In order to reduce NOx emissions, modern gas turbines are often equipped with lean burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, an internally staged scheme of fuel injection is proposed. The pilot and main fuel staging enable fuel distribution control and high turn-down ratio, multi-injections of main fuel leads to a fast and efficient fuel/air mixing. A fuel-staged low emission combustor in the framework of lean burn combustion is developed in the present study, the central pilot stage of fuel injector working singly at low power operating conditions is swirl-cup prefilming atomization and main stage is jet-in-crossflow multi-injection atomization, a combination of pilot and main stage injection is provided for higher power operating conditions. A significant amount of the air mass flow utilised for fuel preparation and initiation is adverse to the operability specifications, such as ignition, lean blow-out, and high-altitude relight etc. The spray characteristics of pilot spray and flow field are one of the key factors affecting combustion operability. This work investigates the effects of the venturi angle on combustion operability, the ignition and lean blow-out performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry to provide insight into the correlation between spray, flow field and combustion operability performances.

Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Part I — Effects of Main Swirl Angle

2016 ◽  
Author(s):  
Cunxi Liu ◽  
Fuqiang Liu ◽  
Jinhu Yang ◽  
Yong Mu ◽  
Chunyan Hu ◽  
...  
Keyword(s):  
Low Power ◽  
High Altitude ◽  
Gas Turbines ◽  
Combustion Stability ◽  
Main Stage ◽  
Lean Burn ◽  
Swirl Angle ◽  
Low Emission ◽  
Flow Interactions ◽  
Air Streams

In order to reduce NOx emissions, modern gas turbines are often equipped with lean-burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, internally staged scheme of fuel injection is proposed. Primary and main fuel staging enable fuel distribution control, multi-injections of main fuel leads to a fast and efficient mixing. A fuel-staged low emission combustor in the framework of lean-burn combustion is developed in the present study, the central pilot stage for low power conditions is swirl-cup prefilming atomization, main stage is jet-in-crossflow multi-injection, a combination of primary and main stage injection is provided for higher power output conditions. In lean-burn combustors, the swirling main air naturally tends to entrain the pilot flame and quench it at low power conditions, which is adverse to the operability specifications, such as ignition, lean blow-out, and high-altitude relight. In order to investigate the effects of the main swirl angle on combustion performances, the ignition and lean blow-out performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry to provide insight into spray and combustion performances. Flow-flow interactions between pilot and main air streams, spray-flow interactions between pilot spray and main air streams, and flame-flow interactions between pilot flame and main air streams are comprehensively analyzed. The entrainment of recirculating main air streams on pilot air streams enhances with increase of main swirl angle, because of the upward motion and increasing width of main recirculation zone. A small part of droplets are entrained by the recirculating main air streams at periphery of combustor and a majority of droplets concentrate near the centerline of combustor, making that entrainment of recirculating main air streams on pilot spray and quenching effects of recirculating main air streams on pilot flame is slight, and the quenching effects can be ignored. A follow-on paper will study the effects of venturi angle on the combustion performances.

Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Effects of Main Swirl Angle

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Cunxi Liu ◽  
Fuqiang Liu ◽  
Jinhu Yang ◽  
Yong Mu ◽  
Chunyan Hu ◽  
...  
Keyword(s):  
Low Power ◽  
High Altitude ◽  
Gas Turbines ◽  
Combustion Stability ◽  
Main Stage ◽  
Lean Burn ◽  
Swirl Angle ◽  
Low Emission ◽  
Flow Interactions ◽  
Air Streams

In order to reduce NOx emissions, modern gas turbines are often equipped with lean-burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, internally staged scheme of fuel injection is proposed. Primary and main fuel staging enable fuel distribution control, and multi-injections of main fuel lead to a fast and efficient mixing. A fuel-staged low emission combustor in the framework of lean-burn combustion is developed in the present study, i.e., the central pilot stage for low power conditions is swirl-cup prefilming atomization, the main stage is jet-in-crossflow multi-injection, and a combination of primary and main stage injection is provided for higher power output conditions. In lean-burn combustors, the swirling main air naturally tends to entrain the pilot flame and quench it at low power conditions, which is adverse to the operability specifications, such as ignition, lean blow-out (LBO), and high-altitude relight. In order to investigate the effects of the main swirl angle on combustion performances, the ignition and LBO performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry (PIV) to provide insight into spray and combustion performances. Flow–flow interactions between pilot and main air streams, spray–flow interactions between pilot spray and main air streams, and flame–flow interactions between pilot flame and main air streams are comprehensively analyzed. The entrainment of recirculating main air streams on pilot air streams enhances with the increase of main swirl angle, because of the upward motion and increasing width of main recirculation zone. A small part of droplets are entrained by the recirculating main air streams at periphery of combustor and a majority of droplets concentrate near the centerline of combustor, making that entrainment of recirculating main air streams on pilot spray and quenching effects of recirculating main air streams on pilot flame are slight, and the extinguishing effects can be ignored. The contributions of main swirl strength to improvement of ignition and LBO performances are due to enhancement of air/fuel mixing by strengthening turbulence level in pilot zone.

Lean-Burn Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural Gas Spark Ignition

2018 ◽  
Author(s):  
Jinlong Liu ◽  
Cosmin E. Dumitrescu
Keyword(s):  
Natural Gas ◽  
Combustion Chamber ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Fuel Injector ◽  
Heavy Duty ◽  
Lean Burn ◽  
Spark Timing ◽  
Heavy Duty Diesel

Increased utilization of natural-gas (NG) in the transportation sector can decrease the use of petroleum-based fuels and reduce greenhouse-gas emissions. Heavy-duty diesel engines retrofitted to NG spark ignition (SI) can achieve higher efficiencies and low NOx, CO, and HC emissions when operated under lean-burn conditions. To investigate the SI lean-burn combustion phenomena in a bowl-in-piston combustion chamber, a conventional heavy-duty direct-injection CI engine was converted to SI operation by replacing the fuel injector with a spark plug and by fumigating NG in the intake manifold. Steady-state engine experiments and numerical simulations were performed at several operating conditions that changed spark timing, engine speed, and mixture equivalence ratio. Results suggested a two-zone NG combustion inside the diesel-like combustion chamber. More frequent and significant late burn (including double-peak heat release rate) was observed for advanced spark timing. This was due to the chamber geometry affecting the local flame speed, which resulted in a faster and thicker flame in the bowl but a slower and thinner flame in the squish volume. Good combustion stability (COVIMEP < 3 %), moderate rate of pressure rise, and lack of knocking showed promise for heavy-duty CI engines converted to NG SI operation.

Lean-Burn Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural-Gas Spark Ignition

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Jinlong Liu ◽  
Cosmin Emil Dumitrescu
Keyword(s):  
Natural Gas ◽  
Combustion Chamber ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Fuel Injector ◽  
Heavy Duty ◽  
Lean Burn ◽  
Heavy Duty Diesel ◽  
Ci Engines

Increased utilization of natural gas (NG) in the transportation sector can decrease the use of petroleum-based fuels and reduced greenhouse gas emissions. Heavy-duty diesel engines retrofitted to NG spark ignition (SI) can achieve higher efficiencies and low NOX, CO, and hydrocarbon (HC) emissions when operated under lean-burn conditions. To investigate the SI lean-burn combustion phenomena in a bowl-in-piston combustion chamber, a conventional heavy-duty direct-injection CI engine was converted to SI operation by replacing the fuel injector with a spark plug and by fumigating NG in the intake manifold. Steady-state engine experiments and numerical simulations were performed at several operating conditions that changed spark timing (ST), engine speed, and mixture equivalence ratio. Results suggested a two-zone NG combustion inside the diesel-like combustion chamber. More frequent and significant late-burn (including double-peak heat release rate) was observed for advanced ST. This was due to the chamber geometry affecting the local flame speed, which resulted in a faster and thicker flame in the bowl but a slower and thinner flame in the squish volume. Good combustion stability (COVIMEP < 3%), moderate rate of pressure-rise, and lack of knocking showed promise for heavy-duty CI engines converted to NG SI operation.

Characterization of Lean Burn Module Air Blast Pilot Injector With Laser Techniques

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
U. Meier ◽  
S. Freitag ◽  
J. Heinze ◽  
L. Lange ◽  
E. Magens ◽  
...  
Keyword(s):  
Flow Field ◽  
Soot Formation ◽  
Test Methods ◽  
Oh Radicals ◽  
Main Stage ◽  
Fuel Injector ◽  
Lean Burn ◽  
Fuel Ratio ◽  
Optical Test ◽  
Planar Laser

For lean burn combustor development in low emission aero-engines, the pilot stage of the fuel injector plays a key role with respect to stability, operability, NOx emissions, and smoke production. Therefore it is of considerable interest to characterize the pilot module in terms of pilot zone mixing, fuel placement, flow field, and interaction with the main stage. This contribution focuses on the investigation of soot formation during pilot-only operation. Optical test methods were applied in an optically accessible single sector rig at engine idle conditions. Using planar laser-induced incandescence (LII), the distribution of soot and its dependence on air/fuel ratio, as well as geometric injector parameters, was studied. The data shows that below a certain air/fuel ratio, an increase of soot production occurs. This is in agreement with smoke number measurements in a standard single sector flame tube rig without optical access. Reaction zones were identified using chemiluminescence of OH radicals. In addition, the injector flow field was investigated with PIV. A hypothesis regarding the mechanism of pilot smoke formation was made based on these findings. This along with further investigations will form the basis for developing strategies for smoke improvement at elevated pilot-only conditions.

Preliminary Study of Low Emission Gas Turbine Combustor With Airblast Fuel Atomizer

1976 ◽  
Vol 98 (1) ◽  
pp. 15-22
Author(s):  
K. Yamanaka ◽  
K. Nagato
Keyword(s):  
Gas Turbine ◽  
Fuel Injection ◽  
Tube Wall ◽  
Combustion Stability ◽  
Exhaust Emission ◽  
Fuel Injector ◽  
Gas Turbine Combustor ◽  
Low Emission ◽  
New Type ◽  
Preliminary Study

Recent papers describe that an airblast fuel atomizer is very effective for reducing emissions from a gas turbine and this type of fuel injector is being applied to practical engines. This paper deals with the new type of airblast fuel atomizer AFIT which comes from “Airblast Fuel Injection Tube” that makes fuel to break up into droplets by atomizing air at several small holes on the tube wall and fuel is well mixed with atomizing air instantly at the exits of holes. Regarding this AFIT, the fuel spray characteristics, combustion stability which is usually narrow for the combustor with an airblast fuel atomizer at lower engine speeds and exhaust emission levels are experimented and its effectiveness is discussed.

The Influence of Geometric and Aerodynamic Boundary Conditions on Fuel Injector Feed and External Aerodynamics for Lean Burn Combustors

2019 ◽  
Author(s):  
Y. Li ◽  
P. A. Denman ◽  
A. D. Walker
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
Combustion System ◽  
Fuel Injector ◽  
Flow Uniformity ◽  
Lean Burn ◽  
Fuel Injectors ◽  
Systematic Assessment ◽  
Flame Tube ◽  
External Combustion

Abstract Lean burn combustion is currently a preferred technology to meet the future low emission requirements faced by aero gas turbines. Previous work has shown that the increased air mass flow and size of lean burn fuel injector alters the necessary redistribution of the airflow leaving the high-pressure compressor. This can lead to flow field non-uniformities in the feed to combustor annuli and the fuel injectors which have the potential to impact the overall performance of the combustion system. This paper presents a systematic assessment of the effect of several aerodynamic parameters on the air flow feed to the fuel injectors and the external combustion system aerodynamics for a generic lean burn system. This includes the effect of changes to the flow splits between various combustor cooling features and annulus flows and the effect of a biased compressor exit profile. Flow field data are generated using an isothermal RANS CFD model which is validated against test rig data. The data show that changes in the flow split between the annuli modified the flow uniformity and loss to both the combustor annuli and the fuel injector feed. Changes in the compressor exit profile have a larger effect introducing more notable variations in both flow uniformity and loss. Changes to the angle of the flame tube did not greatly affect the pre-diffuser but did modify annulus loss. Further analysis showed that changes to the combustor annulus flow split, compressor exit profile and flame tube angle modified the location, at compressor exit, of the flow captured by the annuli or each fuel injector passage. The loss to each of these depends on the flow quality (total pressure and uniformity) and from the source more than the flow uniformity delivered.

Characterisation of Lean Burn Module Air Blast Pilot Injector With Laser Techniques

2013 ◽  
Author(s):  
U. Meier ◽  
S. Freitag ◽  
J. Heinze ◽  
L. Lange ◽  
E. Magens ◽  
...  
Keyword(s):  
Flow Field ◽  
Soot Formation ◽  
Test Methods ◽  
Oh Radicals ◽  
Main Stage ◽  
Fuel Injector ◽  
Lean Burn ◽  
Fuel Ratio ◽  
Optical Test ◽  
Planar Laser

For lean burn combustor development in low emission aero-engines, the pilot stage of the fuel injector plays a key role with respect to stability, operability, NOx emissions, and smoke production. Therefore it is of considerable interest to characterize the pilot module in terms of pilot zone mixing, fuel placement, flow field and interaction with the main stage. This contribution focusses on the investigation of soot formation during pilot-only operation. Optical test methods were applied in an optically accessible single sector rig at engine idle conditions. Using planar laser-induced incandescence (LII), the distribution of soot and its dependence on air/fuel ratio, as well as geometric injector parameters, was studied. The data shows that below a certain air/fuel ratio, an increase of soot production occurs. This is in agreement with smoke number measurements in a standard single sector flame tube rig without optical access. Reaction zones were identified using chemiluminescence of OH radicals. In addition, the injector flow field was investigated with PIV. A hypothesis regarding the mechanism of pilot smoke formation was made based on these findings. This along with further investigations will form the basis for developing strategies for smoke improvement at elevated pilot only conditions.

Flow Field and Hot Streak Migration Through a High Pressure Cooled Vanes With Representative Lean Burn Combustor Outflow

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Tommaso Bacci ◽  
Tommaso Lenzi ◽  
Alessio Picchi ◽  
Lorenzo Mazzei ◽  
Bruno Facchini
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Flow Field ◽  
Fuel Injection ◽  
Leading Edge ◽  
Flame Stabilization ◽  
Lean Burn ◽  
Aero Engine ◽  
University Of Florence ◽  
Hot Streak

Modern lean burn aero-engine combustors make use of relevant swirl degrees for flame stabilization. Moreover, important temperature distortions are generated, in tangential and radial directions, due to discrete fuel injection and liner cooling flows respectively. At the same time, more efficient devices are employed for liner cooling and a less intense mixing with the mainstream occurs. As a result, aggressive swirl fields, high turbulence intensities, and strong hot streaks are achieved at the turbine inlet. In order to understand combustor-turbine flow field interactions, it is mandatory to collect reliable experimental data at representative flow conditions. While the separated effects of temperature, swirl, and turbulence on the first turbine stage have been widely investigated, reduced experimental data is available when it comes to consider all these factors together.In this perspective, an annular three-sector combustor simulator with fully cooled high pressure vanes has been designed and installed at the THT Lab of University of Florence. The test rig is equipped with three axial swirlers, effusion cooled liners, and six film cooled high pressure vanes passages, for a vortex-to-vane count ratio of 1:2. The relative clocking position between swirlers and vanes has been chosen in order to have the leading edge of the central NGV aligned with the central swirler. In order to generate representative conditions, a heated mainstream passes though the axial swirlers of the combustor simulator, while the effusion cooled liners are fed by air at ambient temperature. The resulting flow field exiting from the combustor simulator and approaching the cooled vane can be considered representative of a modern Lean Burn aero engine combustor with swirl angles above ±50 deg, turbulence intensities up to about 28% and maximum-to-minimum temperature ratio of about 1.25. With the final aim of investigating the hot streaks evolution through the cooled high pressure vane, the mean aerothermal field (temperature, pressure, and velocity fields) has been evaluated by means of a five-hole probe equipped with a thermocouple and traversed upstream and downstream of the NGV cascade.

Experimental and Numerical Study for Improved Understanding of Mixed-Convection Type of Flows in Turbine Casing Cavities During Shut-Down Regimes

2021 ◽  
Author(s):  
Oguzhan Murat ◽  
Budimir Rosic ◽  
Koichi Tanimoto ◽  
Ryo Egami
Keyword(s):  
Natural Convection ◽  
Flow Field ◽  
Mixed Convection ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Scale Model ◽  
Unsteady Temperature ◽  
Numerical Predictions ◽  
Wide Range ◽  
Turbine Casing

Abstract Due to increase in the power generation from renewable sources, steam and gas turbines will be required to adapt for more flexible operations with frequent start-ups and shut-downs to provide load levelling capacity. During shut-down regimes, mixed convection takes place with natural convection dominance depending on the operating conditions in turbine cavities. Buoyant flows inside the turbine that are responsible for non-uniform cooling leading to thermal stresses and compromise clearances directly limits the operational flexibility. Computational fluid dynamics (CFD) tools are required to predict the flow field during these regimes since direct measurements are extremely difficult to conduct due to the harsh operating conditions. Natural convection with the presence of cross-flow -mixed convection has not been extensively studied to provide detailed measurements. Since the literature lacks of research on such flows with real engine representative operating conditions for CFD validation, the confidence in numerical predictions is rather inadequate. This paper presents a novel experimental facility that has been designed and commissioned to perform very accurate unsteady temperature and flow field measurements in a simplified turbine casing geometry. The facility is capable of reproducing a wide range of Richardson, Grashof and Reynolds numbers which are representative of engine realistic operating conditions. In addition, high fidelity, wall resolved LES with dynamic Smagorinsky subgrid scale model has been performed. The flow field as well as heat transfer characteristics have been accurately captured with LES. Lastly, inadequacy of RANS for mixed type of flows has been highlighted.

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