Simultaneous Rayleigh scattering and laser-induced CH fluorescence for reaction zone imaging in high-speed premixed hydrocarbon flames

1997 ◽  
Vol 64 (5) ◽  
pp. 599-605 ◽  
Author(s):  
Yung-cheng Chen ◽  
Mohy S. Mansour
Keyword(s):  
Reaction Zone ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Hydrocarbon Flames

The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence

2017 ◽  
Author(s):  
Sean D. Salusbury ◽  
Ehsan Abbasi-Atibeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Flame Front ◽  
Turbulence Intensity ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Turbulent Flame ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flames ◽  
Counter Flow

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities. These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.

Comparison of Flame Dynamics at Stable and Near-LBO Conditions for Swirl-Stabilized Kerosene Spray Combustion

2015 ◽  
Author(s):  
Chi Zhang ◽  
Pengfei Zou ◽  
Bosen Wang ◽  
Xin Xue ◽  
Yuzhen Lin ◽  
...  
Keyword(s):  
Reaction Zone ◽  
High Speed ◽  
Stable Condition ◽  
Axial Direction ◽  
Spray Combustion ◽  
Flame Dynamics ◽  
Major Mode ◽  
The Difference ◽  
Pod Analysis ◽  
Rotation Motion

An experimental investigation was conducted to characterize the flame structures and dynamics at stable and near-lean blowout (LBO) conditions. The current experiments were carried out using a laboratory-scale aero-combustor with an internally-staged dome. The internally-staged injector consisted of pilot and main swirlers, and the pilot swirler was fueled with Chinese kerosene RP-3 while the main injector was chocked. The resulting spray flame was confined within a quartz tube under atmosphere pressure. In the present study, the influence of swirl intensity of the pilot swirler was also investiagted. The OH* chemiluminescence of the flame was recorded by a high-speed camera at a frequency of 2000 Hz. From the high-speed OH* images, the reaction zone was marked and the fluctuation of the reaction zone along axial direction was observed, showing that it became stronger at near-LBO condition than at stable condition. Proper Orthogonal Decomposition (POD) analysis was further used to provide insights into the characteristics of flame dynamics. Based on the POD results, the difference of the flame dynamics between the stable and near-LBO combustion was distinct. While the major Mode l of the flame under stable condition was rotation representing the rotation motion in the swirl flame, at near-LBO condition the flame dynamics included three modes — vibration, rotation, and flame shedding. In addition, for swirl-stabilized kerosene spray combustion investigated herein, the fluctuation of the reaction zone in axial direction became stronger with decreasing equivalence ratio when approaching LBO, and the POD analysis indicated that the Mode l of flame dynamics transitions from the rotation mode to the vibration mode. Although the change of pilot swirl number was found to have little influence on the Mode l of flame dynamics, it was noted to vary the fluctuation energy of the flame.

Characterization of reaction zone growth in an optically accessible heavy-duty diesel/methane dual-fuel engine

2018 ◽  
Vol 20 (5) ◽  
pp. 483-500 ◽  
Author(s):  
Jeremy Rochussen ◽  
Patrick Kirchen
Keyword(s):  
Growth Rate ◽  
Reaction Zone ◽  
Flame Propagation ◽  
High Speed ◽  
Dual Fuel ◽  
Pilot Injection ◽  
Fuel Conversion ◽  
Dual Fuel Engines ◽  
Dual Fuel Combustion ◽  
Zone Growth

The performance of dual-fuel engines in terms of fuel conversion efficiency and unburned hydrocarbon emission is strongly influenced by the turbulent flame propagation through the premixed natural gas. To improve dual-fuel engine design and provide validation data for numerical models, the fuel conversion process must be better characterized, specifically the reaction zone growth rate. In this work, high-speed imaging of OH*-chemiluminescence is performed in an optically accessible 2 L engine operated with port-injected CH4 and direct-injected diesel for different diesel and CH4 fueling rates and pilot injection pressures ( Ppilot). The cumulative histogram time series is introduced for directly comparing high-speed optical data of dual-fuel combustion with simultaneously measured apparent heat release rate. The cumulative histogram time series diagram is also used to evaluate a “global” reaction zone speed, SRZ,g, based on OH*-chemiluminescence images. The SRZ,g calculation normalizes the reaction zone area growth rate by the perimeter of the reaction zone to determine the velocity scale, while a “local” reaction zone speed, SRZ,l, is based on the local displacement of the reaction zone boundary per unit time. From the distribution of SRZ,l for each image frame, a previously proposed metric for determining the transition from pilot autoignition based on apparent heat release rate was validated and used to evaluate a single mean flame propagation speed, [Formula: see text]. Using these metrics, it was noted that increasing ϕCH4 from 0.40 to 0.69 results in an increase in [Formula: see text] from 4 to 8 m/s and 8 to 14 m/s for pilot injection pressures of 300 and 1300 bar, respectively. The spatial distribution of SRZ,l also indicates that autoignition of the pilot jets is not simultaneous (arising from asymmetric injector geometry) and leads to an overlap of the autoignition and flame propagation processes. This is not considered in the conventional conceptual model of dual-fuel combustion and impacts calculation of [Formula: see text] for the small diesel injections commonly used for dual-fuel engines.

Experimental and Numerical Investigations of MILD Combustion in a Model Combustor Applied for Gas Turbine

2018 ◽  
Author(s):  
Huan Zhang ◽  
Zhedian Zhang ◽  
Yan Xiong ◽  
Yan Liu ◽  
Yunhan Xiao
Keyword(s):  
Gas Turbine ◽  
Reaction Zone ◽  
High Speed ◽  
Equivalence Ratio ◽  
Low Noise ◽  
Combustion Characteristics ◽  
Doppler Velocity ◽  
Exhaust Gas ◽  
Mild Combustion ◽  
Jet Velocity

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, stable combustion and low noise for various kinds of fuel. MILD combustion is a promising combustion technology for gas turbine. The model combustor composed of an optical quartz combustor liner, four jet nozzles and one pilot nozzle has been designed in this study. The four jet nozzles are equidistantly arranged in the combustor concentric circle and the high-speed jet flows from the nozzles will entrain amount of exhaust gas to make MILD combustion occur. The combustion characteristics of the model combustor under atmosphere pressure have been investigated through experiments and numerical simulations. The influence of equivalence ratio and jet velocity on flow pattern, combustion characteristics and exhaust emissions were investigated in detail, respectively. Laser Doppler velocity (LDV) was utilized to measure the speed of a series of points in the model combustor. The measurement results show that a central recirculation existed in the combustion chamber. As the jet velocity of the nozzles increases, the amount of entrained mass by the jet increases simultaneously, however, the central recirculation zone is similar in shape and size. The recirculation of the model combustor will remain self-similar when the jet velocity varies in the range. The calculation model and method were verified through comparing with experimentally LDV data and be used to optimize the model combustor. Planar laser-induced fluorescence of hydroxyl radical (OH-PLIF) approaches were adopted to investigate the flame structure, the reaction zone and the OH distribution. OH distribution of the paralleled and crossed sections in the model combustor were measured, the whole reaction zone have been analyzed. The results show that the OH distribution was uniform in whole combustor. The exhaust gas composition of the combustor was measured by the “TESTO 350” Exhaust Gas Analyzer. All measurements emission results were corrected to 15% O2 in volume. Experimental results showed that NOx and CO emissions were less than 10 ppm@15%O2 when the equivalence ratio ranges from 0.63 to 0.8.

scholarly journals Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering

2017 ◽  
Vol 71 (3) ◽  
pp. 341-366 ◽  
Author(s):  
Andreas Ehn ◽  
Jiajian Zhu ◽  
Xuesong Li ◽  
Johannes Kiefer
Keyword(s):  
Gas Phase ◽  
Turbulent Flows ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Dynamic Range ◽  
Laser Doppler Anemometry ◽  
Short Pulse ◽  
High Repetition Rate ◽  
Aerospace Engineering ◽  
Spectroscopic Techniques

Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.

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