Flame Temperature Distribution Research Articles

Spray Combustion Characteristics and Soot Emission Reduction of Hydrous Ethanol Diesel Emulsion Fuel Using Color-Ratio Pyrometry

To elucidate the relationship between physicochemical properties, spray characteristics, and combustion performance, a series of experiments have been conducted in a constant volume vessel with injection of hydrous ethanol diesel emulsion and regular diesel. HE30 (emulsion with 30% volume fraction of 20% water-containing ethanol and 70% volume fraction of 0# diesel) is developed using Shah’s technique and regular diesel is also employed for comparison. Firstly, the physicochemical properties of two kinds of fuels are investigated. Then, the non-evaporating and evaporating spray characteristics are examined through the high-speed shadowgraphs. Finally, spray combustion experiments under different ambient oxygen concentrations are carried out, and color-ratio pyrometry (CRP) is applied to measure the flame temperature and soot concentration (KL) distributions. The results indicate that the physicochemical properties, such as density, surface tension, kinematic viscosity, cetane number, and oxygen content, have significant impact on the spray mixture formation and combustion performance. HE30 exhibits lower soot emissions than that of regular diesel. Further analysis supports the standpoint that the hydrous ethanol diesel emulsion can suppress the soot and NOx simultaneously. Therefore, the hydrous ethanol diesel emulsion has great potential to be an alternative clean energy resource.

Experimental comparison of a 2D laminar diffusion flame under oxy-fuel and air atmosphere

We present an experimental study on the effects of an oxy-fuel atmosphere with 30%Vol.O2/70%Vol.CO2 content on a laminar, non-premixed methane flame based on measured spatial profiles of gas temperature as well as H2O, CH4, OH and CO concentrations, with the aim of providing thermochemical validation data for numerical simulations in the oxy-fuel context. The in situ measurements were performed using temporally multiplexed laser spectrometer based on direct laser absorption spectroscopy in combination with two-line thermometry. The system is validated on a well-characterized air-blown flame at the same burner and found to be in good agreement with reference data. The different behaviors of the oxy-fuel compared to the conventional air-blown flame with respect to the flame structure, species concentrations and temperature distribution are discussed and explained by the altered thermo-physical properties of the oxy-fuel atmosphere and the reactions involved. The altered stoichiometry of the oxy-fuel flame leads to increased CO and H2O concentrations, whereas the increased heat transfer and heat capacity caused a reduction in peak flame temperature.

Visualization of combustion performance and emission characteristics of a four-cylinder diesel engine at various injection timings and engine loads

In this study, the effects of injection timings on engine combustion, performance, and emission characteristics were investigated experimentally using a four-cylinder diesel engine equipped with an endoscopic visualization system. The experiments were conducted at constant speed (1500 rpm) with different start of injection timings and two loads (10 and 25% load, respectively). Premixed combustion was found from the heat release rate and combustion images with advanced injection. Additionally, larger area of luminous flames was obtained for retarded injection timing and higher engine load. It was also found that the area of soot distribution and flame temperature distribution decreased for advanced injection timing. NO x emission increased for advanced injection, however, an opposite trend was observed for lower load.

Spatially resolved laser-induced breakdown spectroscopy in laminar premixed methane–air flames

Laser-induced breakdown spectroscopy was evaluated for the analysis of the structure of laminar premixed methane–air flames. Firstly, breakdown threshold pulse energy and plasma energy in different areas of the flame were measured simultaneously, and an approximate linear relation between them was detected. Secondly, a new approach was proposed to qualitatively characterize the flame temperature distributions based on the plasma energy distributions. Finally, combination of the spatial analysis of the spectrum intensity, plasma energy and equivalence ratio, the laminar premixed flames structure was investigated deeply, including the distribution of the flame temperature, the width and distribution of different flame region (e.g. premixed combustion regions, high temperature regions.),as well as the location of the flame front.

Numerical Study of Turbulent Jet Ignition in a Lean Premixed Configuration

Direct numerical simulations (DNS) of a hot combustion product jet interacting with a lean premixed hydrogen-air coflow are conducted to fundamentally investigate turbulent jet ignition (TJI) in a three-dimensional configuration. TJI is an efficient method for initiating and controlling combustion in ultra-lean combustion systems. Fully compressible gas dynamics and species equations are solved with high order finite difference methods. The hydrogen-air reaction is simulated with a reliable detailed chemical kinetics mechanism. The physical processes involved in the TJI-assisted combustion are investigated by considering the flame heat release, temperature, species concentrations, vorticity, and Baroclinc torque. The complex turbulent flame and flow structures are delineated in three main: i) hot product jet, ii) burned-mixed, and iii) flame zones. In the TJI-assisted combustion, the flow structures and the flame features such as flame speed, temperature, and species distribution are found to be quite different than those in “standard” turbulent premixed combustion due to the existence of a high energy turbulent hot product jet. The flow structures and statistics are also found to be different than those normally seen in non-isothermal non-reacting jets.

Experiments investigation on 2D distribution of soot temperature and volume fraction by image processing of visible radiation

A simple diagnostics method was presented that uses a low-cost camera to simultaneously reconstruct 2D distributions of flame temperature and soot concentration in laminar diffusion axisymmetric flames. A Manta G-504 camera with one million effective pixels was utilized for data collection, equipped with the lens type Computar TEC-55 with one customized double-bandpass filter mounted on front of the camera. This setup was used to obtain 615 and 517nm monochromatic radiation flame images. Firstly, the spectral response spectrums and the directional emissive powers of the measurement system were calibrated. Then, the Tikhonov regularization method was used for inversing the spectral emission source term. Secondly, neglecting the self-absorption effect, the local temperature T(l) and soot concentration fv(l) could be calculated based on the ratio method. Finally, re-considering the self-absorption effect, the iterative computational method was implemented to update the calculated temperature T(l) and soot concentration fv(l). The resulting measurements reported in this study are in good alignment with the LII method and emission spectrum method. The proposed diagnostic method was found to be capable of simultaneous reconstruction of 2D distribution of soot temperature and concentration.

Simultaneous Measurement of Three-Dimensional Particle Temperature, Particle Concentration, and H2O Concentration Distributions Using Multispectral Flame Images

ABSTRACTA new method is proposed for simultaneous reconstruction of three-dimensional particle temperature, particle concentration, and H2O concentration distributions of axisymmetric flames using multi-spectral flame images. The multi-spectral flame images are obtained by cameras, each of which is equipped with one of three filters whose center wavelength is 700 nm, 900 nm, and 950 nm. The absorption of H2O is considered to be represented solely by the monochromatic image obtained at a wavelength of 950 nm, whereas the thermal radiation of particles is assumed to be represented by all three monochromatic flame images. For a signal-to-noise ratio value greater than 70 dB, the temperature and concentration distributions were reconstructed accurately. The experiment results indicate the particle temperature, particle concentration, and H2O concentration are low in the inner cone of the flame and they are high in the outer cone of the flame. The maximum difference between the temperature calculated from the flame images and the temperature measured by the thermocouple is 5%.

Experimental investigation on transverse ceiling flame length and temperature distribution of sidewall confined tunnel fire

This paper presents an experimental investigation on the transverse ceiling flame length and the temperature distribution of a sidewall confined tunnel fire. The experiments were conducted in a 1/6th scale model tunnel with the fire source placed against the sidewall, 0m, 0.17m and 0.35m above the floor, respectively. Experiments of fire against a wall without a ceiling, 0.35m above the floor in a large space, were also conducted as a control group. Results shows that for small heat release rate (HRR), the flame is lower than the ceiling and extends along the sidewall. With the increase of HRR and elevation of burner height, the flame gradually impinges on the ceiling and spreads out radially along it. The flame impingement condition and the flame shapes of the wall fire with and without ceiling are presented. From the viewpoint of the physical meaning of flame impinging on the ceiling, the horizontal flame length should be a function of the unburned part of the fuel at the impinging point. Based on the proportional relation between the flame volume and HRR, the effective HRR (Qef) at the ceiling is determined and the effective dimensionless HRR, Q*ef is defined to correlate the horizontal ceiling flame length. Additionally, predictive correlations of transverse ceiling temperature distribution are proposed for the continuous flame region, the intermittent flame region and the buoyant plume region under the ceiling, respectively.

Interferometric investigation of methanol droplet combustion in varying oxygen environments under normal gravity

Non-intrusive diagnostics of droplet combustion using laser-based interferometric technique have been presented. The experiments have been conducted with methanol droplet as the model combusting material under normal gravity with oxygen-nitrogen mixtures at ambient pressure and temperature. The mixtures contained five different oxygen concentrations of 9, 13, 17, 21 and 25%. Projection data of the temperature field around the combusting droplet have been recorded using a Mach-Zehnder interferometer and the interferograms have been analyzed to retrieve the whole field flame temperature distribution around the combusting droplet. The limiting oxygen index (LOI) has been deduced based on real time interferometric images by varying the oxygen concentration levels. Results of the study showed an increase in the flame temperatures with increasing oxygen concentrations and an oxygen concentration level of 13% has been identified as the LOI for methanol droplet. The whole field temperature distribution has been used to calculate the radial temperature gradients between the flame and the droplet surface. These temperature gradients were seen to be a direct function of oxygen concentration. Based on the radial temperature gradients, instantaneous mass burning rates and burning rate constants were computed and a reasonably close agreement between the interferometric predictions and those based on the videographic method was observed. To the best of the knowledge of the authors, the present work is the first successful application of Mach Zehnder interferometry for investigating droplet combustion phenomena. In contrast to the conventional videography approach, the interferometric technique not merely acts as a visualization tool, but also provides quantitative information in the form of whole field temperature distribution, which plays an important role in the determination of mass burning rates and burning rate constants.

Non-uniform temperature and species concentration measurements in a laminar flame using multi-band infrared absorption spectroscopy

We report in situ measurements of non-uniform temperature, H2O and CO2 concentration distributions in a premixed methane–air laminar flame using tunable diode laser absorption spectroscopy (TDLAS). A mid-infrared, continuous-wave, room-temperature interband cascade laser (ICL) at 4183 nm was used for the sensitive detection of CO2 at high temperature.The H2O absorption lines were exploited by one distributed feedback (DFB) diode laser at 1343 nm and one ICL at 2482 nm to achieve multi-band absorption measurements with high species concentration sensitivity, high temperature sensitivity, and immunity to variations in ambient conditions. A novel profile-fitting function was proposed to characterize the non-uniform temperature and species concentrations along the line-of-sight in the flame by detecting six absorption lines of CO2 and H2O simultaneously. The flame temperature distribution was measured at different heights above the burner (5–20 mm), and compared with the thermocouple measurement with heat-transfer correction. Our TDLAS measured temperature of the central flame was in excellent agreement (<1.5% difference) with the thermocouple data.The TDLAS results were also compared with the CFD simulations using a detailed chemical kinetics mechanism (GRI 3.0) and considering the heat loss to the surroundings.The current CFD simulation overpredicted the flame temperature in the gradient region, but was in excellent agreement with the measured temperature and species concentration in the core of the flame.

On the Suitability of Turbulence Models for the Prediction of Velocity and Temperature Distributions in Methane Non-Premixed Flame

This study focuses on the investigation of the suitability of turbulence models on the predictions of flow field and reactive scalars (temperature and species) of a turbulent non-premixed flame. Turbulence models tested in this study included: the standard k-e , RNG k- e , standard k-ω , SST k-ω (Shear Stress Transport) and the Reynolds Stress Model (RSM). For the sake of ease and simplicity, Eddy Dissipation combustion model (EDM) was used to predict the temperature fields and species concentrations in the flame. Predictions generated by different turbulence models are then validated against experimental data from a turbulent methane-air flame called flame A. Experimental data of flame A provides information on flow field (velocity) and reactive scalars (temperature and species concentrations). Results of the investigation showed that among five turbulence models tested, the standard k-e model provides the predictions that are in closer agreement to the experimental data of flow field, temperature, and species concentrations. In general, it can be concluded that apart from the standard k-e model, other turbulence models are not capable of capturing the position and the value of peak temperature accurately. On the other hand, the standard k-e turbulence model is able to accurately predict the position and the value of peak temperature in the flame. This is attributed to a better prediction of the flow field by the standard k-e turbulence model than those of other turbulence models. These findings indicate that the standard k-e turbulence model in combination with Eddy dissipation combustion model is capable of producing accurate predictions of flame flow field and temperature.

An experimental study on thermal and radiative characteristics of natural gas flame in different equivalence ratios by chemiluminescence and IR photography methods

Natural gas, as the cleanest fossil fuel, has been widely applied in central heating systems and industrial burners. From the perspective of energy saving, abundant sources and enormous use of natural gas together with the high costs caused by the widespread use of this fuel make the investigation of natural gas combustion characteristics important. Consequently, in the present work, the thermal and radiative characteristics, and NOx pollutant emission, of a 100,000 kcal/h natural gas burner, widely used in building heating systems, were investigated in the equivalence ratios of 0.42, 0.62, and 0.72. Non-destructive measurements including chemiluminescence method and IR photography were used to investigate the flame characteristics. The results indicated that increasing the equivalence ratio (in the range of 0.42–0.72) moved the peak of flame temperature from flame up-stream to its down-stream and made the flame temperature distribution more uniform. Also it was found that whereas the maximum temperature of flame occurred in small equivalence ratios such as 0.42, the average temperature of flame was 7.8% greater and the average radiation heat flux was 62% greater in large equivalence ratios such as 0.72. The results also showed that increase in equivalence ratio up to 0.72 raised the rate of soot particles generation in the flame and enhanced the average luminosity and radiation of flame in near IR wavelengths and increased the average emissivity coefficient of flame as much as 20%. Moreover, in flame upstream region, the enhancement of radiation heat transfer by increasing equivalence ratio is dominantly as a result of increase in emissivity coefficient of flame, while in flame downstream region, increasing the flame temperature due to gradual combustion will be important in improvement of radiation heat flux.

A novel calibration method of focused light field camera for 3-D reconstruction of flame temperature

This paper presents a novel geometric calibration method for focused light field camera to trace the rays of flame radiance and to reconstruct the three-dimensional (3-D) temperature distribution of a flame. A calibration model is developed to calculate the corner points and their projections of the focused light field camera. The characteristics of matching main lens and microlens f-numbers are used as an additional constrains for the calibration. Geometric parameters of the focused light field camera are then achieved using Levenberg-Marquardt algorithm. Total focused images in which all the points are in focus, are utilized to validate the proposed calibration method. Calibration results are presented and discussed in details. The maximum mean relative error of the calibration is found less than 0.13%, indicating that the proposed method is capable of calibrating the focused light field camera successfully. The parameters obtained by the calibration are then utilized to trace the rays of flame radiance. A least square QR-factorization algorithm with Plank's radiation law is used to reconstruct the 3-D temperature distribution of a flame. Experiments were carried out on an ethylene air fired combustion test rig to reconstruct the temperature distribution of flames. The flame temperature obtained by the proposed method is then compared with that obtained by using high-precision thermocouple. The difference between the two measurements was found no greater than 6.7%. Experimental results demonstrated that the proposed calibration method and the applied measurement technique perform well in the reconstruction of the flame temperature.

Flame Temperature Distribution and SiO&lt;sub&gt;2&lt;/sub&gt; Particles Distribution in Oxyhydrogen Flame

In the production process of synthetic silica glass, SiCl4 as precursor is imported in oxyhydrogen flame, SiO2 particles generate and distribute with different states along the flame. The flame temperature and the distance above the burner are important factors to affect the particle diameters and morphologies. The 2D distribution of flame temperature was measured using sodium line-reversal method. The diameters and morphologies of SiO2 particles were analyzed by transmission electron microscopy (TEM) at 50mm, 100mm, 200mm, and 300mm above the burner. The results show that the flame temperature ranges from 2130°C to 2320°C, and the average diameter of SiO2 spherical particles increases from 50nm to 105nm as the distance increasing from 50mm to 200mm. The optimum deposition distance was discussed.

On the effect of ionic wind on structure and temperature of laminar premixed flames influenced by electric fields

The general influence of electric fields on flames has been known for many years, the underlying mechanisms, however, are not finally identified yet. The changes observable in the flame structure and the pollutant emission when a flame is exposed to an electric field are mainly attributed to the ionic wind. Yet, especially the resulting flame temperature under the influence of electric fields is still an open research topic. Thus, in the present study the temperature distributions in a laminar premixed Bunsen type flame were measured for different air–fuel-mixtures using point-wise vibrational coherent-anti-Stokes Raman spectroscopy (vibrational-CARS) when a static electric field is activated. Additionally, CH2O- and OH-PLIF (planar laser-induced fluorescence) and particle image velocimetry (PIV) were applied to identify the best-suited locations for the temperature measurements and to visualize changes in the flame structure induced by the electric field for clarifying the underlying mechanisms.The results show that the electric field leads to increased fresh gas and maximum flame temperatures and that this effect is most distinct for rich premixed flames. Both PIV/PLIF and CARS experiments confirm that the flame is constricted and pushed towards the burner due to the ionic wind, which explains the increased temperature of the fresh gas and of the exhaust gas. The increased burner and fresh gas temperatures due to the ionic wind were verified by additional thermocouple measurements. The ionic wind is maximal for the fuel-rich flame, which is explained by the lowest electric resistance due to high charge carrier concentration, and larger flame area, which reduces the gap between the flame and the positively charged electrode. Furthermore, a clear broadening of the hot exhaust gas region was measured, which increases the burn out of UHC and CO reported in the literature. Furthermore, this effect increases the residence time that could also contribute to changed pollutant emission for flames under the influence of electric fields. It can be concluded that the change of the flame temperature is mainly the result of the modified velocity field induced by the ionic wind. Consequently, the ionic wind is the dominant mechanism for many effects observed in flames when applying weak electric fields.

Performance evaluation of premixed burner fueled with biomass derived producer gas

Energy consumption of liquefied petroleum gas (LPG) in ceramic firing process accounts for about 15–40% of production cost. Biomass derived producer gas may be used to replace LPG. In this work, a premixed burner originally designed for LPG was modified for producer gas. Its thermal performance in terms of axial and radial flame temperature distribution, thermal efficiency and emissions was investigated. The experiment was conducted at various gas production rates with equivalence ratios between 0.8 and 1.2. Flame temperatures of over 1200°C can be achieved, with maximum value of 1260°C. It was also shown that the burner can be operated at 30.5–39.4kWth with thermal efficiency in the range of 84 – 91%. The maximum efficiency of this burner was obtained at producer gas flow rate of 24.3 Nm3/h and equivalence ratio of 0.84.

Endoscopic combustion characterization of Jatropha biodiesel in a compression ignition engine

Decline in global resources of petroleum based fuels such as diesel and gasoline have attracted attention of researchers towards alternative fuels which are capable of providing both, energy security and protection against environmental degradation due to emission of hazardous pollutants. As an oxygenated fuel, biodiesel has emerged as a potential alternative fuel, which can be used in diesel engines on large-scale to reduce CO, HC and PM emissions. In this experimental study, Jatropha curcas derived biodiesel (JB100) and its 20% (v/v) blend with mineral diesel (JB20) was tested in a production-grade single cylinder diesel engine for evaluating its combustion characteristics. Since soot and NOx emissions are major concerns in CI engine combustion, it is very important to investigate their in-situ spatial distribution, so that effective control measures can be devised. For this, endoscopic visualization technique was implemented on a modified prototype engine to evaluate the effect of biodiesel blending percentage and engine load on in-situ spatial distribution of in-cylinder soot and flame temperature distributions. Inherent oxygen content of biodiesel helped in achieving superior combustion; as a result, in-cylinder soot formation was lower than baseline mineral diesel. Spatial flame temperature distribution was also relatively lower in biodiesel. Endoscopic visualization technique was found to be effective in evaluating different combustion characteristics in a modified prototype engine.

An experimental study of temperature and heat flux in a channel with an asymmetric thermal plume

A set of small-scale experiments were conducted to investigate the temperature and heat flux characteristics in a channel with an asymmetric thermal plume led by the restriction effect of sidewall. Rectangle heptane pools with different aspect ratios were burned to produce the thermal plume, and distance between the pool and sidewall was varied systematically. The classical McCaffery equation was modified to characterize the vertical flame temperature distribution under the channel ceiling. The ceiling temperature contours were analyzed by which the correlation between ceiling temperature, incident heat flux below, and ceiling flame length were investigated involving the sidewall effects. The dimensionless longitudinal heat flux distribution was correlated to the dimensionless distance to the pool using an exponential equation, while the decay rate of longitudinal heat flux was also investigated taking into account the pool aspect ratio. The heat flux at the fuel level for both symmetrical and asymmetrical flames can be predicted well by introducing a dimensionless heat release rate.

Endoscopic Combustion Visualization for Spatial Distribution of Soot and Flame Temperature in a Diesohol Fueled Compression Ignition Engine

A variety of research studies have been investigating the compatibility of primary alcohols as alternative fuels for diesel engines, in view of depleting crude oil reserves and resulting environmental degradation. Pollutants are formed in the engine combustion chamber and are mostly controlled using exhaust gas after-treatment technologies. However, active characterization of harmful pollutants such as soot and oxides of nitrogen (NOx) can be done in situ, at the locations of their formation in the engine combustion chamber by employing optical diagnostic techniques. In this study, the high temperature industrial endoscopy technique was adapted to a single cylinder diesel engine for in situ optical diagnostics of engine combustion for diesel and diesohols (diesel–alcohol blends) such as E20 and M20 fuels. In-cylinder combustion images were acquired by the endoscopic system and processed further for spatial soot and flame temperature distributions. Spatial distribution of in-cylinder soot was evaluated fro...

Effect of split injections coupled with swirl on combustion performance in DI diesel engines

Engine-out emissions (NOx and soot) have led to serious air pollution problems, and consequently, increasingly stringent emission norms. In order to decrease the emissions and improve the combustion performance of diesel engines, the effect of split injections with swirl (swirl rate of 0 and 1) was experimentally researched, and the mechanism of the fuel/air mixture of split injections with swirl (swirl rate of 0.5–2.5) was numerically researched in this study. The experimental research was carried out on a modified 1132Z single cylinder diesel engine, equipped with an endoscope system. A two-color method was applied to record flame temperature distribution and KL factor. The experimental results indicate that the flame observed using split injections with swirl rotated obviously. Split injections with swirl had a positive influence on improving the fuel/air mixture, accelerating combustion progress and shortening combustion duration. The combustion duration decreased at swirl rate of 1, with a reduction in the range of 19.5–25.7% at various pilot quantities. In addition, brake-specific fuel consumption (BSFC) and soot emission were reduced. BSFC was lower at swirl rate of 1 than that at swirl rate of 0, with a reduction in the range of 1.1–2.01g/(kWh)−1. For KL factor at 12°CA ATDC, it was also observed that at 12°CA ATDC, the KL factor was lower at swirl rate of 1 than that at swirl rate of 0, with a reduction of 34.9%. Related numerical research on split injections with swirl was performed, and the results show that at a specific swirl, the main injection deviated from the pilot injection and entered the area between two sprays, enhancing the utilization of air in the chamber. In addition, the main combustion process accelerated due to the better thermal-atmosphere provided by the pilot injection, so that a better engine performance and lower soot concentration was achieved.