scholarly journals Influence of DC Electric Field on the Propane-Air Diffusion Flames and NOx Formation

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5745
Author(s):  
Sang-Min Kim ◽  
Kyeong-Soo Han ◽  
Seung-Wook Baek

The aim of this research is to investigate the effects of a direct current (DC) electric field on the combustion behavior of a co-flow propane diffusion flame. The flame length and NOx emission were observed and measured. The electric field enhances the combustion process of propane diffusion flame by causing the movement of ions and molecules in the flame, resulting in a change in the shape of the flame. The flame heights decrease with an increase in the applied voltage and polarity, a more dominant effect to be observed with a positive DC electric field. However, for the applied negative polarity, the inner-cone of the propane diffusion flame is shifted by the electric field. Drastic reduction in the NOx emission is observed with an increase in the applied DC voltage and polarity. In the existing system, the reduction percentage of NOx is within the range of 55 to 78%.

2014 ◽  
Vol 660 ◽  
pp. 397-401 ◽  
Author(s):  
Mohd Fareez Edzuan bin Abdullah ◽  
Mohd Hisyamuddin bin Sulaiman ◽  
Noor Aliah Binti Abdul Majid

This paper discusses the nitrogen oxides (NOx) emission characteristics of compression ignition diesel engine operating on diesel fuel blends with different saturation degrees of biofuel and with methanol. In order to investigate the dominant factor of increased NOx in biofuels, diesel combustion tests were conducted under idling condition and the tailpipe exhaust emissions were measured by a flue gas analyzer. The general trend where NOx emission increased and reduced carbon monoxide (CO) emission in the biofuel and methanol blend cases were observed. The NOx emission levels increased as the biofuel saturation degree decreased, where it may be suggested that the prompt NOx mechanism is significant in total NOx formation of biofuel combustion process.


Fuel ◽  
2017 ◽  
Vol 188 ◽  
pp. 621-627 ◽  
Author(s):  
Yanlai Luo ◽  
Yunhua Gan ◽  
Xi Jiang

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Fouad Khaldi

The ability to use a magnetic field as a means for controlling the role of gravity buoyancy on the combustion process is demonstrated by applying a strong vertical magnetic field gradient on a laminar gas jet diffusion flame. The confirmation is based on a comparison of flame appearance; in particular, length variation, to both elevated gravity (higher than earth’s gravity) and zero-gravity combustion experimental data. The comparison parameter is the dimensionless number G, defined as the ratio of gravity level generated by magneto-gravity buoyancy to earth’s gravity. The more important results are as follows. First, for G > 1, good agreement between magnetic and centrifuge length scaling laws reveals that the slight decrease of flame length according to L ∼ G−1/8 is the result of increasing artificial magnetically induced gravity strength. It ensues that flame thinning, bluing, lifting, and extinction are produced by similar mechanisms previously identified in centrifuge diffusion flames. Thereafter, at G ≅ 0, the flame assumes a nearly hemispheric shape and a blue color in perfect similarity to nonbuoyant flames under zero-gravity conditions generated in drop towers. Another important fact is that the magnetic field offers the ability to observe the flame behavior at low gravity levels 0 < G < 1. A primary interesting result is that flame length varies strongly, following the scaling law L ∼ G−1/2.


Author(s):  
Dmitry V. Volkov ◽  
Alexandr A. Belokon ◽  
Dmitry A. Lyubimov ◽  
Vladimir M. Zakharov ◽  
George Opdyke

Laminar flamelet models have demonstrated good quality predictions of NOx emission from diffusion flame type combustors. In this paper, the NOx formation process is analyzed by using a flamelet model and 3D flow calculations to take a virtual look inside a combustor. The main phenomena affecting NOx emission are turbulent mixing and the turbulence-chemistry interaction. Local scalar dissipation is the main parameter responsible for the turbulence-chemistry interaction within the flamelet model. At the same time, scalar dissipation is also related to the mixing process. On one hand, higher values of scalar dissipation correspond to higher fuel consumption rates, which decrease the volume of the high temperature zones. On the other hand, higher values of scalar dissipation lead to higher NOx formation rates. Unfortunately, scalar dissipation is not commonly used by combustion engineers because of the difficulty of the clear physical interpretation of this variable and its relationship with the usual parameters. In this paper, the influence of several design features, such as primary zone equivalence ratio and air flow distribution along the liner, is studied relative to scalar dissipation distributions in the combustion zones and to NOx formation. A real industrial diffusion flame combustor is used as an example, and the results can provide a better understanding of real combustor processes. The NOx prediction results are in reasonable agreement with test data.


Author(s):  
Vivek Sahai ◽  
Dah-Yu Cheng

The so-called “sudden death reaction” theory, for a diffusion flame, assumes that the fuel and oxidizer diffuse toward a stoichiometric concentration surface, and then suddenly disappear, due to their combustion which produces water and carbon dioxide. The presence of NOx and CO in the combustion products cannot be explained by the “sudden death” theory. NOx, due to its high activation energy may not be formed prior to the formation of H2O and CO2. NOx is created when both oxygen and nitrogen are present in a high temperature volume; after all the combustible species are consumed. Appearance of CO indicates a lack of oxygen or a low gaseous temperature. Traditionally, when steam is injected into the combustion air, its high heat capacity reduces the flame temperature, which then reduces NOx formation, and this is usually accompanied by high CO formation. This phenomenon is caused by the dilution of oxygen as a quenching effect. This paper describes a novel approach that reverses the traditional wisdom of using steam to control NOx and CO formation, by accelerating the combustion process. This new approach begins with (1) shrinking the flame envelope, (2) enhancing the oxygen diffusion rate, and (3) suppressing the nitrogen concentration diffusion rate. Test results showed that (1) a high temperature volume could form NOx after the combustion of fuel is reduced to a minimum, and (2) that a very high fuel jet momentum increases the oxygen diffusion rate, thus reducing the flame envelope. Also due to the inward movement of the flame envelope, the residential time for NOx formation is also reduced and with the presence of a diluent, the nitrogen penetration rate into the flame is controlled. When all three phenomena are working together, total NOx was reduced downward to below 2 ppm without losing flame stability. Since this process generates enhanced oxygen diffusion, CO has always been seen to be below 2ppm, which indicates extremely high combustion efficiency. The above theory was first simulated by numerical methods using a 3-step reaction for nitrogen and oxygen, and was further expanded to a 28-step chemical kinetic model. The simulation used gas turbine compressor discharge temperatures to produce real adiabatic flame temperatures. Atmospheric tests of real full-scale gas turbine combustors were used with appropriate air temperatures, to simulate adiabatic flame temperatures. Below 2ppm NOx and CO were consistently obtained, independent of turbine types. Actual turbine tests on GE 6B and W501D5A turbines consistently indicated pressure dependent exponents of 0.1.


Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 348 ◽  
Author(s):  
Rafał Ślefarski

The article presents the results of experimental and numerical investigation of turbulent premixed methane flames diluted by carbon dioxide (up to 30%) at atmospheric and elevated pressures (up to 0.5 MPa). The study included the influence of fuel properties and operation parameters on the emission of NOx and CO as well as flame properties. The investigation has been prepared for two combustion system configurations (axisymmetric flames and flames supported by a pilot flame) in a wide range of air/fuel equivalence ratios (ϕ = 0.42 ÷ 0.85). It has been reported that reduction of NOx emission by CO2 fuel dilution reached a level of up to 45% in atmospheric conditions and 30% at elevated pressure, decreasing with a drop in the equivalence ratio. The results have shown influence of pressure on NOx composition, where for pressurized tests, NO2 was doubled compared to atmospheric tests. Carbon monoxide emission rises with CO2 content in the fuel as a result of thermal dissociation, but this phenomenon is mitigated by a pressure increase. Planar laser induced fluorescence (PLIF) study has shown that flame length decreases with an increase in pressure and CO2 content in the fuel. Fuel staging increased NOx emission, especially for richer flames (ϕ > 0.6) at low pressure, while CO increased in the whole range of equivalence ratios.


Author(s):  
Yu. G. Kutsenko ◽  
A. A. Inozemtsev ◽  
L. Y. Gomzikov

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper, a new turbulent combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. Within the considered approach this equation has two source terms. These terms are responsible for different conditions of combustion process: diffusion flames and premixed flames, and distributed reacting zones. This paper studies the problem, concerning modeling of lean blowout process of diffusion flame front. To test the proposed combustion model we have simulated lean blowout process inside combustion zone of a gas turbine combustor. Good predictions of lean blowout limits were obtained.


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