scholarly journals Improvement of the Combustion Completeness of Hydrogen Jet Flames within a Mesoscale Tube under Zero Gravity

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4552
Author(s):  
Junjie Hong ◽  
Ming Zhao ◽  
Lei Liu ◽  
Qiuxiang Shi ◽  
Xi Xiao ◽  
...  
Keyword(s):  
Air Entrainment ◽  
Combustion Efficiency ◽  
Zero Gravity ◽  
Jet Flames ◽  
Entrainment Ratio ◽  
Convergent Nozzle ◽  
Air Supply ◽  
Fuel Jet ◽  
Inner Diameter ◽  
Micro Propulsion

Microjet hydrogen flames can be directly used as micro heat sources or can be applied in micro propulsion systems. In our previous study, under zero gravity and without an active air supply, the combustion completeness of hydrogen jet flames within a mesoscale tube with an inner diameter of 5 mm was very low. In this study, we were dedicated to improving the combustion efficiency by using a convergent nozzle (tilt angle was around 68°) instead of the previous straight one, and the exit diameter was 0.8 or 0.4 mm. The numerical results demonstrate that the maximum combustion efficiency in the case of d= 0.8 mm was only around 15%; however, the peak value for the case of d = 0.4 mm was around 36%. This happened because with d = 0.4 mm, the fuel jet velocity was around four times that of the d = 0.8 mm case. Hence, the negative pressure in the combustor of d = 0.4 mm decreased to a much lower level compared to that of d = 0.8 mm, which led to an enhancement of the air entrainment ratio. However, the highest combustion efficiency of d = 0.4 mm was still below 36%; therefore, a slightly larger tube or an even smaller nozzle exit diameter will be necessary for further improvements to the combustion efficiency.

Effect of Air Distribution on Solid Fuel Bed Combustion

1997 ◽  
Vol 119 (2) ◽  
pp. 120-128 ◽  
Author(s):  
J. T. Kuo ◽  
W.-S. Hsu ◽  
T.-C. Yo
Keyword(s):  
Combustion Efficiency ◽  
Pollutant Emissions ◽  
Air Distribution ◽  
Gas Temperature ◽  
One Dimensional ◽  
Supply And Distribution ◽  
Air Supply ◽  
Burning Rates ◽  
Side Walls ◽  
Detailed Chemical

One important aspect of refuse mass-burn combustion control is the manipulation of combustion air. Proper air manipulation is key to the achievement of good combustion efficiency and reduction of pollutant emissions. Experiments, using a small fix-grate laboratory furnace with cylindrical combustion chamber, were performed to investigate the influence of undergrate/sidewall air distribution on the combustion of beds of wood cubes. Wood cubes were used as a convenient laboratory surrogate of solid refuse. Specifically, for different bed configurations (e.g., bed height, bed voidage, bed fuel size, etc.), burning rates and combustion temperatures at different bed locations were measured under various air supply and distribution conditions. One of the significant results of the experimental investigation is that combustion, with air injected from side walls and no undergrate air, has the maximum combustion efficiency. On the other hand, combustion with undergrate air achieves higher combustion rates but with higher CO emissions. A simple one-dimensional model was constructed to derive correlation of combustion rate as a function of flue gas temperature and oxygen concentration. Despite the fact that the model is one-dimensional and many detailed chemical and physical processes of combustion are not considered, comparisons of the model predictions and the experimental results indicate that the model is appropriate for quantitative evaluation of bed-burning rates.

Assessment of Stabilization Mechanisms of Confined, Turbulent, Lifted Jet Flames: Effects of Ambient Coflow

2013 ◽  
Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Richard D. Muncey ◽  
Kevin M. Lyons
Keyword(s):  
Turbulent Mixing ◽  
Leading Edge ◽  
Ambient Air ◽  
Turbulent Jet ◽  
Fuel Flow Rate ◽  
Jet Flames ◽  
Combustion Chemistry ◽  
Intermittent Behavior ◽  
Fuel Flow ◽  
Fuel Jet

The aim of this investigation is to determine the effects of confinement on the stabilization of turbulent, lifted methane (CH4) jet flames. A confinement cylinder (stainless steel) separates the coflow from the ambient air and restricts excess room air from being entrained into the combustion chamber, and thus produces varying stabilization patterns. The experiments were executed using fully confined, semi-confined, and unconfined conditions, as well as by varying fuel flow rate and coflow velocity (ambient air flowing in the same direction as the fuel jet). Methane flames experience liftoff and blowout at well-known conditions for unconfined jets, however, it was determined that with semi-confined conditions the flame does not experience blowout. Instead of the conventional unconfined stabilization patterns, an intense, intermittent behavior of the flame was observed. This sporadic behavior of the flame, while under semi-confinement, was determined to be a result from the restricted oxidizer access as well as the asymmetrical boundary layer that forms due to the viewing window. While under full confinement the flame behaved in a similar method as while under no confinement (full ambient air access). The stable nature of the flame while fully confined lacked the expected change in leading edge fluctuations that normally occur in turbulent jet flames. These behaviors address the combustion chemistry (lack of oxygen), turbulent mixing, and heat release that combine to produce the observed phenomena.

The Study of Combustion of Municipal Waste in a Fluidised Bed Combustor

2003 ◽  
Author(s):  
I. Gulyurtlu ◽  
T. Crujeira ◽  
P. Abelha ◽  
D. Boavida ◽  
J. Seabra ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Combustion Efficiency ◽  
Solid Particles ◽  
Gaseous Pollutants ◽  
Fluidised Bed ◽  
Combustion Gases ◽  
Air Supply ◽  
Control Devices ◽  
Emission Limits ◽  
Bed Material

The combustion behaviour of municipal solid waste was studied in a pilot fluidised bed combustor. The waste was pelletised prior to its use. Both co-firing with coal and combustion of waste alone were under taken. The combustion studies were carried out on the pilot installation of INETI. The fluidised bed combustor is square in cross section with each side being 300 mm long. Its height is 5000 mm. There is a second air supply to the freeboard at different heights to deal with high volatile fuels. There was a continuous monitoring of the temperatures in the bed, as well as the composition of the combustion gases. The combustion gases leaving the reactor were let go through the recycling cyclone first to capture most of particulates elutriated out of the combustor. There was a second cyclone which was employed with the aim of increasing the overall efficiency of collecting solid particles. The gaseous pollutants leaving the stack were sampled under iso-kinetic conditions for particulate matter, chlorine compounds and heavy metals. The ash streams were characterised for heavy metals. The results obtained were compared with national legislation. The results obtained suggest that i) the combustion efficiency was very high, ii) there was an enrichment of ashes with heavy metals in the cyclones compared to the bed material, iii) in general, the gaseous pollutants were below the permited limits, and iv) for the compliance with the new European Directive for stricter emission limits adequate control devices, like bag filters, should be integrated with RDF combustion.

An experimental study of flame height and air entrainment of buoyancy-controlled jet flames with sidewalls

Fuel ◽  
2016 ◽  
Vol 183 ◽  
pp. 164-169 ◽  
Author(s):  
C.F. Tao ◽  
Y. Shen ◽  
R.W. Zong ◽  
F. Tang
Keyword(s):  
Experimental Study ◽  
Air Entrainment ◽  
Flame Height ◽  
Jet Flames

A Practical Solid-Propellant Micro-Thruster

2006 ◽  
Author(s):  
E. A. Parra ◽  
K. S. J. Pister ◽  
C. Fernandez-Pello
Keyword(s):  
Residence Time ◽  
Solid Propellant ◽  
Volume Ratio ◽  
Combustion Efficiency ◽  
Macro Scale ◽  
Aerospace Systems ◽  
Composite Solid Propellant ◽  
Active Research ◽  
Micro Propulsion ◽  
Composite Solid

Miniaturization of solid-propellant thrusters is an area of active research that has been motivated by the reduction in size of aerospace systems and the advancement of micromachining techniques. Though this micro-propulsion problem seems simplistic compared to the macro-scale counterpart, an efficient and reliable device has yet to be produced. A millimeter-scale novel composite solid-propellant thruster design that builds on pervious work [1] and increases efficiency is here presented. Current designs made primarily out of silicon suffer from high thermal losses and, in extreme cases, flame quenching due to the augmented surface area to volume ratio associated with miniaturization. Moreover, the reduced device dimensions drive the combustion reaction to complete outside of the thruster, misemploying the majority of the chemical energy. This occurs because the propellant mixing and chemical time do not scale with size, while the residence time does decrease as the size of the thruster decreases [2]. A novel thruster design that increases the propellant residence time is being characterized using ammonium perchlorate/binder composite propellant. The thruster geometry recycles thermal energy to the unburned propellant grain increasing its temperature and, therefore, burning rate and combustion efficiency. In addition, propellant formulation has been optimized for the thruster minimization.

scholarly journals Air entrainment in a vertical dropshaft with limited air supply

2018 ◽  
Vol 8 (5) ◽  
pp. 315-319
Author(s):  
Qiang Ding ◽  
Yiyi Ma ◽  
David Z. Zhu
Keyword(s):  
Air Entrainment ◽  
Air Supply

scholarly journals Nonlinear dynamics of self-organising bubble departures from twin nozzles

Meccanica ◽  
2019 ◽  
Vol 54 (14) ◽  
pp. 2119-2130 ◽  
Author(s):  
P. Dzienis ◽  
R. Mosdorf ◽  
T. Wyszkowski
Keyword(s):  
Nonlinear Dynamics ◽  
High Speed ◽  
Air Pressure ◽  
Air Bubbles ◽  
Pressure Oscillations ◽  
Engine Oils ◽  
Air Supply ◽  
Inner Diameter ◽  
The Mean ◽  
Supply Systems

Abstract The nonlinear dynamics of self-organising bubble departures from twin nozzles in engine oils was analysed. Air bubbles were generated from twin brass nozzles with an inner diameter equal to 1 mm. The flow of bubbles in bubble chains was recorded using high-speed camera. The time series of air pressure oscillations and signal from laser–phototransistor identifying the presence of bubbles over the nozzles outlet were recorded simultaneously. The self-organising bubble departures were observed and their stability was analysed. It was found that self-organising bubble departures become unstable because of successive (during subsequent bubble departures) decrease of the mean air pressure in one of the nozzle air supply system. It was shown that instability of self-organising bubble departures leads to equalization of pressures in both nozzles air supply systems which causes that simultaneous bubble departures appear. In the present experiment, this process was repeated in a cyclic and chaotic way. It was shown that stable self-organising bubble departures are accompanied by periodic air pressure oscillations in one of the nozzles and chaotic air pressure oscillations in the second one.

Structure Analysis of the Stabilizing Region of Plane, Laminar Fuel-Jet. Flames.

1980 ◽  
Vol 22 (5-6) ◽  
pp. 211-216 ◽  
Author(s):  
TAKESHI KAWAMURA ◽  
KATSUO ASATO ◽  
TAMOTSU MAZAKI
Keyword(s):  
Structure Analysis ◽  
Jet Flames ◽  
Fuel Jet
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