The Histogram of Pressure Oscillations Amplitudes, in Lean Premixed Combustions, Caused by Thermo-Acoustic Instabilities

2010 ◽  
Author(s):  
Nasser Seraj Mehdizadeh ◽  
Nozar Akbari
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Combustion Instability ◽  
Premixed Combustion ◽  
Space Distribution ◽  
Rayleigh Criterion ◽  
Pressure Oscillations ◽  
Lean Premixed

Lean premixed combustion is widely used in recent years as a method to achieve the environmental standards with regard to NOx emission. In spite of the mentioned advantage, premixed combustion systems, with equivalence ratios less than one, are susceptible to the combustion instability. To study the lean combustion instability, by experiments, one premixed combustion setup, equipped with reactant supplying system, is designed and manufactured in Amirkabir University of Technology. In this research, gaseous propane is introduced as fuel and several experiments are performed at nearly atmospheric pressure, with equivalence ratios within the range of 0.7 to 1.5. In this experiments fuel mass flow rate is varied between 2 and 4 gr/s. Unstable operating condition has been observed in combustion chamber when equivalence ratio is less than one. To distinguish the combustion instability for various operating conditions, probability density functions, spectral diagrams, and space distribution of pressure oscillations, along with Rayleigh Criterion, are utilized. Accordingly, effect of equivalence ratio on stabilizing the unstable combustion system is investigated. Moreover, convective delay time is calculated for all experiments and the results are compared with Rayleigh Criterion. This comparison has shown good agreement the experimental results and Rayleigh Criterion. Finally, stability limits are identified based on inlet mass flow rate and equivalence ratio.

scholarly journals Engine Performance of a Gardener Compression Ignition Engine using Rapeseed Methyl Esther

2019 ◽  
Vol 4 (2) ◽  
Author(s):  
Hamisu A Dandajeh ◽  
Talib O Ahmadu
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Engine Speed ◽  
Engine Performance ◽  
Combustion Characteristics ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Air Mass

This paper presents an experimental investigation on the influence of engine speed on the combustion characteristics of a Gardener compression ignition engine fueled with rapeseed methyl esther (RME). The engine has a maximum power of 14.4 kW and maximum speed of 1500 rpm. The experiment was carried out at speeds of 750 and 1250 rpm under loads of 4, 8, 12, 16 and 18 kg. Variations of cylinder pressure with crank angle degrees and cylinder volume have been examined. It was found that RME demonstrated short ignition delay primarily due to its high cetane number and leaner fuel properties (equivalence ratio (φ) = 0.22 at 4kg). An increase in thermal efficiency but decrease in volumetric efficiency was recorded due to increased brake loads. Variations in fuel mass flow rate, air mass flow rate, exhaust gas temperatures and equivalence ratio with respect to brake mean effective pressure at engine speeds of 750 and 1250 rpm were also demonstrated in this paper. Higher engine speed of 1250 rpm resulted in higher fuel and air mass flow rates, exhaust temperature, brake power and equivalent ratio but lower volumetric efficiency. Keywords— combustion characteristics, engine performance, engine speed, rapeseed methyl Esther

Flow Fields, Emission and Stabilization in Premixed Centrally-Staged Swirl Flames With Different Air Split Ratios

2021 ◽  
Author(s):  
Tong Su ◽  
Yuzhen Lin ◽  
Chi Zhang ◽  
Xiao Han
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Flow Fields ◽  
Design Stage ◽  
Air Mass ◽  
Split Ratio ◽  
Flame Structures ◽  
The Stability

Abstract The flow fields, emission levels, and static stability characteristics were investigated experimentally under various air split ratios (ASR, the ratio of the pilot stage air mass flow rate to the total air mass flow rate) at a fixed equivalence ratio of 0.8 of both main and pilot stages in a premixed centrally-staged swirl flame. The flame structures were captured by a CH* chemiluminescence high-speed camera and the corresponding results were processed by Abel deconvolution. Besides, the flow fields obtained by using planar Particle Image Velocimetry (PIV) technique were combined with flame structures to make a better study on the aerodynamic structures of the centrally-staged swirl flames. The emission levels of NOx and CO were measured by a gas analyzer. The stability boundaries and flame structures at different equivalence ratios under three ASRs were also studied. It is found that the size of the reacting primary recirculation zone (PRZ) becomes larger as more air is distributed to the pilot stage. This can be explained by the fact that the majority of the pilot fluid participates in the formation of the PRZ and also as a result of a stronger penetrability of the pilot jet. Moreover, the NOx emission levels increase while CO levels decrease, which is because of the longer residence time of the radicals within a larger PRZ and less impingement of the main flame on the combustor liner. Finally, the stability boundary is extended, and the total blowout equivalence ratio was decreased as the air split ratio increases, which demonstrates the flame stabilization effect of the pilot flame. In brief, the above findings can be a help to choose the appropriate air split ratio in the early design stage of the centrally-staged aero-engine combustors.

CH4/Air Mesocombustor at 3 Bar: Numerical Simulation and Experiments

2013 ◽  
Vol 431 ◽  
pp. 137-150 ◽  
Author(s):  
A. Minotti ◽  
F. Cozzi ◽  
F. Capelli
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
High Efficiency ◽  
Ambient Pressure ◽  
Rapid Development ◽  
Thermal Power ◽  
Gas Temperature ◽  
Chemical Efficiency

Improvements in understanding how to design future mesocombustors, currently under rapid development in particular for propulsion, e.g., for UAVs, and as meso-electrical power generators, are mandatory. In view of this scenario and, to advances previous analysis carried out at ambient pressure by the authors, the numerical and experimental investigation of a 254 mm3swirling cylindrical mesocombustor, fed by methane/air at an equivalence ratio =0.7 and at 3 bar, has been performed. The combustion pressure has been chosen based on the values quoted in literature for centimeter sized gas turbine.Exhaust gas temperature and composition have been measured for several mass flow rates. A reduction in chemical efficiency is observed by increasing the input thermal power (i.e. the total mass flow rate) at fixed equivalence ratio due to the shorter gas residence time.The operative condition corresponding to high efficiency and smaller mass flow rate has been numerically investigated adopting the RANS k-ε approach, with finite rate chemistry kinetic mechanism (GRIMech 1.2, 32 species and 177 reactions) and the EDC turbulence-combustion coupling model.Gas temperature at the exhaust section and chemicalefficiency are predicted and compared with the corresponding experiment.Numerical and experimental results show to be in fair agreement, and the predicted chemical efficiency differs from the measured value of about 1 %. Despite the small size of the meso-combustor, it is possible to achieve a relatively high combustion efficiency, making it suitable for miniaturized power generation devices.The relatively high chemical efficiency is due to the relatively long average gas residence time and to a wide recirculation zone that provide heat and radicals to the flame, coupled with the fairly good mixing due to swirl motion and the impinging air/fuel jets.

scholarly journals The Effects of Non-uniform Distribution of Oxidizer Flow on High-Frequency Combustion Instability

2019 ◽  
Vol 257 ◽  
pp. 01005
Author(s):  
Peng Chen ◽  
Wansheng Nie ◽  
Kangkang Guo ◽  
Xing Sun ◽  
Yu Liu ◽  
...  
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Uniform Distribution ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rocket Engine ◽  
Combustion Instability ◽  
Oscillation Amplitude ◽  
Pressure Oscillation

The numerical calculation of three-dimensional unsteady combustion for the combustion chamber of LOX/kerosene high pressure staged combustion rocket engine was carried out. By changing the offset ratio of oxygen mass flow rate in the edge area of the injector face, computational studies were conducted to investigate the effects of non-uniform distribution of oxidizer flow on combustion instability for a liquid-propellant rocket engine. The calculation results show that the offset ratio of oxygen mass flow rate changes the distribution of heat release in the combustion chamber. Within a certain range of offset ratio, the non-uniform distribution degree of oxidizer flow enhances the coupling between the pressure and heat release. As a result, it leads to an increase in the pressure oscillation amplitude in the combustion chamber. However, if the offset ratio is too large, the oxygen-fuel ratio will be too small in some regions, which will reduce coupling between the pressure and heat release and increase the damping of combustion instability.

Development of a Temporally Modulated Fuel Injector With Controlled Spray Dynamics

2002 ◽  
Vol 125 (1) ◽  
pp. 284-291 ◽  
Author(s):  
H. Chang ◽  
D. Nelson ◽  
C. Sipperley ◽  
C. Edwards
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Cone Angle ◽  
Fuel Injector ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Spray Distribution

It is now well established that combustion instability in liquid-fueled gas turbines can be controlled through the use of active fuel modulation. What is less clear is the mechanism by which this is achieved. This results from the fact that in most fuel modulation strategies not only is the instantaneous mass flow rate of fuel affected but so too are the parameters which define the post-atomization spray that takes part in the combustion. Specifically, experience with piezoelectric modulated sprays has shown that drop size, velocity, cone angle, and patternation are all affected by the modulation process. This inability to decouple changes in the fueling rate from changes in the spray distribution makes understanding of the mechanism of instability control problematic. This paper presents the results of an effort to develop an injector which can provide temporal modulation of the fuel flow rate but without concomitant changes in spray dynamics. This is achieved using an atomization strategy which is insensitive to both fuel flow rate and combustor acoustics (an over-pressured spill-return nozzle) coupled with an actuator with flat frequency response (a low-mass voice coil). The design and development of the actuator (and its control system) are described, and a combination of phase-Doppler interferometry and imaging are used to establish its performance. Results show that the system is capable of producing sprays which have little variation in cone angle or spray distribution function despite variations in mass flow rate (number density) of greater than 50% over a range of frequencies of interest for control of combustion instability (10 Hz to 1 kHz).

Development of a Temporally Modulated Fuel Injector With Controlled Spray Dynamics

2001 ◽  
Author(s):  
Hyeonsoo Chang ◽  
Chad Sipperley ◽  
David Nelson ◽  
Chris Edwards
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Cone Angle ◽  
Fuel Injector ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Spray Distribution

It is now well established that combustion instability in liquid-fueled gas turbines can be controlled through the use of active fuel modulation. What is less clear is the mechanism by which this is achieved. This results from the fact that in most fuel modulation strategies not only is the instantaneous mass flow rate of fuel affected but so to are the parameters which define the post-atomization spray that takes part in the combustion. Specifically, experience with piezoelectric modulated sprays has shown that drop size, velocity, cone angle, and patternation are all affected by the modulation process. This inability to decouple changes in the fueling rate from changes in the spray distribution makes understanding of the mechanism of instability control problematic. This paper presents the results of an effort to develop an injector which can provide temporal modulation of the fuel flow rate but without concomitant changes in spray dynamics. This is achieved using an atomization strategy which is insensitive to both fuel flow rate and combustor acoustics (an over-pressured spill-return nozzle) coupled with an actuator with flat frequency response (a low-mass voice coil). The design and development of the actuator (and its control system) are described, and a combination of Phase-Doppler Interferometry and imaging are used to establish its performance. Results show that the system is capable of producing sprays which have little variation in cone angle or spray distribution function despite variations in mass flow rate (number density) of greater than 50% over a range of frequencies of interest for control of combustion instability (10 Hz to 1 kHz).

The standard unit mass flow rate of gas-liquid mixtures

2020 ◽  
pp. 13-16
Author(s):  
V.N. Petrov ◽  
◽  
V.F. Sopin ◽  
L.A. Akhmetzyanova ◽  
Ya.S. Petrova ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Liquid Mixtures ◽  
Unit Mass ◽  
Standard Unit

Prediction of Leakage Mass Flow Rate Through Gas Springs

1987 ◽  
Author(s):  
Roberto Bruno Bossio ◽  
Vincenzo Naso ◽  
Marian Cichy ◽  
Boleslaw Pleszewski
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate
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