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Document search results: "combustion"
 
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Title          
 Rayleigh criteria and Combustion Instability  
 
Abstract    

A short literature review on Rayleigh's Criteria is provided. This criteria is widely used in mechanical and aerospace engineering areas to understand the phenomena of combustion instability. In continuously running combustion systems where combustion occurs inside a volume of relatively low losses, small amplitude pressure disturbance and small amplitude heat release fluctuations can couple with each other in a positive feedback loop leading to very large amplitude pressure oscillations often ending up in limit cycle oscillations. Such oscillations are detrimental to the combustion system (power or propulsion) for it exposes the system to large mechanical fatigue, thermal loads and can lead to catastrophic failures.

 
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Added By - A Ghosh
Subject - Aeronautics and Astronautics
Document Type - Literature Review
 
   
   

 

Title          
 Combustion Instability in Liquid Rocket Engin...  
 
Abstract    

Work on liquid rocket engine combustion instabilities began in the early 1940s (Culick and Yang 1995). One of the most critical concepts in liquid rocket combustion instability, that of time lag (as a coordinating factor in influencing organized oscillations in liquid rocket combustion chambers) originated around this time in von Kármán‟s group at the Jet Propulsion Laboratory around 1941 (cf. Summerfield 1951) shortly after oscillations were observed in early tests in liquid rocket engines in the United States. The essential idea was that there existed a finite time delay when an element of propellant entered the combustor and when heat was released from it. This delay controlled the phasing between heat release and pressure oscillations thereby making the system stable or unstable as per Rayleigh‟s criteria. In the years that followed, this model was applied to various studies involving combustion instability in liquid rocket engines. Gunder and Friant (1950), Yachter (1951) and Summerfield (1951) analyzed low frequency chugging instability arising from the interaction between feed system and combustion process using a constant time lag model. Crocco (1951;1952) introduced the time varying combustion time lag and use...

 
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Added By - A Ghosh
Subject - Aeronautics and Astronautics
Document Type - Literature Review
 
   
   

 

Title          
 Fiber-Optic based Dynamic Pressure sensor for...  
 
Abstract    

Acquiring accurate, transient measurements in harsh environments has always pushed the limits of available measurement technology. Until recently, the technology to directly measure certain properties in extremely high temperature environments has not existed. Advancements in optical measurement technology have led to the development of measurement techniques for pressure, temperature, acceleration, skin friction, etc. using extrinsic Fabry-Perot interferometry (EFPI). The basic operating principle behind EFPI enables the development of sensors that can operate in the harsh conditions associated with turbine engines, high-speed combustors, and other aerospace propulsion applications where the flow environment is dominated by high frequency pressure and temperature variations caused by combustion instabilities, blade-row interactions, and unsteady aerodynamic phenomena. Using micromachining technology, these sensors are quite small and therefore ideal for applications where restricted space or minimal measurement interference is a consideration. In order to help demonstrate the general functionality of this measurement technology, sensors and signal processing electronics currently under development by Luna Innovations were used to...

 
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Added By - ajayvs
Subject - Mechanical Engineering
Document Type - Term Paper
 
   
   

 

Title          
 The Role of Density Gradient in Liquid Rocket...  
 
Abstract    

Experimental and analytical studies were conducted to investigate key physical mechanisms responsible for flame-acoustic coupling during the onset of acoustically driven combustion instabilities in liquid rocket engines (LREs). Controlled experiments were conducted in which a turbulent hydrogen-oxygen (GH2-GO2) diffusion flame, established downstream of a two-dimensional model shear coaxial injector was acoustically forced by a compression driver unit mounted in a transverse direction and excited through a broad range of frequencies (200Hz-2000Hz) and amplitudes. Characteristic interactions between flame and acoustics visualized through OH* and CH* chemiluminescence imaging and dynamic pressure measurements obtained using high frequency dynamic pressure transducers indicated that small acoustic disturbances could be amplified by flame-acoustic coupling under certain conditions leading to substantial modulation in spatial heat release fluctuations. Density gradient between fuel and oxidizer was found to significantly affect the way acoustic waves interacted with density stratified flame fronts. The particular case of an asymmetric flame front oscillation under transverse acoustic forcing indicated that baroclinic vorticity, generat...

 
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Added By - A Ghosh
Subject - Aeronautics and Astronautics
Document Type - PhD Thesis
 
   
   

 

Title          
 The Combustion of Aluminum in Solid Rocket Pr...  
 
Abstract    

The trophy piece of technology in any modern rocket system is without question the liquid bi-propellant engine. Despite their sophistication, power, and precision the workhorse responsible for launching men and machines into space is based on solid rocket technology more than 700 years old. The earliest historical use of gunpowder dates back to the 300 B.C where in modern day China bamboo tubes filed with gunpowder were thrown into fires during celebrations, the noise warding away evil spirits. 500 years later in 1232 A.D at the battle of Kai-fung-fu the Chinese military used the first recorded rockets against the invading Mongol Horde. As the Mongols moved through china, they took emerging technologies with them and by 1241 A.D, the rocket had made it to the battlefields of Europe. By 1300 A.D, arsenals around Europe had some rocket technology, based entirely on the use of gunpowder for propulsive motive. A lack of control over rocket trajectories hindered much development by western militaries, who also found the tendency of a misguided missile to start a fire counterproductive. In the Eighteenth century, work had begun on developing a more powerful propellant, and although some progress had been made the independent work of Rob...

 
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Added By - ajayvs
Subject - Aeronautics and Astronautics
Document Type - Term Paper
 
   
   

 

Title          
 Hydrogen sensors based on titania nano-tubes  
 
Abstract    

This article is a literature survey on the fabrication of novel H2 sensors based on titania nano-tubes prepared using anodization and annealed in an oxygen atmosphere. The as prepared nano-tubes are amorphous but they crystallize on annealing at elevated temperatures and are structurally stable (which is a requirement of any sensor) to at least 600 °C.Titania nano-tubes are grown from titanium foil (≈99.5% pure) of thickness 0.25 mm. The anodization is performed in an electrolyte medium of 0.5% hydrofluoric acid in water, using a platinum foil cathode. A well defined nano-tube architecture results, with nano-tube length of 400 nm in approximately 20 minutes.Measurement of H2 concentration is based on the increase in conductivity of the nano-tube surface in a hydrogen ambient as compared to its original conductivity, and this is quantified by ’sensitivity’ ratio, S = (R0 – Rgas)/Rgas (where R0 is the electrical resistance of the sensor before passing the gas and Rgas that after passing gas and reaching the saturation value). The sensor shows significant hydrogen sensitivity, with a three order of magnitude change in resistance as compared to its original resistance. The major process behind the interaction between the nano-tu...

 
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Added By - sidpatel
Subject - Mechanical Engineering
Document Type - White Paper
 
   
   

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