Correct Answer : Rapid combustion zone
Explanation : Any remaining liquid droplets of propellants get vaporized by convective heating in the rapid combustion zone. In this zone, intensive chemical reactions take place at an increasingly higher temperature.
Correct Answer : vaporization causing fuel-rich and fuel-lean regions
Explanation : Vaporization in this region causes the formation of fuel-rich and fuel-lean regions which do not burn quickly. This is partly the reason why the heat generation in this region is low. The liquids and gases are relatively cold. Flow velocity in the injector zone is low, but that is not the correct reason for less heat generation.
Correct Answer : heterogeneous
Explanation : The atomization zone has both propellants – the fuel and the oxidizer. Some of them exist in liquid droplet form, while the others are in vaporized form. Their combination is hence heterogeneous.
Correct Answer : supersonic compression waves
Explanation : Local turbulence, diffusion of the gaseous species and vaporization of the liquid propellants all aid the mixing process in rapid combustion zone. The flow through the combustion chamber is subsonic in nature. So, supersonic compression waves cannot occur inside the combustion chamber.
Correct Answer : Atomization zone
Explanation : Atomization zone lies in front of the thrust chamber. Out of the remaining options, transonic flow zone lies in the nozzle while the rest of them are in the combustion chamber region.
Correct Answer : immovable
Explanation : The boundaries are not immovable. They are dynamically movable and subject to variations in temperature, locally intense radiation emissions etc.
Correct Answer : Temperature rise increases densities
Explanation : Temperature rise leads to reduced densities. The local mixture ratios, velocities, or reaction rates are non-uniform across the chamber. Turbulent mixing and multiple chemical reactions with major heat releases are common in this region.
Correct Answer : radiation from rapid combustion zone and by convection from moderately hot gases in the first zone
Explanation : Radiation of heat from the high temperature rapid combustion zone and convection from moderately hot gases in the first zone will lead to the evaporation of the atomized droplets of the propellants.
Correct Answer : 7 and 60 m/s
Explanation : The propellant injection velocity typically lies between 7 and 60 m/s. It influences the combustion behavior and any small change in them can have a major effect on its instability.
Correct Answer : Smooth combustion
Explanation : When the pressure fluctuations do not exceed 5% of the mean chamber pressure, the combustion is called as smooth combustion. Combustion in a liquid rocket engine in reality is never smooth.
Correct Answer : Rough combustion
Explaination : If the pressure fluctuations exceed 5% of the mean chamber pressure, the combustion is called rough combustion. Normal liquid rocket engines in reality display rough combustion.
Correct Answer : chugging
Explanation : Chugging is the term used to denote combustion instabilities with low-frequency of occurrence of fairly large concentrations of vibratory energy. The frequency range for this instability is 10-400 Hz.
Correct Answer : screeching
Explanation : Screeching (or squealing) can be caused by acoustically stimulated variations in droplet mixing and/or its vaporization. It can also be caused due to acoustic changes in combustion rates or due to local detonations.
Correct Answer : standing and travelling waves
Explanation : Tangential mode can be considered as two waves: Standing wave and traveling wave. Traveling wave is also called as spinning wave. Standing wave remains fixed in position while the traveling tangential wave has a rotation of the whole vibratory system.
Correct Answer : tangential and radial modes
Explanation : High frequency (HF) instabilities are troublesome as they can lead to destructive results on the engine. Their destructive effect comes from the accelerated heat transfer as a result of these instabilities causing pressure fluctuations of the magnitude greater than about 20% of the mean combustion chamber pressure. Longitudinal and transverse modes are the two modes through which high-frequency instability occurs. The transverse modes can be further divided as radial and tangential modes.
Correct Answer : buzzing
Explanation : Buzzing is the term used to denote combustion instabilities with an intermediate frequency of occurrence of fairly large concentrations of vibratory energy. The frequency range for this instability is 400-1000 Hz.
Correct Answer : squealing
Explanation : Squealing is the term used to denote combustion instabilities with high-frequency of occurrence of fairly large concentrations of vibratory energy. The frequency range lies above 1000 Hz. It is also called screaming.
Correct Answer : Chugging
Explanation : Chugging can occur in test facilities due to the propellant pump cavitation. It can also happen due to gas entrapment in propellant flow or due to tank pressurization control fluctuations.
Correct Answer : Pogo
Explanation : Pogo instability is a longitudinal instability due to propellant flow rate disturbances. They are low-frequency waves, usually lying in the 10-50 Hz frequency zone.
