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Rocket Propulsion - Liquid Propellants Combustion Quiz(MCQ)
A)
Transonic-flow zone
B)
Rapid combustion zone
C)
Supersonic expansion zone
D)
Stream tube combustion zone

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.

A)
liquids and gases are relatively hot
B)
vaporization causing a cooling effect
C)
low flow velocity in the injector zone
D)
vaporization causing fuel-rich and fuel-lean regions

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.

A)
isentropic
B)
isothermal
C)
heterogeneous
D)
homogenous

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.

A)
local turbulence
B)
diffusion of the gas species
C)
supersonic compression waves
D)
vaporization of the liquid propellants

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.

A)
Atomization zone
B)
Transonic flow zone
C)
Rapid-combustion zone
D)
Stream tube combustion zone

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.

A)
irregular
B)
immovable
C)
undulating
D)
local variations

Correct Answer :   immovable


Explanation : The boundaries are not immovable. They are dynamically movable and subject to variations in temperature, locally intense radiation emissions etc.

A)
Turbulent mixing
B)
Multiple chemical reactions
C)
Local mixture ratio variations
D)
Temperature rise increases densities

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.

A)
radiation from rapid combustion zone and by convection from moderately hot gases in the first zone
B)
convection from moderately hot gases in the first zone, but not by radiation from rapid combustion zone
C)
radiation from rapid combustion zone, but not by convection from moderately hot gases in the first zone
D)
neither radiation from rapid combustion zone nor by convection from moderately hot gases in the first zone

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.

A)
105 and 320 m/s
B)
23 and 98 m/s
C)
7 and 60 m/s
D)
0 and 22 m/s

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.

A)
Rough combustion
B)
Smooth combustion
C)
Combustion instability
D)
Complete combustion

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.

11 .
Which of the following terms best describe the combustion when the pressure fluctuations during steady operation is 12% of the mean chamber pressure?
A)
Rough combustion
B)
Smooth combustion
C)
Complete combustion
D)
Incomplete combustion

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.

A)
buzzing
B)
squealing
C)
chugging
D)
screaming

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.

A)
pogo
B)
screeching
C)
traveling wave
D)
spinning wave

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.

A)
standing and travelling waves
B)
spinning and radial waves
C)
travelling and spinning waves
D)
travelling and longitudinal waves

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.

A)
tangential and radial modes
B)
longitudinal and radial modes
C)
longitudinal and tangential modes
D)
radial, tangential and longitudinal modes

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.

A)
chugging
B)
squealing
C)
buzzing
D)
screaming

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.

A)
buzzing
B)
chugging
C)
entropy waves
D)
squealing

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.

A)
Pogo
B)
Buzzing
C)
Chugging
D)
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.

A)
Pogo
B)
Screaming
C)
Screeching
D)
Entropy waves

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.