Engineering Questions with Answers - Multiple Choice Questions

# Rocket Propulsion – Liquid Propellants – Combustion Instability

1 - Question

Which of the following terms best describes the combustion when the pressure fluctuation during steady operation is 4% of the mean chamber pressure?
a) Smooth combustion
b) Rough combustion
c) Combustion instability
d) Complete 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.

2 - Question

Which of the following terms best describe the combustion when the pressure fluctuations during steady operation is 12% of the mean chamber pressure?
a) Complete combustion
b) Incomplete combustion
c) Smooth combustion
d) Rough combustion
Explanation: 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.

3 - Question

low-frequency combustion instability is called ________
a) chugging
b) buzzing
c) squealing
d) screaming
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.

4 - Question

Intermediate frequency combustion instability is called ________
a) squealing
b) chugging
c) screaming
d) 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.

5 - Question

high-frequency combustion instability is called ________
a) squealing
b) buzzing
c) chugging
d) entropy waves
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.

6 - Question

Which of the following combustion instabilities occur due to propellant pump cavitation?
a) Buzzing
b) Chugging
c) Pogo
d) Screaming
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.

7 - Question

Which of the following combustion instabilities happen due to propellant flow rate disturbances?
a) Screeching
b) Entropy waves
c) Screaming
d) 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.

8 - Question

Transverse mode of high-frequency instability propagation can be broken into ___________
b) longitudinal and tangential modes
c) radial, tangential and longitudinal 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.

9 - Question

Tangential mode of instability has the following modes ____________
a) standing and travelling waves
b) travelling and spinning waves
c) travelling and longitudinal 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.

10 - Question

Acoustically stimulated variations in droplet mixing and/or vaporization can cause ___________
a) screeching
b) spinning wave
c) traveling wave
d) pogo