Engineering Questions with Answers - Multiple Choice Questions
Rocket Propulsion – Thrust Chambers – Combustion Chamber and Nozzle
1 - Question
Burning of the propellants take place in __________
c) combustion chamber
d) engine casing
Explanation: Propellants burn in the combustion chamber for both solid and liquid rocket engines. This burning can produce temperatures higher than melting points of many of the chamber wall materials. So, an effective cooling system is used to mitigate this issue.
2 - Question
The volume of the combustion chamber is selected on the basis of which of these factors?
a) Mixing, evaporation and complete combustion of the propellants
b) Mixing and complete combustion of the propellants, but not its evaporation
c) Evaporation and complete combustion of the propellants, but not mixing
d) Mixing and evaporation but not the complete combustion of the propellants
Explanation: All the three factors – mixing, complete combustion and evaporation of the propellants are considered for the choice of the volume of combustion chamber. It is chosen such that the mixing is good, evaporation is less and the complete combustion is ensured at all times.
3 - Question
Which of the following will aid in the selection of smaller combustion chamber volume during its design?
a) Slightly reactive propellants
b) Low chamber pressure
c) Injectors with moderate mixing
d) Possibility for complete combustion
Explanation: If there are means of achieving complete combustion, then the size of the combustion chamber may be reduced. Other than that, using highly reactive propellants (with adequate safety measures), having high chamber pressure and using injectors with good mixing will also act as factors for the selection of a smaller combustion chamber.
4 - Question
Which of the following is true for combustion chambers with large volume and diameter?
a) High heat transfer rates to the walls
b) Smaller total area exposed to the heat
c) Thinner walls
d) Lower wall temperature
Explanation: Heat transfer to the chamber wall will be less if the diameter and volume of the chamber is large. This is due to the large area exposed to heat and due to thicker walls of the chamber.
5 - Question
The combustion chamber mass is not a function of __________
a) payload mass
b) method of cooling
c) chamber pressure
d) nozzle area ratio
Explanation: The combustion chamber mass is not a function of payload mass. But it will depend upon the method of cooling, area ratio of the nozzle and the chamber pressure.
6 - Question
For increased operating chamber pressure, the length of the combustion chamber ________ and the nozzle throat area _________ if the diameter of the combustion chamber (assume the shape to be cylindrical) is fixed and the thrust remains constant.
a) increases; decreases
b) decreases; increases
c) decreases; decreases
d) increases; increases
Explanation: The combustion chamber length will decrease because the combustion chamber volume decreases with the chamber pressure for the same thrust. It will also lead to a decrease in the nozzle throat area.
7 - Question
What is characteristic chamber length?
a) Thrust chamber length without the length of the nozzle
b) Length of the thrust chamber as if it were a straight tube with no converging section
c) Total length of the nozzle
d) Total length of the rocket engine
Explanation: Characteristic length is the length of the thrust chamber assuming that it was a straight tube with no converging section. L* = Vc/At, where Vc is the chamber volume and At is the throat area.
8 - Question
Determine the chamber volume if the characteristic length of a thrust chamber is 150 cm and nozzle throat area is 0.25m2.
a) 0.573 m3
b) 0.735 m3
c) 0.375 m3
d) 0.753 m3
Explanation: Characteristic length L* = Vc/At, where Vc is the chamber volume At is the nozzle throat area. So, Vc = 150 x 10-2 x 0.25 = 0.375 m3.
9 - Question
Typical values of L* for several bipropellants lie between __________
a) 0.8 and 3 m
b) 1 and 2 m
c) 1.5 and 5.5 m
d) 3.2 and 6.4 m
Explanation: L* typically has a range of 0.8 to 3 m. This is the case for bipropellants. For monopropellants, it may lie even higher.
10 - Question
What is stay time?
a) Average time spent by each molecule or atom within the combustion chamber volume
b) Average time spent by each molecule or atom within the thrust chamber volume
c) Average time spent by each molecule or atom within the propellant tank after rocket take off
d) Average time spent by each molecule or atom within the injector manifold
Explanation: Stay time is the average time that each molecule or atom of the propellant stays within the volume of the combustion chamber. It is defined by ts = Vc/mVi, where Vc is the chamber volume, m is the mass flow rate, and Vi is the average specific volume.