This set of Rocket Propulsion Multiple Choice Questions & Answers (MCQs) focuses on “Liquid Propellants – Combustion process”.
1. Which of the following zones is not a part of the thrust chamber?
a) Atomization zone
b) Rapid-combustion zone
c) Stream tube combustion zone
d) Transonic flow 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.
2. The boundaries between the discrete combustion zones inside the combustion chamber is not ________
d) local variations
Explanation: The boundaries are not immovable. They are dynamically movable and subject to variations in temperature, locally intense radiation emissions etc.
3. Which of the following with regards to mixing and reaction in the combustion chamber is incorrect?
a) Turbulent mixing
b) Multiple chemical reactions
c) Temperature rise increases densities
d) Local mixture ratio variations
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.
4. In which of the zones does any remaining liquid droplets of the propellants get vaporized by convective heating?
a) Rapid combustion zone
b) Stream tube combustion zone
c) Transonic-flow zone
d) Supersonic expansion 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.
5. The mixing in rapid combustion zone is not aided by ___________
a) local turbulence
b) diffusion of the gas species
c) supersonic compression waves
d) vaporization of the liquid propellants
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.
6. The liquid droplets that remains in the upstream portion of rapid combustion zone do not transverse downstream with ease.
Explanation: This is because the rapid expansion of gases in the combustion zone increases the axial velocity by more than a factor of 100, so the gas flows quickly in this zone, while it is not so quick upstream.
7. Propellants injected through the injector orifices travel at velocities between _______
a) 0 and 22 m/s
b) 7 and 60 m/s
c) 23 and 98 m/s
d) 105 and 320 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.
8. Evaporation of the atomized droplets can happen due to heat transferred by ________
a) radiation from rapid combustion zone, but not by convection from moderately hot gases in the first zone
b) radiation from rapid combustion zone and by convection from moderately hot gases in the first zone
c) convection from moderately hot gases in the first zone, but not by radiation from rapid combustion zone
d) neither radiation from rapid combustion zone nor 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.
9. The atomization region before the rapid combustion zone is _______
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.
10. Heat generation in the first zone of the atomization region is relatively low because of ________
a) liquids and gases are relatively hot
b) vaporization causing a cooling effect
c) vaporization causing fuel-rich and fuel-lean regions
d) low flow velocity in the injector zone
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.
Sanfoundry Global Education & Learning Series – Rocket Propulsion.
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