Engineering Questions with Answers - Multiple Choice Questions
Rocket Propulsion – System Integration and Engine Optimization
1 - Question
Which of the following is not a method of achieving a variable thrust?
a) Injecting liquid into the gas streams before injection
b) Varying injection element area
c) Varying the nozzle throat area
d) Varying feed system pressure drops
View Answer
Explanation: Injecting gas into liquid streams before the injection is a method for achieving a variable thrust but not vice versa. Varying injection element area can be done via selectable manifolds and movable injector elements.
2 - Question
Which of the following can’t happen if a chemical rocket engine were to use gelled propellants?
a) Increase in specific impulse
b) Increase in density impulse
c) Possibility of short-duration pulsing
d) Much less likely to have explosions
View Answer
Explanation: Depending upon the gelling agent, specific impulse might change. Because of the dilution of the propellants with a gelling agent, there is generally a small decrease in specific impulse. It will also lead to less efficient atomization or combustion.
3 - Question
Which of the following will not happen if small aluminum particles are suspended in the fuel or if small inert solid particles are suspended in the oxidizer?
a) Increase in propellant density
b) Reduction in tank and vehicle size
c) Decrease in density impulse
d) Increase in speed and range of atmospheric rockets or missiles
View Answer
Explanation: Density impulse is the specific impulse of the propellants multiplied by its density. Addition of small inert solid particles will increase the density of the propellant and hence lead to improved impulse density. This also means that the volume required to store the propellants is lesser and the rocket size becomes smaller. It will lead to drag reduction (since the surface area is lesser) under atmospheric operating conditions and improve speed and range of the vehicle.
4 - Question
Propellants that are thick or viscous under static conditions, but flow through valves, injectors, pipes or pumps when adequate shear stress is applied are called __________ propellants.
a) Thixotropic
b) Dilatant
c) Newtonian fluid
d) Non-Newtonian fluid
View Answer
Explanation: Thixotropic fluids become thinner (or less viscous) over time when adequate shear stresses are applied on it. A dilatant material has increasing viscosity with the rate of shear strain. A Newtonian fluid is a fluid in which the viscous stresses arising from its flow is linearly proportional to the local strain rate. Non-Newtonian fluids are those fluids that doesn’t obey Newton’s law of viscosity (which states that the shear stress between two adjacent fluid layers is proportional to the negative value of velocity gradient between those two layers).
5 - Question
For a missile weighing 60 kg cruising with constant velocity 110 m/s, with lift-to-drag ratio of 8 and Isp of 200, determine the range if the final mass of the missile is 25 kg.
a) 119 km
b) 132 km
c) 154 km
d) 198 km
View Answer
Explanation: From Breguet’s range equation, R = u Isp (L/D) ln(Wi/Wf), which gives R = 110 x 200 x 8 x ln(60/25) = 154 km.
6 - Question
A tactical missile is not used for _________
a) attacking ground troops
b) defending ground troops
c) attacking military aircrafts
d) decoy flare
View Answer
Explanation: Decoy flare is an infrared countermeasure taken by airborne vehicles against homing infrared missiles to divert its attention from its target. It is not a kind of tactical missile.
7 - Question
Military missiles generally use ___________ rocket engines.
a) ion-electric
b) chemical
c) nuclear
d) solar
View Answer
Explanation: Because of the simplicity in logistics and its ability to be launched quickly, military missiles are typically chemical rocket engines. Most of the time, they employ solid rocket propellants for similar reasons.
8 - Question
Verification of initial burning or ignition is done via ________ for visual detection and ________ for heat detection in some rocket engines.
a) photocell; pyrometer
b) pyrometer; photocell
c) bolometer; pyrometer
d) load cell; pyrometer
View Answer
Explanation: Bolometer is used for measuring radiant energy, whereas load cells act as transducers which converts force into measurable electrical output. Photocell is used for visual detection, while pyrometer for heat detection.
9 - Question
Which of the following doesn’t happen if the starting controls are improperly designed?
a) Accumulation of unburned propellants in the combustion chamber
b) Explosion upon ignition
c) Eventual damage to rocket engine
d) Increase in dripping flow
View Answer
Explanation: Improper starting control design may or may not lead to an increase in dripping flow. But it can lead to the accumulation of unburned propellants in the combustion chamber, chances of explosion upon ignition and eventual damage to a rocket engine.
10 - Question
Valves are often opened to allow full flow into the combustion chamber.
a) True
b) False
View Answer
Explanation: Valves are often partially opened so that there doesn’t occur any accumulation of unburned propellant mixture in the chamber. Maximum flow into the combustion chamber is not necessary at all times.