Rocket Propulsion - Thrust Chambers Quiz(MCQ)

1 .

Burning of the propellants take place in ______

A)

nozzle

B)

injector

C)

engine casing

D)

combustion chamber

Correct Answer : combustion chamber

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 .

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)

Evaporation and complete combustion of the propellants, but not mixing

C)

Mixing and complete combustion of the propellants, but not its evaporation

D)

Mixing and evaporation but not the complete combustion of the propellants

Correct Answer : Mixing, evaporation and 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 .

What is stay time?

A)

Average time spent by each molecule or atom within the injector manifold

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 combustion chamber volume

D)

Average time spent by each molecule or atom within the propellant tank after rocket take off

Correct Answer : Average time spent by each molecule or atom within the combustion chamber volume

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 t_s = V_c/mV_i, where V_c is the chamber volume, m is the mass flow rate, and V_i is the average specific volume.

4 .

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

Correct Answer : 0.8 and 3 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.

5 .

What is characteristic chamber length?

A)

Total length of the nozzle

B)

Total length of the rocket engine

C)

Thrust chamber length without the length of the nozzle

D)

Length of the thrust chamber as if it were a straight tube with no converging section

Correct Answer : Length of the thrust chamber as if it were a straight tube with no converging section

Explanation : Characteristic length is the length of the thrust chamber assuming that it was a straight tube with no converging section.
L* = V_c/A_t, where V_c is the chamber volume and A_t is the throat area.

6 .

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; increases

B)

decreases; decreases

C)

increases; decreases

D)

decreases; increases

Correct Answer : decreases; decreases

Explaination : 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 .

Which of the following is true for combustion chambers with large volume and diameter?

A)

Thinner walls

B)

Lower wall temperature

C)

High heat transfer rates to the walls

D)

Smaller total area exposed to the heat

Correct Answer : 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.

8 .

The combustion chamber mass is not a function of ________

A)

payload mass

B)

nozzle area ratio

C)

chamber pressure

D)

method of cooling

Correct Answer : payload mass

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.

9 .

Which of the following will aid in the selection of smaller combustion chamber volume during its design?

A)

Low chamber pressure

B)

Slightly reactive propellants

C)

Injectors with moderate mixing

D)

Possibility for complete combustion

Correct Answer : 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.

10 .

The carburetor of an internal combustion engine has a similar function as __________

A)

nozzle

B)

injector

C)

propellant tank

D)

thrust chamber

Correct Answer : injector

Explanation : Injector in rocket engine and carburetor in an internal combustion engine functions in a similar manner. Injector meters, injects and atomizes the liquid propellants into the combustion chamber.

11 .

Which of the following injectors requires large chamber volume for good combustion?

A)

Multiple-hole injector

B)

Showerhead injector

C)

Sheet injector

D)

Impinging-stream-type injector

Correct Answer : Sheet injector

Explanation : Sheet injector requires large chamber volume for good combustion. It is a spray-type injector that can give cylindrical, conical and many other kinds of spray sheets.

12 .

Non-impinging injector is also called as _________ injector.

A)

doublet

B)

like-on-like

C)

showerhead

D)

multiple-hole

Correct Answer : showerhead

Explanation : A showerhead injector is also called as a non-impinging injector. The propellant usually comes out normal to the face cross-section of the injector.

13 .

Which of the following can cause afterburning?

A)

Dribbling flow

B)

Complete combustion

C)

Sloshing in propellant tank

D)

Use of cold gas propellant system

Correct Answer : Dribbling flow

Explanation : Dribbling flow can cause afterburning. The dribble flow may lead to an excess in fuel and this might end up in secondary reactions after passing the combustion chamber and result in afterburning.

14 .

The process by which liquids are broken into small droplets is called __________

A)

disintegrator

B)

pulverization

C)

vaporization

D)

atomization

Correct Answer : atomization

Explanation : Atomization is the process through which the liquid is broken into tiny droplets. One of the functions of injector is atomization.

15 .

________ helps in the distribution of propellant from the injector inlet.

A)

Preburner

B)

Injector hole pattern

C)

Turbopump

D)

Gas generator cycle

Correct Answer : Injector hole pattern

Explanation : By varying the injector hole pattern, it is possible to get different types of propellant distribution from the injector inlet. It is related to feed passages and internal manifolds within the injector.

16 .

A large complex manifold of an injector allows ________ and ________

A)

high flow velocities; poor distribution of flow over the chamber cross-section

B)

low flow velocities; poor distribution of flow over the chamber cross-section

C)

high flow velocities; good distribution of flow over the chamber cross-section

D)

low flow velocities; good distribution of flow over the chamber cross-section

Correct Answer : low flow velocities; good distribution of flow over the chamber cross-section

Explanation : For larger manifolds, the injector flow will be lesser and the distribution of flow over the chamber cross-section will be uniform. This can be seen by considering two passages of varying cross-sections and constant mass flow rate of propellants through it.

17 .

A small manifold volume of an injector results in ________ and ________

A)

less dribble; lighter injector

B)

more dribble; heavier injector

C)

less dribble; heavier injector

D)

more dribble; lighter injector

Correct Answer : less dribble; lighter injector

Explanation : Dribble flow is remaining flow after the valve closes. For a smaller manifold volume of an injector, the amount of dribble flow will be lesser. Since the injector is small, only a small mass of material is used for injector manufacturing and hence it leads to a lighter injector.

18 .

To make a sharp, abrupt start to fuel injection _________ is used.

A)

check valve

B)

safety valve

C)

pop valve

D)

anti-dribble valve

Correct Answer : pop valve

Explanation : Pop valve is used for that purpose. It sharply opens to allow full flow. This type of valve opens only when a certain pressure has been attained.

19 .

The flow through injector manifold after the main valves are shut is called as ______

A)

pipe flow

B)

bleed flow

C)

main flow

D)

dribble flow

Correct Answer : dribble flow

Explanation : Dribble or dripping flow is the flow after the main valves are shut. This uneven flow is undesirable and needs to minimize.

20 .

If dT/dL denotes temperature gradient with respect to thickness L at the surface A, k denotes the thermal conductivity, then the heat transferred per unit area is given by __________

A)

Q/A = k dT/dL

B)

Q/A = -k dT/dL

C)

Q/A = -(1/k) dT/dL

D)

Q/A = (1/k) kdT/dL

Correct Answer : Q/A = -k dT/dL

Explaination : Q/A = -k dT/dL is the expression for heat transferred per unit area. This is called as Fourier’s law of heat transfer. By negative symbol in the equation, we can see that the direction of heat transfer is in the direction of negative gradient (larger temperature to smaller temperature) of temperature along the length of the material.

21 .

The quantity μC_p/k, where μ is the absolute gas viscosity, C_p is the specific heat of gas at constant pressure and k is the thermal conductivity is called as ______

A)

Bartz number

B)

Prandtl number

C)

Froude number

D)

Nusselt number

Correct Answer : Prandtl number

Explaination : μC_p/k is the Prandtl number. It is the ratio of momentum diffusivity to thermal diffusivity.

22 .

The quantity h_gD/k, where h_g is the gas film coefficient, D is the diameter of the chamber and k denotes the gas conductivity is _________

A)

Bartz number

B)

Nusselt number

C)

Froude number

D)

Prandtl number

Correct Answer : Nusselt number

Explaination : h_gD/k is called as the Nusselt number. This is a parameter which comes into picture while dealing with heat transfer problems between a solid body and a moving fluid.

23 .

Which of the following might simplify the determination of film coefficient?

A)

Uniform velocity profile

B)

Complex geometry

C)

Combustion oscillations

D)

Boundary layer behavior

Correct Answer : Uniform velocity profile

Explanation : Film coefficient calculation might be simplified for a uniform velocity profile. In reality, the determination of this coefficient is very difficult because of the presence of combustion oscillations, complex geometry, non-uniform velocity profile and presence of boundary layers.

24 .

_____ largely determines the numerical heat transfer rate and __________ largely determines the value of wall temperatures.

A)

Gas film coefficient; thermal conductivity

B)

Liquid film coefficient; gas film coefficient

C)

Thermal conductivity; liquid film coefficient

D)

Gas film coefficient; liquid film coefficient

Correct Answer : Gas film coefficient; liquid film coefficient

Explanation : Gas film coefficient largely helps in the determination of numerical value of heat transfer rate. Liquid film coefficient largely helps in determining the value of wall temperatures.

25 .

Steady state heat transfer through a liquid-cooled rocket chamber wall can be considered as ___________

A)

series type with weak temperature gradient

B)

parallel type with weak temperature gradient

C)

series type with strong temperature gradient

D)

parallel type with strong temperature gradient

Correct Answer : series type with strong temperature gradient

Explanation : The heat transfer through the liquid-cooled rocket chamber can be considered as a steady state series type process with strong temperature gradients. This involves a large temperature gradient across the thin gaseous film touching the wall, a temperature drop across the wall and a third temperature drop in the presence of the moving cooling fluid.

26 .

The whole process of heat transfer through the chamber wall is a combination of ________ through the chamber wall and ________ through the flowing fluids.

A)

conduction; convection

B)

radiation; conduction

C)

convection; radiation

D)

conduction; conduction

Correct Answer : conduction; convection

Explaination : Heat transfer through the chamber walls includes both the conduction through the chamber wall as well as convection through the flowing fluids. This problem is basically one that is associated with the heat and mass transport associated with through a wall.

27 .

For absolute chamber gas temperature T_g, absolute liquid temperature T_l, overall film coefficient h, gas film coefficient h_g and liquid film coefficient h_l, determine the expression for heat transferred per unit area q.

A)

q = h (T_g – T_l)

B)

q = h_g (T_g – T_l)

C)

q = h_gh_l/h x (T_g – T_l)

D)

q = h/(h_g h_l) x (T_g – T_l)

Correct Answer : q = h (T_g – T_l)

Explaination : q = h(T_g – T_l) is the correct expression for heat transferred per unit area. This relation assumes that the heat flow is radial in direction.

28 .

Which of the following is the correct expression for energy radiated by a body (Assume ε to be emissivity, A to be surface area, T to be temperature, f to be geometric factor)

A)

E = fεσAT²

B)

E = (1/f)εσAT²

C)

E = fεσAT⁴

D)

E = (1/f)εσAT⁴

Correct Answer : E = fεσAT⁴

Explaination : E = fεσAT⁴ is the correct expression for energy radiated by a body. Here σ is the Stefan-Boltzmann constant and it has a value of 5.67 x 10^-8 W/m²K⁴.

29 .

Which of the following gases show a strong emission band in the region of radiant heat transfer?

A)

Oxygen

B)

Nitrogen

C)

Hydrogen

D)

Ammonia

Correct Answer : Ammonia

Explanation : Gases with symmetrical molecules like hydrogen, oxygen and nitrogen typically doesn’t show a strong band in the region of radiant heat transfer. Heteropolar gases, on the other hand, shows strong activity in that band.

30 .

In which of the following ignition techniques does the system use a solid propellant squib or grain of few seconds of burning duration?

A)

Spark plug ignition

B)

Pyrotechnic ignition

C)

Precombustion chamber ignition

D)

Ignition by electrically heated wires

Correct Answer : Pyrotechnic ignition

Explaination : In pyrotechnic ignition, a squib or grain of solid propellant of few seconds of burning duration is used for the sake of ignition. This is one of the common ways of ignition in a solid propellant rocket engine.

31 .

Determine the propellant mass flow rate for a TSFC of 3200 kg/Ns and a total thrust of 50 kN.

A)

21.65 kg/s

B)

16.52 kg/s

C)

15.62 kg/s

D)

12.56 kg/s

Correct Answer : 15.62 kg/s

Explaination : Propellant flow rate m? = F/c, where F is the total thrust and c is the specific fuel consumption.
Then m? = 50,000/3200 = 15.62 kg/s.

32 .

Find the fuel flow rate for a total propellant flow of 10 kg/s and a mixture ratio of 2.3.

A)

1.47 kg/s

B)

4.17 kg/s

C)

4.71 kg/s

D)

7.41 kg/s

Correct Answer : 4.17 kg/s

Explaination : Fuel flow rate m?f = m?/(r+1), where m? is the total propellant mass flow rate and r is the mixture ratio.
So m?f = 10/2.4 = 4.17 kg/s.

33 .

Calculate the flow rate of LOX to the combustion chamber in a LOX-H2 rocket engine if the total propellant flow rate is 17 kg/s and mixture ratio is 3.2.

A)

12.95 kg/s

B)

13.67 kg/s

C)

15.92 kg/s

D)

17.81 kg/s

Correct Answer : 12.95 kg/s

Explaination : m?_o = m?_r/(r+1)
So m?_o = 17*3.2/4.2 = 12.95 kg/s.

34 .

The pressure drop across injector is usually set between _________ of the chamber pressure.

A)

50 and 70%

B)

45 and 65%

C)

30 and 45%

D)

15 and 25%

Correct Answer : 15 and 25%

Explaination : The pressure drop across the injector is set between 15 and 25% of the chamber pressure. This is done partly for obtaining high velocities of propellant injection. High velocities will help in easy atomization and droplet breakup which in turn helps in complete combustion.

35 .

Determine the nozzle throat area for a rocket engine producing a total thrust of 10 kN, chamber pressure of 5.2 MPa and thrust coefficient of 1.9

A)

10.12 cm²

B)

11.20 cm²

C)

12.10 cm²

D)

21.10 cm²

Correct Answer : 10.12 cm²

Explaination : Nozzle throat area A_t = F/P₁C_F, where P₁ is the chamber pressure, C_F is the thrust coefficient and F is the total thrust provided by the rocket engine.
Then A_t = 10000/(5.2 x 10⁶ x 1.9)
= 10.12 cm².