Rocket Propulsion - Chemical Rocket Propellant Performance Analysis Quiz(MCQ)

1 .

Perfect gas equation applies very closely to ________ gases.

A)

high temperature, low pressure

B)

high temperature, high pressure

C)

low temperature, low pressure

D)

low temperature, high pressure

Correct Answer : high temperature, low pressure

Explanation : Perfect gas equations are valid for high temperature and low-pressure gases. In such a case, the inter-molecular forces are negligibly small. PV=RT is the perfect gas equation, with V as the specific volume, P as the pressure, T as the temperature and R as the gas constant for the mixture of gases.

2 .

Consider a mixture of three gases a, b and c at equilibrium. If the individual gas components have pressures equal to P_a, P_b and P_c, determine the total pressure P of the mixture of gases.

A)

P = P_a x P_b x P_c /(P_a + P_b + P_c)

B)

P = P_a + P_b + P_c

C)

P = (P_a x P_b / P_c) + (P_b x P_c / P_a) + (P_c x P_a / P_b)

D)

P = [(P_a x P_b) + (P_b x P_c) + (P_c x P_a)] / (P_a + P_b + P_c)

Correct Answer : P = P_a + P_b + P_c

Explaination : Dalton’s law of partial pressures states that the total pressure exerted by a mixture of gases is the sum of partial pressures of individual gas components. Hence the answer is P = P_a + P_b + P_c.

3 .

Consider two sets of mixture of gases X and Y having the same total temperature of the mixture and having total pressures P_X and P_Y respectively. If P_X = 1.4 P_Y and molecular mass of A M_X = 2.3 x M_Y, determine the ratio of V_{mix_X}/V_{mix_Y}.

A)

0.62

B)

0.52

C)

0.31

D)

0.26

Correct Answer : 0.31

Explaination : Assuming the mixture of gases to be ideal, we have P = R’T/MV_mix where V_mix is the specific volume of the mixture and R’ is the universal gas constant.
P_X/P_Y = (T_X/T_Y) x (M_YV_{mix_Y}/M_XV_{mix_X})
V_{mix_X}/V_{mix_Y} = (M_Y/M_X) x (T_X/T_Y) x (P_Y/P_X)
= (1/2.3) x 1 x (1/1.4) = 0.31.

4 .

In a gaseous mixture, the number of moles and the molecular mass (in their respective units) of each component is given as follows: n_A = 1, M_A = 23; n_B = 2, M_B = 48; n_C = 3, M_C = 19. Find the average molecular mass of the mixture.

A)

25.47

B)

28.67

C)

29.33

D)

31.25

Correct Answer : 29.33

Explaination : M_avg = (n_AM_A + n_BM_B + n_CM_C) / (n_A + n_B + n_C)
= (23 + 96 + 57) / 6 = 29.33.

5 .

What is the number of condensed species in a gaseous mixture, if there are 8 possible species which enter into a relationship and out of these, only 5 are gases?

A)

3

B)

6

C)

9

D)

12

Correct Answer : 3

Explaination : If there are n species that enter into a relationship and if there are only m species out of these, then the total number of condensed species is n-m.

6 .

What is the energy released (or absorbed), or the enthalpy change when one mole of a chemical compound is formed from its constituent atoms or elements at one bar and isothermally at 25°C?

A)

Heat of reaction

B)

Heat of formation

C)

Gibbs free energy

D)

Latent heat of vaporization

Correct Answer : Heat of formation

Explaination : This is the definition of heat of formation. In this reaction, each of the reactants and products are in its thermodynamic standard state and at the reference pressure and temperature.

7 .

The decomposition of solid propellants to reaction mixture is a(n) __________ chemical reaction.

A)

ideal

B)

reversible

C)

irreversible

D)

stoichiometric

Correct Answer : irreversible

Explanation : The whole process of combustion of solid propellants to derive a reaction mixture is an irreversible chemical reaction. It means that the reverse process is not possible.

8 .

Rocket propulsion usually operates in _______ mixture ratio.

A)

oxidizer rich

B)

fuel rich

C)

stoichiometric

D)

All of the above

Correct Answer : fuel rich

Explanation : Rocket propulsion systems typically operate in fuel rich mixture ratio. This allows a portion of lightweight molecules such as hydrogen to be unreacted and contributes to the decrease in the average molecular mass of the combustion products.

9 .

The heat created by the combustion in the thrust chamber of a chemical rocket engine equals the change in enthalpy of the gases.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

Explanation : The heat generated during combustion of the propellants is the heat that is necessary to raise the resulting gases to their final temperature adiabatically. This follows from the conservation of energy.

10 .

If the energy balance in the chemical reaction within the thrust chamber is thought of as a two-step process, what is the initial step in the process?

A)

Adiabatic chemical reaction at the reference temperature

B)

Isentropic chemical reaction at the reference temperature

C)

Isothermal chemical reaction at the reference temperature

D)

Heating of gases with the energy release from the chemical reaction

Correct Answer : Isothermal chemical reaction at the reference temperature

Explanation : The energy balance can be thought of as a two-step process. The first step involved in the isothermal chemical reaction of the propellants at the reference temperature. The second step involves the resultant gases having their temperature raised by the heat released from the previous chemical reaction.

11 .

Out of the following products of the reaction of hydrogen and oxygen, which of them is unstable?

A)

Water

B)

Hydroxyl

C)

Hydrogen

D)

Hydrogen peroxide

Correct Answer : Hydrogen peroxide

Explanation : Theoretically, the reaction between hydrogen and oxygen can give rise to H2O2 and O3 too. But these are unstable materials and they do not readily exist at high temperatures.

12 .

What is the approximate number of species or compounds present in the exhaust for a solid propellant rocket engine?

A)

10

B)

50

C)

100

D)

200

Correct Answer : 50

Explanation : The number of compounds present in the exhaust for a solid propellant rocket engine or a liquid propellant rocket engine with additives can be 50 or more. But many of these chemical species are present in negligible amounts and can be ignored.

13 .

Energy release efficiency is also called as ________

A)

combustion efficiency

B)

isentropic efficiency

C)

propulsive efficiency

D)

polytropic efficiency

Correct Answer : combustion efficiency

Explanation : Energy release efficiency is also called as combustion efficiency. It is the ratio of actual change in enthalpy of the unit propellant mixture to the theoretical change in enthalpy necessary to transform the propellants from the initial conditions to the products at the chamber pressure and temperature.

14 .

Combustion efficiency in liquid propellant rocket engines __________ with an increase in combustion temperature.

A)

increases

B)

decreases

C)

oscillates

D)

doesn�t change

Correct Answer : increases

Explanation : Combustion efficiency increases with increased combustion temperature. It is also depended on the method of injection and mixing.

15 .

Which of the following does the nozzle boundary layer depend on?

I) Axial pressure gradient
II) Nozzle geometry
III) Surface roughness

A)

I, II and III

B)

Only III

C)

Only I and III

D)

Only II and III

Correct Answer : I, II and III

Explaination : Nozzle boundary layer depends on all three factors. In addition to these, it also depends on the heat losses to the walls.

16 .

What is the average diameter of a solid particle in a nozzle flow above which there is a chance of occurrence of thermal lag?

A)

0.1 μm

B)

1 μm

C)

10 μm

D)

100 μm

Correct Answer : 0.1 μm

Explaination : If the average diameter of the solid particles or the liquid droplets in a nozzle flow exceeds 0.1μm, it may lead to thermal and velocity lag. The thermal lag depends upon the convection and radiation means of losing energy and the velocity lag depends upon the drag experienced by the particles.

17 .

In which of the following modes of analysis does the temperature, velocity or pressure at any normal cross-section of an axisymmetric nozzle remain to be the same?

A)

One dimensional

B)

Two dimensional

C)

Three dimensional

D)

N-dimensional, where N can be 1,2,3,…

Correct Answer : One dimensional

Explaination : The simplest nozzle analysis is one-dimensional. In this case, for an axisymmetric nozzle, the flow properties across any normal cross-section will remain to be the same, or the flow properties are said to be uniform.

18 .

Which of the following is not true for an ideal expansion in the nozzle?

A)

Adiabatic, reversible expansion

B)

Conversion of thermal to kinetic energy

C)

Drop in static temperature and pressure

D)

Drop in stagnation temperature and pressure

Correct Answer : Drop in stagnation temperature and pressure

Explanation : Stagnation temperature remains constant for ideal expansion in the nozzle. Ideal expansion is isentropic and involves conversion of thermal to kinetic energy.

19 .

Which of the following effects are neglected for simple cases of nozzle expansion?

A)

Heat exchange

B)

Frictional effects

C)

Reversibility

D)

Divergence angle

Correct Answer : Reversibility

Explanation : For simple cases of nozzle expansion, the effects of friction, heat transfer, shock waves, non-equilibrium and divergence angle are neglected. But the process is considered to be reversible none the less.

20 .

Assertion : The condensed phases (liquid and solid) are assumed to have zero volume.
Reason : Particles or droplets are very small in size.

A)

Both assertion and reason are incorrect

B)

The assertion is correct, but the reason is incorrect

C)

Both are correct but the reason is not the correct explanation for the assertion

D)

Both are correct and the reason is the correct explanation for the assertion

Correct Answer : Both are correct and the reason is the correct explanation for the assertion

Explaination : The condensed phases are assumed to have zero volume. It implies that the droplets or particles are very small in size and have the same temperature as the gas at all the nozzle locations.

21 .

What is the typical value of penalty incurred by assuming a frozen equilibrium rocket performance?

A)

0%

B)

1-4%

C)

12-15%

D)

25-30%

Correct Answer : 1-4%

Explaination : By assuming frozen equilibrium, we assume that the composition of the chemical products remains constant throughout the nozzle and is the same as that under the chamber conditions. In such a case, there are no phase changes or chemical reactions within the nozzle. The typical penalty on the rocket performance by assuming frozen equilibrium is about 1-4%.

22 .

In which of the following cases is the chemical equilibrium maintained instantaneously, even though the gas composition varies through the nozzle due to temperature and pressure variations along the nozzle?

A)

Non-equilibrium

B)

Frozen equilibrium

C)

Shifting equilibrium

D)

Isothermal equilibrium

Correct Answer : Shifting equilibrium

Explaination : In shifting equilibrium, even though there is an instantaneous chemical equilibrium between all molecular species, under the variation of pressure and temperature along the nozzle, the chemical composition varies. The gas composition at the chamber and at the exhaust in such a case would be different.

23 .

Dissociation of the reaction products __________ with the rise in the chamber temperature and _________ with the rise in chamber pressure of a chemical rocket engine.

A)

decreases, decreases

B)

increases, increases

C)

decreases, increases

D)

increases, decreases

Correct Answer : increases, decreases

Explaination : Higher chamber temperature results in higher dissociation of the reaction products. But the dissociation can be suppressed by an increase in the chamber pressure.

24 .

Knocking in spark-ignition internal combustion engines is not the same as _______

A)

pinking

B)

pre-ignition

C)

pinging

D)

detonation

Correct Answer : pre-ignition

Explanation : Knocking and pre-ignition are two separate events. Knocking happens when the combustion of some of the air-fuel mixture doesn’t occur because of the propagation of flame front due to spark-plug ignition, but when one or more air-fuel mixture pockets explode outside the normal combustion front. Pre-ignition refers to the case in which combustion happens even before the spark-plug fires.

25 .

_________ is not a metallic additive in rocket propellants.

A)

Boron

B)

Beryllium

C)

Nitroglycerine

D)

Aluminum

Correct Answer : Nitroglycerine

Explanation : Nitroglycerine is a dense, colorless, explosive liquid. Its chemical formula is C3H5N3O9. It is neither metallic nor an additive.

26 .

Which of the following is a highly refined form of kerosene used as rocket fuel?

A)

RP-1

B)

C-4

C)

RDX

D)

HMX

Correct Answer : RP-1

Explanation : RP-1 is a highly refined form of kerosene. It is short for Rocket Propellant-1 or Refined Petroleum-1. A part of RP-1 includes toxic and carcinogenic hydrazine.

27 .

Which of the following fuels were used in the first stage of Titan I?

A)

RP-1

B)

RDX

C)

HMX

D)

None of the above

Correct Answer : RP-1

Explanation : RP-1 fuel is used in the first stage of Titan 1. Other than that, it was also used in the first stages of Saturn V, Energeia, Saturn I and IB etc. It is a cheaper and less explosive alternative to LH₂.

28 .

The fuel which releases the most energy per unit mass of combustion is ______

A)

RP-1

B)

LH₂

C)

Kerosene

D)

Methane

Correct Answer : LH₂

Explaination : Compared to hydrocarbon fuels, liquid hydrogen delivers most energy per unit mass of combustion. Any hydrocarbon fuel, when subjected to combustion produces more pollution than LH₂.

29 .

1-methyl-1, 2-dicyclopropyl cyclopropane is also called as _______

A)

RP-1

B)

Jet fuel

C)

Syntin

D)

Kerosene

Correct Answer : Syntin

Explanation : Syntin is a high-energy formulation briefly used in the upper stages of rockets developed by the Soviet Union. Its molecular formula is C₁₀H₁₆ and it is a mixture of 4 stereoisomers.