1. DIf 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) Isothermal chemical reaction at the reference temperature
b) Isentropic chemical reaction at the reference temperature
c) Adiabatic chemical reaction at the reference temperature
d) Heating of gases with the energy release from the chemical reaction
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
2. Out of the following products of the reaction of hydrogen and oxygen, which of them is unstable?
a) Hydrogen
b) Hydrogen peroxide
c) Hydroxyl
d) Water
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.
3. Energy release efficiency is also called as ___________
a) isentropic efficiency
b) polytropic efficiency
c) propulsive efficiency
d) 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.
4. Combustion efficiency in liquid propellant rocket engines __________ with an increase in combustion temperature.
a) increases
b) decreases
c) doesn’t change
d) oscillates
Explanation: Combustion efficiency increases with increased combustion temperature. It is also depended on the method of injection and mixing.
5. 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
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.
6. Which of the following is not true for an ideal expansion in the nozzle?
a) Adiabatic, reversible expansion
b) Drop in static temperature and pressure
c) Drop in stagnation temperature and pressure
d) Conversion of thermal to kinetic energy
Explanation: Stagnation temperature remains constant for ideal expansion in the nozzle. Ideal expansion is isentropic and involves conversion of thermal to kinetic energy
7. Which of the following effects are neglected for simple cases of nozzle expansion?
a) Heat exchange
b) Frictional effects
c) Divergence angle
d) 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
8. Assertion: The condensed phases (liquid and solid) are assumed to have zero volume.
Reason: Particles or droplets are very small in size.
a) The assertion is correct, but the reason is incorrect
b) Both assertion and reason are incorrect
c) Both are correct and the reason is the correct explanation for the assertion
d) Both are correct but the reason is not the correct explanation for the assertion
Explanation: 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.
9. What is the typical value of penalty incurred by assuming a frozen equilibrium rocket performance?
a) 1-4%
b) 0%
c) 12-15%
d) 25-30%
Explanation: 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%.
10. 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) Frozen equilibrium
b) Non-equilibrium
c) Shifting equilibrium
d) Isothermal equilibrium
Explanation: 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