Engineering Questions with Answers - Multiple Choice Questions
Rocket Propulsion – Sample Thrust Chamber Design Analysis
1 - Question
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) 12.56 kg/s
c) 16.52 kg/s
d) 15.62 kg/s
Explanation: Propellant flow rate ṁ = F/c, where F is the total thrust and c is the specific fuel consumption. Then ṁ = 50,000/3200 = 15.62 kg/s.
2 - Question
Find the fuel flow rate for a total propellant flow of 10 kg/s and a mixture ratio of 2.3.
a) 4.71 kg/s
b) 7.41 kg/s
c) 1.47 kg/s
d) 4.17 kg/s
Explanation: Fuel flow rate ṁf = ṁ/(r+1), where ṁ is the total propellant mass flow rate and r is the mixture ratio. So ṁf = 10/2.4 = 4.17 kg/s.
3 - Question
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) 11.33 kg/s
b) 15.92 kg/s
c) 12.95 kg/s
d) 13.67 kg/s
Explanation: ṁo = ṁr/(r+1) So ṁo = 17*3.2/4.2 = 12.95 kg/s.
4 - Question
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) 12.10 cm2
c) 11.20 cm2
d) 21.10 cm2
Explanation: Nozzle throat area At = F/P1CF, where P1 is the chamber pressure, CF is the thrust coefficient and F is the total thrust provided by the rocket engine. Then At = 10000/(5.2 x 106 x 1.9) = 10.12 cm2.
5 - Question
If the semi-divergence angle of a conical nozzle is 15°, throat diameter is 8.326 cm and exit area is 0.54 m2, determine the nozzle length.
a) 139.2 cm
b) 239.1 cm
c) 312.9 cm
d) 231.9 cm
Explanation: Nozzle length L = (D2 – D1) / 2tanλ, where D2 is the nozzle exit cross-section diameter, D1 is the nozzle inlet diameter and λ is the semi-divergence angle of the conical nozzle. Exit diameter D2 = √(4*Ae/π), where Ae is the exit area. Then D2 = 82.92 cm So, L = (82.92 – 8.326)/0.536 = 139.2 cm.
6 - Question
The pressure drop across injector is usually set between _________ of the chamber pressure.
a) 45 and 65%
b) 30 and 45%
c) 15 and 25%
d) 5 and 15%
Explanation: 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.
7 - Question
Which of the following is a realistic value of the discharge coefficient?
Explanation: Velocity is maximum for a given pressure drop if the injector discharge coefficient is 1. For rounded and clean injection holes, discharge coefficients can be about 0.80.
8 - Question
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) Ignition by electrically heated wires
d) Precombustion chamber ignition
Explanation: 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.
9 - Question
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 = (1/f)εσAT4
b) E = fεσAT4
c) E = (1/f)εσAT2
d) E = fεσAT2
Explanation: 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.
10 - Question
Which of the following gases show a strong emission band in the region of radiant heat transfer?
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.