# Rocket Propulsion Questions and Answers – Liquid Propellant Rocket Engine – Flow and Pressure Balance

This set of Rocket Propulsion MCQs focuses on “Liquid Propellant Rocket Engine – Flow and Pressure Balance”.

1. The oxidiser flow (mo) through the gas generator is ____________ if its flow rate through the pump is 10 kg/s and through the thrust chamber is 5 kg/s.
a) 5 kg/s
b) 15 kg/s
c) 20 kg/s
d) 25 kg/s

Explanation: mo = (mo)gg + (mo)c
So, (mo)gg = 10 – 5 = 5 kg/s.

2. The fuel flow (mf) through the gas generator is ____________ if its flow rate through the pump is 18 kg/s and through the thrust chamber is 10 kg/s.
a) 18 kg/s
b) 10 kg/s
c) 8 kg/s
d) 28 kg/s

Explanation: mf = (mf)gg + (mf)c
So, (mf)gg = 18 – 10 = 8 kg/s.

3. What is the total mass flow rate through the gas generator if the oxidizer flow through it is 15 kg/s and fuel flow is 18 kg/s?
a) 3 kg/s
b) 48 kg/s
c) 53 kg/s
d) 33 kg/s

Explanation: Total mass flow rate through the gas generator mgg = (mgg)o + (mgg)f
mgg = 15 + 18 = 33 kg/s.

4. In a turbopump, what are are the gear ratios for ao and af (for oxidizer pump and fuel pump respectively) if no gears are used?
a) 0 for both
b) 1 for both
c) 0 for ao and 1 for af
d) 0 for af and 1 for ao

Explanation: If no gears are used, ao = af = 1. For shaft speed N, aoNo = afNf, where the subscript o and f denote oxidizer and fuel respectively.

5. If the gear ratio for fuel pump is thrice that of the oxidizer pump, the shaft speed of fuel pump is ____________ the oxidizer pump.
a) half
b) twice
c) thrice
d) one-third

Explanation: One-third because it follows from the relation, aoNo = afNf.
Given, af=3 x ao.
Using this, Nf = 1/3 x No.
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6. If power of turbines equals PT, power consumed by pumps is PP and the power consumed by auxiliaries is PA, what is the expression for auxiliary power?
a) PA = PP – PT
b) PA = PP + PT
c) PA = PT – PP
d) PA = PT x PP

Explanation: Turbine power produced is consumed by pumps as well as the auxiliaries. This is called as the power balance for turbopumps.

7. The power is expressed as the product of torque and ____________
a) vehicle speed
b) shaft speed
c) exhaust velocity
d) volume flow rate per unit cross-sectional area

Explanation: Torque L x Shaft speed N is a form of representation of the power P. Part of the power produced goes to waste by bearing, seal, transmission, and friction losses.

8. Which of the following expressions is true when there are no gears in a particular turbopump?
a) NT = No ≠ Nf
b) NT ≠ No = Nf
c) NT ≠ No ≠ Nf
d) NT = No = Nf

Explanation: If there are no gears in a particular turbopump, then all the shaft speeds are same. So NT = No = Nf is the correct expression.

9. If L represents torque, and the subscripts T, o, f, b denotes the turbopump, oxidizer pump, fuel pump and bearings respectively, then which of the following expressions is true when there are no gears in a particular turbopump?
a) LT = Lo + Lf + Lb
b) LT = Lo x Lf x Lb
c) LT = Lo = Lf = Lb
d) LT = Lo = Lf ≠ Lb

Explanation: The torque of the turbopump will then be the sum of all the other torques. This is evident from the expression, PT = LTNT = LoNo + LfNf + Pb. When there are no gears, all the N terms will be equal and the expression simplifies to LT = Lo + Lf + Lb.

10. If the pressure rise ΔP across a pump is half the discharge pressure, then which of the following relates the suction pressure Ps to discharge pressure pd?
a) Ps = pd
b) Ps = 2 x Pd
c) 2 x Ps = Pd
d) Ps = 4 x Pd

Explanation: pd = Ps +ΔP.
Since ΔP = 1/2 Pd, Pd = 2Ps.

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