compare three rocket engines having specific impulse values

compare three rocket engines having specific impulse values of 355 s, 300, and 280 s Each of these engines produce a thrust of 500 KN . Caluclate propllant mass flow rate for each engines.Based on this data, expline the importance of high valuse of spicfic impulse.

Solution

Comparison of E1, E2 and E3 : ( E refers to engine )

The higher the specific impulse, the less propellant is needed to produce a given thrust during a given time. In this regard a propellant is more efficient the greater its specific impulse. So, E1 (355 s) consumes the least propellant as compared to others.

Notations :

Specific Impulse Value, I_sp

Thrust, F

Acceleration due to gravity on earth\'s surface, g

Mass flow rate, m

F = m * g * I_sp

ENGINE 1 - E1 :

500 * 1000 = m * 9.81 * 355

So, m = 143.573 kg/s

ENGINE 2 - E2 :

500 * 1000 = m * 9.81 * 300

So, m = 169.895 kg/s

ENGINE 3 - E3 :

500 * 1000 = m * 9.81 * 280

So, m = 182.023 kg/s

Importance of specific impulse :

A propulsion system with a higher specific impulse uses the mass of the propellant more efficiently in creating forward thrust, and in the case of a rocket, less propellant is needed. In rockets, the engine is more efficient at gaining altitude, distance, and velocity. This is because if an engine burns the propellant faster, the rocket has less mass for a longer period of time, which makes better use of the total force times time that was acquired from the propellant.

Hence, Engine 1 isthe most efficient of the three.