What happens when the injector orifice diameter is increased in an ideal hybrid rocket motor?

When the diameter of the injector orifice in an ideal hybrid rocket motor is increased, the flow of the oxidizer into the combustion chamber is enhanced due to the larger cross-sectional area available for the propellant. This alteration typically leads to an increase in the average thrust produced by the motor during operation. The thrust is a function of the mass flow rate of the oxidizer combined with the resultant exhaust velocity.

However, the total impulse—a measure of the total change in momentum provided by the rocket engine over the duration of burn—is generally related to the overall efficiency of the combustion process and the amount of propellant consumed. In an ideal scenario where the system remains balanced, the total amount of propellant utilized will not necessarily increase just because the injector orifice size is larger; therefore, the total impulse remains unchanged.

This reasoning leads to the conclusion that increasing the injector orifice diameter can result in greater average thrust without altering the total impulse. Thus, while the average thrust rises due to a more efficient oxidizer flow and reaction rates, the total impulse stays constant because the operational parameters of the motor are otherwise maintained.