Final answer:
Prior to starting the engine, the fuel selector switch should be set to the appropriate position depending on the type of engine being used. Liquid fuel/oxidant engines require the switch to be set to allow the flow of liquid fuel, while solid fuel engines require the switch to be set to activate the ignition of the solid fuel.
Step-by-step explanation:
Prior to starting the engine, set the fuel selector switch to the appropriate position depending on the type of engine being used. If the engine uses a liquid fuel/oxidant mixture, the fuel selector switch should be set to the position that allows the flow of the liquid fuel. If the engine uses a solid mixture, the fuel selector switch should be set to the position that activates the ignition of the solid fuel.
For example, if the engine has a green flame and has a firing time of 3 s, it indicates that the engine uses a liquid fuel/oxidant mixture. Therefore, the fuel selector switch should be set to the position that allows the flow of the liquid fuel prior to starting the engine.
On the other hand, if the engine has a yellow flame and has a firing time of 4 s, it indicates that the engine uses a solid mixture. The fuel selector switch should be set to the position that activates the ignition of the solid fuel.