Question

why do you think we need to put energy into the cylinder system to get the fuels (like gasoline or diesel) to react with oxygen?

Explanation:

Fuels like gasoline or diesel reacting with oxygen (combustion) has an activation energy. The energy input (e.g., from a spark in an engine) provides the activation energy needed to start the reaction, as reactions require a minimum energy to overcome the energy barrier between reactants and products.

Answer:

We need to put energy into the cylinder system to provide the activation energy required for the fuel (gasoline/diesel) - oxygen reaction to start, as chemical reactions (like combustion) have an energy barrier (activation energy) that must be overcome for reactants to transform into products.