[renault_megane_dci]

The principle of any internal combustion engine is to heat air for it to expand and push down the piston.
For the air to heat up you put an amount of fuel wich held a fixed amount of burning power. The hotter the air you want to heat up, the least burning power you need.
Of course you need the oxygen so air needs to be dense so not too hot.

Writing it simpler : hotter air improves the thermodynamic efficiency of the engine to a point (after that you are out of range of the fuel pump metering ability then in engine failure land)

You need your inlet air to be in the 20°C to 40°C at the air filter mouth after that it is out of the tuning range setup by the car maker.

This is much less a failure issue on a diesel engine, gasoline engine are to be tuned with caution in this department.