Compressing of air generates heat. We can feel it at the bicycle pump but the air in the bottle also becomes warmer. When we launch the rocket - or release the air through the abort valve - it will cools down fast. It just works like a fridge: the pump is the compressor, the rocket is the condenser and the valve the evaporator. Because the coolant is air it will also cool down in the condenser because of the expansion of the gas and we stopped the compressor. I have a thermal camera so I used it to see the temperature changes. I pressurised to 8 bar, let the bottle cool down to ambient temperature and pulled the 'abort' string to release the air fast without the bottle leaving the launch-pad.
