Nitromethane is a fuel that is used in racing, particularily in drag racing, to provide more power. When you hear the term "nitro-burning funny car" or "top-fuel dragster", that means that the engine burns nitromethane.
Nitromethane's chemical formula is CH3NO2. For comparison, gasoline is typically C8H18. The oxygen in nitromethane's molecular structure means that nitromethane does not need as much atmospheric oxygen to burn -- part of the oxygen needed to burn nitromethane is carried in the fuel itself.
You need 14.6 pounds  of air to burn a pound of gasoline, and only 1.7 pounds of air for the same amount of nitromethane to burn. A cylinder can only hold so much air on each stoke, and with that amount of air you can burn 8.7 times more nitromethane than gasoline. By pumping in 8.7 times as much nitromethane per stroke, you get about 2.4 times more power per stroke. Gasoline provides 18,000 BTU/pound. Nitromethane provides 5,000 BTU/pound.  The amount of nitromethane also provides some cooling, making the charge a bit denser and increasing power.
The flamefront does not move as quickly in nitromethane as it does in gasoline, meaning that there is not enough time to burn all the nitromethane in the cylinder when the engine is running at high RPM. When the exhaust valve opens, burning nitromethane flows out through the exhaust pipe. That is why funny cars and dragsters "spit fire" from their exhaust pipes.