When a fuel/air mixture burns it expands. How much does it expand? Is there a formula or known volume increase? After a fuel burns it contracts. How much does it contract? Is there a formula or known volume that it contracts? Gasoline/Air mixture ratio is 15 to 1 for jet engines. A fuel is injected into a pulse jet combustion chamber and mixes with the air in the chamber at atmosphereic pressure 14.7 psi. The fuel ignites and burns and the expanding gas goes out the exhaust tail pipe. The burned fuel then produces a vacuum that sucks fresh air in through the intake valves that mixes with more fuel and it ignites and burns. The cycle repeats over and over. The combustion chamber is typically 2 times the diameter of the exhaust pipe. A 2" diameter exhaust pipe will have a 4" diameter combustion chamber. The cross sectional area of the combustion chamber is 3 times larger than the exhaust pipe. Pretty simple so far but now we need to calculate the volume of the combustion chamber???