English: Working mechanism of a valveless pulsejet engine. The basic idea is that the column of air in the long exhaust pipe functions like the piston of a reciprocating engine. From another point of view, the engine is an acoustic resonator internally excited by resonating combustions in the chamber. The chamber acts as a pressure antinode which is compressed by the returning wave. The intake pipe acts as a kinematic antinode which sucks and exhausts gas. Note the longer length of the exhaust pipe—this is important as it prevents oxygen from entering the wrong way and igniting the system the wrong way. It does this because when the pulse ignites, there is still some exhaust gas in the exhaust pipe. That is sucked in before any additional oxygen is sucked in. Of course, the air intake pipe has already supplied the oxygen by that point and the pulse reignites.