An inflator bottle adapted for controlled release of product gas to deploy an inflatable cushion and a method thereof is provided. The inflator bottle comprises a compartment filled with a combustible gas mixture having a partition that divides the compartment into a first region and a second region. Upon a crash event, an igniter on the inflator bottle ignites initiating combustion in the first region. Combustion propagates in the first region toward a nozzle building pressure in the first region sufficient to rupture a burst disk over the passage of the nozzle releasing product gas through the nozzle. The release of product gas through the nozzle draws combustible gas mixture from the second region flowing through the gas portal on the partition into the first region for combustion. The area of the gas portal between the regions is sized in relation to the size of the minimum area of the passage of the nozzle to supply the combustible gas mixture to the first region at a rate that maintains the flame front while preventing it from propagating out into the second region or out the nozzle until the remaining combustible gas mixture in the compartment is consumed.