Self-Ignition Conditions when Mixing Combustion Products with Air-Fuel Mixture

To date, the possibility of self-ignition of systems obtained due to mixing a cold air-fuel mixture with hot combustion products has been established. The topic of potential generation of such mixtures, however, is understudied. The article attempts to determine the conditions under which self-igniting systems are generated in the case considered. For the studies, a model of an ideal mixing reactor with increasing mass and temperature in the system under condition of constant pressure and mass flow of combustion products inflowing to the system has been applied. The cold air-fuel mixture is initially contained in the system. The mass flow and final mixing temperature are preset. The preset mixing temperature is determined without considering chemical reactions whereas the induction period considers the chemical reactions during mixing. Flaming must not be initiated in the system, otherwise mixing does not occur. This condition complies with the high-intensity turbulence requirement for an energetic cold air-fuel mixture. Less strict requirements are applied to the mixing of highly diluted or non-combustible air-fuel mixtures. The study has adopted the requirement of either the Damkeller number, Da < 1 or the Karlowitz number Ka > 100. As a result of that, requirements for the intensity and scale of turbulence, the velocity and transverse size of the jet, and mixing combustion product are derived. On the other hand, the hot flow parameters are restricted by the condition to ensure the required flow so that the temperature in the system could reach the preset value during a specific period that cannot exceed the induction period by more than 10 times. The latter requirement is the consequence of the adopted scenario of ideal mixing with monotonously increasing temperature in the system. The global quenching condition is met for highly diluted mixtures and even for non-combustible mixtures. These conditions are represented in the plane «elocity — transverse size of the jet» as areas restricted with straight lines that meet the imposed requirements.