Customized Software and Hardware applied to Assesment of Outwardly Spherical Flames Using the Pressure Trace: a Thermodynamic Approach to Improve Accuracy of Laminar Flame Speed Measurements
Outwardly propagating spherical flames are well suitable for measurements of Laminar Flame Speed which is a very important thermochemical property of flammable mixtures. There are several facilities, approaches and methods applied to measure Laminar Flame Speed. Due this variety of measurements, consistency and accuracy of the results are mandatory for useful comparisons. Confined premixed flames were assessed using a customized spherical stainless steel vessel, equiped with a Schlieren setup and a dynamic pressure transducer, allowing the comparison between the syncronized results obtained using both approaches. The thermodynamic method presented in this paper uses experimental pressure traces as input to a FORTRAN code that calculates temporal profiles of flame radius, flame surface area, laminar flame speed and some additional quantities. The proposed algorithm processes the raw pressure trace, controls flow of data to an external code to calculate chemical equilibrium and thermodynamic properties and calculates the rate of reactants burned by the flame propagation. The strategy allows to obtain the laminar flame speed without the need to model heat transfer from the flame, diminishing uncertainties in the calculations. The calculations of the proposed FORTRAN code enables to obtain the Laminar Flame Speed at initial datum and the flame behavior for higher pressures and temperatures, maximizing the results for each experiment. Measurements were carried out for air mixtures with methane, iso-octane, n-heptane, Jet A and Jet A-1. The laminar flame speed is the highest for the Jet fuels at Ti = 408 K and lowest for iso-octane at Ti = 300 K, about 50% higher for stoichiometric mixtures. The faster flames for Jet fuels presented the highest exergy destruction, about 30%. The joint analyses of the results of flame radius, Laminar Flame Speed, the exergetic assessment of the flame propagation and the calculated equilibrium composition of the burned gases showed the consistency and good accuracy of the thermodynamic approach here presented.
Premixed flame propagation; Exergy; Jet fuels; Gasoline PRF fuels; Combustion.