Влияние начальных условий на скорость фронта ламинарного пламени в газовых смесях

The scatter in laminar flame front speed caused by both an error in the composition of the combustible mixture and initial disturbances is reported. It's shown how the configuration of the initially planar front in laminar flame initial disturbances in a gas mixture of the same composition affects the scatter of speeds of expanding spherical flames. The experimental results previously obtained by the authors, demonstrating the scatter in the speed of the laminar flame front in an initially quiescent gas mixture of constant composition under the same conditions, are explained by integrating the Sivashinsky equation with various initial disturbances. The influence of combustible mixture composition errors on the parameters determining the speed of the flame front is analyzed. These parameters were recalculated for a possible scatter in the mixture composition, obtained based on data on the accuracy of the equipment used in previously published experiments.

Experimental Study on the Influence of Pressure and Temperature on the Burning Velocity and Markstein Number of Jet A-1 Kerosene

For accurate prediction of the laminar flame front propagation the influence of the stretch effect on the burning velocity has to be considered. Thus, only burning velocity and Markstein number together give complete information about the laminar flame front behavior. The Markstein number quantifies the influence of the stretch effect on the burning velocity and accordingly, indicates the flame front stability. Due to the analogy between the laminar and the turbulent flames these two parameters, laminar burning velocity and Markstein number must be also considered as essential for describing the turbulent flame front stability [1]. Nevertheless, the experimental data of commercial liquid fuels regarding these parameters are scarce, especially at elevated pressure. Combustion characteristics (laminar burning velocity and Markstein number) of Kerosene Jet A-1 are investigated experimentally in an explosion bomb vessel. For this purpose an optical laser method is employed based on the Mie-scattering of the laser light by smoke particles. Unlike analogous experiments conducted with gaseous fuels [1], the major challenge connected with the present experiments arises from the liquid state of the investigated fuel at ambient condition. Thus, a main difficulty in the present experiments is pre-evaporation of the fuel and achieving of homogeneous gaseous fuel/air mixture prior to ignition. This is solved by mounting a heating system into the walls of the bomb vessel that provides a homogeneous temperature distribution in the vessel and therewith of the mixture itself. The experimental investigation is practically done through the following steps: heating the vessel up to the requested temperature; filling the vessel with an appropriate mixture by the partial pressure method (providing a fuel in gaseous state through the liquid fuel injection and its instantaneous evaporation due to the elevated temperature); attaining an uniform mixture by means of fans; ignition and acquisition of the data; post-processing and data analyses. Within the experimental study influence on the burning velocity and Markstein number of three crucial parameters — initial temperature, initial pressure and mixture composition — are investigated. Observed results for the burning velocity and Markstein number follow the theoretically expected tendencies resulting from the variation of the initial parameters in almost all cases. Where that was not the case the reasons for discrepancies are discussed. Impact of the results on emissions influenced by different operating modes of jet turbines is considered. Due to the common substitution of the kerosene with n-decane in numerical simulations their burning velocities are compared.