Study On Laminar Combustion Characterisitic And Flame Stability Of Hydrogen Blenged Low Calorific Value Gases

With the increasing prominence of energy and environment problems recently, the low calorific value (LCV) gas fuel used as the alternative fuel has become the research focus around the world because of its cleanliness and abundance. The gas engine fueled with the LCV gas is easy to misfire and unstable combustion, which caused the cyclic variations. Researchers found that the flame formation near the spark plug and intrinsic instability are very important factors causing the instable combustion in engine. To dive in to the reason of instable combustion in engine, the experimental and direct numerical simulation (DNS) research of hydrogen blended LCV gas flame were carried out in this dissertation, which focused on the formation and evolution of cellular flame affected by hydrodynamic instability and thermal diffusion instability. This research revealed the mechanism of the formation regime and splitting regime of cellular flame and the internal connecting link between the key factors and flame instability. Theoretical basis of the development of the clean and efficient engine combustion system can be provided by the results.The linear instability of gas fuel flame was studied in this dissertation. The governing equation coupled two step reaction considered activity energy, density ratio and Lewis number is established. The dispersion equation is solved numerically by using shooting method and fourth order Runge-Kutta method. The change of critical wave number and neural wave number with the change of different initial factors was obtained. The modified expression of dispersion relation was proposed.The DNS research of hydrogen blended LCV gas flame was carried out in this dissertation. The non-dimensional governing equations of gas fuel combustion including the multiple species diffusion factors were established. The derivation of non-reflecting boundary condition applicable to planar low calorific gas premixed flame was derivated. The governing equation was solved by DNS methods coupled detail chemical mechanism, and the rule of evolution of hydrogen blended LCV gas flame was obtained.The evolution of instable flame was studied, and regimes of cellular flame-cellular flame splitting, local extinction, lateral movement and so on were obtained; the factors affecting the flame instability were analyzed and the mechanism for cellular flame evolution was revealed; the correlation between flame speed and curvature was obtained; and the pattern of cellular flame after long time evolution in spectrum space was revealed.The laminar combustion characteristic and flame stability of hydrogen blended LCV gas were conducted in the constant volume combustion bomb. The variation trend of laminar combustion velocity under different conditions was analyzed; the schliren photos showing different instability and the characteristic of cellular flame were obtained by the analysis of characteristic parameters and phenomenology; and the self-acceleration power and the critical radius of cellular were obtained by quantitative research on self-acceleration.