Study On The Fuel Distribution Downstream Of An Integrated Design Flameholder In A Multi-mode Combustor

As one of the main components of a Turbine Based Combined Cycle(TBCC)engine,dual-mode combustor should meet the requirements of working in high-speed and lean oxygen conditions,so it is necessary to fully understand the fuel atomization,evaporation and mixing characteristics downstream of the flameholder,thus to estimate and control the fuel distribution in the combustor.This paper mainly researches the fuel distribution characteristics downstream of an integrated design flameholder under wide-range operating conditions with numerical simulation and experimental methods.The main conclusions are as follow:From the simulation results of the flow and fuel distribution downstream of the single-radial flameholder and the flow field of the outer wall flameholder under different inflow conditions we can safely conclude that,for the outer wall flameholder,the reflux area and amounts increase with the inclination angle,and the total pressure loss and unevenness of velocity distribution of exit section increase with the radial height.After considering the influence of structural parameters on ignition performance and resistance loss,the outer wall flameholder is designed with 40 mm radial height and 60° inclination angle.For the single-radial flameholder,the reflux zone axial and circumferential distances and the reflux flow increase with the slot width.When the solt width is fixed,the 30° cone angle has the smallest total preassure for its profile being more streamlined,while the different apex angles have no significant effects on the flow field in the combustor.Take all the factors of the structural parameters on flame stability and resistance loss,the single-radial flameholder is designed with 90° apex angle,30 mm slot width and 30° cone angle.The results of fuel field show that when the fuel spray is injected from the flameholder side,and the injection position is in the middle of the straight section,it is more conducive to the flame stability and propagation.The integrated design flameholder numerical simulation results show that the inlet flow conditions(velocity,temperature and pressure)have little effects on the flow field structure in the combustor.Low inlet temperature and high velocity and pressure,give the rise of the total pressure loss.While the fuel distribution characteristics are mainly affected by inlet flow conditions and fuel supply conditions(fuel pressure,fuel temperature).The momentum ratio of the fuel jet to the mainflow,inlet temperature and fuel temperature are the key factors affecting the dynamic atomization and evaporation procedure.The high inlet temperature and fuel temperature give the rise of the fuel evaporation rate and shorter distance is needed for fuel distribution;while the high inlet pressure and velocity cause low penetration depth,and longer distance is needed achieve fuel distribution.With the increase of inlet velocity,the penetration depth of fuel decreases,and the circumferential distribution of fuel is uneven.Increasing inlet temperature reduces the surface tension and viscosity of fuel droplets,promotes fuel droplets to break up and evaporate,thus leads to more uneven fuel distribute in the circumferential direction.The increase of fuel equivalence ratio increases the injection speed and the penetration depth of fuel jet which is benefit to the uniform circumferential fuel distribution.Although the increase of inlet pressure and fuel temperature is benefit to fuel atomization and evaporation,it has no obvious effect on fuel distribution.Experimental methods to test the distribution of gas phase and liquid fuels downstream of the integrated flameholder are designed respectively.And the fuel spray distribution characteristics of the integrated flameholder under different inlet conditions(V=50~125m/s,T=450~750K,?=0.3~0.5)were tested.The experimental results show that the total equivalence ratio is conserved while the liquid equivalence ratio decreases and the gas equivalence ratio increases gradually along the axis length.The sum of the equivalent ratios of the gas phase and liquid phase on both sides of the stabilizer is relatively high,and the sum equivalence ratios become uniform in the circumferential direction as the axial distance increases.When the fuel temperature increases to 473 K,the gas phase uniformity is achieved within 90 mm downstream of the flamefolder,which is 30 mm shorter than the fuel temperature of 373 K.The results of liquid phase experiments show that the droplets distribution is normally distributed at 373 K,the amount of drops size in the range of 25-40?m is the largest,and the amount of drops size of 60-90 mm has the fastest decline rate along the axial length.When the fuel temperature is 473 K,the amount of the drops in the range of <25?m is the largest.A SMD empirical formula for different sections downstream of the flameholder is proposed,and the error band is in the range of ±10% comparing with the experimental results.