Research On The Gas Generating Method Based On The Direct Combustion Of Air And Kerosene

Gas generating method is investigated by simulation, experiment, and analysis intheory, which include atomization, ignition, flame stabilization and flame blow off. Thepurpose of the investigation is to generate hot gas by directly combustion of air,kerosene and water. Air/Kerosene/Water gas generator is developed to produce stableand high efficiency combustion. This thesis aims at broaden the understanding ofcombustion process and provide some guidance on gas generator design.Firstly, an air assist atomizer is developed by combine an air swirler and a pressureswirl atomizer. Simulations and experiments were conducted to analyze dischargecoefficient, the spray angle and the Sauter Mean Diameter (SMD). Interface trackingmethod Volume of Fluid (VOF) was used to simulate the flow field inside the injectorand the filling process. The influence of gas liquid ratio (GLR) on air blast atomizer andair assist atomizer are compared. The dimension distribution curve of the spray containstwo apexes. Near the film are big droplets, which produced by the primary atomizationof the film. In the center of the spray are small droplets yield by second atomization ofthe big droplets. The total pressure loss mainly produced by the inlet of the fuel swirl,converge segment and the duct before the exit, in which the duct has a bigger totalpressure loss. The spray angle is decreased and pressure loss is enlarged by increasingthe length of the duct. The impact of GLR on the flow field inside the atomizer can beignored in air blast and air assist atomizer. For air blast atomizer, the secondatomization of the fuel is strengthened by increasing the GLR, and the droplets arecloser to the central axis with a smaller SMD. As the air slot close to the film, the SMDdecreases while the mean axial velocity increases. With a small GLR the swirling airenlarged the spray angle of the pressure swirl injector, but the spray area is confined in asmaller space when the GLR is big enough.Secondly, the configuration of bluff-body flame stabilizer on the combustion flowfield is analyzed, and a flame holder that combines gas flame stabilization andbluff-body flame stabilization is provided. Simulation on air swirl flame holder andexperiment on the blow-off of bluff body stabilized partial premixed air/kerosene flameare conducted. The flame holder with a sharp edge has a better flame stability, becausethe boundary is easier to separate. The hybrid flame holder can improve the combustionefficiency of the gas generator and stabilize the flame better. Air injection to the chamber wall from the bluff body can cool the chamber and flame holder, whichincreased the duration of the gas generator. Swirling air can also stabilize flame and geta uniform hot gas, and it also increased the combustion efficiency. Bluffbody stabilizedpartial premixed flames in gas generator is greatly influenced by the atomization andvaporization of fuel. The vibration of atomization increases the collision probability ofdroplet and flame front, which cool the flame and slow down the propagation of theflame. Local extinction happens when flame strain rate exceeds the extinction strain rate,and form holes on the flame front. Fresh reactants entrain into the recirculation zonethrough these holes and react to form new flame kernel which reignite the flame in theshear layer if it has enough energy. Namely “extinction reignition” happens. Thefrequency of “extinction reignition” of rich partial premixed flames is about30Hz,bigger than that of lean premixed flames. The increase of fuel pressure drop improvesthe atomization, vaporization of kerosene and its mix with air. Despite the localextinction, the global flame can persist without blow off. The flame is metastable,which has a frequency of20Hz. With the increase of flame holder temperature, theamplitude of pressure oscillation decreases and the flame is more stable. Localextinction of rich partial premixed flames is mainly influenced by droplets in reactants.Finally, a single injector gas generator using swirling air as flame holder ismanufactured, and experiments were conducted to investigate the ignition andcombustion characteristics. The results show that this gas generator can stable workingand have high combustion efficiency. Gas generator ignition is mainly limited by theignition energy, and torch is a good choice. In order to ignite the gas generatorsuccessfully a good flame holder is needed. The swirling air flame holder can greatlyimprove the flame stabilization and combustion efficiency.