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The demand for alternative fuels has increased significantly during the previous decades in order to reduce pollutants and increase the amount of energy that can be generated from non-fossil fuels. However, the use of new fuels faces many issues especially the problem of stability of operation which sometimes can cause severe damages to the system hardware. Thus the development of flexible combustion systems for gas turbines becomes urgent in order to achieve high reliability with these new sources of energy.\ud Swirl stabilized combustion is the most widely spread deployed technology used to stabilize and control combustion in gas turbines and numerous other systems. However, the interaction of the swirling flows with the burner geometries is very complex and it has been proved that any change in the burner geometry can affect the flow field inside the combustion chamber, close to the burner mouth and downstream the combustion zone. Most burners are generally provided with a diffusive injector that centrally delivers well-known fuels allowing the stabilization of the system previous to entirely premixed conditions. Moreover, the injector anchors the central recirculation zone formed downstream of the nozzle. However, the use of injectors can also affect the stability limits of the system, especially the propagation of flashback through changes of shape of the shear layer since other structures such as the Combustion Induced Vortex Breakdown are suppressed due to the presence of this central body. However, the characterization of the flow and its impacts on the propagation of these and other flashback structures using different injectors has been briefly documented.\ud Thus, this paper presents a series of experiments using a well-characterized tangential swirl burner to determine the impact of different central injector geometries on the flow field characteristics which directly affect the flow stagnation point downstream of the burner mouth and consequently the propagation of the Combustion Induced Vortex Breakdown. Results show how the use of various injectors and swirl numbers can impact on the flashback limits with a minimum outside diameter before which the Combustion Induced Vortex Breakdown is altered.

Many accidents involve two-phase releases of hazardous chemicals into the atmosphere. Rainout results in reduced concentrations in the remaining cloud, but can also lead to extended cloud duration because of re-evaporation of the rained-out liquid. For accurate hazard assessment one must accurately predict both the amount of rainout and re-evaporation of the pool. This presentation provides an overview of the results of a third phase of a Joint Industry Project (JIP) on liquid jets and two-phase droplet dispersion. The aim of the project is to increase the understanding of the behaviour of sub-cooled (non-flashing) or superheated (flashing) liquid jets, and to improve the prediction of droplet atomisation, droplet dispersion and rainout. Phase II of the JIP was limited to scaled experiments for water with initial droplet-size data measured at a single value of the superheat only. Furthermore the modelling simplistically assumed one single averaged droplet size (Sauter Mean Diameter, SMD) with rainout at a single point only. As a result Phase III was started to account for these issues. It was sponsored by DNV Software, Gaz de France, RIVM (Dutch Government), TOTAL, Norske Hydro and Statoil (currently merged into StatoilHydro). The tri-linear modelling approach proposed in Phase II is endorsed in Phase III via additional scaled water experiments at Cardiff University including measurements of flow rate and initial droplet size across the full relevant range of superheats. Phase III also included scaled experiments for cyclohexane, butane, propane and gasoline at the gas turbine research centre (Cardiff University), to ensure that the derived droplet size correlations are also valid for other chemicals than water. Furthermore large-scale butane experiments were carried out by INERIS (France) to ensure that for more realistic scenarios the derived droplet size correlations are accurate. Model validation and model improvements were carried out by DNV Software, including validation of release rate and initial droplet size against the above scaled and large-scale experiments. New refined correlations for droplet size correlation and SMD were formulated and implemented into the Phast discharge model. It was compared against a range of other droplet size and rainout correlations published in the literature, in conjunction with validation against an extensive set of experiments. It was shown that the new droplet size correlation agrees much better against experimental data than the existing Phast correlation. To further improve the rainout prediction, the Phast dispersion model (UDM) was also extended to allow simultaneous modelling of a range of droplet sizes and distributed rainout (rather than rainout at one point). It also included further improvements to pool and dispersion modelling after rainout, and validation for dispersion from LNG and LPG pools