58751 - Provision of Rotating Spindle in Simplex Atomizer to Improve Spray Atomization. 

Fuel atomizer plays a crucial role in the atomization (disintegration) of bulk liquid fuel into a fine spray. The main purpose of any fuel atomizer is to increase the overall surface area to volume ratio of liquid droplets to facilitate quick air-fuel mixing and droplet evaporation in the combustor. Another objective is to disperse the droplets uniformly across the combustor to avoid the formation of local hot spots. Different kinds of atomizers are used in combustors to fulfil these objectives. Simplex atomizer is a pressure based atomizer which is widely used in liquid fuel rocket engines and gas turbine combustors due to its simplicity of construction, ease of manufacture and reliability over other atomizers.

In simplex atomizer, a swirl-flow of the liquid is induced by feeding the liquid into a swirl chamber through one or several tangential ports. The centrifugal motion of liquid within the swirl chamber creates a low-pressure area near the nozzle exit and forms an air core along the centerline. The liquid then extends into the discharge orifice and emanates as a hollow conical swirling film, which further becomes unstable and breaks up into several droplets. The presence of air core is important as it controls the liquid sheet thickness and thus governs the atomization quality. However, the formation of an air core takes place only at high liquid injection pressure in the conventional simplex atomizer, making the atomization quality poor at lower injection pressure.

The important spray characteristics such as spray cone angle, breakup length and Sauter Mean Diameter (SMD) are strongly affected by the geometry of an atomizer. In the present study, an insert in the form of a pointed needle is suspended in the swirl chamber of an atomizer to take advantage of the perks of an air core without the actual formation of the air core, which is mostly achieved at high liquid injection pressure. The performance of atomizers having stationary and rotating insets are investigated and compared with the performance of conventionally used simplex atomizer. Further important spray parameters such as spray cone angle and breakup length of a liquid sheet are measured experimentally, in the immediate vicinity of the injector exit using the shadowgraph technique. Phase Doppler interferometry (PDI) is also incorporated to measure the drop sizes at different axial and radial locations in the domain comprising the spray. The atomization characteristics of a spray generated by the modified atomizer are found to be superior over the conventional atomizer, especially at low injection pressures. At last, the internal liquid flow of different atomizers is also simulated to understand the effect of presence of inserts on the internal flow and subsequently on the spray characteristics.