Designing a motorjet in CAD

 In the realm of engineering, particularly in aerospace and energy sectors, the design of combustion systems holds paramount importance. Annular combustors, a crucial component of gas turbine engines, play a vital role in efficiently converting fuel into energy. Designing these complex structures requires meticulous attention to detail and sophisticated modeling techniques.

Understanding Annular Combustors: Before diving into the design process, it's essential to grasp the fundamentals of annular combustors. These combustion chambers feature a ring-like shape, encasing the turbine section of a gas turbine engine. They are responsible for mixing fuel with air and igniting the mixture to generate high-temperature gases that drive the turbine blades. The design of annular combustors must ensure efficient combustion, minimal emissions, and structural integrity under extreme operating conditions.

Designing:

First, a ring with an inner and outer diameter must be modelled. The inner ring will house the first fuel diffuser, while the outer ring will hold the outer casing. Between the two housings will be a fuel rail with holes drilled into it to disperse fuel.

Now the fuel rail is modelled to wrap around the inner diffuser. It has small holes which evenly mix fuel and air together without creating spots of high concentration which could lead to flameouts or instability.



Next, the inner diffuser is modelled. The diffuser has many small holes drilled into it to allow air to easily pull fuel into the combustion stream. A motor jet does not need to have high compression, so the size of these holes are arbitrary for now.





To finish off the annular combustor, the outer diffuser can be modelled, to have slightly larger holes than its inner counterpart. This creates a low pressure zone in front of the fuel line which reduces pressure in the components and helps liquid fuel atomise.

In its current state, there is no thrust generated by this design. This is because no pressure is generated in front of the combustor - at best, this is an efficient propane/gasoline burner. A casing and nozzle must be added to achieve any measurable thrust.


This shows the final design of the basic motor jet, with a nozzle to accelerate the pressurised hot gases to achieve thrust. Air is supplied through the back with a volute casing air compressor. In the future, I aim to convert this motor jet to a turbojet by creating self sustaining combustion. Until my GCSE's are over however, I will focus on the combustion characteristics of engines before the burden of designing bearings and rotors must be addressed.




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