Ceci,
The Orbital system is pretty neat, one perceived shortcoming being the need for an air compressor, typically around 1/25th of the engine capacity. However, one of the benefits is the very fine atomization of the fuel. This very good atomization allows the use of heavier, thick fuels that can’t be satisfactorily atomized with a single fluid injector, particularly with spark ignition.
Obviously the Ficht single fluid system originally used by the defunct OMC, which I think has evolved into the Etec has got some good qualities as well.
As a result of the fine atomization, Orbital supplies small engines (certainly around 50 cc and maybe more) for use in US drones. The success of these is driven by the US military requirement to use a single fuel type (I think it is Jet Fuel A) for all forms of transport for logistical reasons. See Orbital's website and various associated articles:
https://orbitaluav.com/
https://en.wikipedia.org/wiki/Orbital_Corporation
https://www.australiandefence.com.au...with-big-plans
Happy reading. I would presume the driveline smoothness and light weight give it an advantage over 4 strokes. I believe some of their flights might be in the order of 16 hours, something that is not yet achievable with electric motors. The engines are far from cheap, the drones returning to base for successive use.
"Success is the ability to go from one failure to another with no loss of enthusiasm.”
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