RC compressor jet engine

[sajets]

I am busy designing a jet without the turbo, by using a RC engine, spinning up to around 22 000 rpm, this fan will suck air into the engine, using a cone system to compress
the air and feed into the combustion chamber, the air flow is totally utilised for thrust, losing zero energy to driving a turbine and compressor. The only draw back is the max RPM i can achive on the induction system.  Any thoughts out there? i was thinking of a diesel / gasolene mixture fuel with a diesel injector?
The starter can be a sparkler or a fire clicker starter inserted up the exhaust, no need for spark plugs etc

                                                                           

[enginewhisperer]

you won't get much pressure with a normal propeller, but you could adapt a centrifugal compressor to an R/C engine, which should give you a better result.

It's still very limited compared to a turbine engine, but would be an interesting experiment

[racket]

Hi

An afterburning ducted fan ,motorjet, thermojet............... yep , its been done , you won't get a great increase in thrust over the the standard ducted fan as the pressure ratio will be very low, and theres no way to increase that without a drastic reduction in mass flow, your horsepower levels are too low .

Lotsa stuff about them on Google and Youtube .

One thing to be very careful about and thats thermal choking of the duct , you can only raise the temperature a certain amount before the "acceleration forces" moving the gases down the duct put unacceptable backpressure on the fan and it'll go into surge .

Looking at your diagram , it won't work in that configuration , the nozzling of the fan outlet is unacceptable, the fan will surge .

The simplest you can do is have a parallel duct downstream from your fan with limited fuel burn until the duct chokes .

A divergent duct downstream of the fan with a maximum 15 degree included angle of divergence will act as a diffuser , slowing the flow but increasing its static pressure , the slower air will make combustion easier and the larger diameter duct will allow more fuel to be burnt before duct choking occurs .

The nozzling of the Nye Thermojet outlet www.gas-turbines.com/thermojet/index.html , caused all sorts of problems , there simply isn't enough pressure energy within a thermojet to allow nozzling , nozzling converts pressure into velocity , without that pressure the "backpressure" simply increases with increases in fuel burn until the "fan" stops supplying air .

Cheers
John

[gidge348]

I think the Italians played around with this concept in WW2 with the Campini Caproni CC-2.

www.ams.vr.it/PIER/AircWalkAround/Museo%20Vignadivalle/Campini%20Caproni/Campini%20Caproni%20pag%2001.htm

[racket]

The idea does appeal , but the specific fuel burn rate for the thrust increase is horrendous when the pressures are so low , something like 0.1 psi or a PR of 1.007 across the jet "nozzle"

A 180 mp leafblower is only producing ~0.5 psi of "pressure" , a 1.034 PR across its nozzle

Cheers
John