Hybrid Jet Engine

[Music] so who doesn't want to own a turbojet engine I've wanted one since I was 4 years old and I've looked on eBay and you can look on surplus sources and you can get a jet engine for tens of thousands of dollars military jet engines auxilary power units for commercial jets but these units are huge and unless you've got a lot of skill it's pretty difficult to refurbish them or maintain them and even once you have they're so powerful that there's not a lot you can do with them unless you're planning to build an experimental aircraft or to go off grid in a kind of unusual way and so you can buy one of the RC or modeler turbojet engines there are remarkable pieces of hardware both from a fabrication and a design point of view they're lightweight but they're very expensive the least expensive one you'll find will probably cost $2,000 or so and they can go up to tens of thousands of dollars and in addition because they're so delicate many of them require that you have them refurbished every 25 hours of use and so if you want to have the skills to be able to do that yourself you might think about building your own problem is the precision required in the machining is extremely high because of the very high speeds and stresses involved and the materials you often have to use are rather exotic because of the high temperatures you might decide as an alternative to take say an automotive turbocharger and convert it into a jet engine like we're going to do they've done the hard work and all you really have to do is construct a combustion chamber some oil handling equipment some electronics to be able to monitor and control the engine and although not a dy I type of project for a weekend there's a lot of YouTube videos out there are a lot of forums out there that'll give you instructions and doing that we're going to give you instructions on how to do that but another sort of negative with these engines at least from a flight point of view is that they're built to interface between an exhaust system and a engine block and so often they're very heavily built to take the the stresses involved in sort of a road vehicle and much heavier than they really need to be to just resist the forces and the temperatures of just the turbocharger in addition to that they have kind of unusual plumbing they're feeding an internal combustion engine and so for something that you want compact the Rube Goldberg of the combustion chamber might be something that you want to stay away from so another alternative might be say for example to get a pulse jet engine much lower engineering precision and if you want to buy them less expensive they're lightweight and powerful but because they have a highly supersonic output they tend to be very loud and because almost every one that you're going to be able to find designed or constructed have very limited fuel control systems they tend to burn a lot of fuel for their thrust we're gonna modify this to improve on those things but you might not want to necessarily go to a pulse jet you might want something continuous another alternative would be to get an electric ducted fan these are pretty remarkable pieces of equipment they're relatively inexpensive they're turnkey and you can get from maybe one or two kilograms of thrust up to as much as 20 kilograms of thrust out of these things the problem with them though is they lack the sort of flame and fury of a real jet engine and if you go on YouTube you'll find a number of people who shove tubes on the back of a run-of-the-mill fan squirted some butane or F gas in the back of them and turn them into a blowtorch and I'm not disparaging that because that's done for aesthetic purposes they want a model to look like it's a military jet on after but they produce almost no additional thrust because of the design is not being utilized to do that and so what we're going to do with this bill today is we're going to build a jet engine based on an electric ducted fan with an afterburner now before you click off and discussed understand that in order to get a substantial augmentation of power out of something like this you have to start with an extremely powerful fan and you have to add a lot of heat millions of BTU in addition you have to design it in order to be able to utilize that expansion that occurs in the engine in order to get the maximum thrust you have to size things correctly in order to understand how that works you have to understand a little bit about how a turbojet works and very simply there are three major components to a turbojet for if you have an afterburner and those components are the turbo compressor the combustion chamber the exhaust pipe that has the turbine in it that generates the torque to drive the compressor and if you have one an afterburner now you may believe or have been told that the reason for the combustion chamber is to increase the temperature and the pressure of the gas in order to drive the turbine and in augmented that's not exactly true because water doesn't flow uphill and gases don't flow from a low to a high pressure region what happens in the combustion chamber is the added energy and heat doesn't increase the pressure it increases the volume substantially and so from the exit of the turbo compressor all the way out the end of even an afterburner the pressure continually drops as it must but the volume changes and as the the hot gases from the combustion chamber passed through the turbo turbine the turbine extracts a lot of energy and the gas is cool and shrink in order to keep the engine from melting they divert a fair amount of the turbo compressors output around the combustion chamber and around the exhaust up to keep things cool so it ends up flowing out the end of it engine has a substantial amount of oxygen in it and has cooled substantially in the afterburner additional fuel is added additional heat additional expansion and that allows for additional thrust but in order to not choke the engine what has to happen is you have to increase the cross-sectional area of the engine in order to be able to to get that additional thrust and the way to sort of proportion that or calculate that is you need to increase the exhaust area from an afterburner by the square root of the absolute increase in the temperature that occurs between the compressor and the exhaust and that absolute temperature is from absolute zero so at room temperature which may be say 27 degrees centigrade we're actually at 300 degrees absolute or Kelvin so if we were to quadruple the temperature and raise it 1,200 degrees Kelvin you measure 900 degrees centigrade what we will do is we will quadruple the temperature and therefore we must double the cross-sectional area of the exit from the afterburner and that's why most turbo jets that have afterburners all of them have adjustable nozzles in order to get maximum thrust without afterburner and to open up and not choke the engine and obtain the improve thrust that occurs with the afterburner so what I'm going to demonstrate outside is a built up engine based on this fan and based on a few components that I'll lay out for you and then we're going to demonstrate that engine and show you kind of how it works and show you where we're going from there so come on with me and I'll show you what's gonna happen outside okay so here's the layout of the engine we have the famish OD inside located in front and behind the fan is a cone or steel cone that acts to deflect the air to a small and or gap between inside of the tube and the edge of the cone what that does is it accelerates the air in this part of the engine and creates a much larger pressure gain when the air then stagnates inside of the combustion chamber the cone also serves to protect the engine from the intense infrared radiation that's given off in the combustion chamber and finally the cone produces a rather stagnant area of air behind it where we've got located a weed burner this is a commercial weed burner propane powered weed burner that is self aspirating and what that means is that the propane as it exhausts through the small nozzle will draw in air and produce a stable flame that comes out of the end of the tube it's rated at about 500,000 BTU we've measured it though and it's closer to about 400,000 BTU of output because the flame that comes out of here is about a 40 centimeter a 40 centimeter long jet you wouldn't get very good mixing of the annular flow of air around here and so behind the weed burner is a deflector or flame holder these strips are actually made out of tungsten and the tungsten allows us to run the exhaust temperatures much higher than you can in a typical turbojet because we don't have any sensitive materials inside here in addition we've got the inside of the tube from about that back half from the halfway point backward coated with a ceramic material that reduces the oxidation at very high temperatures that very high temperature gain is what allows us to gain something back for the rather low compression ratios in these fans finally we have in back here what looks like an adjustable nozzle for an afterburner on a jet engine this isn't really adjustable and a real-time basis but what it allows us to do is by sliding these strips in and out we can fine-tune the exhaust diameter as I was talking about earlier to maximize the thrust based on the temperature gain because even though those ratios I gave you before with theoretical depending on the efficiency of your mixing and the flow obstructions that occur inside the engine you might want to tweak those and so once you've established what the diameter is you could certainly elimin this complexity with a simple constricting comb so to run the engine we have three propane tanks here as I said 400,000 BTU that isn't nearly enough so with these additional entrance ports we're going to be putting in about a total of 2 million Btu in order to get the flame temperature up here to around 1,500 degrees centigrade which is just about the melting point of stainless steel and finally a spark plug that's that triggers the initial burn but once the burn occurs here it's very stable no matter what the settings are with the fan we have a very powerful ESC that will produce up to 5,000 watts in the fan here and the entire thing is mounted on a slide that will allow us to sort of compare thrust levels depending on how we're running the engine so you ready let's get started I take 100 jocks and send it to the fan in order to ventilate the tube I then open up the propane to the weed burner and fire the spark plug in order to get a stable flame for it once I've done that I can it doesn't seem to wipe starters until I get to about four you can see very early on trust spring before flame temperature addition of any in order to increase hurry epic and when I get to a claim fam from JP Bobby is the 90 millimeter additional fans preparation and and in future videos as we increase the thrust and increase the compression ratios [Music] walking this was a lot fun and you had a great [Music] [Music] [Music] [Music] [Applause] [Music]

Channel: Tech Ingredients

Views: 314,831

Keywords: Jet, Jet engines, Turbojet, Hybrid jet, Electric ducted fan, Afterburner, Propane, Weed burner, Flame holder, JP Hobby, Ceramic coatings, Tungsten

Id: 3SVBqCBzmpU

Length: 15min 23sec (923 seconds)

Published: Mon May 14 2018

Reddit Comments

[u/Freeblebotham]

If you want to see a pulse jet hooked to a turbo compressor check this out https://www.youtube.com/watch?v=jTsQxwWcqJI (SRL footage) It is hard to get a fan driven jet to be stable. When your back pressure goes up due to increased exhaust output it reduces the incoming air so your fuel mix changes.

[u/T-Bolt]

Skip to 8 minutes if you want to avoid his general explanation.

[u/TechN9nesPetSexMoose]

That was great.