Catching Fire - Refining the Jet

[Music] [Music] [Music] [Music] [Music] hi couple of months ago we began our series on the conversion of turbochargers into turbojet engines and if you're interested in that topic you might want to take a look at those videos because they go into a considerable amount of detail on the principles the terminology the design the assembly the operation of one of these conversions and today I'm just going to touch on some of the high points the major caveat is that these engines are not well-suited to produce raw thrust and I know people have done it Colin fuse has done it Morris has done it a number of other individuals have done it so it can be done but when I say that it's not optimized that has to do with the fact that there are a couple of very important physical principles that make these things not not well-suited for that purpose their first one is momentum you have to momentum couple the exhaust and the vehicle in order to try to get maximum efficiency and what that means or how that impacts is that you need to have the exhaust velocity from whatever you're using to move that air whether it's a jet or a propeller to be as low as possible now it always has to exceed the forward velocity of your vehicle so that you have a net zero momentum but nevertheless you wanted to exceed that velocity as little as possible and the reason that is is that the thrust that's produced is related to M V or mass times the velocity of the exhaust if you increase the mass you'll increase the thrust if you increase the velocity you'll increase the thrust but because the M and the V are linearly related to thrust but the amount of power necessary to create that thrust is related to M V squared as you increase the mass you linearly increase the thrust as you increase the velocity you increase the power used as the square so very quickly the power usage goes up very very fast now as you can see for example if you took a regular say a propeller or a jet and you were to power a vehicle and you wanted to double the thrust you could for example double mass and you would double the amount of power you need easiest way to visualize that is you could just simply put a second engine on your vehicle you would double the power you would double the mass but the velocity would remain the same but if you took the same engine and you tried to get that doubling of thrust by doubling the velocity you'd have to quadruple the amount of power that you need in order to do that now when you have a vehicle like a scooter or a bicycle or a little boat and you want to power it with one of these Jets that vehicle is gonna be traveling at 20 maybe maybe as much as 30 meters per second but the exhaust from these jet engines can be supersonic and so you're gonna get an exhaust that's three or four hundred meters per second and it's a very poor coupling to the velocity of your vehicle now that problem is going to be less if the vehicle is traveling very fast like an aircraft however these engines are not well-suited for an aircraft application for two reasons one they're extremely heavy and they're build because they're designed to be interfaced with an exhaust system from a from a car or a truck they have very heavy bearing housings they've got cast-iron components and so as a result it's very very heavy and in addition these devices are not well-suited to an aircraft because of the fact that the output and the input into the engine from the compressor and into the turbine are right angles so they're not aerodynamic however if what you do is you make a major modification and you change the scroll from the compressor and into the turbine into something more coaxial around the shaft and you placed an annular combustion chamber within the gap between the two just as they do with say an RC turbojet you can produce a very compact lightweight aerodynamic engine and that's why RC turbo jets are such elegant machines nevertheless this engine type does produce a lot of power there's over a hundred horsepower being circulated through this engine and it's not at all difficult for you to extract as much as 40 horsepower from the output of this engine and therefore in order to be able to couple it more efficiently into a vehicle we have left both of these engines or mounted Li with these exhaust nozzles on them we're not fully expanding or trying to convert all of the pressure that comes out of the turbine into velocity we're retaining some of that pressure in order to be able to easily couple this into a turbine and that's why the funny looking design on the back of these engines is because we never intend to use this just to thrust something we always intend to use this to drive another turbine now in doing this project I learned a lot in the process of running this engine and found that there were a number of shortcomings in this engine and because our intention is to move from this engine to a compound turbo charging system which is basically series turbochargers we're gonna be using two compressors in series two turbines in series to generate more efficiency and more power in addition we're gonna be driving a big turbine and running vehicle so rather than dealing with all the shortcomings in this engine I just went to the next stage and built this new engine and I incorporated a lot of improvements and I want to show those to you the first one is that if you look inside the inducer of the small engine you can see that with this pencil I can rotate this pretty freely it's not a lot of resistance to motion but because this is a journal bearing and has more resistance you can see that the dual bulb ceramic ball bearings that we have in the larger turbocharger have much lower rotating resistance therefore there's less parasitic losses in running this engine even though it's bigger than this one as a result it's a lot easier to get this engine to self-sustain secondly the flow resistance within the engine is based somewhat on the surface area inside the engine as you scale the engine up the surface area inside the engine over which all the high velocity gases are flowing does not scale linearly the combustion chamber doesn't grow as fast as the inducer diameter and so there's a little bit less surface resistance in addition to that turbulent laminar and especially orifice flow that occurs within the engine will actually drop is the engine increases in size again reducing parasitic losses the bigger the engine is the easier it is to get it to run furthermore as you can see this burner in the original engine is much shorter than the other burner there's much more time for the fuel in the air to burn within the larger tube and so it's a lot less demanding and the precision of the spacing and diameters of all the holes it's just more forgiving for lower tolerances it's easier to do the other modification we made in this engine is you can see the input for the compressed air into the combustion chamber was placed at the end here and one of our viewers had suggested that this is not an optimal place and in fact it is not as you can see because we blast air into one side the burn tube has a very uneven burn pattern around its periphery because of that uneven blast that occurs with that tube so what we did on the other engine is we moved that input from the compressed air backward about halfway back along the combustion chamber and to a point where it is intermediate between the primary and the secondary holes and that provides a much more homogeneous flow around the primary holes which are critical for getting a very even burn theoretically it would be better to move it back even further but for design limitations it was it was inconvenient to move it that far back but this did do a good job in providing a much more even flow into the into the engine so as you can see we have a single point fuel exhaust here which is coming out in a cone and when you take that cone and you spray it into the flame tube it takes a while for that expanding cone to mix thoroughly with the air that's coming in from the periphery and that leads to a lot of burn instabilities that we discovered when we ran the engine so what I did is I made a modification when I went to the larger engine and what I did is on the main plate on the back of that engine removed the spray nozzle and I replaced it with a thin super alloy disc called hastelloy it has a much higher temperature tolerance under an oxidizing environment than say the stainless steel it doesn't warp like stainless steel it's a bare - machine but it's been fabricated with a small 1 millimeter gap all the way around its periphery and so when this plate grows red-hot inside the chamber what happens is the fuel as it enters from the back then sprays or vaporizes atomizes and moves laterally outward here and that lateral spray then interfaces here with the input from the first primary holes of the flame tube and we get a much more homogeneous mixing now another little thing you'll also notice if you look at the side of this burn plate and the original it's much thicker three millimeters six millimeters the reason being is that when we go to compound turbocharging with this engine we could get up to 60 70 psi gage puts over half a ton against this monolithic flat plate so I went to a much thicker piece of material so that it wouldn't bow outward another thing that we discovered is that I was in love with liquid propane as a source for the fuel because we didn't need to use a fuel pump problem with the liquid propane is that when it flows into the system we have to have a throttle we have to be able to control it and when you put a throttling valve somewhere in the line you get a pressure drop across the valve what that means is that certain settings that high vapor pressure fuel will partially vaporize and form bubbles and you get this irregular spray of fuel liquid fuel gaseous fuel going into the engine and it produces a lot of burn instability within the tube a lot of people commented on what looked like surging occurring in that engine when we went to just pure gaseous propane instead of the liquid we found that all that surging and all that burn irregularity went away smooths out the flow so we decided we're gonna use gaseous propane in this engine and we're gonna show you the first demonstration with this engine with gaseous propane little issue with Ethel is that the amount of fuel that this engine uses means that the evaporation of the fuel in this tank is occurring at a rate that cools the liquid off at about five to ten degrees centigrade per minute so with this engine and anything any bigger this fuel gets so cold that the vapor pressure drops and over a couple of minutes we have to keep goosing the throttle in order to get the power to remain at a stable level so the final modification we've made is that we're going to be going to a liquid fuel system which we're going to demonstrate which uses this pump and a basin of fuel and then we're basing a fuel down there and then we're gonna go ahead and send liquid fuel up in here and see what kind of efficiency this thing runs at so those are most of the modifications with the final little adaptation that I did here which is I semi-permanently mounted a powerful EDF fan as a starter and this is kind of nice because rather than taking this sort of leaf blower and holding it underneath my arm while I'm trying to start it adjusting the fuel and looking at the gauges it's kind of kludgy this is kind of nice because they can just turn the engine up get things to run and then when we're done operating the engine I can actually run this at a low level for a couple of minutes cool off the insides and within two or three minutes I can enter the chamber and inspect what's going on so it makes it very convenient so that's that's the changes that's what we've learned what I'm gonna do is I'm gonna go ahead I'm gonna put the parts together install them get everything set up and then we're gonna run the engine and you're gonna see just how well it works okay let's go turn on the power we're gonna turn on the pumps just the fuel pressure to about 20 psi looks good now I'm gonna go ahead and turn on the fan you won't be able to hear me anymore after that this thing is loud the first engine that we built was really loud and you really had to wear headphones but with this thing they're critical if you don't wear this headphone when this thing is running at full power it's like sticking a pencil in your ear it's it's it's dangerously loud it's just it's a beautiful thing so I want to thank you very much for watching and like I said we're gonna be working on the tert the compound turbo charging as well as the free turbine and I'm not sure which is gonna be in the next video but both are being worked on simultaneously so please subscribe because if you like this kind of programming we're going to be producing a lot more of it so you have a wonderful afternoon and so will we see you soon hey you want to run this thing up again let's do it yes [Music] [Music]

Channel: Tech Ingredients

Views: 126,736

Keywords: Turbojet, Jet, Engine, Turbo, Turbocharger, Combustion, Turbo Charger, Jet engine, turbofan, DIY, thrust

Id: KGIVXvqjpg4

Length: 17min 28sec (1048 seconds)

Published: Fri Jul 19 2019