New member and first DIY Turbojet build

[The Lazy Destroyer]

New member here, someone forwarded me the link to the forum here. Been peeking around a little at some of the threads but wanted to show some pics of a turbojet build I am working on over the last couple months. Engine itself is mostly done, have some details and flametube drilling to finish up still. And the fuel & oiling system needs to be built, have most of the parts just need the time now. Ignition system is done but not installed.

Anyways, here's some pics. Except for the turbo and fittings, pretty much built everything including rolling all the tubing from sheet metal. 
It looks the part, at least. 

I didn't have too much resources, just kinda looked at a few YouTube builds and Jetspec program for the chamber/FT sizing. Wish I saw this forum before I started but I'm here now at least lol. 

[racket]

Hi

Welcome to the Group , hopefully we can give some support :-)

Nice welds , someone knows what they're doing .

Just a tad concerned about the compressor to turbine stage matching, the comp scroll appears to be a lot larger.................what turbo specs are you using , comp and turb wheel dimensions??

Have you read jetandturbineowners.proboards.com/thread/680/diy-turbines , just click on the icons in the various sections

Cheers
John

[The Lazy Destroyer]

Thanks John!

I’ll take a look at the turbo and post some specs when I can.
It’s just the typical Chinese eBay t3/t4 hybrid variety w/50mm comp inducer so yes they’re a little different. I saw on a couple threads here that may be an issue altho I’m not sure how much of a problem or if there’s a way to overcome/help this problem at all.

This ones just a fun project and isn’t going on anything or has any purpose other than to learn new fabrication & welding techniques, so max thrust is not required or a big deal. Hopefully no significant surge or anything like that. But I’ll also look through the tips page you linked, I took a quick look and I’ll probably wanna sit down and read through as much as I can this week.

I just kinda bought a generic turbo, threw some #’s into JetSpec, and ran with it lol. Wasn’t aware at the time much about turbos at all so it’s already been quite a learning process.
If it runs without headache I’ll be happy
But I did build it so it’s in sections so changes are possible aside from main combustion chamber sizing.

[The Lazy Destroyer]

Here are some specs on the turbo... I assume most of these $100 Chinese variety are knockoffs off of the same hybrid turbo model (Garrett maybe?) but not sure.
Either way, here are the #'s:

Compressor:
Trim: 44
A/R: .5
Inducer: 50.5
Exducer: 76

Turbine:
Trim: 73
A/R: .63
Inducer: 65.5
Exducer: 55.9

[racket]

Thanks for the numbers , yep, you might be OK , but may I suggest not having a jet nozzle on the engine for the initial spoolups, it'll make starting easier and safer , and hopefully produce some running jetpipe temperatures that are in the 500-550 deg C - 900-1000 deg F range, low enough to allow fitting a jetnozzle to increase backpressure, and as a consequence ,increase temperatures on the engine and to create thrust .

[The Lazy Destroyer]

Ok thanks! I"ll be busy reading some of the documents in the page you linked to, a few I have looked at seem pretty helpful already. When I started I didn't even know what T3/T4/Hybrid even meant so I've learned a lot already just from diving in and just doing it.

I had some questions regarding fuel nozzles and expected temperatures at various spots, but I think I see a few threads and pages that might cover this so I'll do some research on here this week and come back with any questions I haven't found answers to on the existing info here. I just finished the majority of the fabrication and am now at kind of a pause-point for me to re-assess everything and plan next steps.

FYI, I don't think I mentioned it but this will be run with propane. The primary-side plate on my combustion chamber will have a NPT fitting in the center for fuel inlet, NPT fitting on the inside also so fuel nozzle can be changed around to experiment. And a spark plug bung added there as well. That's about I think the only thing pictured here that isn't technically done yet. I have the flame tube but it's not drilled yet and I have to cut the final length to match the combustion tube length.

The exhaust nozzle I have, I wasn't sure on the science/math so I just went with a 25% (or maybe it was 30%) reduction in area for the nozzle's reduction. This one is technically just a temporary non-afterburner nozzle... however I couldn't resist the temptation to fit in fuel/spark fittings into it "just in case". Not sure if I'll actually try AB on this nozzle but it's there if I want to give it a go, I guess.

[The Lazy Destroyer]

Is it okay to run these without any nozzle at all? My v-band clamp extends about 1" past the turbine outlet so I could leave the main nozzle off and just keep the very short part there if needed. My turbo has the hole for I assume a blow off valve, so keeping the exit flange on I assume is pretty much required.

One question I did have that I assume other posts may not cover, for my turbo #'s and configuration... is it still fine to use the JetSpec #'s for the flame tube construction?
Are there any changes/modifications I may want to do considering my turbine side is a little smaller than the compressor side? Or does it not matter for the FT hole configuration? I was planning on drilling based on the 50.5mm inlet value in the JetSpec program. 

[racket]

With your flametube length , it needs to allow for expansion when running as it'll be a lot hotter than the outer can , so leave several millimetres of axial expansion space , you'll need some sort of "rattly"slipjoint .

Yep , perfectly safe to run without a jet nozzle , all that happens is lower temperatures at the various compressor discharge pressures ( P2s) compared to when one is fitted.

I gather there isn't any wastegate valve fitted into your turb scroll , normally we need to fix the wastegate valve shut , all gasses must go through the turb wheel otherwise temperatures spike badly .

Use your V band section of jetpipe but please have your thermocouple fitted to prevent any overtemperature excursions during spoolup .

Yep , use Jetspecs , the division of hole area between the various Zones is more important than any minor increase or decrease in actual vs theoretical hole requirements .

Theres info on jet nozzle and A/B sizing in the Link , but a safe non A/B nozzle size is roughly the comp inducer diameter , so ~50mm for you ...............if after running with the 50 mm nozzle and jetpipe temps are still "modest" ,, then the nozzle can be incrementally reduced in size until jetpipe temps climb to design levels of ~650 C - 1,200 F at full power.

If running propane , a very simple injector producing 6 to 12 fuel squirts radially towards the Primary wall holes is all thats required , nothing complicated ..............but there mustn't be any axial injection down the flametube , its in the Link

Cheers
John

[turboron]

Lazy, there are two approaches on the spark plug fitting. The approach used on my unit is to silver braze a bung for the sparkplug directly to the flame tube. The sparkplug then locates the flame tube versus the OCC when it is insert through a hole in the OCC. The "advantage" is that start air can be introduced before the propane is emitted to the flame tube (liner). The second approach is the have the sparkplug inserted through a loose hole in the liner. In that case, I have been told, the propane must be introduced first and ignited to prevent the start air from prevent ignition. Perhaps John can explain further since he is familiar with this approach.

Thanks, Ron

[The Lazy Destroyer]

John,
Good call on the FT expansion with heat, I hadn't thought about that but it's certainly good to know. I'll leave a little wiggle room for length which is fine with how I've made this one as it kinda sits within a 5mm or 6mm flange hole on each end(somewhat snug fit around the sides to keep it centered within the chamber).

Correct no wastegate. This turbo has a hole on the exit flange of the turbine side that appears to be an accommodation for wastegates to be mounted directly to the turbo, I think. But my exit flange blocks this hole off and only leaves the turbine exit. The exit flange I made pretty much looks like all the generic 5-bolt t3/t4 exit flanges I saw online.

for reference, the current exhaust nozzle is 2.5" diameter for about 6-7" length, then tapers over 4" to a final diameter of 2.1" diameter... although with my cut's kerf it may have been closer to 2.0" final. But I can pretty easily run less taper by just cutting a little off the end.

Ron,
Thanks for the input! I'll look into some of the projects posted here and see how they did theirs. I'll post pics of what I had planned for mine here in a minute..

[The Lazy Destroyer]

Here are a few pics of the chamber and also what I had planned for the fuel inlet and spark on the chamber's end plate:

Chambers end flanges inner diameter are a match to the FT's diameter, so the FT slides in there and the chamber's flanges keep it centered in place on each side. Flanges are maybe something like 5mm for the metric guys. 3/16" plate I think is what I used. 




Here is roughly how I planned to mount the fuel inlet and spark plug to the chamber's end plate, sorry I'm not much of a hand model:





I hadn't welded the fuel inlet yet because I wanted to double check my propane/fuel line plans before I welded in the 3/8 NPT bung. In case a different fitting/thread would work better for propane (or future liquid use). Spark plug I just will mount between the center (fuel inlet) and the FT wall. Spark plug is an extended length one so that it reaches a little further within the chamber, maybe about an inch past the end plate inside. But this isn't set in stone, mostly just what I've seen a few other projects do. It's trigger by a solid state flasher relay controlling a diy buzz coil using a generic coil and battery pack. 

Also, I think the only ones of these diy turbojets I really looked at to any detail during my build were TechIngredient's, rcdon's GR1 build, and Colin Furze's turbojet. Assuming you guys have seen those posted here, maybe. TechIngredients vid is posted in a thread here on compressor surge actually, I saw earlier today. Lots to go through here, so I look forward to learning more and asking random questions as I finish her up. 

[racket]

Hi

Your 2" jet nozzle should be OK , but don't try any afterburning with it , its far too small for that , you'll send the comp into surge with the potential of killing your engine .

Your 3/8" NPT bung should be fine for the fuel , but I'm not a great fan of endplate mounting of the sparkplug , maybe alright for propane if its positioned at the lower side of the flametube, propane tends to fall to the bottom where it'll be ignited

I prefer a side wall mounting of the sparkplug .

Lucky for you that you found the Site that your "inspiration suppliers" have also used over the years , RC Don does beautiful construction work and I've recommended his Site to guys for that reason , but his "theory" isn't the best , Tech Ingredients are newcomers to the hobby who are slowly finding their way even though their presenter has great presentation skills giving the impression they know what they're doing ...........and lastly , good ol' Colin , a very "smart" guy making lotsa money from acting stupid , he's paid for it with horrible burns from one of his engine builds that went wrong , his vids are not to be recommended for anyone serious about building an engine , only for those who fantasise a lot and construct nothing because they spend too much time on YouTube .

Yep, have a good read through the various builds , theres a huge amount of experience available from Members here , then ask away about anything you're not certain about :-)

Cheers
John

[The Lazy Destroyer]

Yikes, been a while since I posted updates. It sat around for a while as I worked on other projects and jobs. 
So started back working on it again this summer. 

I’ll try and get more pics up as I find time. 



Aluminum oil tank:

[The Lazy Destroyer]

Finally got back to working on this one some more. 
Finished up the frame, electronics, ignition, oil tank and oiling system, gauges, etc etc. 
Just have to drill the holes for the flame tube, make the injector, and figure out the propane situation. 

Some pics: 












Walkaround video link: 

youtu.be/Qf23tH5UWa4

[The Lazy Destroyer]

The only thing I need to check on is the flametube holes and how to go about the propane tank setup (USA). 

Below is my JetSpecs screen with my planned flametube holes (for 2" inducer diameter): 
PRIMARY: x25 of 7/32" holes
SECONDARY: x8 of 5/16" holes
TERTIARY: x8 of 1/2" holes

Does this seem ok? I can also do x19 of 1/4 holes on the Primary, not sure if there is a too-many or too-few thing for these holes. 





For the propane, after reading some posts, I'm guessing a 20 lbs BBQ bottle may not work as they seem to have safety features that may limit flow (I'm in USA). 
So I'm a little concerned here on how to go about a propane setup for this. 

I picked up a cheap adaptor to see how they are, converts the 20 lb bottle to 1/4"NPT. it seems they come with some type of check valve or something, as well as a pretty tiny hole. I hooked on up to a propane bottle I have and it seems like it doesn't allow flow much at all. Or maybe it needs backpressure and doesn't allow opening into "atmosphere" as some type of safety thing?
Looks like this: 



If I drill this check/orifice out, is it still possible to use the small USA 20 lb bbq bottles?
Watching the TechIngredients video, I see they're using some other type of propane bottle, not the BBQ one, maybe some industrial type. It doesn't have the same type of tank valve that the BBQ ones have. 

I do have to swing by my welding gas supplier and I believe they sell propane there too. So I may check with them on if they supply something that may be more "unregulated". 

Any of the USA people here have any input or what they used? Or is there some way to get the 20 lbs BBQ bottles to work?
Mines a 2" inducer diameter, I still need to calculate what the ideal fuel consumption is, I just haven't gone through the older threads to find it again. Saw it somewhere but didn't save it.