A bunch of questions in before starting a build

[joel076]

Me and my friend are planning on building a turbojet as a school project which we'll have about 4 months on us to build. 

My first question is if it's realistic for us two who don't have any prior experience welding(We do have access to a welding machine though), working with metal or constructing the plumbing needed for the oil system to be able to do this project? I feel that our theoretical knowledge is okay but not our practical.

My second question(s) is about the fuel. Here in Sweden, it seems rather difficult to get your hands on pure propane(please tell me if you know otherwise) but we have something called gasol(not gasoline) which is a mix of propane and butane. Would it be possible to use gasol as fuel? Would I have to make any changes to the construction? Would it be as easy as using pure propane to start the engine? What would be the differences between gasol and propane?

My third question is mainly about the connections and plumbing. Is there a risk or possibility that the fuel somehow could ignite down into the fuel tank and make it explode? Could it also be possible to use some sort of cheaper and flexible material for the connection between the turbo inlet and the combustion chamber?

I also wonder how to construct the oil systems. Does anyone have a link to a really cheap oil pump or could I just salvage one from a car? Does the oil pressure have to be changed during running? Is it necessary to have gauges for oil pressure and temperature or could I do without them?

Does the rod that injects the fuel into the combustion chamber need any special dimensions?

We are likely going to use a small turbo, possibly from a Saab, how much thrust could you get from one of those?

Lastly, is jetspecs good or should I use other dimensions?

And yes, I've looked through that thread with all the info.

[racket]

Hi Joel

It would be possible for you guys with your limited abilities to build something that spins around and makes some noise and a small amount of thrust.

Fueling , use your gasol and keep the cylinder warm to maintain vapour pressure .

Ignition of the cylinders contents is impossible , theres no oxygen in there ...............construction would be the same .

Flexible coupling between turbo and combustor is possible with suitable tubing .

Oil pumps off Ebay , no need to change pressure during running as long as its as high as it was when being used as a turbo on an IC engine , you will need a pressure gauge , temp g/g not necessary , just feel the tank .

Fuel injector dimensions will vary with size of turbo used , but a short length of 6mm tubing with the end blanked off and 4 small 1mm holes drilled in the side to produce radial injection will work for a small turbo

Thrust level .............depends on mass flow of air , but for a car sized turbo , it'll be a few kgs .

Jetspecs works , use it .

All the best

Cheers
John

[joel076]

Thanks for the info!

I did find a small turbo today. The intake seems to be around 3.5cm around its narrowest point. Are there any downsides to using as small a turbo as this? It did have a split exhaust inlet but how much does a split inlet affect performance and should I grind it down into one? The turbo was also used for a diesel car, are there any important differences between diesel and petrol turbos that could affect the performance? If you could make another guess, how much thrust do you think it would produce with this information? Also, is it easier to use a glow plug than an ignition coil because of the need for high voltages? My last question is what material should be used for the combustion chamber, I guess steel?

[racket]

Hi Joel

35 mm inducer is pretty small and with a split scroll housing it won't produce much thrust, maybe 3 kgs , as its a diesel turbo hopefully the matching of comp/turb are adequate , but without a detailed measurement of components its impossible to say if it'll be OK .

glowplug OK , steel for the outer can and preferably stainless for the flametube

I'd suggest looking through the builds here and simply copy one of them .

Cheers
John

[noshell]

My 29mm inducer engine runs a treat on pure butane, itl go from a low idle to an absolute roar, its plenty.

And as John said, follow jetspecs

[ausjet]

The first jet I made wasn’t much bigger than yours. It had a split turbine housing too. Still ran and made a lot of noise. Was successful enough for me back then!
The high voltage spark generators you can get from eBay work well igniting gaseous fuel. They’re compact and cheap. Get a 12v one ~100-500kv.

www.ebay.com.au/itm/DC-6v-12V-500KV-Boost-Step-up-High-voltage-Generator-Transformer-Ignition-Coil-/112495065227?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=705-154756-20017-0

Use a solid core ignition cable from it to a spark plug with the gap opened up. (Normal car ignition leads won’t work as they’re a fiber core)



Note: as you can see my combustion chamber air entry is positioned tangentially at the lower cap end (primary hole area). These days we position it square on to the combustion chamber diameter and around the dilution zone with a bellmouthed entry to slow the air speed down.

[joel076]

The planning continues...

We're now at the stage of gathering materials but we're having a hard time finding the right dimensions for the steel tubes. Our only choice seems to be to use a flame tube which has about a 3 mm too large diameter and an outer tube which has almost a 20mm too large diameter. I guess a 3mm too large flame tube will work but will a 20mm too large outer tube work? Can we change our design to use that large tube?

My second question is about oil pumps. I found that shurflo pump but i also found out that I could get away much cheaper with a volvo servo pump.
Like this guy: jetandturbineowners.proboards.com/post/30758/thread
Would that oil tank be large enough on the servo pump or are there any other problems that could make a shurflo that much more worth it?

[racket]

Hi

Oversized tubes are OK , undersized are a NO NO

Our oil gets hot pretty quickly if the volume is small , we need 4-5 litres of oil unless theres an oil cooler

[joel076]

We've now gotten our hands on the turbo and oil pump. We settled for a volvo power steering pump however the reservoir is only about 1 litre but i guess we could somehow enlarge the reservoir? Further, how is the offset placement of the air tube into the combustion chamber calculated now that we have a oversized tube as our outer shell? And lastly, what dimensions should be used for the flame tube holes? Jetspecs suggests 6, 10 and 16mm which results in 10, 2 and 2 holes for each row/stage of holes. I guess we should change the diameters to accomodate more holes but is there a correct amount of holes or desired diameter of each one?

[racket]

Use 6 8 and 10 mm holes

[joel076]

When I use the diameters 6, 8 and 10mm the number of holes become decimal which results in 10.2, 3.8 and 6.1 holes. Should I round these numbers up to 11, 4 and 7 to not undersize the total area or are there any other way?

Where should I place the holes along the tube and how large should the distance be between the primary, secondary and tertiary holes if the flame tube length is 210mm?

Because of the small amount of holes should I only do one row each for the primary, secondary and tertiary?

[racket]

Go 10 4 6

one row each

Primary holes opposite fuel spray , secondary 100 mm lower and 100 mm to tertiary

[joel076]

Today we tried to start the jet but to no success. The first problem was that the glow plug didn’t seem to ignite the gas at first. Instead, we blew a little air into the engine, lit the gas from the outside and then cranked up gas and air. The engine did then start to rumble a bit and blue flames came out of the exhaust.

Firstly, shouldn’t the glow plug ignite the gas from the inside without any help? Secondly, was the blue flames spewing out from the exhaust caused by lack of air inside the engine? Is our compressor going to be enough or is a leaf blower needed? And lastly, do we need to remove the gas regulator to supply enough gas?

[racket]

Hi

Yep , you need to remove the regulator , just use the valve as a throttle, ...............what sized cylinder are you using ??

Your compressor should be able to spin up a small turbo by impinging on the comp wheel , if not , then the exhaust from a decent sized workshop vacuum cleaner should work .

The glow plug should ignite the fuel as long as there no air blowing fuel away from the plug as can happen if the plug is fitted through a large hole in the flametube , let the glow plug get up to max temp before feeding in the fuel , once it ignites , apply the starter

Cheers
John

[slittlewing]

Hi Joel,

I would use spark plug for gas like butane or propane. Or you can continue to try and light it at the back of the turbine. You can buy small dc hv on eBay or Amazon to power the spark plug, just be careful not to run them too long or they get hot and fail.


www.ebay.co.uk/itm/High-Voltage-Generator-DC-6-12V-To-1000kV-Step-Up-Power-Module-High-Efficiency-/224751651818?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=710-127635-2958-0


You could try a leaf blower to start the engine, a normal 7bar compressor might not provide enough power/speed for the engine to start and “self sustain”.

Cheers
Scott