New member running problems

[ryan12345]

Hi all, 
I recently built my first ever engine and tried to run it for the first time. Unfortunately it would not run correctly and I was hoping someone would be able to offer some advice on why it wont work and how to fix it. 
After reading some of the troubleshooting on here I have reason to believe that it could be my flame tube design. Unfortunately I did not see the jetspecs design until after I had completed my own and I am guessing the holes could be the problem. At a guess the compressor inlet is about 50-55mm. The flame tube is around 325mm in length with the primary holes being 24 x 6mm separated into 2 rows. The secondary holes are 7x15mm holes and tertiary 7x19mm holes. I am guessing this is incorrect and that the 6mm holes may be preventing air from entering the flame tube in the primary area. This could explain the high temperatures I am experiencing towards the turbine. 


Any ideas on how to fix this will be appreciated 
Cheers.

[racket]

Hi Ryan

with a 55 mm inducer you have ~2375 sq mms of area , with 30% for the Primary Zone thats 712 sq mms , 20% Secondary at ~475 sq mms and 50% Tertiary at ~1187 sq mms .

If 6 mm Primary holes , then your 24 holes is OK , but your Secondary holes are too many and too big , with only a need for 475 sq mms you'll be needing maybe 8 mm dia holes and 9 of them , the Tertiary holes with 1187 sq mms to be divided up , go for 12 mm holes and 10 of .

Currently you have too much Secondary and Tertiary hole area , and being of large diameters the air will pass thru them rather than the 6mm Primary holes , starving the Primary Zone of air and delaying combustion until further down the flametube.

You didn't mention your flametube diameter, you'll be needing a minimum of ~100 mm ID , any skinnier and your air/gas speeds will be too high for stable combustion irrespective of how long the flametube has been made in an attempt to "compensate??".

What fuel are you using and how is it "injected"?

Hope this helps

Cheers
John

[ryan12345]

Thanks for the reply John.

The flametube has an ID of 100mm so should be fine. I am using propane as a fuel, which is being supplied via a nozzle which has a number of ~1-1.5mm holes running radially along it.

So I am guessing my initial plan of action is to manufacture a new flametube with hole numbers and sizing as you have suggested above??

Cheers

[racket]

Hi Ryan

OK , flametube size shouldn't be the problem , just those holes in it , may I suggest you accurately measure your compressor wheels inducer and "adjust" my recommendations accordingly .

How is your flametube located in the combustor ??

There mustn't be any large gaps where air can bypass the wall holes .

With regards your propane injector , there mustn't be any axial hole/s , only radial ones , and for your sized engine probably 12 X 1 mm dia holes 30 degrees apart around your injector will provide a good spread of fuel across the flametube.

How are you regulating fuel supply to the engine ??

If using the usual large BBQ cylinder the cylinders valve is probably adequate for regulation though a quick shutoff ball valve in the line is an added safety feature , don't use any sort of regulator , they generally dont have large enough flow passageways, also some cylinders have "safety" cutoffs .

All the best with your next testrun.

Cheers
John

[ryan12345]

John,

The flametube is located inside the combustor running along its entire length apart from a smooth converging section that connects the combustor to the turbo. It has a gap of around 15mm between itself and the combustor outer for the air to travel. Also the air from the compressor enters the combustion chamber approximately in line with the primary holes.

In terms of the fuel, I am doing similar to as you have mentioned but at the moment I DO have an old rotameter that I am using to regulate the flow. I can always remove it if this turns out to be a problem but I will probably leave it for the time being.

I will make a new flametube ASAP and get back to you with the results

Cheers

[racket]

Hi Ryan

Having the delivery tube connected at the Primary Zone isn't helpful for good combustion due to asymmetric air flows/pressures at/into the wall holes , better if its well away from there

Cheers
John

[ryan12345]

Hi John

In regards to the nozzle design, how far inside the combustion chamber should it be located??

Cheers

[racket]

Hi Ryan

Have the fuel injection holes roughly adjacent to the Primary holes .

Cheers
John