Fuel vaporizer explained please

[ckliever]

So I am trying to design my flame tube and I have been doing much reading on the forum. I want to run off kerosene but use propane to warm the engine up. I’d like to use a vaporizer system rather than the high pressure fuel nozzle. Could someone point me
To a thread that explains the vaporizer setup? Or provide me with some info regarding vaporizer tube sizes, placement, and how the fuel is delivered to the vaporizing tubes?

Thanks so much!

Chris

[racket]

Hi Chris

Before you progress too far with vapouriser ,..........what is your reasoning for not using a high pressure spray nozzle ??

Having built engines with both types I feel the single spray nozzle is the simplest , there can be a bit more work involved with getting the right pump and throttling , but there is less "flametube work" when compared to the vapouriser system .

Theres some info here jetandturbineowners.proboards.com/thread/680/diy-turbines.

A build thread jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build?page=2

and another jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart?page=3

The total flow area of the vapouriser bores is ~10% of total flametube hole area , another 20% is fed through the flametube wall in the Primary Zone to make up the Primary Zones 30% of total area ( total area = comp wheel inducer area ) , the wall area of the vapourisers needs to be ~6 times inducer area so as to provide sufficient heating surface .

Hope this helps

Cheers
John

[ckliever]

Thanks for the input and links John! I will read through them and try to decide if I still want to go the vaporizer route. I know there’s more flame tube work to be done with the vaporizer but if I think I’m up to it the system fascinated me and I’d enjoy creating one. My other reason was thinking the pump situation would be easier to source and less to worry about without the extreme pressures that the fuel lines would need to sustain. Maybe after investigating further into the vaporizers I’ll be intimidated and change plans. I hope not!

[racket]

Hi Chris

Another option ,......... if you use the Variflo spray nozzle assets.delavan.com/delavan-oil-burner-nozzles-and-accessories.84l1k9.pdf ( half way down the page) the pressure can be kept at more reasonable levels due to good atomisation at lower pressures.

All the best with the build

Cheers
John

[ckliever]

Thanks again John. Just when I was set to go with a vaporizer system similar to yours, you provided me with another option lol! Do you have experience with the variflow nozzle? That looks like a viable option. It appears that there would be plenty of flow at 100psi. How well do you suppose this nozzle can atomize fuel at flow rates around idle? That would be my only concern initially as I think about it.

If I go the vaporizer route, how critical is the sizing and lengths of the tubes? It would seem the alignment with the flametube air holes would be the most important thing. My flametube will have .065” walls. Would you recommend the same amount of the tiny air cooling holes as used in your engine? Also, for simplicity sake, if I use propane just to heat the vaporizers prior to spool up, could I make a nozzle that sprays propane across the exterior of the vaporizer tubes rather than directing propane through the tubes?

Thanks again for your help!

Chris

[racket]

Hi Chris

From the Link ............

.........."The maximum to minimum discharge flow rate at constant supply pressure is referred to as the “turndown ratio”. The standard catalog nozzles have turndown ratios of approximately 5 to 1."


A 5:1 ratio is more than enough for our usage , our idling flows are quite high compared to an IC engines .

Because the Variflo has max fuel flow rates always going through the nozzle , the atomisation doesn't suffer when most of that fuel goes back to the tank when at idle .

Vapouriser lengths and diameters are based on your compressor inducer area , so some juggling of sizes are required to get the 10% for the bores but 600% for the surface area , as well as having sufficiant number of outlets to cover the flametube cross sectional area , this is why I recommended going the single spray nozzle route , its simpler .

Yep you could use "external" propane injection rather than through the tubes.

No need for all the small holes , thats just me being overly pedantic ;-)

Cheers
John

[ckliever]

Ok well it certainly sounds like the veriflow is perhaps the wise choice, especially seeing as how this is my first build. Let me ask you this then - what is the downside, if any, to using the veriflow instead of a vaporizer setup?

Thanks,
Chris

[racket]

None

[ckliever]

Well I suppose that settles it then. What’s the best way to calculate the fuel demands so that order the correct nozzle?

Oh, and compared with the jetspecs or the vaporizer setup, how should airholes in the flametube be arranged, especially in the primary zone.

Thanks again and sorry for so many questions. Hopefully I’ll have some progress to show as a result soon!

Chris

[racket]

You need to know the air mass flow per second at maximum power , then the fuel flow will be roughly the same mass but per minute , ie, air mass flow 1 lb/sec fuel flow 1 lb/min, this needs to be converted into gallons per hour as most nozzle are calibrated that way , generally at 100psi .............1 lb/min of fuel = 60 lbs/hr , kero weighs ~ 6.7 lbs per US gallon , so a 9 US GPH nozzle

Then if your pump flows at say 100 psi , just find the nozzle that provides that 9 gph flow

[ckliever]

Ok perfect! I did see in the specs for the nozzle that there is a chart for the fuel rate at 100psi. So I just need to track down a flow map I guess. It’s a holset T46 type.

I edited my last post to add an additional question but didn’t realize you had already responded. I’ll paste it here:

Compared with the jetspecs or the vaporizer setup, how should air-holes in the flame-tube be arranged, especially in the primary zone? I’m assuming I’ll want a wide spray angle nozzle and arrange the holes so that the spray impacts them?

Thanks again and sorry for so many questions. Hopefully I’ll have some progress to show as a result

[miuge]

Check out the other recent topics:
jetandturbineowners.proboards.com/thread/1292/kerosene-injector-placement-propane-starter

[ckliever]

One clarification... I’m still intrigued by the vaporizer system and haven’t ruled out trying it. John, when you gave the length and diameter of the tubes, those percentages were for the total amount of vaporizer tubes, not for each tube individually correct? My inducer has a diameter of 2.85” which gave me a vaporizer diameter of roughly .25” if I used 4 of them. My math could be suspect, but that tube diameter seemed rather small compared with yours, although your turbo was bigger than mine. Just want to make sure I’m on the right track.

Thanks,
Chris

[racket]

A 2.85" inducer is 72.39mm dia with an area of 4116 sq mms , 10% of that is 411 sq mms , if 4 tubes then 103 sq mms/tube =11.45 mm dia of the bores , roughly half inch , so you could use 5/8" stainless tubing with 1/16" WT, which compares reasonably with the 19mm/3/4" tubing I used in my kart with the 3.5" inducer jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build?page=2.

If we go for 6 times inducer area for heating surface , 4116 X 6 = 24696 sq mms , 5/8" tube has a circumference of 49.87 mm , so you'd need 495 mm of tube length for the 4 of them , so roughly 125 mm each one .

[ckliever]

Ah! So my math was wrong. I will work backwards from your numbers so I can see where I went wrong. I have reviewed your setup and I like it very much. I may try to build something similar. Thank you again!!

Chris