Turboprop Build

[jeffreyguy]

Well this is my first turbine build but with the help of the forum I'm pretty confident! I'm planning to build a turbo based engine with a sore thumb type combustor and a 3rd stage Allison C20 compressor wheel for a freepower. This will in turn drive a 59" 3 blade variable pitch propeller via a chain or belt reduction at a maximum speed of 3000 rpm.

    The turbo is a Mitsubishi TD-13M meant for a 37 litre V16 Detroit diesel. It has a 95mm compressor inducer, a 113mm turbine exducer and an unknown A/R. Its absolutely massive!








    The flame tube and outer shell will be rolled from 14ga 304 stainless sheet and the ends and flanges will be made from 5/16 plate. Would there be any advantage to doming the end plate? I can use a power hammer with hemisphere dies at work. The fuel will be kerosene or diesel. I used Jetspecs to calculate the hole areas and I'm thinking
Primary: 67 holes 0.25"
Secondary: 20 holes 0.375"
Tertiary : 30 holes 0.5"


    So far the plan is to use six 3/4" evaporator tubes with hollow cone mist nozzles spraying the fuel into the evaporator to hopefully get good coverage. Fuel will be supplied by an electric pump controlled by a pwm.

[racket]

Hi

Nice turbo :-)

Before you go too far , could you give a few more specs on the turbo , the turb scroll appears to be rather "fat" , is there an A/R number cast in near its inlet "foot" ??

Theres not much info available , but I just found this bit www.turbomaster.info/eng/mitsubishi_parts_list/49182-03120.php it appears theres a NGV inside the turb scroll which might account for it being fat .

You may need to remove those 8 bolts on the scroll exducer side to check the NGV throat areas so as to determine their flow area and whether or not its going to be suitable for a high or low Pressure Ratio ..............we can soon work it out once we have a "number"

Cheers
John

[jeffreyguy]

Well it seems like Mitsubishi doesnt list A/R for their turbos. The Garret T18a40 was also used in the same applications with an A/R of 1.36, but the compressor and turbine wheels were a couple mm smaller. Id imagine its around there but I'll take it apart tomorrow after work to get some real numbers if I can figure out what exactly to measure haha. I read some breakdowns online so I can probably figure it out

[racket]

Hopefully the total throat area of the NGV will be ~4.5 sq ins - 2,900 sq mms.

[jeffreyguy]

After getting those retainer clips off without damage



I got the ngv disc out, but it felt like there was a threadlocker on the bolts. Does anyone know of a thread locking compound that can stand up to the heat found in a turbine?




I measured the smallest point between the vanes and got 3.97 square inches which seems on the small side. I'm still working on calculating the A/R but my freepower parts arrived today and I had to stop and play with them!

[jeffreyguy]

My admittedly crude method of measuring the A/R came out to 1.26. Even if I was off a little that seems to be in the right range. I picked up some stainless sheet for the combustor today so I just need to work out a flame tube pattern

[racket]

Don't worry about A/Rs , yours doesn't have one , your scroll is simply a duct to spread the gases around the NGV stator .

At 3.95 sq ins ,thats nice and "tight" , so there shouldn't be any problems getting up to a decent pressure ratio without any temperature issues , though once you start developing the engine and want to run higher temperatures to optimise power output you might find the NGV is a tad tight, its probably been configured for "lowish" diesel exhaust temps

Cheers
John

[jeffreyguy]

Well that's good news I suppose. If I ever need a more open NGV I can machine a new one out of stainless but I'm glad It'll work for now. Ill draw up a file for the flame tube and I can probably get some time on the plasma table this weekend

[racket]

You'll only need to open the area by ~12% , so a bit of machining on the original vanes at the throat will be enough , theres plenty of metal there............but for now the NGV will be OK as long as your jetpipe temps are kept to ~650 C there shouldn't be any adverse flow reduction

[jeffreyguy]

That shouldn't be a problem, I'm in luck! I'm thinking it would be ideal to mount the combustor straight up for balance as well as to allow it to be cooled by the air stream. The only downside I can think of is there is a potential for unburnt fuel to enter the turbine although there may be a way around that. Something like this:

[racket]

A vertical chamber is good ,I used one on the GT60 build jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart if fuel does accumulate it can easily be blown into/through the turbine stage where it won't be a problem , better to be blown through than burn in the combustor and cause an over temp/over speed situation .

But please don't copy that combustor with it "high" air delivery position

[jeffreyguy]

Here's my idea for the flame tube with the hole scheme from my first post. It's 7.5" in diameter and 22.5" long, it'll be free floating at both ends with slip joints and have a cone transition from the combustor to the turbine inlet

[racket]

Are you using single point spray nozzle or multiple vapourising tubes ??

You've got far too many small holes for the Primary Zone , I'm assuming your drawing is " upside down".

With a 7.5" dia flametube you need larger holes to achieve adequate penetration of the air jets , those small holes will only provide a cooling blanket down the inside of the flametube, lotsa small holes are OK with radial propane injection as the propane generally hits the wall , we need different hole arrangements for different fueling methods .

With a 95 mm inducer - 7088 sq mms and a 3 times inducer area ratio for the flametube area - 21,264 sq mms = 165 mm dia - 6.48" is all you need if you provide good fuel and air presentation , which it appears shouldn't be a problem for you ...............Jetspecs provides a very generously proportioned flametube able to cope with rudimentary construction and fuel/air presentation , with extra effort put into the build the FT can be a bit more compact.

[jeffreyguy]

The plan is to use 6 evaporator tubes with the fuel supplied to them with hollow cone spray nozzles. You're right it is drawn upside down from how it will be installed. If I go down to 6.5" on the flame tube and keep the hole areas as suggested by Jetspecs would I be better off to go to larger diameter holes? Maybe
Primary: 0.375
Secondary: 0.5
Tertiary: 0.7

[racket]

With evap tubes we need to get combustion pretty much completed by the time the gases pass the "bottom" of the tubes to maximise heat transfer to them , so wall hole arrangement needs to take that into account .

The evap tubes discharge a rich mixture against the endwall of the FT , ideally we want the rest of our Primary air to mix with that rich mixture and get combustion going before it moves down the flametube and contacts the discharge end of the tubes.

If you look at the FT pics in the GT60 Link I provided earlier you'll notice I have a pair of holes discharging across the outlets of each evap tube , and further down the Ft there are holes that discharge up between the tubes to "force" combustion gases back towards the top of the FT to promote turbulence around the tubes.

Care needs to be taken to position the Secondary holes so that they don't discharge onto the tubes and cool them .

When in doubt about a design , do as I do , copy shamelessly :-)

Cheers
John