miuge
Veteran Member
Joined: March 2014
Posts: 199
|
Post by miuge on Jun 16, 2014 12:41:17 GMT -5
If I would order a casting, I would expect a better quality Just my two cents.. Anyway you need to get it machined or are you going to grind it by hand? About the turbo you're using, turbo used in our current project is equal size in/out, that should work if the type of combustor won't make big difference..
|
|
|
Post by madpatty on Jun 16, 2014 15:53:45 GMT -5
Hi Miuge,
Yea hopefully the turbo will work.
Regarding the casting....every surface will be machined on lathe except the ones between the wedges.,.. They will be hand filed or using a small hand drill fitted with small grinder depending on what gives better results...
Cheers.
|
|
|
Post by madpatty on Jun 16, 2014 20:05:43 GMT -5
Hi John,
Done a few calculations:-
Hx35 flows 40lbs/min at 123000 rpm at 75% efficiency and a pressure ratio of 3.0
Tip speed- 534.27 m/s Air Outlet temperature- 98 degree celsius Density of air at compressor exit- 1.6477 kg/m3 Radial velocity- 139 m/s Supply value- 0.261 Blade angle- 65 degrees(approx) Overall speed vector- 469.45 m/s
Therefore outflow angle- 16.49 degrees
Now all this i have calculated....
How to calculate the throat area for maximum mass flow...
I wasn't able to find that section in the book..
Thanks, Patty
|
|
|
Post by racket on Jun 16, 2014 23:31:21 GMT -5
Hi Patty
Use the Continuity Equation ..............Mass = speed X density X area
The slight increase in density between the comp outlet and diffuser throat will be minimal and easily balances out any boundary layer reduction in the flow area at the throat .
Cheers John
|
|
|
Post by madpatty on Jun 17, 2014 5:22:06 GMT -5
Hi John,
Can the normal steel ball bearings be used as the rotating elements at such high rpm's....at the place of brass bushes?
Or there is some special arrangement to use them?
Thanks. Patty
|
|
|
Post by racket on Jun 17, 2014 16:55:21 GMT -5
Hi Patty
Don't even think about using ball bearings unless you want to have a whole new level of complication and extended development time, not to mention the possibility of wrecking several rotating assemblies until you get the bearing arrangement sorted .
Cheers John
|
|
|
Post by madpatty on Jun 17, 2014 17:31:46 GMT -5
Thanks John,
In my present engine build The size between the brass bushes is just about 40-45mm and so the main portion of combustion chamber will be at most 60mm(approx)..... Is it ok for such a small comstion chamber??
If at all i will use ball bearings then it will be a whole new setup incorpoating axial turbine wheel(designs taken from GR130 and GR180 etc).....in that case also normal ball bearings won't go??
Cheers, Patty
|
|
|
Post by racket on Jun 17, 2014 19:49:52 GMT -5
Hi Patty
60mm is long enough IF the fuel and air presentation is good , BUT if you don't have a well designed combustor the engine won't work :-(
Normal "off the shelf" ball bearings are OK to get an engine to idling rpm , but for full power high rpm ratings those standard bearings aren't going to be good enough, using ball bearings raises a whole level of complexity you don't need, and unless you have access to precision machining facilities you'll only end up wrecking parts when the bearings fail , failed bearings generally sends the rotor into uncontrolled gyrations where bits can fly off and wreck other parts of the engine, you could be up for a lot of new parts each time a bearing fails , and they can fail within seconds of firing the engine up .
Cheers John
|
|
|
Post by madpatty on Jun 17, 2014 20:02:08 GMT -5
Thanks John,
I was also thinking of rejecting that idea...off the shelf bearings cant handle those extreme conditions.
I will try the present design first....anything i can do to elongate the standard shaft a bit of i have missed some technique of doing that on the forum.??
I think a bit long cc would be good to start with....
Or i try fabricating a whole new shaft with standard compressor and axial turbine and run it on standard bushes...??
Your thoughts.
Thanks, Patty
|
|
|
Post by racket on Jun 17, 2014 20:58:32 GMT -5
Hi Patty
Lengthening the shaft requires extremely precise machining of any extensions , there have been designs that have done it , but not many successfully , then theres still the problem of the relatively large diameter turbo shaft which means rpm are generally limited , its better to use an unaltered shaft if possible to limit possible consequences .
You really should join the GTBA , theres a wealth of information on that Site with regards building micro engines , well worth the joining Fee , and it'll save me having to type up these replies about a very complex subject :-)
Cheers John
|
|
|
Post by madpatty on Jun 19, 2014 9:19:21 GMT -5
Just a mini update...
Journal bearing assembly almost done....will post some pics shortly...
Now will be fabricating the oil inlets for the bearings...that will two small holes drilled just above the two bearings reaching exactly the midpoints on the periphery of the journals from which pressurised oil will be fed to bearings.
I am facing the problem of making that oil sump inside the shaft tunnel (idea courtesy- Ander's build) for collecting the oil from the bearings at the oil outlet due lack of milling option...
Can there be some other possible way of doing that??
Cheers, Patty
|
|
|
Post by racket on Jun 19, 2014 16:42:27 GMT -5
Hi Patty
I used "offset?" turning on the lathe to make my sump ...............3 jaw chuck with one jaw put in "late"
Cheers John
|
|
|
Post by madpatty on Jun 19, 2014 22:25:20 GMT -5
Hi John, Thanks for the technique....i used that technique once for making a cam from a cylindrical shaft....
I am thinking of buying a Milling Machine for my workshop....work will be fabricating small parts for engine... "Main driving force was lack of milling for that compressor DIffuser plate."
Can you suggest what size mill will do the job.....any specific product suggestions are also welcome...
Thanks, Patty
|
|
|
Post by racket on Jun 19, 2014 22:56:54 GMT -5
Hi Patty
Mill size .............as big as possible , my mill is now too small :-(
Cheers John
|
|
|
Post by madpatty on Jun 19, 2014 23:02:05 GMT -5
Hi Patty Mill size .............as big as possible , my mill is now too small :-( Cheers John Thanks John, For the "Optimistic Approach!!!". Cheers, Madpatty
|
|