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Post by racket on Apr 19, 2024 3:44:08 GMT -5
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Post by racket on Apr 19, 2024 2:52:41 GMT -5
You mentioned that your combustion chamber will be...... "radial" ............ ?? Please explain your overall design , just a quick sketch will do
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Post by racket on Apr 18, 2024 20:21:34 GMT -5
I just had a bit more of a read of your pics...... and I'm confused :-(
What Paper are you basing your calcs on ??
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Post by racket on Apr 18, 2024 18:38:51 GMT -5
Hi
Have you worked out your vapourising tubes yet , the number of them will determine the number of holes at each Zone as the air needs to not impact the tubes .
Total tube bore area needs to be ~1/3rd of the Primary zone allocation , the total surface area needs to be ~6 times inducer area
For small engines , 12 tubes would be appropriate .
Cheers John
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Post by racket on Apr 18, 2024 18:28:42 GMT -5
Hi Richard
A new 50Ah deep cycle battery already on order , here next week .
Combined with my 75Ah deep cycle battery that should take care of things .
The 2 X 12V car batteries will be for the starter only.
Its surprising how time flies , its only my batteries dying that provide some indication that the years are going past :-(
Cheers John
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Post by racket on Apr 18, 2024 3:12:20 GMT -5
Lotsa turbulence from those edges :-(
Restricting flow, and PROBLEMS
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Post by racket on Apr 18, 2024 0:07:51 GMT -5
Hi Guys
The sun was shining and with a forecast of thunderstorms this afternoon , a test run was planned after charging batteries and heating the oil tank .
Drove out to my test area , got everything setup.
Checked fuel to oil pressure interlock was working , set the prestart fuel pressure , cameras all turned on .
Hit the starter toggle switch ...........nothin :-(
Bummer , it was working OK at the last test .............then I noticed the oil pump wasn't spinning very fast .............OK , oil pressure interlocked with fuel pump which is interlocked with the starter .
Turned everything off and had a think ............the ancillaries battery was being charged right up until I hooked up the trailer to the car along with the oil tank heater.
Turned on the oil pump , produced its 70 psi for several seconds then started dying away :-(
Packed up and came home .........I'll look at it all tomorrow, ......some days we shouldn't get out of bed .
The rain is bucketing down, thunder and lightning all around ........... LOL , at least the weather forecasters got it right :-)
Cheers John
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Post by racket on Apr 13, 2024 18:57:04 GMT -5
Hi Richard
Yes , most reputable turbos should contain the shrapnel , but that hole at the back can still allow stuff out , the competition turbos have "cross bars" in the scroll exhaust to prevent a detached turb wheel from exiting and spinning off into the crowd .
Cheers John
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Post by racket on Apr 13, 2024 18:00:24 GMT -5
Hi Richard
I should add a warning to Members about trying to run high pressure ratios using turbo parts.
Unless the heritage of the turbo is known , we should keep to more sensible RPM/ tip speeds/PRs ............ the DIY Turbine Community LIMITS were 1450 ft/sec tip speed and 1450 deg F going INTO the turb stage, take a few hundred degs off for turb outlet temps .
With small turbos designed for wide maps and limited PRs , 20 psi P2 would be a reasonable limit , for larger truck sized turbos ~30 psi .
If the turbo is a high quality new unit then follow whats on the comp map and any warning from the manufacturer .
Generally speaking , theres not much point pushing the RPM/tip speed/PR limits as the potential thrust gains aren't there for most turbos We need to be careful if the turb stage is "oversized" as its possible to go into the choke region where overspeed at modest PRs is possible
We don't want exploding turbos :-(
Cheers John
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Post by racket on Apr 13, 2024 16:56:14 GMT -5
Hi Richard
The Nene did a pretty good job considering its rather crude compressor by todays standards .
High compression isn't really needed for a pure jet producing thrust , we end up with too much wasted energy going out the nozzle , but better if theres extra turb wheels to extract power to drive a fan or produce SHP and reduce that exhaust speed and temp .
A 4:1 PR is about the upper limit for a pure thrust engine , we only want enough jetpipe energy to choke the jetnozzle
Cheers John
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Post by racket on Apr 13, 2024 16:47:21 GMT -5
An "afterburner" is possible as long as theres no nozzle on the end of it , you could still end up with thermal choking of a straight tube if its not large enough , this would probably send your comp into surge and/or your turb temps to be excessive
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Post by racket on Apr 13, 2024 5:59:42 GMT -5
Yep , they're the thermocouples I use , very fast response :-)
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Post by racket on Apr 13, 2024 5:57:54 GMT -5
Hi Richard
Yep , shock waves are my current "unknown", just how much compression is there across a shockwave ??
I looked at some numbers for my comp today and with the high inducer tip angle , to reduce incidence to zero between blade and incoming air at the RPM I'm running , the air going in would need to be at ~900 ft/sec and the relative tip velocity is ~M-1.5 , so well into transonic conditions over a large portion of the inducer.
But the throat area of the inducer can't swallow the amount of air that the inducer is biting off at the density available .
So is there an increase in density across the shock that then allows the inducer to swallow what is being bitten off ................I don't know .
LOL.........to answer your question about 5:1 being too great a PR for a single stage comp , nope , some of the tractor pulling guys use 100psi of boost from a single turbo , 7.7:1 PR :-)
Cheers John
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Post by racket on Apr 12, 2024 18:37:48 GMT -5
LOL...........if I had an Amp meter :-(
Its drawing heaps , the starter gets hot to handle very quickly.
I'd sooner the spoolup is as quick as possible , less chance of doing damage from overheating the turb wheel .
I've gotta have a good think on things , theres been so many different tests with different bits added and removed that I'm getting lost.
Running a 5:1 PR should mean a choked NGV , but with a choked point , what happens downstream can't affect things upstream of it, unless what is done downstream removes the choke , I'm getting the feeling that its a fine line between one and the other at the moment .
A challenging scenario :-)
Cheers John
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Post by racket on Apr 12, 2024 15:53:58 GMT -5
Yep , spoolup time , theres ~3 seconds improvement
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