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Post by madpatty on Oct 8, 2019 22:56:20 GMT -5
What RPMs are you achieving with that motor? and I think you must disengage the starter.. Remove the starter and try to start it with a leaf blower.
I painted a spot on the drive shaft and used my optical tachometer just now. I was measuring about 23,000 RPM before the tach started giving stupid readings. I don't know what the limit is on my cheap chinese unit, but something tells me it's around 23k. I was at about 70% throttle when I hit 23Krpm and that last 30% was definitely a lot faster. A conservative guesstimate would be 30K, maybe 35K RPM. The air flow coming out the exhaust was on par with a simple electric leaf blower. Definitely not one of those backpack units with a 2hp engine but the air coming out was considerable.
I'm not ready to give up on the electric motor start yet. Since it's my intent to use it as a generator in the future I want to see how much I can get working before I give up and grab a leaf blower.
I also wanted to say the motor should be capable of well above 35-40k rpm at full power...it’s a 5.5kw continuous rating motor with peak power of 10kw and 53k no load rpm. I think it may be as simple as combustion happening too late like Racket said and flames coming out from the turbine end sort of proves it. Also you should be giving enough throttle once combustion starts where it should be happening. Cheers. |
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robosilo
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Joined: June 2019
Posts: 15
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Post by robosilo on Oct 9, 2019 8:29:13 GMT -5
Hi What size is the compressor wheels inducer ?? Any turbo in the 50-60 mm inducer range will need to idle at between 70,000 and 60,000 rpm with a 40,000 rpm self sustain speed Cheers John Thanks for the info on the idle speed. I looked back through my notes and the inducer is 63mm. I picked a larger sized turbo so I could work with "lower" RPMs that are also more compatible with the drive motor I'm using. |
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robosilo
Member
Joined: June 2019
Posts: 15
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Post by robosilo on Oct 9, 2019 8:31:31 GMT -5
I painted a spot on the drive shaft and used my optical tachometer just now. I was measuring about 23,000 RPM before the tach started giving stupid readings. I don't know what the limit is on my cheap chinese unit, but something tells me it's around 23k. I was at about 70% throttle when I hit 23Krpm and that last 30% was definitely a lot faster. A conservative guesstimate would be 30K, maybe 35K RPM. The air flow coming out the exhaust was on par with a simple electric leaf blower. Definitely not one of those backpack units with a 2hp engine but the air coming out was considerable.
I'm not ready to give up on the electric motor start yet. Since it's my intent to use it as a generator in the future I want to see how much I can get working before I give up and grab a leaf blower.
I also wanted to say the motor should be capable of well above 35-40k rpm at full power...it’s a 5.5kw continuous rating motor with peak power of 10kw and 53k no load rpm. I think it may be as simple as combustion happening too late like Racket said and flames coming out from the turbine end sort of proves it. Also you should be giving enough throttle once combustion starts where it should be happening. Cheers. Thanks. I'm hoping that once I sort out the spray nozzle that I get closer to a functioning engine. I appreciate all the input that y'all have been giving me. I'm learning a lot! |
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Post by racket on Oct 9, 2019 15:56:56 GMT -5
63 mm inducer is getting a tad large for feeding off a BBQ bottle, you may have difficulties getting up to full power , but OK for lower powers .
You'll still be needing at least 50,000 rpm for a reliable idle speed and ~40,000 for self sustain.
Even at idle you'll be needing a lot of fuel to heat the ~0.3-0.4 lbs/sec of airflow , so a similar "number" per minute of propane , a drawoff of 0.3 lbs/min of propane will soon chill the contents and lower its vapour pressure.
Cheers
John
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robosilo
Member
Joined: June 2019
Posts: 15
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Post by robosilo on Oct 26, 2019 15:29:16 GMT -5
I made a new fuel nozzle that has a bunch more holes compared to the original nozzle and I tried testing the engine again today. I definitely had more fuel flow but still no luck in self sustained running. I used a different battery pack this time so I was able to test longer and I made a few observations:
1. when the motor is running and combustion is occurring the air flow from the exhaust is a lot low than when combustion isn't occurring. I'm guessing this has to due to the pressure in the combustion chamber pushing back against intake air.
2. I have a compressor outlet pressure gauge and I noticed that there is virtually no pressure being generated. I would expect maybe 1 or 2 PSI but the needle isn't moving at all, ever. I double checked that the gauge works and it seems fine.
3. The turbo I bought has anti-surge holes built into the compressor housing. I didn't think it would matter but I'm now thinking that I've never noticed anyone else's engine having those.
All this is making me think that this engine won't run in it's current configuration because it'll never be able to generate enough chamber pressure to maintain enough air flow to the combustion chamber and in turn not enough air to match the fuel flow from the nozzle.
Any thoughts on this? I'm thinking my next step would be filling the holes with some epoxy. or maybe I'm just not reaching a high enough RPM to generate enough PSI for self sustained running. I still figured I'd see the gauge needle wiggle a bit.
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Post by racket on Oct 26, 2019 16:33:05 GMT -5
Hi
Don't worry about the comp housing holes , they're not your problem .
Could you please post a pic of your new fuel injector .
What are your turbine stage specs , scroll A/R and wheel exducer diameter?? .....................there could be a "blockage" there .
You'll need to get more reliable spoolup RPM numbers .
Cheers
John
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robosilo
Member
Joined: June 2019
Posts: 15
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Post by robosilo on Oct 28, 2019 18:07:29 GMT -5
I've attached an image of the nozzle I'm using. The holes along the perimeter aim right at the 2nd set of combustion chamber holes and the spray nozzle at the end aims a little bit below the holes.
I decided to modify the shaft coupling system I'm using and in the process I found some turbine damage. So that's fun. I can't tell if it's F.O.D. or if the turbine side was cooked so much that it flew apart. I'm leaning towards FOD. I don't remember leaving any parts in the engine but the engine has been stored outside so maybe some squirrel left some nuts in there. I was tempted to buy a rebuild kit but I think it'll be safer to just buy a new complete unit.
here is a link to what I bought (and will buy again).
Compressor Trim Inducer Diameter Exducer Diameter A/R
57 61.5 mm 81.5 mm 0.7
Turbine Trim Inducer Diameter Exducer Diameter A/R
84 68 mm 62.4 mm 0.63
 best free image hosting |
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Post by racket on Oct 28, 2019 19:39:51 GMT -5
Hi
Your fuel injector is "wrong", you didn't take the advice I offered in my email of 8 Oct , hence the overtemp damage to the turb wheel.
Unless you rectify the injection , your next turbo will probably suffer the same fate :-(
The turbo in your Link will need to run "cool" as the turb scroll has a pretty tight A/R, the stage will restrict flow and could send the comp into surge if temps are high.
Cheers
John
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robosilo
Member
Joined: June 2019
Posts: 15
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Post by robosilo on Oct 29, 2019 6:21:24 GMT -5
I somehow totally misread your post on the injector. I had it in my head to aim the holes at the second holes I think because I thought those were "primary holes for combustion" and the first set were for aiding in mixing.
Thanks for catching my error.
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Post by racket on Oct 29, 2019 16:24:29 GMT -5
Hi
Yep , we need to get combustion going in the first third of the flametube length, by the time the combustion has travelled down to the Secondary holes it should be just about completed , the Secondary holes add enough air to finish off any unburnt fuel but not enough air to quench the flame , that is left to the Tertiary holes which add the bulk of the air and cool the gases so that the turbine wheel can survive .
By having the fuel injected too far down the flametube you need more fuel than "design" to form a combustable mixture , the Tertiary holes then can't add sufficient air to cool that extra mass of hot gases produced , the result is a dead turb wheel .
Get that propane injected radially towards the middle row of your Primary holes and the engine should work , the air coming in through the Primay holes will collide with the propane "head on" maximising turbulence , mixing and fast combustion , with propane the combustion should be finished before the Secondary holes are reached due to propanes speed of combustion, unlike "slow" burning liquid fuel .
All the best with the next run
Cheers
John
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Post by madpatty on Oct 30, 2019 9:07:58 GMT -5
I've attached an image of the nozzle I'm using. The holes along the perimeter aim right at the 2nd set of combustion chamber holes and the spray nozzle at the end aims a little bit below the holes.
I decided to modify the shaft coupling system I'm using and in the process I found some turbine damage. So that's fun. I can't tell if it's F.O.D. or if the turbine side was cooked so much that it flew apart. I'm leaning towards FOD. I don't remember leaving any parts in the engine but the engine has been stored outside so maybe some squirrel left some nuts in there. I was tempted to buy a rebuild kit but I think it'll be safer to just buy a new complete unit.
here is a link to what I bought (and will buy again).
Compressor Trim Inducer Diameter Exducer Diameter A/R
57 61.5 mm 81.5 mm 0.7
Turbine Trim Inducer Diameter Exducer Diameter A/R
84 68 mm 62.4 mm 0.63
best free image hostingDID you open the turbo to check what damage happened? By looking at it i think the turbine tips are gone. |
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robosilo
Member
Joined: June 2019
Posts: 15
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Post by robosilo on Oct 30, 2019 11:10:10 GMT -5
I haven't pulled it apart yet but the tip are definitely gone. The new unit should be here in a few days and when I swap out the parts i'll try and do a basic root-cause analysis and snap some pics or the carnage. I never heard squealing of metal on metal and never saw sparks fly out the rear so the pieces must have slowly eroded away from heat.
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robosilo
Member
Joined: June 2019
Posts: 15
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Post by robosilo on Nov 4, 2019 17:40:10 GMT -5
Just a quick update:
I made a new spray nozzle and installed the new turbo core. I've attached some pictures of the carnage. You can also see there is a fair amount of oil on the turbine side. I had some leaking out on the last run after I shut everything down. I was running 0w-5 oil because I wanted the pump I'm using to have an easy time. I came across a post on another site that mentioned not using thin oil because it may leak past the seals. The bushing on the turbo seem to be in good shape but I'm sure the seals on the turbine side are shot now. I pulled the oil out and will be replacing it with 15W-30 soon. I'm running about 30PSI using a simple brass regulator. The overflow from the pump is routed to the turbo casing for cooling. I figured that was easier than dealing with water based coolant and a second pump/reservoir.
I've also added a proper tach sensor (hall sensor with magnet) to the motor and surprise-surprise my laser tach readings were way off. The motor was peaking at 25Krpm according to the tach system I installed and I confirmed it with my oscilloscope. That's not at all near the 35K that the laser tach was giving me. So now i'm waiting on a bigger motor driver that should be able to spool up higher. I purposely got an undersized ESC for the motor because I figured I wasn't using it for actual work so why get a bigger one. The current unit handles a 6s battery (22.2v) and 100 amps. My readings were showing that I was only pulling about 15 amps at full speed. But since I'm maxing out at 25K that means the voltage is too low to drive the amps necessary for higher RPMs. The new ESC is rated for 12s (about 48v) and 200 amps. I'm sure I won't get anywhere near that 200 amps but at least it should drive the motor faster and hopefully closer to a speed to make it operate.
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