Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 85521 times)

Online strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #315 on: October 26, 2018, 08:27:55 PM »
This is very interesting, considering that  one of the main enemies of any compression ignition engine is detonation.

Jim

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #316 on: October 26, 2018, 09:01:38 PM »
Isnt it? I thought so too. I knew you'd want to see this.

http://www.aero-news.net/index.cfm?do=main.textpost&id=08312146-cc40-476d-a000-57401f63f5b9

don't want to pull you guys off this interesting thread but Im sure you all will find it quite interesting how detonation is being used as a friend instead of the enemy.  Really cool technology is.

Email you later JA
TTYS

Online strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #317 on: November 25, 2018, 04:35:54 PM »
After testing many different tuned pipe prototypes we can finally show a dedicated chamber for use with 32 to 35 cc displacement gas engines. The bottom two prototypes will be going into production for this purpose. The posted photo clearly shows the difference between what is available on the market & what is necessary in an attempt at achieving maximum HP. A tuned pipes maximum internal volume, compared to the displacement of the engine in question, is definitely one  controlling factor in the design of any tuned pipe!

Jim Allen

« Last Edit: November 25, 2018, 07:51:49 PM by strictlybusiness1 »

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #318 on: November 25, 2018, 09:53:04 PM »
It might be the light or eyes deceiving me, but - is the bottom pipe in the picture having a continuously changing angle on the first diffuser cone ?

I ask, because I always felt that this would be the optimum, just like when used for sound (speakers, trombone etc.) or fluid dynamics (turbines etc.), where any kind of sharp edges are usually a no, no ....

Online strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #319 on: November 27, 2018, 06:50:37 PM »
Per,

Yes. We attempted to make a smoother transition from the header pipe through the diffuser sections to the mid-section by adding more pieces. Instead of the standard 2 or 3 sections found on most pipes there are 5 sections in the diffuser section. What is important is that there is no long length flat area from the exhaust window to the mid section of the chamber. The next thing is to CNC machine the sections to eliminate any flat area whatsoever.

Jim

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #320 on: November 27, 2018, 07:03:51 PM »
Fascinating  ::)  :headscratch:  :ThumbsUp: There is so much to learn about two stroke engines
Best regards

Roger

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #321 on: November 27, 2018, 08:07:27 PM »
Ah and I thought that it was hydroforming as the first photo didn't show the welds of the cones but looked like it was two sheets welded end to end and then "blown up" to shape.

Very nice work none the less  :ThumbsUp:

Online strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #322 on: November 28, 2018, 05:17:55 PM »
Ah and I thought that it was hydroforming as the first photo didn't show the welds of the cones but looked like it was two sheets welded end to end and then "blown up" to shape.

Very nice work none the less  :ThumbsUp:

No Hydroforming but two pieces formed in a mold & then welded together. This is not the best method for making a prototype pipe because it cannot be easily modified or changed. Machined pipe sections are fitted to join inside or outside of their matting pieces. This method makes a completely smooth inside surface & a very strong joint even when the joint is silver soldered. The joint is typically .050" wide with each joining piece's thickness cut in half, typically .010" thick.  This method can also be used when joining sections that have a radius.

Jim Allen

« Last Edit: November 28, 2018, 07:31:01 PM by strictlybusiness1 »

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #323 on: February 22, 2019, 09:33:55 PM »
Finally got the shop put back together. There are more than 20,000 screws in the inventory plus dowel pins, washers, nuts, rolled pins, etc., etc.
Building & re-building the necessary engines for this season. The last photo's are the new assembly, disassembly die being made.

Jim Allen

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #324 on: February 23, 2019, 11:35:21 AM »
I'm building a new die set for the assembly & disassembly of three piece crankshafts. After assembly they will be zeroed within + or - .0002" from end to end in a four jaw chuck.

Jim Allen

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #325 on: February 23, 2019, 04:23:56 PM »
I don't know how you keep your shop so neat.  Too many projects and boats in too little space.  At least I found the chuck key on the mill table.

Lohring Miller

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #326 on: February 23, 2019, 06:53:17 PM »
Lohring,

I finally finished cutting three sets of 1/16" thick, #9850 Garlock gasket material, which is used between all the surfaces on the intake side. The gasket material is composed of carbon fibers with a nitrile binder. Maximum temperature of 900* F &  a maximum continuous temperature of 650* F. I carefully re-machined the delrin isolation block to match the 19 MM carburetor bore.

This stuff should take care of the sealing on the intake side. Oh, I forgot, the two extended water fittings are enlarged & they are made of 6AL4V Titanium.

Jim
« Last Edit: February 24, 2019, 02:56:32 AM by strictlybusiness1 »

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #327 on: February 24, 2019, 05:10:12 PM »
I've been playing with a Tillison clone carb with a 21 mm venturi bore in simulations.  Intake tuning helps a little as well.  Below are the formulas I found.

RPM = 108K ( 1st hamonic ) 97K ( 2nd harmonic ) 54K ( 3rd harmonic )  / L ( inches )
 
So examples are 1st Harmonic 6000 rpm = 18",and 12,000 rpm = 9"
                            2nd Harmonic 6000 rpm = 16.16" and 12,000 rpm = 8.08"
                            3rd Harmonic 6000 rpm =  9" and 12,000 rpm = 4.5"
Rearranging the above:
L=54,000/rpm for the third harmonic.

The higher rpm we run at makes the 3rd harmonic realistic.  At 18,000 rpm that would be 3" or 76 mm.  We found that a little shorter isolator block helped Zenoahs at high rpm.  Velocity stacks were too long and hurt power.  I think Quickdraw has experimented with intake tuning as well.  Our engines came with several thick gaskets that we were told not to change. 

Lohring Miller

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #328 on: February 24, 2019, 08:21:06 PM »
Very interesting formula, but it "breaks Math" as the definition of Harmonics is :

1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + 1/8 + 1/9 + .....

Fundamental + second + third + fourth + fifth + sixth + seventh + eight + ninth + .....

So where does the 2/3 as the second and the 1/2 as the third come from ?

Or are "real harmonics" part of the "original formula" in such a way that it solves into what you wrote Lohring ?

I'm NOT trying to say that the formula doesn't make sense or isn't useful - it is more a definition thing.
If it was music, the 2/3 interval is one of the most important harmonics and is funnily enough named the Fifth (as it is the fifth note in the Major Scale).

Online strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #329 on: February 24, 2019, 10:15:27 PM »
Lorhing,

Very interesting numbers! I have not lengthened or shortened the length of the intake track since I began modifying theses engines. Everything is in nearly the same position, including the throttle arms, as when the engines came from QD. This would include the Walbro & .625" bore automatic fuel metering carburetors. All of the systems are using tuned pipe pressure, but the 19 mm Tillotson carburetor uses both tuned pipe pressure & the crankcase pulse. My pulse line is very short & very rigid. One area that is very different is the smooth transition between the rectangular shaped intake window (.845" X .480") & the round 19 mm (.748") hole. Their areas are also similar, .406 sq in ( rectangular window) to .439 sq in (round hole). The total length of the intake track has remained at approximately 3.500". The engine is now making more HP in the over rev range beyond 19,600. The difficulty with shortening the length is that it can only be done in the delrin isolation block.

Jim Allen
« Last Edit: February 24, 2019, 10:23:26 PM by strictlybusiness1 »