Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 88080 times)

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #60 on: August 20, 2014, 03:28:28 PM »
For several years I have been testing carburetors without fuel metering, no diaphragms, no butterflies, no choke plates, no metering circuits, no pop-off springs, no filtering screens & only one needle to adjust, but with a needle valved controlled air bleed system which prevents the carburetor from loading up at low throttle settings. Opening the air bleed circuit at the correct time is critical as well as controlling the amount of addition air that is necessary to prevent the engine from going to a rich setting & eventually flooding out. Since there is no obstruction of any kind (butterflies, choke plates, metering tubes or fuel delivery tubes) in the incoming air stream, maximum air flow through the carburetor's .625" bore is easily possible. The same features of the the .625" bore automatic fuel metering (100% maintenance free, extremely reliability & wear resistance) are found in the .625" bore air bleed type carburetor. Throttle response from 3,000 to 22,000 RPM is instantaneous. The necessary amount of fuel to be delivered to the carburetor is a function of the pressure developed in the custom designed tuned pipe. The entire fuel system is pressured & that pressure follows exactly the engines RPM's.

Jim Allen

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #61 on: August 20, 2014, 08:46:08 PM »
Another amount of great information and pictures - thank you very much  :praise2:

Best wishes

Per

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #62 on: August 21, 2014, 02:34:00 PM »
Construction of the tuned pipes used on both the gas & nitro methane powered engines are machined from solid bar #1018 cold rolled steel. A typical wall thickness of .020", with .010" at the joining points of the overlapping  sections, which are silver soldered, gives a chamber that is precise & very smooth inside. Silver soldering is done while the tuned pipe is slowly rotating between centers in the lathe. Tuned pipes are painted with, baked on, high temperature exhaust paint. There will be no discussion of the technical aspects of the tuned pipes or how they work. I will say that just about any tuned pipe will work to increase the engine's HP. However,  there will be only one tuned pipe capable of increasing the engine's HP 45 to 50% at a particular RPM range. Finding that tuned pipe is not easy!

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #63 on: August 22, 2014, 01:39:28 AM »
I have no idea where to begin when discussing the hydraulic dynamometer. Maybe if some engine builders out there posted questions we could begin this discussion. As a start this water brake is modeled after the Kahn, single perforated disk, hydraulic dynamometers. It uses a sealed housing mounted in a Rulon lined trunnion type mount. Rulon is used because it has the lowest stick slip rating of any known material. Using sleeves for the trunnion bearings in place of ball or roller bearings helps dampen vibrations & also gives a very high load carrying capability to the trunnion mount. Align boring of the trunnion sleeve bearings was done after both ends of the mount were fastened & doweled pinned.

More to come.

Jim Allen
« Last Edit: August 22, 2014, 01:43:20 AM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #64 on: August 23, 2014, 12:15:28 PM »
The dynamometer's housing, which can rotate freely in it's Trunnion mounts, is very precisely machined & requires no type of sealing ("O" rings, gaskets or sealing compounds). Sealing is accomplished with an interference fit of the two housing pieces & 16, 6-32 SHCS. Machined holes or pockets in the rotor & the housing inside faces create an annulus as the rotor rotates, which is rotating at approximately half of the angular rotor's speed. The resulting drag created by the annulus formed applies a resisting force to the rotors rotation & an equal force to turn the dynamometer's housing.

The very high centrifugal force which results from this process forces the hot water out of the housing through the metering valve shown in the photo. The precisely machined, double sealed, outlet valve controls the amount of water (size or depth of the rotating water annulus) & therefore the amount of power that can be absorbed. This feature allows the dynamometer to apply infinitely variable loads the the engine. A water reservoir, which maintains a constant pressure, supplies incoming cold water to the dynamometer's housing from both sides of the rotor.

The rotors in my dynamometer are machine from 7075 T-651 aluminum. Rotors used in larger size hydraulic type dynamometers would be made of hardened stainless steel. They would be Blanchard ground & the entire rotor assembly would be dynamically balanced. A hardened stainless steel rotor provides superior resistance to corrosion & cavitation erosion.

Jim Allen
« Last Edit: September 07, 2014, 05:39:53 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #65 on: August 23, 2014, 12:23:24 PM »
Additional photos..................

Offline smfr

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #66 on: August 23, 2014, 05:04:16 PM »
Fascinating stuff, Jim. Keep it coming  :ThumbsUp:

Simon

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #67 on: August 26, 2014, 07:13:09 PM »
Interesting stuff, thank you.  :ThumbsUp:  :ThumbsUp:  To my understanding you are really using fuel injection rather than carburation. The fuel flow is set by the engine RPM (exhaust pressure).  :headscratch:
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #68 on: August 29, 2014, 01:41:04 PM »
Roger,

I don't think the "very simple system" I'm using would qualify as a fuel injection system.  I am aware that a fast enough, fuel injection system with small injectors, that could keep up with engine RPM's from 22,000 to 30,000, does not exist. I guess my system could be described as a continuous indirect injection system with some measure of fuel metering. Injectors, operating under high pressures, deliver very small fuel droplets that can be easily atomized. My system is dumping fuel into the incoming air stream under the maximum pressure of 120 inches of water (4.336 psi). A fuel injector could inject the fuel at 2.5 BAR (36.259 psi).  One advantage of injecting in the intake tract is the big end connecting rod bearing is lubricated & cooled by the fuel spray.

Jim Allen
« Last Edit: August 29, 2014, 01:49:02 PM by strictlybusiness1 »

Online lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #69 on: August 29, 2014, 06:00:31 PM »
Tuned pipe pressure to the tank has been the standard in glow ignition engines for a long time.  Crankcase pressure has also been used, most successfully with a pressure regulator.  The use in a gasoline fueled engine is a lot less common due to the readily available carbs like the Walbro.  However, at high rpm the pumper carbs can't keep up.  We have had consistent problems in our straight line record engines that turn over 20,000 rpm.  Jim's "simple" system avoids this issue and feeds fuel proportionally with the pipe pressure.  Pipe pressure is related to power, so in the system can be adjusted to work well.  However, it's not as fool proof as the pumper carbs for low performance, industrial engine use.

Lohring Miller

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #70 on: August 29, 2014, 08:21:26 PM »
My thought was that the fuel flow is controlled by the exhaust pressure (load) rather than the manifold depression. Some simple single point automotive fuel injection systems had a continuous flow into the entrance to the manifold rather that pulsed injection by each valve.
Best regards

Roger

Offline karolh

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #71 on: August 29, 2014, 08:26:37 PM »
Absolutely amazing and impressive work and all I can say is wow. So very glad that I found this thread. Please continue to share your outstanding work with us.

Online Jo

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #72 on: August 29, 2014, 08:52:23 PM »
Hi Karol,

Any chance of posting an introduction to yourself and your modelling interests in the introduction section?

It will let the other members get to know you and they may be able to help you in the future  ;).

Jo
Enjoyment is more important than achievement.

Offline karolh

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #73 on: August 30, 2014, 02:06:03 AM »
Hi Karol,

Any chance of posting an introduction to yourself and your modelling interests in the introduction section?

It will let the other members get to know you and they may be able to help you in the future  ;).

Jo

Will do.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #74 on: August 30, 2014, 02:00:13 PM »
Tuned pipe pressure to the tank has been the standard in glow ignition engines for a long time.  Crankcase pressure has also been used, most successfully with a pressure regulator.  The use in a gasoline fueled engine is a lot less common due to the readily available carbs like the Walbro.  However, at high rpm the pumper carbs can't keep up.  We have had consistent problems in our straight line record engines that turn over 20,000 rpm.  Jim's "simple" system avoids this issue and feeds fuel proportionally with the pipe pressure.  Pipe pressure is related to power, so in the system can be adjusted to work well.  However, it's not as fool proof as the pumper carbs for low performance, industrial engine use.

Lohring Miller

Recent test have shown that a tuned pipe pressurized system, without any fuel metering, can operate at low performance levels as well as very high RPM levels. A key factor in this system is the needle valved controlled air bleed circuit similar to the type that GBritnell used on his barrel type carburetor. Control of the amount of air added as the barrel is closing & control of the exact time when the air is added is required for proper operation. When both are done correctly the engine can idle indefinitely at 3,000 RPM & accelerate instantly, without hesitation or stumbling, to 22,000+ RPM. Even though the engine can sustain a continued low idle of 3,000 RPM, the lowest operating RPM needed when operating under load is 9,000 RPM. An additional important feature of this system is the high performance sparking coil used which can fire a spark across a .040" gap. Most engines of a 26 cc to 35 cc size will run spark plug gaps of .015" to .020".  I run a .025" to .030" gap which gives a longer duration spark. Also the spark plug wire used is a low resistance, stranded copper conductor 8 mm in size with high performance connectors at both ends. I make the ignition wire used & crimp the connectors with a special tool. A special digital multi-meter tells me the resistance of the spark plug wire is much less than .1 ohm.

Jim Allen