Jet  engines

YOU could save a child's life! >>>

You have arrived at the Original   SYNCHRODYNE  jet engine design page!

The  SYNCHRODYNETM  project - November-December 2001 (last content update: 03 Dec 2001)

• Synchrodyne_TM engine design history:
  
  • CORRECTIONS TO 12/02/2001 EDITION -
    Bruno Ogorelec has kindly contributed a couple of corrections, which have been incorporated into the history below: [a] Bruno is not the moderator of Ken Moller's pulsejet site -- he is just a participant like anyone else taking part in the discussions; [b] The "World's Simplest Engine" is not Bruno's invention -- it is his name for a device proposed in the 1950s by no less than C. E. Tharratt himself. Bruno has so dilligently promoted the building and testing of this engine that it is sometimes informally spoken of as "his", but is really Tharratt's design, as most participants in the forum probably know. I regret my ignorance of the literature, and apologize for the error.
  
  
  
  • 11/19/2001 - Larry Cottrill, as a fairly new participant in the Valveless Pulsejet Forum of Kenneth Moller's pulsejet site, www.pulse-jets.com, receives a reply giving him, for the first time, a clear explanation of C. E. Tharrat's famous "World's Simplest Engine" (so named by long-time participant Bruno Ogorelec), essentially a fuel-injected pipe with a slightly oversized and carefully spaced end cap.
  
  
  
  • 11/20/2001 - Larry proposes the basic prototype design for what would become the Synchrodyne engine in the thread For Bruno - The Cottrill Pump on the forum. This was followed by much back-and-forth discussion with a few other participants and several attempts at drawing engines using text characters, with varying degrees of success. The initial idea was a perfectly straight pipe closed at the front end, drilled transversely straight through at the 'one-third point' to form two sections (a 'stopped' pipe followed by an 'open' pipe) merging at two intake ports. The idea is that the closed front end would act like a reflective pulse compressor with the rear end acting as a bidirectional-firing combustor, with air/fuel carburetion being induced by one port on both forward and rearward flow. Larry claims that this will be an attempt to produce, at least in imaginary form, "the world's simplest carbureted engine", and hopefully a worthy challenger to the 'injected' design.
  
  
  
  • 11/20/2001 - Bruno responds to the design proposal, voicing some skepticism, particularly concerning the absence of a "venturi" structure to lower static pressure for carburetion. This was followed by more discussion by a few participants, and more 'text drawing' attempts showing various engine concepts.
  
  
  
  • 11/21/2001 - In a response to comments by participant Don Lawn, Larry concedes the need to go to a 'waisted' design (a practical way to provide Bruno's "venturi") and simplifies construction slightly by reducing the intake ports to a single large port. Otherwise, the basic theory of the design is still unchanged, with compression and regeneration at the front end and air/fuel mixture being drafted in on both phases of bidirectional flow between the compressor and combustor stages.
  
  
  
  • 11/21/2001 - In a response to another forum participant, Larry reiterates the inherent simplicity of construction of the prototype design, even with the adopted modifications, still claiming that this remains in fact "the world's simplest carbureted engine".
  
  
  
  • 11/22/2001 - Larry does the initial cutting of the tube, using 1/2-inch (nom.) EMT ('Electrial Metal Tubing' - aka rigid conduit), and forms the intake port aperture and flattens the tube to form the velocity duct 'waist'. Total time, including setup and cleanup: 87 minutes.
  
  
  
  • 11/23/2001 - In a response to Bruno on the forum, Larry announces that construction of the prototype model has begun.
  
  
  
  • 11/24/2001 - The engine mount plate is drilled and cut; welding is completed on the front end, spark plug mount and engine mount; spark plug hole is drilled and tapped. Total additional time: 95 minutes. Total construction time so far: 182 minutes.
  
  
  
  • 11/26/2001 - In a response on the forum, Larry posts progress on prototype model construction.
  
  
  
  • 11/26/2001 - The fuel/air pipe mount is cut and formed, based on the use of a "flowjector" type assembly already built for the prototype Pulsodyne(TM) engine; final smoothing of the intake port edges is done; fuel pipe mount is welded to the main tube and some touch-up welding is done on the engine front end; existing "flowjector" is fitted to the pipe mount and aligned with the center of the intake port. The Synchrodyne Version 1 prototype working model is complete! Added time: 113 minutes. Total time: 295 minutes - just under 5 hours total time to construct! (Making the fuel/air pipe would have added a couple more hours if the existing "flowjector" assembly could not have been used.)
  
  
  
  • 11/27/2001 - Larry announces on the forum that construction is complete; he also announces intent to use the Synchrodyne name as his trademark for the design. Testing only awaits getting some photos of the model to post on the forum, etc. plus reasonable weather and getting through a few prior commitments.
  
  
  
  • 12/01/2001 - INITIAL TESTS!   See Test Journal page ...
  
  
  
  

• Synchrodyne_TM engine - functional description:
  
  • The device consists of the following elements, of high temperature materials and circular or other suitable cross section (listed in essentially front-to-rear order):
    • Compressor stage - a chamber (properly called the Pulse Synchronous Compressor, but hereinafter simply called the 'compressor stage'), fully closed at the front end and opening rearward into the larger end of the forward nozzle;
    • Forward nozzle - a smooth cone acting as an efficient nozzle for accelerating rearward flow from the compressor stage into the velocity duct, and acting as an efficient diffuser for pressurizing forward flow from the duct into the compressor stage;
    • Velocity duct - a smooth narrow duct of constant cross section connecting the reduced-area ends of the forward and rear nozzles and perforated at its midpoint by the intake port (the duct and nozzles are arranged in a symmetircal configuration around the port);
    • Intake port - a relatively large, smooth-edged perforation in the midpoint of the velocity duct for entry of normal air/fuel mixture;
    • Fuel/air pipe assembly - a very narrow pipe for fuel delivery terminating in one or more small fuel nozzles positioned at the point of lowest static pressure in the intake port; and (for engine startup) a very narrow air duct whose exit stream will flow with high velocity directly around the fuel nozzles and into the intake port in a generally rearward direction (so as to flow through the rear nozzle toward the primary combustion zone);
    • Rear nozzle - a smooth cone acting as an efficient nozzle for accelerating forward flow from the primary combustion zone into the velocity duct, and acting as an efficient diffuser for pressurizing rearward flow from the duct into the combustion zone;
    • Tailpipe and primary combustion zone - the tailpipe receives all rearward flow gases through the rear nozzle (acting as a diffuser) and supports ignition and combustion in its forward section, called the 'primary combustion zone'; after ignition of the fuel/air mixture, the primary combustion zone supplies combustion product gases forward through the rear nozzle, to initiate the first aspiration phase of the next engine cycle; for starting, a high-voltage spark plug is provided near the front end of the primary combustion zone.
  
  

  The velocity duct area, showing fuel & air pipe mounting bracket, with needle valve & fuel pipe assembly in place -- dual fuel ports (too small to see here) are centered in the intake port opening (Jason Wemer photo)

  The velocity duct area with mounted fuel & air pipe assembly, showing fuel pipe penetrating the intake port -- Champion V-3 spark plug is at bottom in this view, just to right of the rear nozzle of the duct (Jason Wemer photo)

  
  
• Synchrodyne_TM engine - basic theory of operation:
  
  1. An explosion in the primary combustion zone drives half the expanding gases rearward and half forward. The rearward gases proceed down the tailpipe unimpeded (i.e. normal pulsejet exhaust phase inertial action).
  2. The forward gases are accelerated through the rear nozzle (where flow velocity is greatly increased while pressure and density decrease) into the velocity duct, past the intake port perforating one side of the duct, through the forward nozzle (which acts as a simple diffuser in the case of forward flow) into the compressor stage. New air and fuel are picked up as the gases stream past the port, due to the reduced static pressure of the high-velocity flow. This 'venturi suction pump' action produces increased gas density and somewhat slows the flow beyond the port, although with such high-temperature flow, net gas flow momentum actually increases (similar to the 'thrust augmentor' principle), which assists in initially pressurizing the compressor section.
  3. Meanwhile, the rearward-moving gases in the tailpipe decrease static pressure in the primary combustion zone. After the passage of the forward flowing gases past the intake port in the velocity duct, this decreasing pressure in the primary combustion zone extends through the rear nozzle to the intake port, allowing a normal pulsejet draft phase to be initiated (i.e. flow of air/fuel mixture inward through the intake port and rear nozzle, diffusing into the primary combustion zone of the pipe).
  4. Meanwhile, in the compressor stage, the gases are slowed by diffusion in the forward nozzle (so density and static pressure are regained), are reflected off the front end plate of the compressor stage chamber, experience a significant pressure increase due to the secondary combustion of the air/fuel mixture that was previously picked up through the intake port, and are forced back through the forward nozzle in a rearward direction into the velocity duct.
  5. The returned gas passes through the duct at very high velocity and reduced density and static pressure, thus picking up yet another charge of fuel/air mixture. Once again, there is a net momentum gain, but this time in the rearward direction. The gas continues rearward, following the rearward flow of air/fuel mixture already picked up by normal draft phase action into the primary combustion zone.
  6. The returned gas is slowed by diffusion into the primary combustion zone, thus undergoing an increase in pressure and density, promoting another combustion cycle with resultant gases again dividing between rearward and forward flows, thus causing the entire multi-phase action to re-start.
  7. Maximum output is obtained when the aspirated gas charge pumped rearward by the compressor stage synchronizes its entry into the combustion zone with substantial completion of the normal (i.e. tailpipe driven) intake draft phase. Another way of stating this is that 'ideal' or 'maximum efficiency' operation will occur when the three aspiration phases (forward flow into compressor stage, tailpipe draft, rearward flow from compressor stage) are closely coupled, with each picking up just as the previous phase begins winding down. This synchronous operation can be optimized by proper sizing of the compressor stage chamber in relation to the tailpipe length and volume at normal operating temperatures.
  
  
• Experimental prototype (version 1.0) - basic construction specifications:
  
  • Main tube materials: .625 inch ID mild steel tubing, formed and welded, with high-strength steel nose
  • Air / fuel pipe assembly: Brass tubing, formed and silver soldered
  • Pulse compressor section length: 4.5 inches (114 mm) approx.
  • Compressor section ID: .625 inch (15.9 mm); cross-sectional area: .307 sq.in. (198 mm^2)
  • Compressor section area / tailpipe area: 100 %
  • Forward nozzle length: 1.0 inch (25 mm) approx.
  • Velocity duct section length: 1.5 inches (38 mm) approx.
  • Velocity duct inside dims: .915 x .130 inch (23.2 x 3.30 mm); cross-sectional area: .112 sq.in. (72.3 mm^2)
  • Velocity duct area / tailpipe area: 36 % approx.
  • Rear nozzle length: 1.0 inch (25 mm) approx.
  • Intake port location: Velocity duct midpoint, approximately
  • Intake port dimensions : .28 inch x .63 inch (7.1 mm x 16 mm) oval, approx. (major axis transverse to engine centerline); cross-sectional area: .160 sq.in. (103 mm^2) approx.
  • Intake port area / tailpipe area: 52 % approx.
  • Initial combustor/tailpipe section length: 14.25 inches (362 mm) approx. [may be shortened experimentally]
  • Combustor/tailpipe ID: .625 inch (15.9 mm); cross-sectional area: .307 sq.in. (198 mm^2)
  • Distance - engine nose to spark plug mount: 8.0 inches (204 mm)
  • Distance - engine nose to first mounting hole: 7.875 inches (200 mm)
  • Distance - engine nose to second mounting hole: 8.875 inches (225 mm)
  • Mounting holes - diameter: 3/16 inch (4.8 mm)
  • Engine Total Machine Weight [may vary experimentally]: 9.25 ounces (262 g) approx.

	Larry Cottrill with the original SYNCHRODYNETM engine prototype (Jason Wemer photo)
The  SYNCHRODYNETM  miniature jet engine

        Now under development by

Corporate Main Office
11905 NE 110th Ave
Mingo,    IA 50168-9500
Contact:   synchrodyne@cottrillcyclodyne.com

Page updated: 28 August 2002

Copyright 2001 Cottrill Cyclodyne Corporation
- All rights reserved -