Uniflow Steam Engine John Cozby, August 2012
The uniflow steam engine has been around for a long time. It was first used in Britain in 1827. A patent was granted on it in 1885. The first commercial stationary engine was produced in 1908. It was popularised by German engineer Johann Stumpf. (Ref. Wikipedia) Dr. Stumpf referred to the design as the una-flow steam-engine. It has been referred to by Prof. Dr. Nägel and Dr. Mollier as the Stumpf cycle. Around 1920 the Stumpf Una-Flow Engine Company, Inc. of Syracuse, N.Y. designed and built una-flow engines for automotive purposes. Three different sizes were built. This engine is illustrated in Fig. 33, page 271 of The Una-Flow Steam-Engine by J. Stumpf, 1922. The following quote is from page 272, Ibid.:
“The cylinders are cast in pairs, which are arranged at 90° with one another . . . . . The cylinder bore is 3.375 inches and the stroke 3.75 inches. The single-beat valves are operated by cam shafts which are movable endways. These cam shafts are provided with a neutral cam, and cams for 9%, 25%, and 80% forward cut-off, and one for 80% cut-off for reversing. All the working parts are enclosed.”
Automotive uniflow engines have been around for a long time. Many of the automotive engines built in the 1960's and 1970's were of the uniflow type. Several people since that time have worked diligently to improve upon the automotive type uniflow engine. One of the best known men to do this recently is Harry Schoell of Florida and his Cyclone Engine. Mr. Schoell’s engine is a radial uniflow engine. It can operate at high temperature and high pressure. His design has been referred to as the Schoell cycle engine by James D. Crank. Many others are working on or employing uniflow steam engines in automobiles, and are designing improvements. There have been promising and encouraging results. The “Steam Automobile Club of America” encourages these efforts. Simplicity of design and construction is an advantage of the uniflow engine. In general, a re-heat engine is more complex and difficult to construct. As strange as it may seem, the uniflow engine work of Johann Stumpf, Harry Schoell, and others has done much to affirm, confirm, and support the design criteria chosen for and employed in the more complex advanced Rankine cycle Unitary re-heat engine system.
Our previous website was hosted by Microsoft Office Live. Earlier this year Microsoft Office Live dropped all of their websites, including ours. On our previous website, CozInc-MT-USA.com, we did not address the subject of the uniflow engine. We were not ignorant of the uniflow engine. We began research on various steam engine designs in 1966 – 1967. Frank Graham’s text dealt with the uniflow steam engine. Mr. Graham’s text was the first which we began to study. Later, Mark’s Handbook, 4th Ed., described the uniflow. We studied and considered the uniflow. We chose a different path for several reasons. The single stage, non re-heat uniflow engine seemed to be too limited in efficiency, especially when higher load conditions are encountered. There seemed to be some mechanical issues, particularly when following load shifts. There seemed to be lubrication problems, especially at high temperatures. There seemed to be steam contamination problems which are a special concern for closed loop systems. The uniflow design did not seem to be adaptive to an engine braking function in vehicles because of the type of exhaust employed in uniflow engines. Engine braking for automobiles and trucks seemed an important aspect to us. Engine braking does not consume steam or energy in the counter flow engine. There seemed to be no way to employ re-heat in uniflow design, again, because of the type of exhaust employed in uniflow engines. We chose to focus on counter flow engines with multiple stages and with multiple re-heats as the best means to achieve the greatest efficiency with a steam engine and include engine braking function. For instance, a multi-stage engine at high over-load can still be getting twice the expansion ratio of the uniflow engine running at economy. (Generally, the higher the expansion ratio is the better the efficiency is.) The counter flow engine in braking mode can also retard a vehicle’s motion, or stop the vehicle, or hold the vehicle stationary. The uniflow engine is simpler in design and construction. The uniflow can operate effectively. The uniflow has its sincere adherents. All piston type steam engines have a number of characteristics in common. Choosing the “right design” depends upon what criteria and priorities for a given application dominate the selection process. Where the best efficiency at all loads is a major concern and engine braking is an important consideration then the multiple stage, with multiple re-heating and multiple bleeds for feedwater heating will likely be the engine of choice.
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Why Some Steam Engines Cannot Seal High Pressure Steam
John A. Cozby December 8, 2012
I. For best efficiency steam engines use high pressure and high temperature steam
II. The effect of steam leakage past rings: [What pressure? 2,500 3,000 3,200 psi?]
1. Loss of efficiency
2. Loss of power
3. Greater condenser load
III. Statement of the issue: “Some piston steam engines cannot seal high pressure steam”:
1. Tom Kimmel presentation, SACA/IAASP Meet, 2012 (Leakage about 10%)
2. SAE papers confirm
3. SAAB could not seal; used 7 rings, SAE paper
4. Carter’s engines, sealing problems, SACA Bulletin, Nov-Dec 2012
5. SACA member in conversation at SACA Annual Meet: “Rings cannot seal steam.”
6. Fact: Rings cannot seal steam; rings cannot even seal cool low pressure air
6.1 Example; my lawn mower experience
IV. What is necessary for good sealing?
1. Close tolerances at ring/cylinder interface
2. Adequate continual supply of cool oil to cylinder and rings
V. The unique case of most uniflow engines (Why they leak)
1. Tolerances
1.1 Hot end, cool end (extreme difference/expansion; hotter steam, worse problem)
[How hot? 1,200˚ 1,500˚ 1,652˚? How cool? 193˚ less? Saturated]
1.2 Lose close tolerances (lose oil film seal)
1.3 At the worst point (highest pressure and temperature)
2. Quantity and dispersion of oil
2.1 Too little
2.2 Injected into steam (diluted, dispersed, suspended through cylinder volume)
2.3 Flushed out the exhaust (not retained)
3. Temperature of oil: Too hot (injected into steam)
4. Failure on all points results in lack of sealing and serious leakage or worse
VI. Other related aspects
1. Start-up and slow speed operation
2. Late cut-off for greater power
3. Combined start-up and late cut-off
4. Higher temperatures create greater loss (heat value) [3,000 psi at 695˚F contains 1020 Btu, at 1200˚F contains 1575 Btu, and at 1500˚F contains 1764 Btu]
5. Extreme piston loads (result of high pressure and single stage)
VII. Piston steam engines of the Cozby type design do not suffer these detrimental defects
(Steam engines should be steam tight)
FOOTNOTE: “The Rest of the Story”
During the 1960's and 70's many uniflow automotive type steam engines were built. Abner Doble built and sold uniflow steam engines. Abner Doble had this to say about uniflow engines: “The uniflow engine was found unsuited for use in a motor vehicle. Its economy in motor vehicle service was definitely less than the compound, it was heavier, uncertain in maneuvering, apt to block on hills (due to the long compression), and undesirable for high speeds due to the very heavy long pistons. The early cut-off necessary to give sufficient expansion produced an irregular torque, quite unsuitable for a motor vehicle,”1. The Keen, Pritchard, Williams, Saab, Carter, Scientific Energy Systems (SES), General Motors (GM), and Steam Power Systems (SPS) companies built uniflow automobiles, buses, and engines. Some were better than others and the designs varied, but none really succeeded. Many millions of dollars in government and private funding has been spent on “leaky” uniflow engine designs. This fiasco has “poisoned the well” of advanced steam engine development before advanced steam engine development had a real chance to begin. (“Steam is dead”: U. S. Department of Energy, Department of Commerce)
John Cozby Dec. 12, 2012
1 DOBLE STEAM CARS, by J. N. Walton, 3rd Ed. 1975, LIGHT STEAM POWER, Kirk Michael, Isle of Man, Britain page 19 (last note, June 1997)
From: The White Steamer by A. T. Edmonson, Chicago, Ill. 1910; pages 13, 14
“Lubrication . . . enumerated in the order of their importance:
1st. The cylinders. Applied energy is obtained from a steam engine by means of the steam pushing a piston up and down in a closed cylinder. This piston must fit close enough to be steam tight and at the same time be free to move up and down. From this fact it can readily be seen that the power and economy of the engine depends upon a steam tight joint between the moving piston and the cylinder walls. Proper cylinder lubrication helps preserve this steam tight fit and helps to prevent leakage past the piston by forming a film on the cylinder surface. . . .
On the scale of importance, the second place for lubrication is given to the engine crank case.”
The White Steamers injected oil into steam at 735 degrees F.
Doble injected one drop of oil into 765˚ F steam for four cylinders once for every 50 revolutions.
Besler, successor to Doble, used 800˚ F and 825˚ F steam in their engines.
SES, ERDA Contract E(11-1)-2701, used 900˚ F to 1,100˚ F steam in a uniflow engine.
