Engines and Boilers
We continue working on all sorts of ideas and learning from prior art and new developments. Below are current projects and some old ones.
Tony Nardi's Unity Uniflow Rotary Engine
United States Patent 6503072
The most exciting thing to come along has been the Unity Uniflow Rotary Engine, designed and patented by Anthony Nardi. He and his family contacted me in November of 2006. I took a look and wasn't sure, but was intrigued.
The Nardis were persistent and Tony got on the phone and explained it to me. Over the next few weeks I studied the design with an open mind, and a few more phone calls later I had made a small model.
I have been given permission to post our tests and results here but understand this in no way is permission for the commercial manufacture without express written consent of the patent holder.
I continued trying to understand how pressure articulated star shaped pistons could whirl around triangle shaped cylinder heads without jamming. It wont turn by hand more than a third of a rotation, but apply pressure and inertia and the pistons do what they are designed to do. Very little metal to metal contact.
The pistons float in their nests. At exhaust, the piston lobe (due to centrifugal force and the release of steam pressure) touches the rim and drags, it then starts its turn around the virtual cylinder head. With precisely timed steam admission and inertia the piston is forced back into its nest and is held by equal forces tight in its nest. While it looks like it is a gear meshing, there is very little metal to metal contact. Sounds like a VW bug engine.
I machined the intricate but simple engine from stock. Aluminum and brass. In February it was ready to test. And while it is very small it worked fine. The piston area is only .35 by 1". And because there are three power strokes per revolution it runs smooth even at slow speeds.
There are issues with startup and shutdown that can be resolved with good design. The pistons and rotor must have some drag as the pressure drops to zero so they hold in position for the next startup. This was achieved with a pressure plate which has zero clearance to the pistons and rotor, but presses away a thousandth of an inch as pressure is admitted to the cylinders.
Anthony Nardi's original engine is 18" diameter with 5" x 2.5" pistons. It is made from castings and is a first class job all around. It is rated at 150 hp and its top speed is not known.
Something interesting about this engine is that while it is similar to a turbine it is a positive displacement engine. This engine also has no compression cycle. If you have ever turned a reciprocating engine by hand you know that it kicks down but on the up stroke you feel the energy it takes to come back to TDC. It takes a threshold of stored energy in the flywheel to overcome the compression and kick over the top of stroke.
Not so in the Nardi rotary. The pistons chase the exhaust out. To visualize this, imagine a steam cannon. It is infinitely long. The cannon ball is the piston and under pressure it just goes and goes. Or imagine a cat chasing its tail round and round.
You can feel it as you turn it by hand with some steam presure (2-10psi). There is no resistance. The pistons just spin around the cylinder heads as designed.
Now, the naysayers will tell you rotary engines can't work because they are impossible to seal against steam leakage past the piston and the rotor.
Here are the results of the testing: Steam leakage was bad, but at this small size the 1-2 thousandths clearance was huge in proportion. At a larger scale this clearance is not too bad with saturated steam. A typical piston engine even with rings will leak too. And a high pressure steam engine with superheated steam will leak no matter what you do. It is a compromise to be dealt with by good design. With the Nardi Rotary engine the prototype proved two important things:
1. It works
2. It needs to be made in at least a ten inch diameter and run on 100 psi or more.
So what's next?
We are working on a new prototype this spring which encompasses much of the original Nardi Rotary design. We have found a way to make it close to steam tight similar to a ringed engine, simpler still, and with a 4" piston area. The torque arm is 5" and at 100 psi will deliver an average of 300 foot pounds of torque at 50% cutoff. All this in a 9" diameter insulated case with just a shaft protruding from the front bearing. The cutoff will be adjustable with a lever from off, 25, 50, 75, 100% . This will allow the engine to run like an engine with a four speed transmission.
What we will try is to allow the steam to expand fully just as the cycle is completed. The theory is to allow the steam to collapse and condense so that with the next cycle the piston is chasing a vacuum. 100 psi on one side and -10 psi on the other ,with water as exhaust. May not work but will be interesting to try.
Once we conclude the testing we will proceed to commercialize this engine as a solar/biofuel generator engine. It will be perfectly suited for many applications, third world, standby generator, hybrid engine etc.. Big dreams start with hard work!
What's the big deal, why a new engine?
The reciprocating engine suffers from a few drawbacks:
1. Any accidental introduction of water into a reciprocating engine is catastrophic. It can break rods, heads, or pistons.
2. Start up of a big steam engine (other than toy) is not push button start. The steam has to be bled, the cylinder warmed, and timing adjusted for start. Not that hard, but a novice will be puzzled, or make a mistake.
3. To get good efficiency you need a high pressure high temperature steam which requires a multiple expansion engine to make good use of. A triple expansion engine is best. Very complicated, not available, and costly to make.
4. High pressure high temperature steam is perfectly safe in the hands of the experienced. But out of the box, and into the hands of a housewife - not a good idea.
The rotary engine:
1. Can run with very wet steam and even water on startup.
2. Can start by hand or with electric start. Just turn on the lever to start 100% admission cutoff. If there is pressure it will go.
3. Can run on saturated steam very efficiently. In fact the water molecule is five times bigger than a super heated steam molecule so will help seal and lubricate. Expansion ratio can be 1000:1 or 1 with this engine. Operator will adjust cutoff for best running with steam quality delivered from boiler.
4. 30-150 psi steam is not regulated as stringently as pressures over 150. These pressures and temps are not as dangerous. You might get burned, but not dead.
5. Making an entire system that can utilize solar preheat and biofuel boosted heat is of interest in many countries. This endeavor is being watched closely by many who hope it is the key to unlock their energy independency one day. We certainly hope we can help in that.
The Rotary Valve counter-flow engine is a double acting simple expansion engine utilizing rotary valves. It is compact and smooth with little compression. The rotary valves are made from tapered (constant zero clearance) teflon valve bodies.
Positives - separate inlet and exhaust allows for separating temperatures, and cutoffs. Smooth power cycle with just one cylinder.
Drawbacks - more complicated to make and the cooler exhaust draws inlet temperature down by cooling cylinder, piston and head.
The Uni-flow engine is a good idea because the heat moves one way. The hottest steam enters through the inlet port, the piston travels to BDC and the expanded steam is exhausted through ports uncovered by the piston. This keeps the head, and inlet port at very near the highest temperature. We also use auxiliary exhaust, which compromises the principle advantage of uni-flow somewhat but it runs better. Otherwise we have trouble with too much excess expanded steam recompressing. With the auxiliary exhaust the engine runs smoother with less condensation in the steam.
The Bash Valve engine is a simple idea but it is difficult to make it work. We use a ball bearing seated in a port which when the piston is at 10 degrees BTDC is pushed open by a metal pin projecting from the top of the piston. We have had no luck with this even after varying timing, clearances etc. The problem has been that we are trying to make this design work with low pressure steam. It just wont develop enough power to overcome the early admission inherent in the bash valve engine.
There also is the problem of port area. To get the right amount of opening the port either needs to be open earlier or the ball has to be larger. We have tried using larger mushroom shaped valves much like an upside down poppet valve.
The only way we see using this very simple method of valving is to delay the in-rush of steam after the valve opens by conducting the inlet steam through about 7 feet of tubing through a super-heater coil. This requires a double valve - bash valve. The piston pin opens the port and also acts on a valve above which allows steam to enter the 7' coil of superheater and back to the open ball bearing port. The length of 7' is approximately sized for the velocity of the steam to traverse and get back just at TDC. This slight delay may be enough to utilize the bash valve without experiencing inlet BTDC.
Another way is to use a pushrod outside of the cylinder running off a cam to accuate the bash valve. This has worked really well with low pressure steam. See the engine run on the homepage video. Its still a uniflow and still a bash valve but without the early admission problems. Just a little more complicated but worth the trouble. We have listed a 2" by 2" model on the products page. One extra advantage of this design is that if there is water in the cylinder to be worked through it wont break things. It squeezes past the piston and will even release by the ball bearing like a pressure relief valve.
This engine could be made larger and with mostly injection molded plastics.
The Lawnmower Steam engine is, we think, interesting because it is so simple for the home tinkerer.
Take a lawnmower engine and turn it very simply into a uni-flow steam engine. It is already nicely balanced and all the parts are there. Many lawnmower engines are thrown out due to bent crankshafts (you dont want these). We pay $5 a piece for thrown out used mower engines. Or buy a new engine on line for a few dollars believe it or not! See our section on converting a mower engine.
A couple of things about the lawn mower steam engine. The steam chest pressure can't be much more than 40 psi or the pressure overcomes the valve spring and steam enters before the valve opens. You can install a stronger spring to get nearer to 100 psi. But at 40 psi the little mower engine puts out some serious power. So its good for starters and its cheap. Don't use ecentrics because they can't be mechanically tied to the poppet valve. You only want to push the poppet valve open and let it close with spring pressure.
The condensate that builds up in the crankcase turns engine oil to mayonnaise in a hurry. It doesnt seem to hurt anything. We just let the excess condensate flow out through an overflow. Steam oil holds up better, but we havent noticed much in the way of wear on moving parts as long as there is some form of lubricant.
The lawn mower - double acting simple engine is the other engine which is much more work and is also a converted lawnmower engine. The cam has to be reground carefully. The cylinder is insulated and stands off from the mower engine enough to keep the crankcase clean and free of condensate. This engine can be setup as a uni-flow or counter-flow or a mix of the two. But man what a lot of work compared to the simpler single acting uniflow. I wouldn't do it again.
Because the cam operates two pushrods it is easy to have separate inlet and auxillary exhaust.
Boiler Safety
The following rules for the "miniature boiler" classification is intended more for water tube and fire tube boilers. But because there are no specific rules for monotube boilers these rules apply. These laws are State laws and vary state to state. Check out your state laws through the department of labor.
A small monotube boiler with a proper safety relief valve and some kind of temperature control is as safe as the kitchen stove. There just isn't enough water in the tubing to cause a problem. The best solution here is to have an ASME welder do the job and install the safety valve. And, also keep the size down into the "miniature boiler" category, (less than 16" D and 100 psi). Here is an excerpt from Iowa's Boiler Safety laws.
CHAPTER 206 MINIATURE BOILERS
[Prior to 9/24/86, Labor, Bureau of [530]] [Prior to 1/14/98, see Labor Services[347] Ch 45] IAC 4/4/01 875-206.1(89) Scope - miniature boilers.
Rules 206.1(89) to 206.3(89) apply to boilers which do not exceed the following limits: Sixteen-inch inside diameter of shell, 20 square feet of heating surface, 5 cubic feet gross volume, exclusive of casing and insulation, and 100 psig maximum allowable working pressure.
Where any of the above limits are exceeded, the rules for power boilers apply. If the boiler meets the "miniature" classification, rules 206.1(89) to 206.3(89) shall supplement the rules for power boilers and take precedence over them when there is a conflict. 875-206.2(89)
New installations. 206.2(1) Installations- March 31, 1967, to June 30, 1995. No miniature boiler shall be installed unless it has been designed, manufactured, installed, inspected, and stamped in accordance with the requirements of the ASME Code, Section I, for miniature boilers and is inspected and stamped in accordance with the requirements of the National Board and the requirements of ANSI/ASME CSD-1 1992 with 1994 addenda.
206.2(2) Installations July 1, 1996, to December 31, 1997.
All miniature boilers covered by this chapter installed and reinstalled shall be constructed and installed in accordance with national and international standards such as DIN, BSI, ASME, JIS, Canadian National Standards. Only national and international standards acceptable to the division of labor services may be utilized.
Miniature boilers installed and reinstalled after January 1, 1996, must be inspected by a National Board commissioned inspector and be registered with the National Board. The boilers must comply with the requirements of ANSI/ASME CSD-1 1995. 206.2(3)
Installations January 1, 1998, to December 31, 2000.
All installed and reinstalled miniature boilers covered by this chapter shall be constructed and installed in accordance with national and international standards such as DIN, BSI, ASME, JIS, or CNS (1995 with 1997 addenda). Only national and international standards acceptable to the division may be utilized.
Miniature boilers installed and reinstalled after January 1, 1998, must be inspected by a National Board commissioned inspector and be registered with the National Board. The boilers must comply with the requirements of ANSI/ ASME CSD-1 (1995 with 1997 addenda).
206.2(4) Installations on or after January 1, 2001.
On or after January 1, 2001, all installed and reinstalled miniature boilers covered by this chapter shall be constructed and installed in accordance with national and international standards such as DIN, BSI, ASME, JIS, or CNS (1998 with 1999 and 2000 addenda). Only national and international standards acceptable to the division may be utilized. Miniature boilers installed and reinstalled on or after January 1, 2001, must be inspected by a National Board commissioned inspector and be registered with the National Board. The boilers must comply with the requirements of ANSI/ASME CSD-1 (1998 with 1999 addenda).
206.2(5) Inspections. All miniature boilers shall be inspected by the commissioner or a special inspector upon completion of installation and at least annually thereafter shall be subjected to a regular internal inspection. 875-206.3(89) Existing installations.
206.3(1) Maximum allowed working pressure. The maximum allowed working pressure is to be determined by 875-Chapter 205.
206.3(2) Safety valves. Each miniature boiler shall be equipped with a sealed spring-loaded pop safety valve of not less than 1/2 -inch pipe size. The minimum relieving capacity of the safety valve shall be determined in accordance with 875-205.4(89). In addition to these requirements, the safety valve shall have sufficient capacity to discharge all the steam that can be generated by the boiler without allowing the pressure to rise more than 6 percent above maximum allowable working pressure.
206.3(3) Steam stop valves. Each steam line from a miniature boiler shall be provided with a stop valve located as close to the boiler shell or drum as is practicable except when the boiler and steam receiver are operated as a closed system.
206.3(4) Water gages. a. Miniature boilers for operation with a definite water level shall be equipped with a glass water gage for determining the water level. The lowest permissible water level for vertical boilers shall be at a point one-third of the height of the shell above the bottom head or tube sheet. Where the boiler is equipped with an internal furnace, the water level shall not be less than one-third of the length of the tubes above the top of the furnace tube sheet. In the case of small boilers operated in a closed system where there is insufficient space for the usual glass water gage, water level indicators of the glass
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