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Concept: The Ultra-Efficient, Two-Stroke Bonner Engine

Phantom view of the Bonner engine. Click to enlarge.

In a poster session at the upcoming 25th Army Science Conference, to be held 27-30 November 2006 in Orlando, the Army Research Laboratory’s Vehicle Technology Directorate is presenting an overview of three unconventional engine concepts being developed under its sponsorship.

The three engines are: a low-power, high energy-density Nutating engine targeted at unmanned air and ground vehicles, auxiliary power units, and generator applications; a turbine concept that uses semi-closed engine cycle synergistically coupled with a vapor-absorption refrigeration system; and the Bonner Engine, a new, two-stroke combustion engine concept in which two cylinders reciprocate in a 90° X-configuration, each between two semi-fixed, movable pistons.

...The Bonner Engine is unmatched in its ability to operate at maximum efficiency over its entire RPM range, and in its ability to deliver constant power at any desired altitude. It is expected to be the most fuel-efficient intermittent combustion engine ever conceived. The Bonner Engine will greatly reduce fuel consumption for power generation applications, and will allow both air and ground vehicles to achieve significantly increased range and/or payload.

—P. L. Meitner, Army Research Laboratory
Cross-section of the Bonner Engine.

The pistons contain the fuel nozzles—and, in a gasoline application, the spark plugs. Each moving cylinder incorporates the intake and exhaust ports/valves and is open on its ends. A novel, dual-offset crankshaft which generates zero side loads on the cylinders and pistons enables the Bonner’s geometric configuration. (See diagram at right.)

Each reciprocating stroke is stopped and countered (at dead center) by compression and ignition—not by the crankshaft—and all pressure on the crank is power-producing.

Features of the Bonner Engine include:

  • Pre-Compression. A pre-compression chamber surrounds each end of the moving cylinder, and provides an initial boost to the incoming charge. The pre-compression chamber can be configured to provide a constant boost pressure, regardless of altitude or air density.

  • Variable Compression and Induction. Each semi-fixed piston has a small range of motion (actuated hydraulically) which is used to continuously vary the overall compression ratio with engine speed. At low speed (idle) the piston is in its lowest (innermost) position, resulting in the highest overall compression ratio. At higher speeds the piston is moved progressively outwards, giving lower overall compression ratios.

    This mechanism also allows for continuous variation of air inlet size, timing and duration with engine speed.

  • Exhaust Energy Recovery. Exhaust passes through a rotary valve which, at the appropriate time, routes it to a chamber above the moving cylinder, helping to push the cylinder downward during its power stroke. During the moving cylinder’s upward motion the rotary exhaust valve vents the exhaust overboard.

Unlike conventional 2-stroke engines, the Bonner Engine utilizes separate fuel and oil supplies, and conventional piston rings provide complete isolation between the lubricating oil and the fuel/air flow, resulting in a cleaner burn.

Since the engine’s combustion chamber intake and exhaust are located at opposite ends of the moving cylinder, the incoming charge does not have to change direction between inflow and outflow, thus enabling uni-flow scavenging. This, plus the totally controllable exhaust back pressure, combined with the variable intake charge timing assures that scavenging losses will be negligible.

Because the Bonner Engine uses conventional piston configurations, all knowledge in existing data bases can be utilized to optimize the burning characteristics (for heavy or gasoline fuel), thus minimizing engine emissions. Also, the unique, two stage compression process of the Bonner Engine allows for the best possible mixing of fuel and air. This generates a very even combustion event, and offers an excellent chance of achieving Homogeneous Charge Compression Ignition (HCCI), the holy grail of piston engine research.

Phase I development of the Bonner engine has been completed, and the developers are working on a 600cc prototype engine under a current Phase II contract.

(A hat-tip to Larry!)



John W.

I'm amazed they release this info to the general public. It all sounds fascinating: complex, yet simple all at once. I keep wondering what's next in the evolution of the combustion engine.


I have a bit of cynical view of ICEs, I call them smog pumps. No matter how clean you get them, they still pollute. As others can probably guess by now, I am an SOFC fan.


SOFC would do nicely for some applications, but the fragility, and mass and volume it currently takes up is not conducive for utilization as a milspec powersource.


Since this is US Government based research, hopefully the invention will be patent free, and be leveraged to the private sectors.


The military has funded several SOFC APU programs that have gone on to the next phase. The low noise and heat signiture is good for battlefield stealth. They are simple, reliable and can run on reformed fuel that is used in military vehicles.

Rafael Seidl

Too bad the first picture is a broken link. Follow the one ot the poster session and scroll down for better illustrations. You can see the exhaust cams are mounted directly on the floating crankshaft, which performs a complex translation-cum-rotation motion thanks to a clever arrangement of excentrically driven gears. The internal gears double as bearings for the crankshaft and have to absorb the lateral reaction forces. This implies high contact forces on the gear tooth flanks, i.e. longevity could be an issue.

The kinematic transfer function from piston to crank is similar to that of a Scotch yoke, but without any lateral forces on the sliding parts. In that sense, it is quite different from e.g. the Bourke engine.

However, it shares with that concept one major drawback: there is a lot of reciprocating mass without compensation. With just two pistons, the free mass forces will be similar to those of a V configuration with a 180 degree bank angle, but rotating in direction. Similarly, there will be rotating free mass moments.

The uniflow scavenging mode borrowed from large marine diesels works best for very large swept volumes and very low RPM - just what you want for driving a propeller that's directly attached to the crankshaft. Here, however, total swept volume will be just 600cc, implying short strokes and high RPM operation. Hence, vibration levels will be high and scavenging efficiency less than stellar, negating some of the benefits of the design.


allen Z:  planar SOFC's are now being made on substrates like stainless steel screen.  They are quite suitable for use in a vehicle.

Roger Pham

Wow! I have to admire Mr. Bonner for his creative imagination! A well-thought-out concept that tries to incorporate the most advance features of modern-day IC-piston engines all in one package. What would be the estimated the basic thermal efficiency base on thermodynamic-cycle calculation?

Still, I would have to agree with all the issues that Rafael has raised, such as large reciprocating mass that would be difficult to balance. It is easy to balance a light piston, but how can one balance a much heavier reciprocating mass such as the cylinder?

Additionally, there are a lot of moving parts sliding against each other such as the rotary valve and the intake ports that can increase engine friction as well as requiring strict tolerance during manufacturing to achieve adequate sealing that requires lubrication that can escape into the combustion chamber causing increase exhaust emission.


This isn't really from creative imagination.
This isn't even a very innovative design, Anydine Corp. built a very simular engine back in the early 1970s.

They went belly up before anything could come of it though.

Tina Peterson

Just for the record. There is no "Mr Bonner"; that refers to the location of the engine. This is the invention of Walter Schmied.

This is not a government funded project, nor the project of a think tank. This is the concept of an individual and the work has been funded mostly by friends. The government is funding only a specific application of this engine.

I heard a lot of comments to the effect of, "If the big companies can't come up with something wonderful, why do you think some guy in his home shop can?" This is an important question. Actually, I think someone who is not part of the box is better situated to think outside the box.

Walter Schmied's engine is incredibly simple, with just 3 moving parts. It is amazingly light -- a basic unit might be 18" by 18" by 12" and weigh 50 lbs. It has a 3:1::Power:weight ratio. Torque is generated directly off the crank shaft. Each reciprocating stroke is stopped and countered at dead center by compression and ignition, not by the crankshaft, eliminating destructive centrifugal forces. And the scavenging rate is almost nil.

And this simplicity includes the functions of super-charging, turbo-charging, "variable compression ratio", and re-using (and thus decreasing) exhaust energy.

This engine would work well in cars, and it uses all common, familiar parts. And would also be light enough for an extreme snow machine. In an airplane it would require a change in the airframe shape because the its lighter weight would change the center of gravity. This would also make a great generator for bush communities.


Regarding above comment and the likelihood that not the big corporations but an individual will come up with a novel and perhaps even good concept is for sure correct. In fact, only individuals invent things, rarely it is a team effort.

Even at companies and R&D groups, it is the individuals that are coming up with ideas, always. Working in a frame work of a company (not to use the word box) there is very little freedom individuals have, as they are usually 'told' what they must do. So there is no 'room' for inventions.

On the other hand being an individual working at home and developing a new engine, does by no means assure that the outcome will be useful. Either the individual is very versed in the field and does develop something good, which is rarely the case, or this individual is a dreamer with vague ideas that can not be made to work. Unfortunately, home inventors fall mostly under the last group.

In view of technical merit of above engine, I have not spent much time on it. Do I see it correct that the housing and cylinders rotate? If so, there might be little change of it succeeding.

Tina Peterson

The only thing that rotates is the crankshaft. The other two moving parts are the partitions, one in each cylinder, dividing each into a compressing and an expanding chamber.

Yes, Walter is that rare genius who is not only well versed but also not hide-bound.

Remember that it's not Walter Schmied's people making claims about the engine now. It's Peter L Meitner, Senior Aerospace Engineer, US Army Research Laboratory,
Vehicle Technology Directorate, John Glenn Space Center, NASA.


Thanks Tina,

The workings are not too well explained. I see the two cranks move linearly up and down. I know that works on a 2:1 gear ratio.
Would you have the info on the mechanism. Gear sizes of internal and external gear, eccentricity and stroke. How do you get the linear motion?
Am I correct that the gears are 'loaded' by the combustion forces?
Your comments are appreciated.

Roger Pham

Thanks, Tina, for your additional insightful responses. Please correct me if I'm wrong, but for every action, there is a reaction, F=Ma (force is equal to mass time acceleration) The larger the mass, the larger the force, in this case the shaking force of the reciprocating cylinder. Using compression and ignition to counteract the inertia of the cylinder is not such a good idea, because compression and ignition forces tends to be fairly constant at a given volumetric efficiency whereas the momentum of the moving cylinder vary directly with the engine rpm. So, at low rpm, momentum of the slow-moving cylinder may not be sufficient to overcome the force of compression, and at high rpm, force of compression will not be enough to arrest the momentum of a fast-moving cylinder.

In a conventional crank-driven piston engine, the mass of the piston is balanced at least partially by counterweight on the crankshaft, mass balanced against mass, so rpm is less of a factor in causing vibration. Still, an engine with cast iron piston will show a lot more vibration than an engine with aluminum piston. A pair of cylinders grouped together and going in opposite direction may be used to balance each other out in ONE PLANE, but there is still rotational moment in another plane of 3-D space that will cause vibration. The engine can best be balanced in one narrow rpm band that would make it more suitable in a genset or in a serial hybrid vehicle.

With the above, let's discuss power to weight ratio. All IC engines require mass to contain the large pressures and forces inherent within. The higher the rpm or the higher amount of force for a given mass of an engine, the higher the stress level in an engine and the higher the failure risk or wear rate. Since the Bonner engine will have problem with mass balancing above certain speed, it will be incapable of high rpm operation, and power to weight ratio will suffer. The only way for a small engine with low mass to achieve high power to weight ratio is to turn real fast, and in order to turn real fast, mass-balancing is crucial.

Tina Peterson

First let me say, I'm not a mechanic.

Floram, I don't know what it means for gears to be "loaded", but I do know the drive comes directly off the crank shaft, so the gears themselves are not necessary to the functioning of the engine. And it's crankshaft singular, not plural. Like I said: 3 moving parts -- 1 crankshaft, 1 divider in the x-axis cylinder, and 1 in the y-axis cylinder. The crankshaft is Fig 7, in Pete Meitner's post to the Army Science Conference.

Here's the patent site
And here's the Patent No 6032622.

Roger, I repeat, I'm not a mechanic. And I'm not interested in arguing, defending, or selling anything. However, Peter L Meitner is not only qualified to comment, he is also a disinterested party. He is Senior Aerospace Engineer, US Army Research Laboratory,
Vehicle Technology Directorate, John Glenn Space Center, NASA. I provided a url to his post above.


Hi Tina,
Thanks for your response and for the links.

By the gears being 'loaded' I meant to ask, if the power from the gas pressure to the output shaft is 'flowing' through the gear.

I looked at the patent only and noticed that the internal - external gearing is not necessary at all for the mechanism to work, but is an add-on to reduce output speed.

I now understand how the linear movement is generated. It is the 2:1 'gear' ratio I had talked about above, however, no gears are needed by using two 'sliders' (here pistons) that are dispositioned at 90 degrees to each other.

However, the claim of no side thrust is incorrect. Although the statement is true looking at only one piston, it is not correct when looking at both, where both generate a force, as the down force of one piston must be fully supported by the side thrust of the second piston. The force transmission between the two sliders is sinusoidal. So, friction would actually be higher than in an RPE.


Add-on to the above. (I even had misspelled my own name)

Nature can not be tricked. Each action has the same and opposite reaction. I am talking about piston side loads and output torque.

The power output shaft turning at a certain speed develops a certain torque (Nm) on the driven machinery. The reaction torque to that shaft torque must be supported by the engine housing and somehow, internally, housing and shaft must be connected to transmit this torque between them.

How is the done? In the reciprocating engine it is the side thrust of the pistons against the cylinder walls, and that is here exactly the same.

So, the answer is, the back torque transmitted between pistons and housing is here the same as in an RPE. Not more, not less. The actual force between cylinder and pistons depends on the radius of where the force is applied. However, the total friction losses should be equal in both engine types.

bonner watcher

In fulfilling the Phase 1 Analysis for the SBIR grant, a preliminary 1D cycle analysis of the Bonner engine was completed by a third party.

Results for a 100 LBS engine, 600cc displacement (stroke 2.56 in), with a 97% Mechanical Efficiency (patented balancing features of the engine are not revealed in Green Car Congress info):

207 Hp @ 6,500 RPM and 456 Hp @ 10,000 RPM with a projected thermal efficiency of 40%.

Bonner Engine has an estimated achievable power density of about 4.5 HP / 1 lb. of engine weight.


Interesting data.
First we need to establish what the real displacement per engine shaft revolution is.
Are you calculating like in the Wankel just one chamber? My guess is that the 600 cc refers to the displacement of one cylinder. Since it is a two-stroke and there are four cylinders, am I correct in assuming that 2.4 Liters are being displaced and 'burned' per shaft revolution?

The stroke given at 2.56" is 65 mm. The piston or cylinder diameter is then 108.4 mm or 4.27 inches. Again, is that correct? The H/D would be 0.6 (racing engine territory).

At a throughput of 2.4 L/rev and 6500 rpm we have near .6 MPa or 86 psi mean effective pressure, not a great number. At 10,000 rpm mep would be .85 MPa or or 123 psi. Alone the fact that mep is higher at 10,000 rpm then at 6,500 raises questions.

Regarding the 'projected thermal efficiency of of 40%', I would rather like to see the fuel consumption in lbs / hphr or in g/kWh. Would you have such data available?

The weight of only 100 lbs for a 2.4 Liter two-stroke is surprisingly low. At this point we can only accept what is being said. 97 % mechanical efficiency? Hmm.

The 'patented' balancing feature not being revealed is also not shown in the above given patent. There must be more? If they have been issued, perhaps you could share them with us.

bonner watcher

Sorry, I neglected to add that the 1D Analysis was done with a 2 cylinder (2 pistons and 1 moving cylinder) configuration. The bore diameter was 3" giving an actual total high pressure volume of 36.1911 cubic inches (593 cc) for the engine.

Specific fuel consumption (lb/hr/hp):
@6500 RPM: 0.3298
@10000 RPM: 0.3459


Well, If these numbers are right, I can only say 'good luck'.


Car engines range usually between 60 and 100 (high) hp/Liter.

F1 engines produce about 800 hp at 19,000 rpm from 2.4 L displacement or near 330 - 350 hp/l. They burn a lot of fuel, meaning they have very low fuel efficiency.

The Bonner makes 456 hp at 10,000 rpm from 600 cc. That equals some 760 hp/Liter displacement. Outstanding. Really impressive. To top it all off, the Bonner burn 30 to 50% less fuel than car engines, not to mention F1 engines. It's miraculous.

bonner watcher

It remains to be seen what Bonner Motor Corp will finally decide to name this engine, but some have called it the "elegant engine" as it is certainly superior to what we have become accustomed to.

It is going to revolutionize ICE technology.

Kudos to Walter Schmied!

Roger Pham

NOt so fast, bonner watcher!

You haven't told us how Mr. Schmied manages to balance the potentially humongous vibration from this "Boner" engine, (ie. a heck of a banger, if u caught the drift, he he he!).
Happy Thanks Giving 2006!


Sorry, most of you guys are wrong.. Russell Bourke succeeded with these engine principles over 60 years ago Bourke Engine aka HCCI engine principles. Today his engine is still running.

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