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FEV Developing Efficient Two-Stroke Diesel Engine

FEV Engine Technology is working on a new, two-stroke, light-weight, high-efficiency diesel concept engine that also promises to address the emissions issues associated with two-stroke designs. The approach could support a family of engines applied either as standalone engines in vehicles, as power sources for APUs, or as powerful and efficient engines in a hybrid configuration.

The OPOC (opposed-piston, opposed-cylinder) engine combines two engine designs pre-dating World War II: an opposed-piston, two-crankshaft diesel aircraft engine developed by Hugo Junkers and the opposed-cylinder boxer engine developed by Ferdinand Porsche. (Diagrams below left. The diagram below right depicts the design of an OPOC module. Click to enlarge.)

Opoc1 Opoc2_2

A two-stroke cycle engine differs from the more common four-stroke cycle by having only two linear movements of the piston instead of four, although the same four elements of the cycle (intake, compression, power, exhaust) still occur.

The new engine thus generates one power stroke per each crank revolution per cylinder. The OPOC configuration consists of two cylinders per module. Each cylinder has two pistons moving in opposite directions, and the crankshaft is placed between the two cylinders.  (See diagram above, right.)

There are no valves or camshafts in this design; intake and exhaust ports are at opposite ends of the cylinder. The crankshaft controls the position of the pistons in such as way as to open the exhaust ports before the intake ports and then close the exhaust ports before the intake ports. This asymmetric timing is a must and provides for proper exhaust-blow-down and enables intake supercharging.

The combined intake and exhaust process in a two-stroke engine that clears the cylinder of exhaust gases and fills it with a fresh mixture of air and fuel is called scavenging. Managing combustion control and cylinder scavenging have proven problematic in the past, and have led to one of the major problems with two-stroke design: emissions control.

The OPOC engine optimizes its scavenging over the entire engine range through the use of uniflow scavenging controlled boost pressure, pulse turbocharging and the asymmetric intake and exhaust timing noted above.

An electrically-assisted turbocharger (both exhaust gas driven and electrically driven) allows the boost pressure to  be independent of the engine operation. Thus, high pressure boost is available for acceleration at low engine loads and low rpm without any associated mechanical drag.

Without the turbocharger, according to the designers, the reduction of emissions along with other engine benefits are unachievable.

[Turbocharging] also helps to reduce the NOx emissions by enabling higher than normal EGR rates and enables monitoring and maintaining a constant fuel to air ratio. The electrically-assisted turbocharger can rapidly compress and recycle air in order to heat to 100ºC in less than one second to ensure easy start in cold weather without needing glow plugs, which are costly and add complexity. Compression ratios in the range of 15-16 could be achieved resulting in lower fuel consumption and reduced NOx emissions.

With this optimized scavenging process, the OPOC engine offers:

...a significant step towards the theoretical potential of the two-stroke engine having double the power density of a four-stroke engine. An estimated 90% scavenging efficiency has been achieved with unique gas exchange characteristics of the opoc engine and the use of APT’s electric assisted turbocharger.

— Peter Hofbauer, FEV Engine Technology

The engine offers a number of advantages:

  • High power-to-weight ratio

  • High power-to-volume ration

  • Use of a variety of fuels including gasoline, diesel, natural gas, JP8 and hydrogen

  • Assisted HCCI combustion using proprietary diesel fuel system

  • Conventional parts, materials and maintenance

The original OPOC concept was invented by Prof. Peter Hofbauer, prior to his joining FEV as executive vice president for Research and Development. The intellectual property and trademarks relating to the original OPOC design have since been acquired by Advanced Propulsion Technologies (APT). FEV is working under contract to APT, DARPA and other interested parties to design and develop for-production variants of the basic OPOC concept. FEV has been selected by APT as their exclusive development partner for the OPOC engine.

It would be very interesting to see how this might work in an aggressive hybrid or plug-in hybrid application, as well as to get initial fuel efficiency and emissions data.



Ben  Christie

The most advanced two-stroke engine I had ever seen or worked at in 35years screwing at lorries was the Commer two stroke engine known also as the Rootes diesel. This engine was developed by Tillie & Stevens as far as I know just after WW2, The Commer 2 stroke came out about 1950-52;Foden also had a 2 stroke lorry out in 48. The commer was different as it had a 3 cylinder 6 piston 1 crankshaft engine with series of
internal rocker arms to transmit power from the horizontal cylinders on top to the crankshaft at the bottom. There were 2 sizes 199cu inch & 215cu inch about 3.25 litre or so, My father had 3 of them ,we never had no trouble with them. You also needed a good oil pressure gauge to tell you when to change the oil as the pressure rised by 5lb to 55lb when there was too much carbon in the oil. These engines were only 2thirds in size to the Perkins 6354s & more often could pull out & pass them,They also done about 15 mpg.They were never developed any further which is a shame.


I really think this is the way to go. With a strong commitment by the feds, we could grow and process all the biodiesel we need from algae grown around the Salton Sea.

This is what we should be building right now. In my opinion Ford and GM will go bankrupt before they even begin to catch on.

For about the past year I have offered anyone who would listen the following info: None of the American automobile companies have even responded. I have had some positive response from several educational institutions but - as far as I know - none have done any experimental work to verify my claims.

Here is what I have been proposing:

In one scale or another everyone of these systems have been proven.

Like to produce a vehicle that can burn rubber on takeoff on all four wheels and get 90+ mpg?

What I would like to see the automakers working on would have:

A turbocharged, two cylinder opposed, 2-cycle, air-cooled diesel directly
driving a generator. (It would not be running most of the time.) A 111 volt Lithium-Ion Polymer battery pack. Nothing but wires going from the controller to every wheel, except for the necessary additional friction
brakes (of course). An added advantage of this would be the ability to recharge from the electrical grid while at home, saving even more on fuel.

Each wheel, depending on the feedback to the controller from wheel speed sensors would drive with just the right power depending on the accelerator position. You would get recharging from deceleration just as you do in today's hybrids. You would also use this feedback to stop the wheel from skidding.

Each wheel would have a stationary stator and a series of fixed magnets closely adjacent all around the inside of the wheel. In a sense it would operate each wheel in a very similar fashion that the mag-lev trains use,
except the motion would be circular, of course. Something very different about this type of motor is that the stators are fixed to the axles and the magnets are driven around them. This gives a significant increase in
mechanical advantage. That's like turning an ordinary electric motor inside out.

There would be no need for ordinary electric motor brushes. In fact, many electric motors operating today are brushless.

Such motors already exist in the model airplane field and their efficiently
is amazing - approaching 90%. I've got a couple and doubt that I would ever buy any other type.

It's possible to hang the model on the prop right out in front of you and
accelerate straight up, like a rocket, with this type motor

In the vehicle the motor/generator would not turn on to recharge the
batteries until they needed it. There are already experimental Lithium-Ion
driven cars that can get in excess of 200 miles before they have to be
recharged by plugging them in. You would top off your batteries overnight by plugging them in. Some cutting edge research by Toshiba - employing nano-technology - indicates that recharging can be done so fast that you could top off while eating lunch.

Lithium -Ion battery technology is so new that I doubt that very many
automotive engineers have even heard of them, much less thought to use them in this manner. Their energy density exceeds that of any other form of rechargeable energy storage.

The Lithium Ion battery is the most efficient battery available right now. So is the outer rotor electric motor the most efficient motor.

Build an Automobile right and it will weight less and have simpler, easier to repair/replace modules.

Lets see what we can eliminate while improving performance and efficiency.

Transmission - None

Ignition system - None

Liquid cooling - None

Valves and valve train - None

Use bio-oil/fuels for both fuel and lubrication.

Feel free to pass this along to anyone you know in the Transportation business.

I bought a Honda Civic Hybrid last summer. I enjoy it more than any vehicle I've ever owned. I will Never buy another vehicle that isn't a Hybrid and doesn't get at least 50 mpg.

As far as I can tell, Detroit isn't even thinking the same way I and the vast majority of it's potential customers are.

William Lucas Jones
490 Mauldin Rd.
Sautee, GA 30571-3159

(706) 219-3333

Kenneth Rickman

First of all, the engine. It looks intriguing, but I can't help wondering if there is any real advantage to having the outside cylinders driving the central crank, instead of the Junkers arrangement of separate cranks, or the Deltic arrangement of a central crank below the cylinders, driven via rockers. Conversely, one could ask if there is any real disadvantage.

Regarding Mr. Jones' proposal. I am working on a design for a vahicle similar to what you suggest. I feel that you've missed a couple points, though. For one, the motor-in-wheel arrangement, for all of it's advantages, is heavy. It puts a lot of weight on the wrong end of the suspension, making for a harsh ride (and reduced life of the parts). It also generally means that standard parts (such as rims) cannot be used, thus requiring more costly custom parts.

Li-ion batteries are nothing particularly exotic, and I am willing to bet that any serious electrical engineer (at least one who knows anything about batteries) knew about them long before you and I. Yes, they are light and efficient, but they are also considerably more expensive than most other batteries. They also have a relatively short life span. Ni-Cad batteries are nothing special, and they're not as light as the various lithiium batteries, but they ase cheap and they can last for decades.

All that said, the vehicle you describe could, in theory, be build cheaply, but not at this time. Do not forget that the auto makers are in business to make money, not to make efficient cars. The current mania about SUVs is a perfect example. If tomorrow everyone decided that, like you, they would not drive anything that got less than 50 mpg, we would see an almost overnight shift in the product lines available. The fact is that, with today's technology and culture, a truly efficient hybrid vehicle would be a very expensive flop on the market.

Kenneth Rickman

Tom B

Has anyone been aware of the rand cam rotary diesel engine developed by Reg Technologies which is a four stroke with just two types of moving parts vanes & rotor. Regus is the ticker designation.It is able to generate 24 cylinder firings per rotation & provides continuous power that is vibration-free & extreamly quiet. The engine can also be used as a generator running on propane hydrogen or natural gas. When one lookes at the size & weight of this engine for power output you will be stuned


what is a hcci

steve cook

I'm working on a hybred vehicle and need assistance. Anyone who understands 2-cininder diesel application can assist me. Steve Cook


Is the same engine as Doxform made long ago?


Is the same engine as Doxford made long ago?


I think having two crankshafts is a bad idea. You have to transfer both shafts to one central output which increases likelyhood of mechanical failure. I believe an efficient 2 stroke diesel can be acheived through a conventional style.

Roy Bauer

I believe the opoc engine is going to be a very productive engine. It is a new generation of alternative fuel engine. It is a basic simple light engine. That could be used with a wide range of fuels.
This country and others need to be more flexable, what I mean is that we can not be so dependant on oil. This motor could be very profitable in the coming years with the intro to biofuels.

Steve Brown


could anyone tell me what the minimum compression ratio would be needed to run a normally aspirated 80cc 2 stroke diesel.

Thanks in advance. Steve

Chloe Finnan


This year am taking As DT and for my system case study my topic is transportation. I am researching alternative fuel and engine design for a lorry that travels long distances. These lorries travel carrying a heavy load. I was wondering whether the developing two-stroke diesel engine could be suitable and efficient for this type of vehicle. Would this alternative engine reduce the amount of fuel used? If you could email me back with relative information I would appreciate it sincerely.

Thank you

Chloe Finnan


As regards to the future, the new battery technology is the way forward. Motor in hub and Lith-Ion, Lith-Poly, or the new Toshiba battery which recharges to 80% in 3 minutes and 100% in 5, is the way to go. Then locval charging points can be built. The largest trucks in the world are driven by electric motors using on-board diesels-electric generators. Mitsubishi are launching a dedicated all electric car in about 4 years time. Motor in wheel hub and a Lithium battery pack. The mechanical arrangement is sparse and simple. These may go 200-300 miles on one charge.

The bitch by environmentalists is that electricity is dirty and inefficient from power station to point use with large latent heat and line losses. True when looking at heating buildings and domestic hot water, where natural gas can be burnt at point of use at 90% efficiency (heating your domestic hot water by electricity is about 30% efficient end to end). However power generation is now more efficient with energy reclaim measures in place in the newer and more advanced stations - not to mention wind, solar, hydro etc.

The vehicle is another matter. It is more efficient to pour fuel into an engine at a power station with advanced stack scrubbers, that drives a generator, that sends the electricity down a line, then into a cars battery and propel the car, than pour the fuel directly into a current car. 75% of energy stored in your tank is wasted, while only a few percentage points of energy is wasted from a battery pack - and the electric car is 100% clean at point of use, cleaning up cities at a stroke.

Regarding the OPOC two-stroke engine. Instead of a rod attached to poppet valves at the other end of a cylinder the have a piston. The main contributor to advancement appears to be the electrically assisted turbo/scavenging, which could easily be adapted to the Australian Orbital company engine.

The best opposed piston two-stoke diesel engine built and fitted in a vehicle was, as been mentioned, the Rootes TS3 engine fitted in Commer trucks from 1954 to 1972, using one crank and large rockers. It had an amazing power to weight ratio for the time, impressive even today, and was remarkably economical with other similar powered trucks consuming twice the fuel. A much improved 4 cylinder version, the TS4, was developed and was just about ready for production when the dreaded Americans came along.

Rootes had fallen into financial problems because of poor management in the car division. Chrysler swept in, in 1968, and bought out Rootes. They didn’t understand and eventually dropped the remarkable TS3 motor and ordered the 14 prototypes of the TS4 scrapped. The last TS3 engined truck was in 1972. Only a few TS4 prototypes were scrapped, with Rootes staff hiding them or using them as backup generators to preserve them. Chrysler wanted their existing engine ranges, or contracts with Cummins, to used and replaced the TS3 with an antiquated Cummins unit – the specs sheets alone should have told the Chrysler engineers that the TS4 engine was something special. With such crass stupidity and lack of foresight no wonder Chrysler went belly up. They were only interested in vested interest, not advancement.

A few TS4 engines have made their way to New Zealand where they were brought back to new condition, with one about to be fitted in a revamped Commer truck. A few people are looking into installing modern fuel management systems of the TS3. The TS3 is still used in boats and the likes mainly in Australia and New Zealand. This new web site is dedicated to the TS3 and TS4 engines, with lots of info on all types of diesel two-stokes. Nice one Kiwis!


How does Indian Economy effected if we use air as fuel in automobiles instered of petrol or diesel?

Timothy Logsdon

I think this is a brilliant design! Now I'm wondering where/when can I buy one?


Please take a look at where it is presented a different approach of high speed Diesels of two and four strokes, even compact Junkers.

Mike Swift

To Tom B, the term HCCI means Homogeneous Charge Compression Ignition. With this technology the incoming charge with fuel already mixed is adjusted so that when the piston reaches top dead center the charge ignites from the compression alone. Some small two stroke diesel model airplane engines used this principle. The compression ratio was changed by screwing down the top of the cylinder until the engine ran smoothly. On modern development engines they change valve timing, and cylinder scavenging to control compression ratio. It takes lots of computer power, and sensors to make it run, but gives good fuel economy with no high pressure fuel injection.


I got this in my NASA Tech Briefs:
Now here's a new engine, check it out!


HI friends,
I have a concept of a Two stroke diesel engine which works (approaches) both Otto and diesel cycle .if anyone interested in joining with me to develop it plz mail me

rich easton

Everybody look at the Bourke engine, a 2-stroke boxer with Scotch yoke. Simpler than OPOC, built first in 1932, now being revived by enthusiasts. Very high fuel efficiency because of long dwell at TDC. Also a HCCI multi-fuel capability is promised.Google Bourke engine.


there are very pretty engines worldwide as and nasa-diesel,but since 5years i promised i`ll no more buy a car without such a two stroke machine.


Peter bring his baby into FEV :)) This is very nice that concept reached production...and this concept has a big potential in reducing the weight further being updated by connection rod free mechanism

>>FEV has been selected by APT as their exclusive
development partner for the opoc(TM) engine.


The original opoc(TM) concept was invented by Prof. Peter Hofbauer, prior
to his joining FEV as executive vice president for Research and Development.
The intellectual property and trademarks relating to the original opoc(TM)
design have since been acquired by Advanced Propulsion Technologies, Inc.
(APT), of Goleta, California. FEV is working under contract to APT, DARPA and
other interested parties to design and develop for-production variants of the
basic opoc(TM) concept. FEV has been selected by APT as their exclusive
development partner for the opoc(TM) engine.

Tanay Patel

I think that the idea of the 2 stroke diesel is great. I am from India and live i a city where the major source transport is a vehicle which is known as a 6 seater an can carry 20 people at a time.
This amazing vehicle is cheap and runs on a 0.5 litre 4 stroke diesel engine.

Now...i am planning to design such a vehicle which replaces the current engine with a 2 stroke diesel OPOC engine along with an alternative fuel. The worry is what alternative fuel i should use. If any of you have any bright ideas of what should be the perfect alternative fuel teaming up with a diesel engine please mail me.

Any comments or suggestions are welcomed

Peter Hughes

Hello, I am completely new to this forum but would sincerly welcome some advice/help. I am in the process of comissioning a marine detroit Diesel eng into a boat, this unit is 2 stroke, and engine system that I am very familiar with when used in scooters/lawn mowers etc etc. However, the detroit is another thing, my past profession was a vehicle mechanic but I am looking for help with the basics of this engine and the fuel system.

Can anyone help.

Thanks pete.


Please visit
Regards Andrew

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