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NEVIS Engine Company Closes Seed Round; New Two-Stroke Concept Engine Claims to Nearly Double Fuel Efficiency

14 June 2007

The Bortone cycle. Click to enlarge.

The NEVIS Engine Company Ltd. has successfully closed its first round of seed funding to help it further test and develop its current two-cylinder prototype engine as well as to develop awareness of the technology. The Italian company has been developing the prototype with €2.5 million (US$3.3 million) in government grant money.

The NEVIS (New Exhaust Valve & Intake System) engine embodies a new two-stroke combustion cycle (the “Bortone” cycle after its inventor) and a new design than combines, among other features, annular (i.e., doughnut-shaped) pistons, modular cylinder construction and a sinusoidal camshaft similar to those adopted in engines with cylinders arranged co-axially around the shaft.

A NEVIS module. Click to enlarge.

The company claims that the engine offers efficient combustion at all levels of power demands, and that it can nearly double the fuel efficiency obtained by conventional internal combustion engine technologies.

Although the NEVIS engine is lighter and smaller than a conventional ICE engine of comparable cylinder displacement, it offers more power, due in part, the company says, to the engine offering six times the number of power strokes per revolution than a traditional four-stroke engine.

The two-cylinder prototype was put through a bench test with engine ignition for the first time in Lecce, Italy in early 2006 as part of the review process by MUIR (Ministry of Education, University and Research) for the government grants that funded the development of the prototype.

First NEVIS prototype
Cylinders 2
Displacement 1,000 cc
Bore 80mm int., 178mm ext.
Power kW (hp) Est. 187 (250) @ 2,000rpm
Average piston velocity 7.5 m/sec
Engine block Steel/aluminum
Weight 80 kg
Power/Weight ratio (kW/kg) 2.38
Compression ratio 7:1 to 38:1
Injectors per cylinder 3
Sparkplugs per cylinder 3

This first test confirmed the correct functioning of the Bortone Cycle and the basic mechanical operation of the NEVIS engine.  Preliminary testing without ignition also confirmed nearly 50% less friction/pumping resistance for an engine with a comparable displacement. 

The five key design concepts of the engine are:

  • Obtaining optimized scavenging without the need for an additional turbine or compressor.

  • Development of a new two-stroke cycle that allows partial loads to have an expansion stroke greater than the compression stroke (like the Miller cycle in a four-stroke engine, but in a two-stroke cycle). Enabling that is a controlled annular exhaust valve that allows for variable duration and phasing of its opening.

  • The use of a sinusoidal camshaft to transform the alternate motion of the pistons into rotary motion. The shaft in the NEVIS provides the ability to complete three combustion cycles within a single shaft revolution.

  • A variable compression ratio made possible at all rpm and power loads by the regulation of an annular screw element within the shaft.

  • The use of annular pistons to enhance thermal efficiency, allow for a light structure, and to integrate the engine’s other key concepts.

Within all that, the principal innovation of the NEVIS engine, according to the company,  is the system used to vary load needs.

The extended opening of the exhaust valve allows the piston to expel the air that has replaced the exhaust gases through the cleaning phase. The longer the valve stays open, the smaller the amount of air available for the combustion that follows, and as the compression ratio may be varied as desired, it is possible to have very small quantities of air charge. In other words, the load is reduced but not the efficiency of the engine that totally utilizes the expansion of the combustion with an expansion stroke that is inversely longer in relation to the load entity.

If the opening time of the exhaust valve is short and the air is prevented from flowing out of the exhaust duct, the compression ratio can turn back to the initial proportion and significant loads can be achieved, especially if the inertia of the air in the intake duct causes some supercharging. For the sake of efficiency, it is better not to run the engine under pressures that are too high as this requires greater depressions in the combustion chamber that can only be obtained using the kinetic energy of the exhaust gases which, flowing out at high velocity, cause depressions.  The more these are intense and durable the higher the velocity and the quantity of the exhaust gases. Thus, anticipating the opening of the exhaust valve when there is still a certain pressure in the combustion chamber improves the filling process, but causes a loss of efficiency as expansion doesn’t take complete advantage of the pressure given by the combusted gases.

The NEVIS engine overcomes a number of issues with traditional two-stroke engines:

  • The increased size of the intake and exhaust ports enable higher flow.

  • The scavenging of the NEVIS engine differs from that of the traditional two-stroke and it can be compared to four-stroke efficiency. It can be complete at all rpm and at all loads with an optimal expulsion of all combustion residues due to the new cycle, to the particular unidirectional outflow and to the longer scavenging phase.

  • The variable lifting law of the exhaust valve and its regulating timing system, in combination with the new “loading” method, avoids the losses of any quantity of fuel at the end of the scavenging phase; in fact, the exhaust valve during this precise phase will always be closed. The NEVIS engine also provides a time for vaporization that is 2.6 times longer than in the normal two-stroke engine: this allows the use of direct injection operating with relatively modest pressure and ensures good injection even at high rpm and high loads.

  • There is a longer-lasting pressure at the end of the stroke due to the modest height of the intake ports and that the opening of the exhaust begins at a point similar to that of a four-stroke engine (55-60 degrees of angle of crank) with respect to the bottom dead point.

The company is also exploring adapting the NEVIS for HCCI (Homogeneous Charge Compression Ignition).  The NEVIS engine adapted for HCCI would not only increase efficiency further but would also do away with NOx without the PM (particulate matter) emissions of a diesel, according to the company. 


June 14, 2007 in Concept Engines, Fuel Efficiency | Permalink | Comments (15) | TrackBack (0)


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If this engine can truly deliver the goods, then the big three better figure out a way to get a piece of the pie. Here is why: With such a high power density, you could probably make an engine of about 50 Hp with less of 30 Kg of mass. Why would this be important? Because if this engine can brake the 50% thermal efficiency barrier, that would make it the best engine for a genset in a series electric dominant hybrid.

As with all new engine proposals, it only becomes relevant after they can produce a working example at power outputs usable in the real world that meets all requirements.

Yeah there have been people trying the reinvent the ICE for over a hundred years now, almost all of them have come out with unsuccessful products. I remember the quiseturbine craze just a few years ago, what a load that was: they have not made a working gasoline burning version yet, works great with air and steam though.

Does this design solve the pollution problem associated with 2 stroke engines?
I thought the 2 stroke is a dying engine (except for chainsaws and unique applications) due to it's high pollution of burning oil mixed in the gas?

yeah, no info above on pollution
However, a 1000cc 80Kg engine with 250hp@2000rpm *IS* a usable size and power output, if they could succesfully apply HCCI that should help with any potential pollution issues.

A very well-thought out engine concept that has inherently much lower friction than trational piston-crank 4-stroke cycle engine.

Coupled with the inherent variable compression mechanism and Kadenacy uniflow scavenging mechanism taking advantage of the inertia of the exhaust gas, along with the variable exhaust valve timing in the compression stroke in order to throttle the air intake charge without require a power-robbing negative-pressure throttle plate, partial-load efficiency will be much better than traditional gasoline engine and even diesel engine, given the much lower internal friction level.

Peak efficiency will probably be no more than about ~15-20% higher than of the best of current optimized 4-stroke cycle engine due entirely to reduction in friction, BUT, partial-load efficiency can easily DOUBLE the best of current engines, given the lower friction level, variable compression, and the extended time in the cycle for exhaust, scavenging, and combustion.

Conceptually, this engine operates similarly to the 2-stroke Detroit Diesel or Orbital 2-stroke GDI, but it has much improved scavenging mechanism, much improved flow, and even lower internal friction due to the use of one large annular piston replacing 2-3 smaller pistons having much larger side-wall surface subjected to friction loss. However, some oil loss from the piston rings to the intake air on the upward compression stroke may be inevitable, and unless this oil can be burned completely within one combustion cycle, higher HC emission may be possible. The longer combustion duration when the piston is at TDC may help in this respect.

The high heat in the combustion chamber may impair lubrication of the "Guillotine" exhaust valve sliding up and down on the inner surface of the cylinder head. Perhaps some advance tribology method may be required to overcome this issue.
Of course, more problems may surface during further development process, but so far, this concept looks very promising.

No oil and gas mixing required here. Lubricating oil can be sprayed on the lower cylinder when the piston is near TDC.

Series hybrids certainly would profit by a more efficient engine, but the cost better not be much since
greater all-electric ranges are becoming greater as battery prices decline, making greater engine economies more and more irrelevant. The series hybrid is only a transitional vehicle anyway.

If one can make a H2-ICE-HEV that can match the efficiency of electrical generation and transmission via the grid, then why bother with plug-in charging nitely and expensive and heavy battery?

Instead of burning the coal, natural gas or waste biomass to generate electricity, one will just need to convert these directly into H2 via gasification process at even higher efficiency than electrical generation. Then, if the FC-HEV or super-efficient ICE-HEV can utilize the H2 with an overall efficiency from-source-to-wheel higher than BEV, one can forget about low-cost battery development. A 1.5kwh of battery capacity per HEV will be all that will be needed.

What to do with solar and wind electricity? Just feed it directly to the grid, while conserving coal, natural gas, or waste biomass to generate H2. Do not make H2 from electricy using normal-temp electrolysis of water, because this is an expensive and inefficient way to produce H2. 4kg of H2 energy can be stored in mobile tanks 160-liter size at a BEV-equivalent capacity of 115 kwh, with the cost the storage tank of ~$2000 USD, for a range of 300 miles. Fuelcell costing too much? Possible! Now, do you see the beauty of a low-cost superefficient ICE? Try to calculate how much it would cost for a BEV with that much battery capacity?

Posted by: Kerry Buehrt | Jun 15, 2007 6:40:34 PM
If one can make a H2-ICE-HEV that can match the efficiency of electrical generation and transmission via the grid, then why bother with plug-in charging nitely and expensive and heavy battery?

Why bother?
Because what you are saying is not physically POSSIBLE, it defies the laws of physics.

Furthermore, hydrogen infrastructure does not exist.
So why couldn't we just make electric quickcharge infrastructure?
Can fill up for about a hundred mile drive in 1 minute.

I have debunked Ulf Bossel's defamation of the Hydrogen Economy many times here in GCC.

His assumption is that H2 will be produced by room-temp electrolysis of water using electricity from either the grid or wind or solar. He is correct to say that H2 produced this way will give H2-Vehicle 1/2-1/3 the efficiency of electric BEV.

But, commercially, H2 is not produced by electrolysis of water. It is produced by steam reformation of natural gas with about 70% efficiency, or even higher when the resultant heat will be recycled into electricity production. Gasification of coal or waste biomass can produce H2 at comparable efficiency as from natural gas.
In contrast, a Combined-cycle natural gas power plant is rated at 55-60% efficiency. Coal-fired powerplants has 35-40% efficiency. Distributon of this electricity through the grid cost 8% of the energy in the electricity.
If the H2 is produced locally, distribution of the H2 locally within a 15-mile radius only cost 3% of the energy within the Hydrogen. If the H2-Vehicle is fueled right where the Hydrogen is produced within the city limit, the cost of distribution will be even less. Compression of the H2 will cost ~7-9% of the energy of the H2, but a substantial portion of this energy is recoverable to do useful work, for example, to run accessories in the vehicle. See website, in which a car is run entirely on compressed air.

Finally, a FCV like the latest Honda FCX was quoted by Honda to have 60% efficiency tank to wheel. A BEV is recognized to have about ~70% efficiency grid to wheel, factoring in losses in the charger, battery's internal resistance, heat production in power semiconductors and in the motor, requiring liquid cooling, and battery self-discharge.

So, for H2-V: 70% x 94% (distr+compressn)x60%= 39% source-to-wheel efficiency!
For BEV: 55% x 92%(distribution)x70%= 35% source-to-wheel efficiency! Note that coal-fired electricity will result in even lower overall efficiency for BEV, but I am a kind person.

What about wind and solar electricity? Don't bother to make H2 with them. Just feed them to the grid and save the coal or biomass for H2 generation. There will be plenty of waste biomass to serve as H2 source to meet all transportation need.
In the future, high-temp electrolysis for H2 production, having twice the electrical efficiency of normal temp can be used, using the waste heat from biomass or coal gasification, will make wind and solar electricity H2 equally efficient as BEV from renewable electricity.

Roger Pham,

That a very good run down, and I like it, only one problem: how much is a FCV going to cost? Surely PEM Fuel Cells with composite fuel tanks with hydrogen absorber, decompression generator, electric batteries and motor will cost more then just larger electric batteries and motor (as in a EV). Also add in the cost of a new infrastructure for transporting and making hydrogen, which EV and biofuels need to a much lesser extent. Electric grids already exist and off-peak power is just begging to be used, all that needed is the cars. Many biofuels can run in existing cars and can us existing infrastructure for gasoline and diesel, all that needed is the production. Hydrogen needs new cars, new infrastructure and new production!

Good question. That's why a very efficient ICE but low cost, with peak efficiency approaching that of the Fuel Cell would be a great alternative. Don't dismiss the ICE as yet, that's the gist of this discussion. Development on the FC front is also promosing, with prediction that cost of the FC stack can be reduced to $4000 USD/vehicle eventually. GM and Honda have plan to put FCV in limited production by 2008.

Infrastructure for H2? Very simple. Put a gasification plant for every 10 x 10 =100 square miles of urban area, and then each vehicle will have to travel but 5-7 mile one-way trip to fuel up, initially. No need to put H2 into tankers to travel down the road. Definitely not a station every street corner like we have for gas station now, but such is a waste and not really necessary. When more H2 vehicle will show up, there will be sufficient commercial justification for additional pipelines to conduct H2 from these plants to the more local stations.

Honda has a device whereby you can make H2 from home from natural gas, if you happen to live too far away from a H2-filling station. This device also provide heat for your hot water and home heating also, I would presume, from the exothermic reaction of NG to H2 conversion, thus higher efficiency of conversion than calculated when waste heat can be utilized.

Expect that H2 will cost the same as gasoline now for an equivalent energy content, but H2-Vehicles can travel twice as far as gasoline vehicles, so you can bet that you'll pay 1/2 as much for energy cost to travel the same distance. This energy cost saving will pay for the higher initial cost of the H2-capable vehicles.

a ICE with near Carnot effiecency would be nice, but I doubt its viable. There have been many claims from many companies over the years of new kinds of engines but none work out as good as claimed.

Still the amount of change need for hydrogen is far more extensive then EV or biofuels, time for change is very short if peak oil is a consideration. Also what happens when natural gas peaks (Soon after oil by most estimates) and coal is restricted by greenhouse gas initiatives? Water electrolysis my be the last viable option for hydrogen, even so high efficiency electrolysis of water is under development.

Why hydrogen, why not zinc paste? Zinc can be recycled at high efficiencies (~70%) at room temperature and can be recycled at the fuel station. Zinc paste is also not explosive or combustible (as long is does not dry out) and as a silvery toothpaste consistancy like paste it’s far easier to store then hydrogen. Zinc-air fuel cells are also more efficient then PEM.

hydrogen powered turbines with high speed alternator/generators are the best bet. anyone with water and electricity can make their own fuel. my company will be developing hybrid turbogensets for vehicles in the next year or so, but 500 mile range systems will cost about $50k. roughly 80% efficient with a 90% efficient turbine, 95-99% efficient mechanical to electric conversion, and 96-98% efficient power conditioning. The main advance will be in ultra efficient liquid hydrogen and liquid oxygen production.

With all the claims of 50%improvements in this and 30% improvement in that, and so on and so forth, at the end of the day there is 100% B.S., if half of these exagerated claims were true- when you opened your gas cap- gas would gush out of it. Where does it say the engine even runs- but I guess it will spin a darn good yarn. I'm not just talking about this engine but I read about countless engine technologies every week and research galore but come on, wolf boy, sooner or later no one will listen if the truth is thrown about sooo loosely. Sorry if I snapped but these claims are friggin rediculous-I Digress I WANT FACTS AND I WANT EM NOW -is this turning into politics?

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