NEVIS Engine Company Closes Seed Round; New Two-Stroke Concept Engine Claims to Nearly Double Fuel Efficiency
|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|
|Bore||80mm int., 178mm ext.|
|Power kW (hp)||Est. 187 (250) @ 2,000rpm|
|Average piston velocity||7.5 m/sec|
|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.
NEVIS Engine technology backgrounder