Funcionamento e composição do motor NEVISTranscrito do site da NEVIS:
NEVIS is a ground-breaking internal-combustion engine, and more particularly an engine concept that comprises an innovative exhaust valve and intake system, hence its name NEVIS (New Exhaust Valve and Intake System).
In illustrating the concepts behind the NEVIS engine, this document uses published data from the field of mechanical engineering as well as test results derived from proven engines.
In terms of the fluid dynamic characteristics of the NEVIS engine, time and cost has limited the numeric data currently available. What has been set out in this document has been derived through simplified mathematical modeling.CONCEPT AND DEVELOPMENT GOALS
The following goals were pursued in the development of the NEVIS engine:
a) Reduction in wasted energy from the exhaust as well as from heat radiation
b) Improved efficiency at all rpm and power loads
c) Optimal combustion for improved consumption and performance as well as reduced emissions
d) Application versatility (aeronautical, automotive, nautical, etc.)
e) Fuel versatility (gasoline, diesel, hydrogen and biofuels)
f) Engine block modularity allowing for a wide range of power options
g) Design simplicity excluding the need for complex or expensive technology and precious materials
h) Compactness and reduced weight allowing for easy assembly and maintenance
All these goals were taken into account in developing the NEVIS engine and have been applied through the adoption of five key concepts inherent in the engine’s design:
1) The first concept incorporated within the NEVIS engine relates to a method conceived and experimented by Kadenacy to obtain the scavenging of a two-stroke engine by means of the inertia of the air found in the intake duct and withdrawn by the depression existing in the combustion chamber immediately after the exit of exhaust gases. This method provides considerable advantages in terms of efficiency and overcomes the need to use turbines or compressors generally implemented for scavenging needs.
2) Importantly, the second concept included within the engine addresses the serious limitations of the Kadenacy effect that is typically only useful within a very small range of rpm. To resolve this issue, the NEVIS engine incorporates a controlled annular exhaust valve of ample size. This exhaust valve allows for variable duration and phasing of its opening by varying the amount of residual pressure remaining from combustion expansion and thus giving the opportunity to correctly phase the scavenging at all rpm’s and loads. At the conclusion of the scavenging phase, the quantity of air that must be kept in the combustion chamber can also be regulated for the varying load demands of the subsequent combustion. Consequently, a new cycle has been implemented within the NEVIS engine. This new cycle allows partial loads to have an expansion stroke greater than the compression stroke like the Miller cycle but with the advantages of a two-stroke cycle. In contrast to what happens with butterfly throttling in the intake duct, the air is free to enter copiously into the combustion chamber with a better fluxing efficiency, thus providing an optimal scavenging even at partial loads and at minimum rpm.
3) The third concept is based on the adoption of a special shaft for the transformation of the alternate motion of the pistons into rotary motion. This shaft is a sort of sinusoidal camshaft similar to those adopted in engines with cylinders arranged coaxially around the shaft (see the DYNACAM 12- cylinder engine below). However, the new shaft differs in many aspects. First, it has reduced mass and dimensions. Furthermore, it allows for very low average piston velocities with the cam providing for constant acceleration and deceleration of the piston along with the capability of allowing a brief full stop at both top and bottom dead centers in order to provide more time for combustion and scavenging. The shaft incorporated within the NEVIS engine also provides the ability to complete three combustion cycles within a single shaft revolution. The DynaCam engine
4) A variable compression ratio is the forth concept inherent within the NEVIS engine. This is made possible at all rpm and power loads by the simple regulation by of an annular screw element within the shaft itself - unlike the complicated mechanisms necessary in traditional engines to achieve this capability.
5) The fifth concept incorporated within the NEVIS engine is the adoption of annular pistons which enhance the engine’s thermal efficiency and allow for a light and compact structure as well as a rational integration of the engine’s other key concepts.STRUCTURE OF THE ENGINE SHAFT AND ITS CAMTriple-lobed disk attached to the engineshaft of the cylinder block
The shaft is hollow and has anterior and external grooves along with posterior and interior ones. One groove allows the joining to the shafts of other modular engine units that may be added. A substantially cylindrical support coaxially connected to the engine shaft, via respective grooves, hastwo protrusions encompassing it with a cyclic undulated profile. Between the two protrusions operate three couples of ball bearings attached to three supports of an annular piston; when they are pushed by the pistons on the inclined parts of the profiles the resultant forces cause the rotation of the profile support, and therefore of the engine shaft.
Conversely, when it is the support on the engine shaft to set the ball bearings in alternate motion through its rotation, the ball bearings will follow the constant accelerations and decelerations caused by the undulations of the profiles that, by the way, are flat at their vertices to allow the pistons to briefly stop at the dead points. One of the two profiles is used to push and the other to call back the ball bearings depending on whether it is the engine shaft to drive the pistons’ motion or visa versa. Likewise, the ball bearings invert their task to push and to decelerate the piston with every stroke. STRUCTURE OF THE PISTONSide, Top and Bottom views of the NEVIS pistonSTRUCTURE OF THE COMBUSTION CHAMBERSTRUCTURE OF THE EXHAUST VALVESTRUCTURE OF THE EXHAUST TIMING SYSTEMImage of Bearing and Rocker Arm of Exhaust Valve SystemCYCLE TIMING DIAGRAM AND LOADING THE ENGINE
The principal innovation of the NEVIS engine 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 use of ducts with variable geometry and lamellar valves could widen considerably the range of rpm at which the aspired versions of this engine can be utilized.
In those cases in which turbine compressors would be used, or passing from a gasoline version to the diesel version, it will be possible to reduce or increase the compression ratio as needed by reprogramming the software that assists the actuators of the timing and of the variable compression ratio system, in order to allow optimal regulation for any possible load need.
One cycle is completed in 120 degrees of engine shaft rotation. However, to establish a direct comparison with the four- or two-stroke classic cycle diagrams, it is necessary to consider NEVIS shaft rotation 4.5 times slower.
Accordingly, one degree of its shaft rotation is comparable to 4.5 degrees of traditional four- or two- stroke shaft angle rotation. In this way it is possible to represent graphically a diagram that in 540 degrees describes the entire new cycle including the standstill of piston at top and bottom dead points (the rectilinear parts of the oval diagram that follows). To be more clear, if the four-stroke cycle needs 720 degrees of shaft rotation to be completed and the two-stroke needs 360 degrees, the NEVIS cycle occurs in 120 degrees. What we are trying to do is to compare the single cycles, and if the shaft rotation angle degrees are considered as a function of time, expanding the time is like increasing the amount of degrees. Therefore, the timing of a single stroke can be represented with 180 degrees instead of 40; if rotation timing is 4.5 times slower, similarly the graphic description of an entire NEVIS cycle can be expanded on the diagram in 540 degrees instead of 120 as represented in the first diagram that follows.
Diagrams of the timing system of the NEVIS engine are represented below.