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INDEX THE NEVIS PROTOTYPE SPECIFICATIONS STRUCTURE OF THE ENGINE SHAFT AND ITS CAM STRUCTURE OF THE COMBUSTION CHAMBER STRUCTURE OF THE EXHAUST VALVE STRUCTURE OF THE EXHAUST TIMING SYSTEM STRUCTURE OF THE VARIABLE COMPRESSION RATIO CYCLE TIMING DIAGRAM AND LOADING THE ENGINE VIBRATIONS AND BALANCING ASPECTS COOLING SYSTEM AND THERMAL ASPECTS NEVIS PREROGATIVES AND GENERAL CONSIDERATIONS 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 In
illustrating the concepts behind the In
terms of the fluid dynamic characteristics of the Only four types of engines have been
commercialized on a large scale in the history of engines: the four-stroke
engine, the two-stroke engine, the Wankel engine and the gas turbine. Many
other engines and power sources have been studied and tested such as the
electric engine, the steam engine, the Stirling engine, the fuel-cell engine,
hybrids and engines operating with compressed air, but the current stage of
their development does not allow these alternatives to adequately compete
with the main four internal-combustion engines because of excessive
production costs, inefficiency or inferior functionality. In the 1970s, the gas turbine
seemed capable of replacing the traditional four-stroke engine within the
automotive sector because of its simplicity and contained dimensions. In
aeronautical applications, the gas-turbine engine showed even better
efficiency than reciprocating engines: it was durable and powerful, produced
little vibration and operated in a relatively clean manner. On the other
hand, acceptable efficiency was obtainable only if a very high temperature
could be reached in the combustion chamber. Accordingly, it was necessary to
build the turbine with special materials, too expensive for large-scale
automotive production. The success of the Wankel engine, that possesses similar characteristics to the gas turbine without its prohibitive costs, has been hindered by its modest fuel efficiency and durability only recently improved. Nevertheless, it continues to be used in those applications where fuel consumption is not the main concern . Until a few years ago the
two-stroke engine had a large number of defects, such as high fuel
consumption, excessive emissions and irregular functioning at low rpm or idle
speeds. However, recent advances have led to very respectable levels of efficiency
and functionality along with dimensions that are almost half the size for the
same power output. A good example is provided by AVL two-stroke diesel engine[1]
with a controllable exhaust timing system. The following goals were pursued
in the development of the 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 1) The first
concept incorporated within the 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 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
The DynaCam engine, an updated design of this is now called the Axial Vector Engine 4) A variable
compression ratio is the forth concept inherent within the 5) The fifth
concept incorporated within the THE
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1st |
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Cylinders |
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2 |
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Displacement |
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1,000 cc |
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Power density Kw/L |
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190.0 |
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Bore |
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80mm internal - |
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HP/Kw |
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Estimated:
250/187 » @ 2.000 rpm |
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Average piston velocity |
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7.5 meters/second |
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Engine Block |
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Steel /aluminum |
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Weight |
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80kg |
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Dimensions |
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64 x 36 |
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Power/Weight ratio (Kw/kg) |
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2.38 |
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Compression ratio |
7:1 to 38:1 |
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Injectors per cylinder |
3 |
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Sparkplugs per cylinder |
3 |
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Triple-lobed disk attached to the engine
shaft 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.
The piston velocities and
accelerations are represented in the graphic below where, for simplicity,
only one operative cycle has been considered, while in reality the cycles are
three for every revolution.
Side, Top and
Bottom views of the
Bearing at the
base of the annular piston running along triple-lobed disk
The piston is structured such
that its top surface can be interchanged in order to allow for the
possibility of future variations of the
An internal thread, close to the
external segments, enables a secure
and easy assembling of the two possible tops; the blocking is ensured by two
bolts opposing each other on the thread to prevent unscrewing (the prototype piston crown was
forced into its position after being cooled in liquid nitrogen).
The interchangeable crown of the
piston can be of aluminum, but the structural elements of the piston are best
suited for materials like steel which have the advantage of restricted
expansion and of greater strength of the cavities for the segments that are
often subjected to wear. Furthermore, the robustness required for the support
of the ball bearings would be difficult to achieve if it was made of
aluminum.
The function of the cylindrical
surrounding wall of the piston is to be considered as structural support for
the annular piston, or as an obstruction of intake ports to avoid oil leakage
from the basement, but no longer as a surface able to contain the lateral
pressures caused by the traditional connecting rods that here have been
eliminated together with all balancing problems.
While the external segments are traditional, the two
internal
elastic rings of the piston obviously tend to contract towards the inside;
their hardened face is also internal and they require accurate definition and
experimentation.
The annular piston is subject to forces that cause it to
rotate on its axis when the profiles of the cam engage the ball bearings to
move. To solve this problem, a further 6 small ball bearings have been
appropriately inserted on the walls of the basement block to contrast the
guides at the sides of the of the
piston ball bearings support, the guides force the piston only in its
reciprocating movement .
A thermodynamic analysis of a the
annular piston has been carried out by the
One of the most serious
limitations of the normal two-stroke engines is due to the dimensions of the
of the intake and exhaust ports that have very modest space on the cylinder
walls. In annular chamber of the
The combustion chamber was
designed in order to have unidirectional scavenging to achieve an efficient
fluxage and a uniform distribution of temperature, which, together with the
cooling of the internal and external cylinders of the chamber, helps prevent
undesirable deformations of the chamber near the intake ports that typically
occur in classic two-stroke engines.
The head is well cooled due to
the absence of a traditional valve that normally subtracts space to cooling
liquid
To achieve a certain degree of
symmetry of in the expansion of the flame front and for security reasons in
aeronautical applications, three spark plugs have been positioned on the head
at a distance such that the farthest point that has to be reached by each
flame front of is
Near each spark plug there is a
fuel injector to allow a good spray and a good ignition anywhere in the
chamber. The additional cost of a spark plug and two injectors per cylinder
is compensated by the fact that a single annular piston realizes in the same
amount of time a number of operative cycles comparable to four normal
pistons, as later explained in greater detail.
The
Like the annular piston, it
involves less inertia to complete a lift which is half that of a traditional
valve lift. Its larger mass, due to considerable diametrical dimensions, is
distributed on 6 short stems symmetrically distant in order to avoid
undesired flexion of the ring that is, in any case, lighter than 6 traditional
valves.
The sealing of the annular valve
has to be ensured at the top with an internal boarded edge of the valve that
lies on another boarded edge created on the engine head, where a thin
trapezoidal spring ensures the desired sealing due to its shape and
elasticity. For the realization of this trapezoidal spring, it was necessary
to choose a material also capable of retaining its elastic properties at
relatively high temperatures since as it can be affected by the blow-by of
gases despite being protected within the boarded edge of the head.
The shape of the trapezoidal spring must ensure that the valve has a hermetic closure variable in height, considering that it is not possible to have a perfect matching of the head with the cylinder block and that the valves are integral with the head; if the coupling is not strictly accurate leaks may occur from the superior edge of the valve, or
if the head is
too distant from the cylinder block, leaks would occur from the lower part of
the valve that is not able to close the fissure completely, as it already
knocked against the upper edge of the head. With the trapezoidal spring
mentioned before such problems are avoided, considering that the amplitude of
the spring flexion will be higher than the amplitude of the coupling
tolerance of the head with the cylinder block.
Sealing Ring of Exhaust Valve
In any case, the spring requires
small oscillations and has to withstand a relative amount of mechanical
strain; it can therefore be realized with a thin section that, together with
the ample diameter, will not require elevated pressure to obtain the desired
vertical deformation. The edge where the trapezoidal spring lies is removable
from the top of the cylinder head to allow the disassembling of the valve.
The lower part of the valve
presents no sealing problems, as it can be considered like a valve with a
very large diameter; a traditional coupling is therefore easily created with
the point of contact between the valve and the higher part of the cylinder
block with an inclination of the edge of contact of 30-45 degrees. Of course, the contact
surface between the valve and the cylinder will be covered with material
similar to that of traditional valve seals.
Traditional exhaust valves have a very serious disadvantage: they open towards the inside of the combustion chamber and struggle against the normal outflow of exhaust gases which, after having increased the valve temperature, burn the stems too. This often leads to the necessity of using more resistant materials (chromium silicon steel, austenitic steel with a high content of nickel chromium) or realizing complex parts, such as hollow valves or parts partially composed of metallic sodium or
lithium or
potassium salts that improve the heat transmission from the head to the stem
of the valve.
The temperatures that can be
reached are very high in comparison to those of the intake valves: the combustion chamber is therefore
destined to have considerably different temperatures in the two respective
areas, with all the consequences this entails for pre-ignition.
The
The small quantity of heat that may
be absorbed when it is closed is easily drawn through the stems and the lower
edge that is close to the cooling liquid.
Six radial deflectors gently
direct the exhaust gases toward the duct that collects the exhaust in order
to utilize in the best possible way the kinetic energy of the exhaust.
Exhaust assembly
In a future version of the
The current system to recall the
valve in the
The roller tappets for the
annular valve consist of three ball bearings; each ball bearing is pivoted to
a structure whose top side holds a recalling spring; the same axle of each
ball bearing has room to join two rocker arms on each side connected with the
two relative stems of the valve to be lifted.
Image of Bearing and Rocker Arm
of Exhaust Valve System
If two stems are lifted at the
same time by one roller tappet, then the lifting of the valve can be
effectuated with three cams acting on three roller tappets.
The adoption of rockers helps
eliminate the vibrations caused by the alternate motion of the valve.
The stems are very short and
being fitted, but not welded, to a rather cold valve, they shouldn't be
subject to appreciable lengthening when the engine’s operating temperature
rises. Anyhow, their elongation does not cause the roller tappets to come
close to the cams , but to draw away from them. For this reason the
adjustment of the roller tappets is not necessary and the initial positioning
has to be done by putting the roller tappets in contact with the surface of
the disc or flat support of the cams that lies below , obviously in the point
where it's flat and not where the cams are located.
Unassembled accelerator
To vary the loading of the
engine, it is necessary to vary the duration of the exhaust opening: this is
possible through the special cams illustrated above. They are free to slide
along the perimeter of their support that has an ample diameter in order to
allow the three cams a sufficiently extended area to develop on the plane
along the perimeter.
The regulation of this slide is
obtained with a “regulating cylinder” that has internal and external
helicoidal grooves and is located coaxially between the cylindrical part of
the support of the cams and the concentric cylindrical part of the sliding
cams. They are coupled via their respective helicoidal grooves; consequently
moving back and forth the “regulating cylinder” it is possible to obtain the
desired sliding of the cams. Although the “regulating cylinder” rotates at
the same engine rpm, it needs to be supplied with a ball bearing fixed on its
edge that can be grabbed while rotating This ball bearing has three
protrusions on the external ring that are inserted in inclined fissures of
two other concentric cylinders, one cylinder being fixed to the cover of the
head, the other one free to rotate on its axis to solicit, with the edges of
its contrasting fissures, each ball bearing protrusion for a lift or a
lowering of the “regulating cylinder”. The external cylinder, free to rotate,
has teeth on its lower edge engaged with a smaller gear that has an axle to
transmit the rotation to the external part of the block, allowing the
adjustment of the accelerator through extended devices.
Like the accelerator, the timing
of the lifting phase is variable. The