The "Siamese" is an internal combustion engine, 4 strokes, with a variable volumetric ratio and an over expansion stroke (compared to intake). The piston describes a real Miller cycle.
Why an over expansion stroke ?
In a conventionnal piston engine, exhaust pressure starts at 3 bars. Those gas
can provide energy again.
This graphic indicates the theorical engine torque in function of over power stroke and charging pressure. The end of compression pressure is still contant (50 bars), the volumetric ratio decreases when charging pressure increases.
Consequently, over power stroke improve the engine efficiency and moreover at high charging pressures.
Nevertheless, because of medium friction pressure (m.f.p. 1 to 2 bars), overs power stroke is useful on and after a 2 or 3 bars charging pressure..
In addition, gas exhaust are enough energetical to run a turbocharger.
Why changing the volumetric ratio ?
The engine theoric efficiency increases with high volumetric ratio. But too
high, it generates thermal losses, dangerous cylinder head pressures and pinking
for spark-ingnition engines.
Changing the volumetric ratio allows high charging pressures, compensates load
and temperature variations of intake, to provide the best combustion and power
stroke.
Rods Architecture - Variable compression ratio
The particular movement of the piston is realized by three rods, from two parallel
crankshafts. A "slow" crankshaft is turning twice slowly than the
"fast" other one. The crankshafts are synchronized by gearing. The
small dephasing of the two crankshafts provides the variation of the volumetric
ratio.
Piston path
The piston describes a real Miller cycle (there is not waiting or unuseful
stroke).
The expansion stroke is progressive and continues during a third of the cycle.
The exhaust stroke is faster.
Vibrations
From 3 cylinders, the "siamese" is correctly balanced in static compared
to a four cylinder in line engine.
Acceleration levels of rods and piston are equivalent to a classical con-rod
system.
Delivered torques
In practise, the slow crankshaft delivers the most of power. Depending on rods
configurations (crankshaft excentric and rod length), volumetric ratio and combustion,
the fast crankshaft delivers from +30% to -10% of engine power.
In addition, crankshafts are averaging the instantaneous torque of the pistons.
Consequently, little power circulates by the gearing between the two crankshafts.
The slow crakshaft is the best engine shaft.
Technological standardization
It is a piston engine. It can receive all classical and modern technologies
:
· Diesel fuel, gas, petrol... or multifuel (adjustment depending on octane
and cetane number)
· Carburretor or injection (direct, high pressure)
· Supercharging, turbocharging...
· Catalyst, particle filter
· Multivalvle, electric valves
· …
It's an engine with... rods and crankshafts ! which are elements controlled
and industrialized.
"downsizing" = Massic power over doubled !
This engine, thanks to variable compression ratio, appreciates high charging
pressures.
At same power, supercharging provides the decrease of engine volume reducing
its weight, friction and vibrations.
The siamese engine architecture, with a 4,5 bars charging ensures the doubling
of massic power, compared to a classical atmospheric engine.
Consumption reduced
In addition to the gain due to variable compression ratio and downsizing (from
30% up to 45%, claimed by most of engine makers, see Other
engine makers/links), comes the economy from the over power stroke, abble
to reach 25%.
Globally, the Siamese engine, provides efficiency closed to 50% ! The range
of high efficiency is very large, especially with poor mixtures.
Valve crossing
The two high piston positions are dissociated. The high position of exhaust/intake
can be pulled down to provide a better valves crossing.
Applying
Wherever massic power and efficiency are needed :
· Cars, road haulage tractors
· "Industrial" engines (generating plants, air compressors,
marine propelling, railroad hauling)
· Private and unmanned aircrafts : torque and speed are well adapted
to helix propelling
Diesel engine prototype for cars (virtual)
 |
· 3 in line cylinders, 4 valves per cylinder · Crankshafts spacing 170 mm · 2 turbochargers with variable geometry in series, reaching 4.5
bars, with intercooler and aftercooler
|
Animation (siamois.avi
to download - 383 ko - and read on loop)
