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The detonation combustion mode is
superior
to the deflagration mode used in today engines.
Detonation is efficient and so fast that no piston engine has yet stand it!
Theory - Detonation Engine
Successful - Low Power Piston - Detonation
Engine manufacturers are not much explicit about their said modern
detonation (HCCI) engine, and for good reasons: Piston Detonation
is successful only at low power, and will never be at high power
(where it should be most) with piston, because crank shaft machines are too
slow to match the very high speed of detonation. Quasiturbine AC is a much
shorter pressure pulse machine suitable for fast detonation at all power
level, due to its ability to convert early pressure into
mechanical work.
Note: Variable compression ratio technique (either mechanical on
the crankshaft, or through intake valve early closing control) is not what
is needed to achieve detonation at all power level. Rather, compression
ratio must be extremely high at all time, but mechanical pressure pulse
duration must be much shorter than what eccentric crankshaft engine can
generate.
Present Engine Limitations
There are 4 main factors
detrimental to the gasoline engine efficiency:
1 - The throttle valve which absorb engine power in making intake piston vacuum
(early intake valve closing produces the same vacuum piston effect, and
valve control further result in variable piston compression ratio);
2 - The relatively low power compression ratio which reduce the expansion efficiency;
3 - The heat lost during expansion.
4 - The slow combustion, which is not quite completed by the end of the expansion (at high rpm).
The detonation (HCCI) is a major stake as its offers solutions
to these four limitations at once, by suppressing the need of trottle valve,
by increasing considerably the compression ratio,
by producing a much faster gas expansion reducing heat lost to the engine block,
and by a much faster combustion by detonation.
HCCI Homogeneous Charge Compression Ignition" and PhotoDetonation processes are not
completely strange to one another. HCCI within piston (slow machine) is a
borderline process, where combustion may begin stochastically by
conventional thermal front waves, which turn out in detonation spots and
subsequently in shock wave driven combustion. More simply,
photo-detonation occurs well over this borderline process, where extreme
conditions favor photon volumetric combustion, and is only manageable in
very fast (short pulse) machine like the Quasiturbine AC.
With our today Beau de Rocha
(Otto) mode piston gas engine,
about half the gasoline used in the
transportation sector is literally wasted to fight the intake atmospheric
vacuum depression generated by the carburetor or injector manifold
butterfly-valve (The engine-braking effect). This is half the pollution of
the transportation activities.
The high RPM also imposes constraints which require a reduced piston
course, which calls for a reduction of the crankshaft diameter and a
reduction of the engine torque, and consequently a more severe need for
the gearbox and on the kinetic aspects like the flywheel, which severely
reduces the engine accelerations. The modern conventional engine fitted with a three-way catalyst can
be seen as a very clean engine. But it suffers from poor part load
efficiency, mainly due to the throttling.
Engines in passenger cars operate most of the time at light and part
load conditions. For some shorter periods of time, at overtaking and
acceleration, they run at high loads, but they seldom run at high loads
for any longer periods. This means that the overall efficiency at normal
driving conditions becomes very low.
Diesel engine "non-homogeneous combustion challenge" is still subject
to some potential improvements, which could lead to harvest about the same
extra efficiency as the Hybrid Concept tends to do. Europeans major
manufacturers favor advanced diesel over hybrid vehicles.
The Diesel engine has a much higher part load efficiency,
but fights with great smoke and NOx
problems. Soot is mainly formed in the fuel rich regions and NOx in the
hot stoichiometric regions. Due to these mechanisms, it is difficult to
reduce both smoke and NOx simultaneously through combustion improvement.
Today, there is no well working exhaust after treatment that takes away
both soot and NOx.
For over 50 years, researchers have been
dreaming about the perfect engine,
having uniform combustion, with a small combustion chamber (high
compression ratio).
This is what the Quasiturbine does by producing a much shorter pressure
pulse (particularly QT-AC with carriages),
and furthermore accepting detonation, because compression and
relaxation slopes are very nearby in time.
Gas and Diesel versus Detonation
Photo-detonation
self-fires similarly to Diesel,
but burn homogeneously, faster and cleaner.
This mode uses a « detonation chamber »
instead of a « combustion chamber ».
Beau de Rocha (Otto) cycle compresses fuel mixture (not pure air).
Intake air pressure is controlled by the throttle valve
making vacuum intake
to proper mix air with the small fuel quantity coming in... This is a near stochiometric
engine which cannot be made a detonation engine
because of low intake vacuum pressure (at low load factor),
which once compressed cannot generally provides the
amount of heat required for detonation. Making the intake vacuum requires
about 50% of the gas energy in vehicle applications.
Unlike Beau de Rocha (Otto), Diesel compresses pure air (no fuel mixture).
Air temperature raises due to high compression ratio,
to such a level that any fuel injected do burn (no detonation).
The fuel jet injected goes through the
3 combustion modes: air excess on the exterior of the spray, stochiometric in mid area, and fuel rich in the spray center
(very difficult to control...).
Because the Diesel accepts all the intake air, its efficiency is not reduced by the intake vacuum as
in Beau de Rocha (Otto).
Diesel cycle is a fuel lean engine.
Otto mode engine is near stochiometric, and detonation in this kind of
mixture are unwelcome on all regards, as it is too hot and polluant. The
"excess air detonation" is however the best of all engine modes.
It is homogeneous combustion without vacuum intake manifold lost. It is
very violent combustion and not quite compatible with the piston
sinusoidal crankshaft movement. The Quasiturbine (specially model AC) with
volume pulse 15 to 30 times shorter near the tip, and with fast linear
auto-synchronizing raising and falling ramps would provide a solution with
the potential to save 50 % gas in transportation applications.
Detonation Research
Everyone probably recall using a lens
to concentrate the sun light and burn papers. Amazingly, radiation in a
cylinder acts quite like a gas and as the compression increases, the
density of photons increases (like with the lens), and similarly the
associated electric field which is ultimately responsible for sparks,
combustion and detonation. Compression also increases the gas temperature,
so does the combustion itself, further adding radiation into the cylinder,
but very high compression ratio is dominant in getting the high photons
density (in absence of anti-detonation additive photon absorbent
molecules) needed to trigger a volumetric combustion (sort of a detonation
not mainly driven by shockwave).
Contrary to popular belief,
detonation is not a phenomenon that occurs when an air/fuel mixture is
compressed to the point of thermo-self-ignition. The point of self-ignition is a
highly irregular and non-homogeneous condition where ignition does not
occur uniformly, but rather by patches. As pressure increases, the mixture
reaches first the thermo-self-ignition, where the following combustion is still governed by conventional slow thermal
waves between the patches (alike the sparkplug ignition). With additional
pressure, the ignition patch can develop a shock wave, which can then
drive a detonation (common detonation source). With still higher pressure
(and mostly in absence of anti-detonation additive, which role is to
absorb radiation), the radiative ionization is taking over the shock wave
as photo-detonation becomes dominant. In Beau de Rocha (Otto) engine mode,
shock waves are the dominant phenomena mainly because at the time of
maximum compression ratio, a substantial part of the fuel is still in
liquid state as micro-droplets, limiting the power and radiation
production of the full photo-detonation (true detonation mode requires
full evaporation at the time of maximum compression ratio). Because
engineers have not yet succeeded in controlling the less demanding shock
wave detonation phenomena, photo-detonation is today mainly a curiosity
among scientists. To actually achieve photo-detonation, a fast and narrow
pressure pulse like in the Quasiturbine AC is necessary to rapidly skip
straight through the sequence of events, and rapidly access the
photo-detonation mode. The Quasiturbine AC geometry is not especially attractive for
ignition patches, not even for shock wave detonation, but quite
indicated for the photo-detonation, the end of the combustion road! However, because
of its short pressure pulse and rapid ramp near top dead center, the
Quasiturbine AC handles all types of detonation, which the piston cannot.
Variation of detonation combustion
studies are still limited to very few labs around the world, and a poor
result with piston engine is fuelling exasperation and is quite confusing
to the public. Similar radiation ignition and photo-detonation occur in
high light intensity condition of chemical or nuclear bomb, and can be
produced under control and study in confined chamber by modest power
pulsed laser beam. See for example "Simultaneous Measurements of current
and magnetic field in laser-produced plasma at variable pressure" Appl.
Phys. Lett., 29, 469 (1976). Once photo-detonation gets engineering
applications, Internet search engines will document it better! To
find out about detonation driven by shockwaves, electrical sparks,
microwaves, radioactive particles, thermal radiation (photons), laser
light ... search for "trigger detonation" "radiative detonation" "optical
detonation" and "triggering detonation". Quasiturbine research associates
photo-detonation specifically to fuel mixture, a designation useful to
dissipate confusion in the world of detonation.
Detonation Combustion
Detonation is referred to as HCCI"Homogeneous Charge
Compression Ignition" or SCCI Stratified Combustion, CTI - Controlled
Auto Ignition or ATAC - Active Thermo-Atmosphere Combustion.
Detonation is the enemy of the piston engine, and is
referred to as knocking / pinking. Despite all effort done to avoid
detonation in piston engine, this is a superior combustion mode which is
not discarded for the future engines. Detonation threshold objective is to achieve higher
compression ratio while maintaining homogeneous fuel mixture, hoping the piston engine
will stand it... HCCI "Homogeneous Charge
Compression Ignition" idea is to make thermo-ignition
controlled threshold
detonation in some piston areas while some of the combustion will still
progress under the slow deflagration combustion mode. Such a control with
piston engine required exhaust recycling which results in reduced
efficiency and not so clean
combustion...
HCCI "Homogeneous Charge
Compression Ignition" and photo-detonation processes are not
completely strange to one another. HCCI within piston (slow machine) is a
borderline process, where combustion may begin stochastically by
conventional thermal front waves, which turn out in detonation spots and
subsequently in shock wave driven combustion. More simply,
photo-detonation occurs well over this borderline process, where extreme
conditions favor photon volumetric combustion, and is only manageable in
very fast (short pulse) machine like the Quasiturbine AC.
Photo-detonation
self-fires similarly to Diesel,
but burn homogeneously, faster and cleaner.
This mode uses a « detonation chamber »
instead of a « combustion chamber ».
Detonation combustion mode is driven by a supersonic
choc wave. It is very fast, and is generally initiated by an other combustion
mode followed by an excessive compression level.
Photo-detonation combustion mode is the fastest and
the cleanest way, driven by volumetric black body radiation density, alike
a powerful laser beam. Reference to laser light is a good way to
see it; an other way is to remember burning a piece of paper at the sun focal
point of a lens. It requires no anti-detonation fuel additive, and
piston will likely never stand it ? The road to photo-detonation goes
through some deflagration, some thermo-ignition auto lit, some threshold
detonation and some supersonic detonation, all adding to radiation
process, and finally radiative combustion driven photo-detonation. This
mode is almost independent of the shape of the combustion chamber and
accepts almost any type of fuel.
Notice that detonation modes, just like Beau de Rocha (Otto) mode,
compress a gas-air mixture, while the diesel mode compresses only pure
air. However, Beau de Rocha mode is a near stochiometric combustion,
while diesel and detonation are globally fuel lean modes...
Thermo-lighting due to very high pressure is not an
homogeneous effect and can depend upon the geometry of
the combustion chamber and be distributed in time. On the other hand,
the photo-detonation is a voluminal combustion due to the high
radiation concentration ( as the paper which ignites at the focal of a lens directed towards the sun), which is homogeneous and independent of the shape of the combustion
chamber. Additives added to the fuels to increase the octane rate are
essentially photonic absorbents, which prevent the high density of radiation.
Photo-detonation mode prefers the cheap
fuels without such additives. In practice, thermo-lighting is initiating
the first combustion which increases the pressure to the point of reach of photo-detonation.
The
photo-detonation is a very violent phenomenon that only the fast linear
slopes of pressure and relaxation of the Quasiturbine can contain (preferably
models QT-AC with carriages). The shorter Quasiturbine presses pulsates is
self-timing. In experiments on photo-detonation with
piston engines, the researchers attenuate the violence of the detonation
by reducing the oxygen concentration in admission by mixing the air with
exhaust. By doing so, combustion is not perfect and releases HC - unburn hydrocarbons (this is
not however an intrinsic deficiency of detonation).
Advantages of Detonation
The HCCI engine is always un-throttled, a high compression ratio is used
and the combustion is fast. This gives a high efficiency at low loads
compared to a conventional engine that has low efficiency at part loads. If an HCCI engine is used instead of an
ordinary gasoline engine in a car, the fuel consumption can be reduced to one half! Another advantage is that the HCCI engine produces low amount of
nitrogen-oxides (NOx). The formation of nitrogen-oxides is strongly
dependent on combustion temperature. Higher temperature gives higher
amount of NOx. Since the combustion is homogeneous and a very lean
mixture is used the combustion temperature becomes very low, which
results in very low amounts of NOx. The HCCI engine does not produce the
same levels of soot as the Diesel engine.
The HCCI engine has much higher part load efficiency than the
conventional engine
and comparable to the Diesel engine, and has no problem with NOx and
soot formation like the Diesel engine. In summary, the HCCI engine beats
the conventional engine regarding the efficiency and the Diesel engine regarding
the emissions.
Over the Hybrid Concepts
The detonation engine
suppresses all interest and need for hybrid vehicle concepts,
since a powerful detonation engine would have a small low regime
efficiency penalty, and the objective of hybrid is exactly to harvest the
present low regime efficiency penalty of the piston engine!
A Must for Hydrogen
In order to do work on a piston, the fuel-air mixture needs to burn at
a speed faster than the piston is moving. Low hydrogen flame speed is a
disadvantage shared with most other gaseous fuels. For comparison, a
gasoline-air mixture has a flame front speed that ranges typically from 70
up to 170 feet/second in IC engines, while an ideal hydrogen-air mixture
has a flame front speed of about 8 feet/second. An average vehicle engine
rotating at 2,000 rpm (33 revolutions per second) produces piston linear
speed of 45 feet/second in the middle-stroke, which is already 5 times
faster than the hydrogen flame front speed ! The fact that a hydrogen-air
mixture has a flame front speed of about 1/10 that of a gasoline-air
mixture, contributes to explain why hydrogen engines only run at reduced
power and low rpm under load. However, the photo-detonation mode is
extremely rapid and totally removes this limitation. This is why the
detonation mode (not compatible with piston, but with the Quasiturbine) is critical for the future of the hydrogen engine.
Quasiturbine Detonation Solution
Contrary to piston-crankshaft concept confined to near sinusoidal chamber
volume pulse, the Quasiturbine is a family of engine concepts based on 7
independent geometrical parameters, which allows a multitude of designs quite
different one an other. Because the Quasiturbine can accept carriages, it is
possible to define sets of parameters which can shape "almost at will" the
chamber volume pressure pulse. To withstand the detonation, a Quasiturbine with
a chamber volume pulse of 15 to 30 times shorter than piston, with rapid raising
and falling linear ramps has been proposed. The QT-AC (With carriages) is intended for photo-detonation mode,
where high surface-to-volume ratio is a factor attenuating the violence of detonation.
Quasiturbine Model AC for expander or detonation mode
Most piston minded experts think the research work
should go toward the thermal ignition "control",
with several difficult considerations...
However, this is not at all the way to go with the Quasiturbine.
Because of its much shorter tip pressure pulse,
the Quasiturbine does not care about ignition considerations since the
temperature increases occur at the short pressure tip,
and exceed by far all ignition parameters
(does not care the engine wall temperature or otherwise...).
The shorter Quasiturbine pressure pulse is self-timing.
Why does the Quasiturbine Stand It?
Because kinetics in the vicinity of the TDC of the
"piston" and the "QT-blade" are diametrically opposed, both in
volume and speed. In volume, because the piston passes at the TDC at almost constant volume, whereas
QT-blade (specially Model QT-AC) passes the TDC with a discontinuous varying
volume (volume vary quickly linear downward and ascending, where the tip is an abrupt turn
around). In speed, because the piston
passes at the TDC with one discontinuous speed (deceleration, stop, and
acceleration in opposite piston), whereas the QT-blade passes the high
point at constant speed (with moreover a null radial component). Two
mechanical considerations rise directly from these physical
characteristics. Firstly, the piston is in rise (kinetic ascending) when
early photo-detonation comes to strike it (kinetic downward), and like two
objects moving in opposite direction run up very violently, the
piston resists badly, whereas the QT-blade passes the TDC at constant kinetic
and null radial speed. Second, the short tip impulse of the Quasiturbine retains the pressure less longer than the long
sinusoidal impulse of the piston, and consequently the QT-blade tires much less.
Centrifugal force on the blades of Quasiturbine also helps to contain high
pressure.
Notice that because of its crankshaft, the Wankel behaves like piston
near TDC.
The Best of Engines
The Quasiturbine detonation combustion is a combination of
the best elements of other internal combustion engines:
(1) Quasiturbine detonation of the homogenous fuel/air charge eliminates the electronic ignition requirement of most fuel engines.
Electronic ignition in piston gasoline engine is required because of intake vacuum and incompatible long duration compression "pulse structure" limitations in the cylinder.
(2) Detonation will completely combust the fuel in the fuel/air charge because of the short, but powerful, pressure pulse
and because of the fast nearly linear variation of the QT maximum pressure zone, which rapidly closes and re-opens the combustion chamber. The diesel engine can only incompletely combust the fuel injected into the heated, compressed air in the cylinder. The QT (unlike the diesel) is therefore a "clean combustion" engine. It will have virtually no emission other than the standard products of combustion, e.g., CO2 and H2O. "Clean combustion" also implies that the QT engine is more fuel efficient than the diesel.
(3) Detonation in the QT occurs rapidly at top dead center. In the diesel engine, ignition of the injected fuel occurs somewhat after top dead center, usually about 12 degrees or so, and is progressive with time to mechanically protect the piston. The QT's power stroke is therefore somewhat longer "with early and late mechanical energy conversion" and the exhaust somewhat cooler, which also implies a more efficient engine.
(4) Because the temperature of stator/rotor is not significant in Detonation mode (light ignition), and because the shorter QT pressure pulse is self-timing, premature ignition is not a concern. The combustion QT can have a very simple cooling mechanism, such as air cooling, even when operating on a low volatility fuel like natural gas.
(5) The Quasiturbine is suitable for multi-fuel use,
including hydrogen combustion. It can also be operated in a combine thermal cycle mode (including steam and Stirling mode hook-up on the same shaft) thereby increasing further the efficiency.
(6) Finally, the Quasiturbine can operate in the more conventional Otto mode, yet retains its added value characteristics when compared to the piston engine.
For all these reasons, and considering what
it is intended to achieve, the Quasiturbine cannot be considered as a "rotary piston engine". Piston
paradigms do not apply to the Quasiturbine!
The future of detonation
The paradox of the detonation in slow machines
The crankshaft piston engine « volume of the chambers » varies
approximately like a sinusoidal, which spends a lot of time at top and
bottom dead center. This is a characteristic of basically slow machine,
with only two degrees of freedom at design (the translation of the piston
and the crankshaft rotation), and therefore enables to meet the super fast
detonation requirement. In the world of the piston, the problematic of
detonation is reduced to a problem of delaying the outbreak of detonation
in a relatively stationary state, the top dead center. In an attempt to
make detonation to work, crafts such as variables connecting rods or fast
mini-pistons are added as up front solution, but these artifices do not
seriously address the other downstream key problem, which is the ability
of the machine to early transform pressure energy into rotational energy.
For decades, the piston - HCCI process focused on controlling the outbreak
of detonation and to get there, choking and weakening the power of the
detonation by contaminating admission with the exhaust gases; this is why
the HCCI mode ( and not open detonation) does not burn the fuel
completely. The HCCI is a (border line) marginal below threshold
detonation process, where combustion may begin with a conventional heat
wave front, which can degenerate into multiple points detonation, and
subsequently in combustion-driven shock wave. This is not a pure
detonation. It works (if it can be said so?) as long as no power is taken
out of the engine! The field of HCCI is possibly still in a dead end, but
moving toward PhotoDetonation...
The detonation in a fast machine
A machine with more degrees of freedom at design that allows shaping of
the volume pulse as the cursive letter " i " with a 15 to 30 times shorter
duration than the piston better suited to detonation, and that is what the
Quasiturbine AC www.quasiturbine.com
accomplished, while allowing for early transformation of pressure energy
into rotational energy. With a fast machine, detonation begins in a steep
slope of increasing pressure, immediately followed by a steep descendant
slope, so there is no need to juggle with the issue of postponing the
outbreak of the detonation. HCCI mode is detonating, but not purely
photonic, while PhotoDetonation
quasiturbine.promci.qc.ca/ETheoryDetonationEngine.htm is a
pure and full detonation (not choking and weakened by contamination),
possible only with much faster pressure cycles than the piston. Obviously,
the HCCI and PhotoDetonation are not stranger to one another. Simply said,
PhotoDetonation occurs well over the HCCI borderline process, where
extreme conditions favor photonic volumetric combustion, and are feasible
only in very fast machine (short pulse, such is the Quasiturbine AC an
example).
Detonation versus hybrid
The PhotoDetonation removes the need for intake depressurization which
allows a considerable gain in efficiency (in the car uses, nearly half the
energy of the fuel is used to produce the intake depressurization). In
this mode, the engine efficiency remains high even at low power.
Consequently, the detonation and hybrid are two different ways to harvest
the conventional piston efficiency reduction at low power, and both
methods are compatible with super-efficient electric propulsion train
(engine wheel). The detonation engine is however a more direct and
efficient way than hybrid, and because « the fuel on board is already a
form of energy storage», the detonation engine avoid re-stocking that
energy on electrical form into batteries. Some chemical energy stored in
the fuel is degraded when transferred in batteries.
Distributed power perspective
Presently, large thermal power utility stations are more efficient that
local small fuel engine generators, which handicap the « distributed
electric production », and favor high voltage transmission lines and
grids. However, PhotoDetonation has the potential to offer small engines
with the same efficiency as large utility stations, and make « distributed
electric production » feasible, with eventually some environmental
benefits. Not everyone may have the same interest in the PhotoDetonation
engines development...
More Technical
Photo-detonation engine
Why is the Quasiturbine
Exceptional?
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