The problematic of performing engine:
... toward the detonation QUASITURBINE
(HCCI Homogeneous Charge Compression Ignition - SCCI Stratified Combustion
- Controlled auto ignition - Thermo active atmosphere)
With our OTTO mode piston 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,
but also half the sales of the petroleum companies in that sector...
Why are the governments not also listening to their scientists ?
Present day gasoline fuel injector are not in the combustion chamber.
Contrary to the Diesel, they are gasoline injectors near the intake valve, within the vacuum intake manifold...
The intake manifold vacuum still is there, carburetor or injector
(butterfly vacuum valve is the problem, not the fuel means).
With carburetor or injector, the Otto cycle has the advantage to premix the air and the fuel,
such as to produce after compression, a uniform pollution controllable combustion.
Direct fuel injection in the combustion chamber is done with a spray with is fuel rich inward,
stochiometric in the periphery (too hot), and fuel lean on the outward.
Quality of this type of combustion is hardly impossible to control.
The Direct-Injection Spark-Ignition (DI-SI) gasoline engine will probably one day become a reality,
but will likely still use the intake vacuum of Otto cycle, and still will produce a non-uniform polluting combustion.
However, the fuel-injection process in future compression-ignition engines (CIDI or direct-injection diesels)
is difficult to achieve and is not yet commercial
It has also the main inconvenient to produce a "non-uniform combustion"
like in Diesel engine, which generates pollution.
Sorry, there is no way out for "vacuum free intake, while having uniform low pollution combustion",
except through photo-detonation (intake uniform fuel mixture at atmospheric pressure)
... and the Quasiturbine short pressure pulse device is designed specifically for that...
Pertinent introduction overview references:
"The internal combustion engine at work"
by Charles Westbrook, Laurence Livermore Laboratory http://www.llnl.gov/str/Westbrook.html (on line paper)
A Low-Pollution Engine Solution - New sparkless-ignition automotive engines gear up
to meet the challenge of cleaner combustion" par Steven Ashley - Scientific American, June 2001
and more at:
http://www.vok.lth.se/~ce/Research/forskning_en.htm (See the text at the end of the page)
HCCI "Homogeneous Charge Compression Ignition" versus Photo-detonation ?
Conventional combustion in piston engine result from a heat front wave starting from the sparkplug
and propagating progressively in the combustion chamber (smooth pressure build-up).
Because the piston engine does not stand well the knocking, many years ago, researchers focus on HCCI ignition,
without spelling out the nature of the actual combustion mode following it.
The initial idea was to get the engine working on the threshold condition where HCCI ignition will occur,
while maintaining some of the thermal wave smooth combustion condition.
Unfortunately, this unstable threshold mode was not reliable and knocking (photo-detonation) came with the ignition !
Instead of HCCI (which focus on ignition and not the combustion), photo-detonation engine works well off the threshold condition,
where there is no ambiguity about the later combustion mode achieved, which is the violent photo-detonation (the knocking mode).
Summary of the engine performance problematic
Ideal mode: engine with knocking with high compression ratio, while being with homogeneous combustion.
The effectiveness increases with the compression ratios, but pollution also,
The specific power increases with the RPM, but pollution too.
- The homogeneity of the mixture is highly desirable,
but the high compression ratios cause the knocking.
- Stochiometric Otto combustion requires a depressurisation of the intake wasting half of the gasoline in transportation applications.
- Diesel does not have the disadvantage of this depressurisation,
but has a strongly inhomogeneous and polluting combustion
Problem: This mode is incompatible with the piston pressure pulse.
Solution: The linear slope pressure pulse near the TDC of the Quasiturbine (AC) is 15 to 30 times shorter and self-synchronizes the photo-detonation. The photo-detonation removes the need for the hybrid - Weak penalty at low power regime!
Consequence on the saving in gasoline in transportation: 50 %.
As the compression ratio goes up in machine design,
there are successively :
- deflagration (Otto heat wave front combustion),
- auto lit (hot spot triggering still deflagration),
- Thermo lit (a very irregular process where several little pocket of mixture
lit spontaneously, but where inter-region goes deflagration),
- and photo-detonation (there the compression temperature is high enough
to generate a high concentration of black body radiation
increasing as the power 4 of the temperature).
Notice that photo-detonation mode like Otto mode compresses a fuel-air mixture,
while the diesel mode compresses only air.
However, Otto is near stochiometric combustion,
while photo-detonation is in abundant air excess mode...
Reference to powerful laser light is a good way to see it.
An other way is to remember burning a paper at the sun a focal point of a len.
Because piston does not stand the violent detonation,
gas contains anti-detonation additives,
which essentially act as photon radiation absorbents.
The Quasiturbine photo-detonation compatibility
comes form the fact that the pressure tip is 15 to 30 time shorter,
which means auto-synchronization and much less mechanical stress.
Furthermore, ability of the Quasiturbine to extract
precoce (early) mechanical energy is most favourable.
Of course, this will be the end of anti-detonation additives !
Knocking and pinging is a manifestation
of partial and non homogeneous photo-detonation
for which the sine wave movement of the piston
is far to slow at pressure tip to properly synchronized
and manage the violent radiative volumetric combustion.
HCCI process with piston engine is not quite a pure photo-detonation,
because in order to control somewhat the timing
and the stress, the intake is contaminated with exhaust...
which of course make some people conclude
that HCCI is not a pollution free combustion...
while pure photo-detonation can be !
Efficiency improvement by Asymmetric compression ratio !
To increase piston efficiency, the intake valve can be keep open late which reduces the amount intaked,
and the compression ratio experienced by the mixture.
However, during combustion, the mixture experienced a high compression ratio equivalent
since the expansion occur on a larger range.
With the Quasiturbine, this is possible without any valve, just by making the intake port to a late angle !
Compression ratio becomes say 10:1 at intake (spark plug needed) and 20:1 at combustion...
However, as efficiency goes up, specific power goes down... Up to the user to decide...
This is called either Atkinson or Miller Cycle... See definition from http://www.wordiq.com/definition/Engineering
Atkinson cycle :
The Atkinson cycle engine is a type of Internal-combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power. The Atkinson cycle allows the intake, compression, power, and exhaust strokes of the Four-stroke cycle to occur in a single turn of the crankshaft. Owing to the linkage, the expansion ratio is greater than the compression ratio, leading to greater efficiency than with engines using the alternative Otto cycle.
The Atkinson cycle may also refer to a four stroke engine in which the intake valve is held open longer than normal to allow a reverse flow into the intake manifold. This reduces the effective compression ratio and when combined with an increased stroke and/or reduced combustion chamber volume allows the expansion ratio to exceed the compression ratio while retaining a normal compression pressure. This is desirable for good fuel economy because the compression ratio in a spark ignition engine is limited by the octane rating of the fuel used, while a high expansion ratio delivers a longer power stroke and reduces the heat wasted in the exhaust. This makes for a more efficient engine. Four stroke engines of this type with forced induction (supercharging) are known as Miller cycle engines.
Miller cycle :
In engineering, the Miller cycle is a combustion process used in a type of four-stroke internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, in the 1940s. This type of engine was first used in ships and stationary power-generating plant, but has recently (late 1990s) been adapted by Mazda for use in their Millenia large sedan. The traditional Otto cycle used four "strokes", of which two can be considered "high power" – the compression and power strokes. Much of the power lost in an engine is due to the energy needed to compress the charge during the compression stroke, so systems to reduce this can lead to greater efficiency.
In the Miller cycle the intake valve is left open longer than it normally would be. This is the "fifth" cycle that the Miller cycle introduces. As the piston moves back up in what is normally the compression stroke, the charge is being pushed back out the normally closed valve. Typically this would lead to losing some of the needed charge, but in the Miller cycle the piston in fact is over-fed with charge from a supercharger, so blowing a bit back out is entirely planned. The supercharger typically will need to be of the positive displacement kind (due its ability to produce boost at relatively low RPM) otherwise low-rpm torque will suffer. The key is that the valve only closes, and compression stroke actually starts, only when the piston has pushed out this "extra" charge, say 20 to 30% of the overall motion of the piston. In other words the compression stroke is only 70 to 80% as long as the physical motion of the piston. The piston gets all the compression for 70% of the work.
The Miller cycle "works" as long as the supercharger can compress the charge for less energy than the piston. In general this is not the case, at higher amounts of compression the piston is much better at it. The key, however, is that at low amounts of compression the supercharger is more efficient than the piston. Thus the Miller cycle uses the supercharger for the portion of the compression where it is best, and the piston for the portion where it is best. All in all this leads to a reduction in the power needed to run the engine by 10 to 15%. To this end successful production versions of this cycle have typically used variable valve timing to "switch on & off" the Miller cycle when efficiency does not meet expectation. In a typical Spark Ignition Engine however the Miller cycle yields another benefit. Compression of air by the supercharger and cooled by an intercooler will yield a lower intake charge temperature than that obtained by a higher compression. This allows ignition timing to be altered to beyond what is normally allowed before the onset of detonation, thus increasing the overall efficiency still further. A similar delayed valve closing is used in some modern versions of Atkinson cycle engines, but without the supercharging.
The Photo-detonation mode : A necessity for the hydrogen engine
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 photo-detonation mode (not compatible with piston, but with the Quasiturbine)
is so critical for the future of the hydrogen engine.
The 4 strokes piston of our cars fires once every 2 revolutions and produces a positive torque about 17% of the time, dragging 83% of the time. To obtain a reasonable specific power density, we must use the combustion chamber the most often possible in every minute, which means rotating at undesirable high regime, where it is difficult to avoid the limitations due to gas flow and valves inertia. The high RPM also imposes constraints which require a reduced piston course, which call 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.
Furthermore, the engine combustion chamber is a non-desirable parasite volume from the stand point of energy efficiency, since it must be pressurized in pure lost before being able to produce strong forces on the piston and so to make useful mechanical work. Ideally, the combustion chamber should be the smallest possible, which would imply a high compression ratio. However, the piston meet at least 3 major obstacles which limit the compression ratio : the mechanical robustness, the self-firing (photo-detonation), and the production of polluants. At low compression ratio with a pre-mixed intake, the sparkplug produces a lighting thermal wave which propagates into the chamber, driving a progressive and uniform combustion, but somewhat incomplete. In a similar situation but with a high compression ratio, it is the radiation (light, somewhat like the one of a laser) which light spontaneously, completely and uniformly the combustion (detonation or knocking that piston can not stand, because of the too long pressure pulse that it produces). Already to reach the Diesel mode, a substantial concession has been done, which was the abandon of the uniform combustion from a carburetor for the much less desirable combustion of the localized jet of a fuel injector. Except for the additives which absorb the radiations and increase the octane index, the recent researches aim at optimizing the piston engine deal with variable length connecting rods allowing to continuously set the compression ratio just under the photo-detonation threshold, regardless of the engine regime, but without ever exceeding it. Notice that the photo-detonation occurs at slightly higher pressure than the thermal ignition designated in the US as "Homogeneous Charge Compression Ignition" HCCI combustion, in Europe as "Controlled Auto Ignition" CAI combustion, and in Japan as "Active Thermo Atmosphere" ATA combustion. Even if the subject passionate the researchers, the thermal and photonic ignition control in the piston is still an unsolved problem, and possibly a dead-end that the Quasiturbine does overcome!
At low load factor, the intake depressurization of the Otto cycle dissipates power from the engine since the throttle valve is almost closed and the descending piston acts as a clogged vacuum pump against the atmospheric pressure, which vacuum is subsequently partially destroyed by fuel vaporization during the compression. Due to this effect, the engine in Otto cycle opposes to all RPM revolution increase (well known as the engine compression braking) and this intrinsic resistance to speed augmentation is compensated by a constant and important fuel consumption. The photo-detonation mode does not use any throttle valve and accept without constraint all available air at atmospheric pressure (similarly as the Diesel, where the pressurization energy is restituted at the time of relaxation). For this reason, the efficiency at low load factor of the photo-detonation engine is twice that of the conventional Otto cycle, and considering that the load factor of a car is in average of about 10 to 15%, this is not a small difference (saving is still superior in traffic jams...). See http://www.vok.lth.se/~ce/Research/forskning_en.htm
Fortunately, the Quasiturbine allows to solve those dilemma by two unique characteristics (... and they are not the only ones), which are:
First, to fire 8 times by two revolutions in four stroke mode, which allows to use the combustion chambers much more often without having to increase the engine RPM, and without facing the fast gas flow problem, nor the valves inertia since there is none.
Secondly, to produce shorter pressure impulses with linear ramps permitting to control the thermal and photonic ignition and to overcome the obstacles limiting the high engine compression ratio, so increasing the efficiency, while maintaining the uniform combustion capability and simultaneously reducing the polluants. Since the combustion is initiated by the radiation and the pressure pulse is much shorter, the shape of the combustion chamber and its surface / volume ratio has little effect here, contrary to the case of the piston. In fact, the high ratio S/V help attenuate the violence of combustion. Because it was conceived for thermal and photonic ignition, the Quasiturbine can not be considered as a "rotary piston engine", nor be correctly characterized by the piston paradigms.
Note however that the Quasiturbine can as well be operated at lower compression ratio, in standard Otto and Diesel cycle modes.
Thermo-lighting due to very high pressure is not a 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 (a little 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 - unburnt hydrocarbons (this is not however an intrinsic deficiency of detonation).
Here is a list of the main conceptual deficiencies which limit the piston engine :
- The 4 engine strokes should not be of equal duration.
- The piston makes positive torque only 17% of the time and drag 83% of the time.
- At mi-stroke, the gas would push more efficiently on a moderated speed piston,
while it is in fact at its maximum speed escaping in front of the gas.
- The gas flow is not unidirectional, but changes direction with the piston direction.
- While the piston descent, the ignition thermal wave front has hard time trying to catch the gas moving it that same direction.
- The valves opens only 20% of the time, interrupting the flows at intake and at exhaust 80% of the time.
- The duration of the piston rest time at top and bottom are without necessity too long.
- Long top dead center confinement time increase the heat transfer to the engine block reducing engine efficiency.
- The non-ability of the piston to produce mechanical energy immediately after the top dead center.
- The proximity of the intake valve and the exhaust valve prevent a good mixture filling of the chamber.
and the open overlap lets go some un-burnt mixture into the exhaust.
- The non-ability of the piston to efficiently intake mixture right after the top dead center.
- The piston does not stand fuel pre-vaporization, but required fuel pulverization detrimental to combustion quality and environment.
- The instantaneous torque impulse is progressive, and would gain to have a plateau.
- The component use factor is low, and those component would gain to be multifunctional.
- The average torque is only 15% of the peak torque, which imposes a construction robustness for the peak 7 times the average.
- The flywheel is a serious handicap to accelerations and to the total engine weight.
- The connecting rod gives an oblique push component to the piston, which then required a lubrication of the piston wall.
- The lubricant is also heat coolant, which require a cumbersome pan, and imposes low engine angle orientations.
- The need of complex set of valves, of came shaft and of interactive synchronization devices.
- The valves inertia being a serious limitation to the engine revolution.
- The heavy piston engines require some residual compressed gas before top dead center to cushion the piston return.
- The internal engine accessories (like the came shaft) use a substantial power.
- The poor homokinetic geometry imposes violent accelerations et stops to the piston.
- Quite important noise level and vibration.
- At low load factor, the intake depressurization of the Otto cycle dissipates power from the engine (vacuum pump against the atmospheric pressure).
Why is the photo-detonation
Quasiturbine so revolutionary?
In short: The asymmetry of the strokes and the precocity of the mixture intake and gas expansion
(without excess volume during expansion) allow for a better initial mechanical energy conversion.
During 2 rotations, the 4 strokes piston completes 4 strokes while the Quasiturbine completes 32 !
Continuous intake and exit flow make better use of intake and exhaust manifold,
and allow to reduce the weight and the volume of the engine by a factor 4.
A faster reduction in the combustion chamber of the temperature,
the pressure and the confinement time leads to less NOx production,
and less heat transfer toward the engine block, all contributing to improve the efficiency over the piston engine.
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 pulses (particularly QT-AC with carriages),
and furthermore accepting photo-detonation, because compression and relaxation slopes are very nearby in time.
The photo-detonation Quasiturbine suppress all interest and need for hybrid vehicle concept,
since even a powerful Quasiturbine engine would have a small low regime efficiency penalty !
QUASITURBINE PHOTO-DETONATION COMPARISON
For a "short course" in understanding the principles of
Quasiturbine design and performance, See: http://quasiturbine.promci.qc.ca/MarchettiCorrespondance0210.html
Otto cycle required to compress fuel mixture (not pure air).
Further, intake air pressure is controlled by the throttle valve,
making the intake manifold at vacuum
to proper mix air with the small fuel quantity coming in...
Otto cycle is a near stochiometric engine.
Otto cycle can not be made a photo-detonation mode
because of low intake vacuum pressure (at low load factor),
which once compressed can not generally provide the
amount of heat required for photo-detonation.
Unlike 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.
The fuel jet injected goes through the
3 combustion modes: air excess on the exterior of the spray jet,
stochiometric in mid area¸ and fuel rich in the spray center
(very bad and very difficult to control...).
Because the Diesel accept all the intake air,
its efficiency is not reduced by the intake vacuum as Otto is.
Diesel cycle is an air saturated rich engine.
Photo-detonation is the best of both.
It is homogeneous combustion without vacuum intake manifold lost.
Most piston minded expert 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 shorted pressure pulse,
the Quasiturbine do not care about ignition considerations since the
temperature increases occurs 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.
Quasiturbine turbo compressored or turbochargered,
would not effectively recycled the waste heat of combustion
because energy spent in increasing the intake charge
does increase de specific engine power,
but do not substantially affect the efficiency...
With natural gas or volatile,
the Quasiturbine true photo-detonation mode
would not required any added liquid fuel.
The combustion QT is a combination of the best elements
of other internal combustion engines:
(1) Quasiturbine photo-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) Photo-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 emissions 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) Photo-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 photo-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.
Click here for a 2000 pixels high resolution image
These diagram explains the sequence of operation of internal combustion
and pressurized fluids (air or steam) Quasiturbine. Notice the 32 strokes per 2 revolutions!
Table comparing the power output of different engines in different operation modes.
This graph compares the volume variation within the piston and the Quasiturbine AC.
notice the Quasiturbine linear pressure ramp with discontinuity at TDC.
This graph shows the improved intake characteristics of the Quasiturbine AC (with carriages) compare to the piston engine.
The Quasiturbine acts naturally aspirated almost like a piston engine having a turbo!
But why does the Quasiturbine stand what the piston can not tolerate?
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, it 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.
For all these reasons, and considering what it is intended to achieve,
the Quasiturbine can not be considered as a "rotary piston engine". Piston paradigms do not apply to the Quasiturbine!
What is an ATAC engine?
The ATAC engine can be described as a combination of the well-developed spark ignition (SI) engine and the Diesel engine. A premixed air-fuel mixture is used just like in a SI- engine but the fuel is compressed to auto-ignition like in a Diesel engine.
ATAC is an abbreviation of "Active Thermo-Atmosphere Combustion". Some Japanese scientists that studied combustion in Two-stroke engines named this engine. They discovered that at some engine speeds and loads, the combustion became more stable and the engine was running smother when the fuel was auto-ignited instead of being ignited by the sparkplug.
Another name for the ATAC engine is HCCI, which is an abbreviation for "Homogeneous Charge Compression Ignition". The name implies that the homogeneous ("well mixed") charge of air and fuel is ignited by compression heat. This name is better to use since it describes how the engine works and we use it in our reports.
The principle of the HCCI engine
As mentioned above, the HCCI engine can be seen as a hybrid of the SI-engine and the Diesel engine. First, we will describe the SI and Diesel engine.
In the SI-engine, a homogeneous mixture of fuel and air is ignited at the end of the compression stroke by a spark. The spark causes a flame kernel that grows and propagates throughout the combustion chamber. By controlling the mixture flow to the engine with a throttle plate, the engine load (torque) is changed. The mixture ratio between air and fuel is kept almost constant at all loads.
In the diesel engine, pure air is compressed. The fuel is injected under high pressure at the end of the compression stroke, into the warm compressed air. The fuel is vaporized and mixed partially before self-ignition occurs. The load is adjusted by varying the amount of fuel injected.
In the HCCI engine homogeneous air-fuel, mixture is compressed so that auto-ignition occurs when the piston is near the top dead center position. A high compression ratio is necessary in order to ensure auto-ignition. Very lean mixtures have to be used in order to get slow chemistry that reduces the combustion rate. Diluted mixtures can be achieved by using a high air-fuel ratio or by Exhaust Gas Recycling (EGR). Varying the amount of fueasl controls the load. Just like the Diesel engine there is no throttle plate i.e. the engine will always get maximum amount of air flow (the engine is unthrottled).
Advantages of the HCCI engine
The HCCI engine is always unthrottled, a high compression ratio is used and the combustion is fast. This gives a high efficiency at low loads compared to a SI-engine that has low efficiency at part load.
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 are used the combustion temperature becomes very low, which result in very low amounts of NOx. The HCCI engine does not produced the same levels of soot as the Diesel engine.
Disadvantages with the HCCI engine
The control of the combustion is more difficult in the HCCI engine than in the SI or Diesel engines. The HCCI engine provides no direct control of the start of combustion. The start of combustion depends on several parameters. The strongest ones are the compression ratio and the inlet temperature. By adjusting these parameters in "the right way", it is possible to control the start of combustion to a desired moment. Another disadvantage is high levels of hydrocarbons (HC, unburned fuel). The low combustion temperature causes this; the fuel is not burned completely.
Potential of the HCCI engine
An appropriate field of operation is power plants were the engines operate with constant speed. The HCCI- engine could compete with natural gas driven SI-engines due to the higher efficiency and lower NOx emissions. One interesting concept would be to use HCCI combustion at part load conditions and SI combustion at high loads in a car engine. In this way, the fuel combustion would be reduced significantly. If the emissions standards would raise and the problem with the HC emissions could be solved, the HCCI engine would be able to compete with the Diesel engine, since the Diesel combustion causes high NOx emissions and soot particulates.
The modern conventional SI engine fitted with a three-way catalyst can be seen as an very clean engine. But it suffer from poor partload efficiency. As mentioned earlier this is mainly due to the throttling. Engines in passenger cars operates most of the time at light- and partload 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.
The Diesel engine has a much higher part load efficiency than the SI engine. Instead the Diesel engine 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.
The HCCI engine has much higher part load efficiency than the SI 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 SI engine regarding the efficiency and the Diesel engine regarding the emissions.
The following research will be focused on combustion control.
Comments and questions to: Ola Stenlåås Lund University
It is anticipated that the Quasiturbine, specially in photo-detonation mode,
would also permit a substantial improvement in transportation propulsion
Readers unfamiliar with rotary engines are invited to read also the section :
Why is the Quasiturbine so exceptional ?
Why is the Quasiturbine superior to the piston engines ?
Why is the Quasiturbine not a Wankel's type engine ?
Return to home page
Quasiturbine Agence Inc., Promotional Agent for the Quasiturbine Continuous Combustion Rotary Engine or Compressor
Casier 2804, 3535 Ave Papineau, Montréal Québec H2K 4J9 CANADA (514) 527-8484 Fax (514) 527-9530