La problématique des moteurs performants:
... vers la QUASITURBINE à photo-détonation
(HCCI Allumage par compression d'un mélange homogène - SCCI Combustion stratifiée
- Auto allumage contrôlé - Atmosphère thermo-actif)

Avec nos moteurs à pistons en mode OTTO, environ la moitié de l'essence consommé dans le secteur
du transport est littéralement gaspillé pour vaincre le vide d'admission de la dépression atmosphérique
générée par la vanne papillon des tubulures de carburateurs ou d'injecteurs (L'effet frein-moteur) !
C'est la moitié de la pollution due au transport,
mais aussi la moitié des ventes des pétrolières dans ce secteur...
Pourquoi les gouvernements n'écoutent-ils pas aussi leurs scientifiques ?

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,
http://www.jsme.or.jp/English/awardsn32.html
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
http://www.transportation.anl.gov/ttrdc/engine/ct15-APS.html
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...

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).

Résumé de la problématique de la performance moteur

L’efficacité augmente avec les taux de compression, mais les polluants aussi,

La puissance spécifique augmente avec le RPM, mais la pollution aussi.

L’homogénéité du mélange est hautement désirable,
mais les hauts taux de compression provoquent le cognement.

La combustion stochiométrique Otto exige une dépressurisation de l’admission gaspillant la moitié de l’essence en transport.

Le Diésel n’a pas l’inconvénient de cette dépressurisation,
mais a une combustion fortement inhomogène et polluante

Le mode idéal : Le moteur à cognement à haut taux de compression,
tout en étant à combustion homogène
Problème : Mode incompatible avec l’impulsion du piston
Solution : L’impulsion à rampe linéaire près du point haut de la Quasiturbine (AC) est de 15 à 30 fois plus brève et auto-synchronise la photo-détonation

La photodétonaiton supprime la nécessité de l’hybride – Faible pénalité à bas CV !
Conséquence sur l’économie d’essence en transport : 50 %

As the compression ratio goes up in machine design,
there are successively :
- deflagration (Otto heat wave front combustion),
- autolit (hot spot triggering still deflagration),
- Thermolit (a very irrégular process where several little pocket of mixture
lit spontaneously, but where inter-region goes déflagration),
- and photo-détonation (there the compression temperature is high enough
to generate a high concentration of black boddy radiation
increasing as the power 4 of the temperature).
Notice that photo-détonation 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 otherway 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 absorbants.
The Quasiturbine photo-détonation compabitilité
comes form the fact that the pressure tip is 15 to 30 time shorter,
which means autosynchronization and much less mechanical stress.
Furthermore, hability of the Quasiturbine to extract
precoce (early) mechanical energy is most favorable.
Of course, this will be the end of anti-detonation additives !

Knocking and pinging is a manifestation
of partial and non homogenious photo-détonation
for which the sinewave mouvement of the piston
is far to slow at perssure tip to properly synchronized
and manage the violent radiative volumetric combustion.
HCCI process with piston engine is not quite a pure photo-détonation,
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-détonation 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.

Le piston à quatre temps de nos voitures fait feu une fois à chaque deux tours et produit un couple moteur positif environ 17% du temps, étant 83% du temps en traînée. Pour obtenir une densité de puissance raisonnable, il faut donc utiliser la chambre à combustion le plus grand nombre de fois possible par minute, c’est à dire tourner à des régimes élevés indésirables, là où les limitations dues aux écoulements et l'inertie des soupapes sont difficilement contournables. Le haut régime impose aussi des contraintes qui requièrent une course réduite des pistons qui engendre une réduction du diamètre du vilebrequin et une réduction du couple moteur, et conséquemment un besoin plus sévère sur la boîte de rapport de vitesse et sur les aspects cinétiques comme le volant d’inertie, lequel réduit sévèrement les accélérations.

D’autre part, la chambre à combustion des moteurs est un volume parasite indésirable du point de vue de l’efficacité énergétique, puisqu’il faut la pressuriser en pure perte avant de pouvoir produire de fortes pressions sur le piston et ainsi faire du travail utile. Idéalement, il faudrait donc que la chambre à combustion soit la plus petite possible, ce qui implique un taux de compression élevé. Or le piston rencontre au moins 3 obstacles majeurs qui limitent son taux de compression : la robustesse mécanique, l’auto-allumage (photo-détonation), et la production de polluants. À bas taux de compression avec un carburant pré-mélangé, la bougie produit une onde thermique d’allumage qui se propage dans la chambre, produisant une combustion progressive et uniforme, mais quelque peu incomplète. Dans la même situation avec un haut taux de compression, c’est la radiation (lumière, un peu comme celle d’un laser) qui allume spontanément, parfaitement et uniformément la combustion (détonation ou cognement que les pistons ne peuvent supporter en raison de la trop longue impulsion de pression qu’ils produisent). Déjà pour atteindre le mode Diesel, il a fallut faire une concession de taille, c’est à dire abandonner la combustion uniforme d’un carburateur pour une combustion beaucoup moins désirable qu’est celle du jet localisé de l’injecteur de carburant. Mis à part les additifs qui absorbent les radiations et augmentent ainsi l’indice d’octane, les récentes recherches visant à optimiser le moteur à pistons portent sur des bielles de longueurs variables permettant d’ajuster de façon continue le taux de compression pour qu’il soit juste en dessous du seuil de la photo-détonation, quel que soit le régime moteur, mais sans jamais l’excéder. Notez que la photo-détonation se produit à des pressions légèrement supérieures à l’allumage thermique désigné aux É.-U. par "Homogeneous Charge Compression Ignition" HCCI combustion, en Europe par "Controlled Auto Ignition" CAI combustion, et au Japon par "Active Thermo Atmosphere" ATA combustion. Bien que le sujet passionne les chercheurs, le contrôle de l’allumage thermique et photonique dans le piston demeure un problème non encore résolu, et possiblement une impasse que la Quasiturbine contourne!

À faible facteur de charge, la dépressurisation à l'admission du cycle Otto dissipe de la puissance moteur puisque le papillon est presque fermé et que le piston descendant agit en pompe à vide colmatée contre la pression atmosphérique, vide qui est subséquemment partiellement détruit par la vaporisation du carburant durant la compression. En raison de cet effet, le moteur en cycle Otto résiste à toute augmentation RPM de vitesse (bien connu comme frein moteur en compression) et cette résistance intrinsèque à l'augmentation de vitesse est combattue par une consommation constante et importante de carburant. Le mode photo-détonation n'utilise pas de papillon et accepte sans contrainte toute l'air disponible à pression atmosphérique (comme le Diesel d'ailleurs, où l'énergie de pressurisation est alors restituée à la détente). Pour cette raison, le rendement à faible facteur de charge du moteur à photo-détonation est le double de celui du cycle Otto conventionnel, et considérant que le facteur de charge d'une auto se situe en moyenne autour de 10 à 15%, cela n'est pas peu dire (économie encore plus grande dans les embouteillages...). Voir: http://www.vok.lth.se/CE/research/HCCI/i_HCCI_uk.html

Or, la Quasiturbine permet de résoudre ces dilemmes grâce à deux des particularités originales (… et ce ne sont pas les seules), qui sont :
Premièrement de faire feu 8 fois par deux tours en mode 4 temps, ce qui permet d’utiliser les chambres à combustion beaucoup plus souvent sans avoir à élever la vitesse de rotation du moteur et sans rencontrer les problèmes d’écoulement, ni d’inertie des soupapes puisqu’elle n’en a pas.
Deuxièmement, de produire des impulsions de pression plus courtes et à rampes linéaires permettant le contrôle de l'allumage thermique et photonique et le contournement des obstacles limitant les hauts taux de compressions moteurs, augmentant ainsi l’efficacité, tout en conservant la capacité de combustion uniforme et tout en réduisant la production des polluants.
Comme la combustion est provoquée par la radiation et que l'impulsion de pression est beaucoup plus brève, la forme de la chambre à combustion et son rapport surface / volume ont ici peu d’effet, contrairement au cas du piston. En fait, un haut rapport s/v contribue à atténuer la violence de la photodétonation. Parce qu’elle est conçue pour l’allumage thermique et photonique, la Quasiturbine ne peut pas être considérée comme un « moteur à piston rotatif », ni être correctement caractérisée par les paradigmes du piston.

Notez cependant que la Quasiturbine peut aussi fonctionner à plus bas taux de compression, dans les modes standards des cycles Otto et Diesel.

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).

Voici une liste des principales déficiences conceptuelles qui limite le moteur à piston :
- Les 4 temps moteurs ne devraient pas être de durée égale.
- Le piston est en poussée 17% du temps et en traînée 83% du temps.
- À mi course, les gaz pousseraient plus efficacement sur un piston à vitesse modérée, alors qu'en fait il est à sa vitesse maximal en fuite devant le gaz.
- Le flux du gaz n'est pas unidirectionnel, mais change de direction avec la direction du piston.
- Lors de la poussée du piston, le front d'onde thermique d'allumage à de la peine à rattraper le gaz en mouvement dans le même sens.
- Les soupapes ouvrent seulement 20% du temps, interrompant le flot d'admission et d'échappement 80% du temps.
- Les temps de séjour du piston à l'arrêt en haut et en bas sont inutilement trop long.
- Le confinement prolongé au point haut augmente le flux de chaleur au bloc moteur et réduit l'efficacité moteur.
- Incapacité du piston à produire de l'énergie mécanique immédiatement passé le point haut.
- Incapacité du piston à aspirer immédiatement après le point haut.
- Le piston ne supporte pas la pré-vaporisation du carburant, mais requiert une pulvérisation nuisible à la qualité de la combustion et à l'environnement.
- La proximité des soupapes d'admission et d'échappement empêche le bon remplissage de la chambre lors du chevauchement ouvert des soupapes,
et laisse passer une partie des gaz d'admission imbrûlés dans l'échappement.
- L'impulsion de couple instantanée est progressive, et gagnerait à présenter un plateau.
- Le facteur d'utilisation des pièces est faible, et celles-ci gagneraient à être multifonctionnelles.
- Le couple moyen est de seulement 15% du couple de crête, ce qui impose une robustesse pour la crête 7 fois plus grande.
- Le volant d'inertie est un handicape aux accélérations, et au poids total du moteur.
- La bielle donne une composante de poussée oblique qui ovalise le piston, et oblige une lubrification de paroi.
- Le lubrifiant est aussi caloporteur, ce qui nécessite un carter encombrant, et impose des inclinaisons faibles du moteur.
- Requiert un jeu complexe de soupapes, de cames et de tringles interactives de synchronisation.
- Les inerties de soupapes sont une sérieuse limitation à la vitesse de révolution.
- Les moteurs à pistons lourds requièrent un peu de gaz résiduel comprimé avant le point haut pour amortir le retour.
- Les accessoires internes au moteur (comme les arbres de cames) consomment une puissance substantielle.
- Mauvaise qualité homocinétique : violentes accélérations et arrêts du piston.
- Niveau de bruit et de vibration relativement élevé.
- À faible facteur de charge, la dépressurisation à l'admission du cycle Otto dissipe de la puissance moteur (pompe à vide contre la pression atmosphérique).

http://quasiturbine.promci.qc.ca
En bref: L'asymétrie des cycles et la précocité de l'admission du mélange et de la détente des gaz
(sans volume superflu en cours de détente) permettent une meilleure extraction initiale de l'énergie mécanique.
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.
Une réduction plus rapide dans la chambre de combustion de la température,
de la pression et du temps de confinement conduit à une production moindre de NO_x,
et à un moindre transfert de chaleur vers le bloc moteur, le tout accroissant l'efficacité au-delà du moteur à piston.

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.

La Quasiturbine en mode photo-détonation supprime tout intérêt et nécessité du concept de véhicule hybride,
puisque même un puissant moteur Quasiturbine n'aurait qu'une faible pénalité d'efficacité à bas régime !
(Voir http://quasiturbine.promci.qc.ca/QTVehiculeF.html )

QUASITURBINE PHOTODETONATION 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.

Photodetonation 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 photodetonation mode
would not required any added liquid fuel.

QUASITURBINE SUPERIORITY

The combustion QT is a combination of the best elements
of other internal combustion engines:

(1) Quasiturbine photodetonation 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) Photodetonation 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) Photodetonation 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 photodetonation 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.

Mais pourquoi la Quasiturbine supporte-t-elle ce que le piston ne tolère pas?
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 paradigmes do not apply to the Quasiturbine!

Extrait de http://www.vok.lth.se/CE/research/HCCI/i_HCCI_uk.html

Background

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 throttleplate 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.

Why HCCI?

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 aftertreatment 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.

Projects

The experimental research has been directed towards finding possibilities and limitations of the HCCI engine.
Especially, towards how different parameters affect the engine performance and emissions.

Future research

The following research will be focused on combustion control.

Comments and questions to: Ola Stenlåås Lund University