Quasiturbine> Theory> Piston Differences


The piston engine has been primordial to the planet recent development,
Why was it so difficult to replace it by a better concept?
Could it be because scientists are more interested by atoms and cosmos?

Theory - Quasiturbine versus Piston

Engine Deficiencies

What are the Conventional Engine Deficiencies? The piston being the most common engine reference, the Quasiturbine researcher team has initially established a list of 30 conceptual piston deficiencies open for improvement (see below). The Quasiturbine innovative concept is the result of an effort to improve the piston engine, and indirectly other engines as well, not excluding the Wankel. To achieve major engine improvements, the Quasiturbine concept suppresses the use of the limiting sinusoidal crankshaft and offers up to 7 degrees of freedom at design.

Engine Displacement

Engine comparison can be made on different basis, as good one another. It is generally of public evidence that engine power goes up with displacement, but because of historical definition, this is not quite true, and led to substantial confusion in the world of engines. For all piston engines, the displacement is the total of the maximum cylinder volume, but for example, the 4-stroke piston does intake this volume of fuel mixture only once every 2 revolutions. In order to compare different types of engine, one has to get back to basics where the power of a theoretically good engine  (which piston and Quasiturbine are, but not the Wankel because of the PV diagram), is proportional to its fuel-mixture intake capability per revolution, and not its displacement. As an example, the Quasiturbine may compare 1 to 1 by chamber displacement, but 1 to 8 by total intake fuel-mixture volume and power, because the chambers are used 8 times more often by revolution.

Typical comparison:
Engine displacement
versus the Total engine volume

4 strokes engine type         Unit displacement         Engine volume

Piston                                  1                         15 to 25
Wankel                                1                          10 to 15
Quasiturbine                        1                          1.5 to 5

The Quasiturbine is a positive displacement turbine
with a total displacement almost equal to the engine volume

(Imagine one day, a 3 liters car engine into a 3 liters volume!)


Piston Deficiencies

Piston engine deserves respect and should not be arbitrary and globally condemns. However it has deficiencies that no one seems to be willing to list ? Here is our list of the main conceptual piston engine deficiencies :

  • A one-chamber-does-all-strokes is not good (opposed to split cycle) - Hot process (combustion) destroys efficiency of cold process (intake), an cold process (intake) destroys efficiency of hot process (combustion). Rotary engines have cold area in distinct location of the hot area leading to improve thermodynamic efficiency.
  • 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 moderate 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. Complete reversal of the flows from intake to exhaust.
  • While the piston descents, the ignition thermal wave  front has hard time trying to catch the gas moving in that same direction.
  • The valves open 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 prevents 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 intakes mixture right after the top dead center.
  • The piston does not stand fuel pre-vaporization, but requires fuel pulverization detrimental to combustion quality and environment.
  • The instantaneous torque impulse is progressive, and would gain to have a plateau.
  • The components use factor is low, and those components 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 requires a lubrication of the piston wall.
  • The lubricant is also heat coolant, which requires a cumbersome pan, and imposes low engine angle orientations.
  • The need of complex set of valves, of camshaft and of interactive synchronization devices.
  • The valves inertia being a serious limitation to the engine revolution.
  • The seal wears most at rest near TDC and BDC, when they stop surfing (rotary seals never rest).
  • The heavy piston engines require some residual compressed gas before top dead center to cushion the piston return.
  • The piston tumble and swirl flows effects are largely compensated by gas rolling effects in-between the rotary 2 near surfaces in relative motion.
  • Limited combustion flame front velocity soon limits the piston rpm when scaling up to large displacement, while the Quasiturbine splits each piston chamber in 8 smaller chambers allowing shorter cycle duration corresponding to higher rpm for large engine.
  • The internal engine accessories (like the camshaft) use a substantial power.
  • The poor homo-kinetic 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).
  • Multi-piston crankshaft twists under load while the cam do not, failing to keep optimum operation timing on forward pistons.
  • Too slow chamber movement near top dead center to support detonation.
  • Square piston (stroke equal to diameter) as the Wankel produce near TDC in the combustion chamber a modest converging draft toward the cup, while the QT converging draft is much more important, and favor better ignition.
  • QT Uniflow Characteristic - In piston, the flow reverses its direction at each stroke (counter-flow) to exhaust which cools the head and extra energy is needed to restore the temperature (piston uniflow provides an exhaust port at the end of the stroke, but has the inconvenience of recompressing residual gas, meaning reversibility losses, and the pressure increases makes a substantial restriction to the initial flow into the chamber, not to ignore the truncated cycle near bottom dead center). Quasiturbine is a uniflow engine, with none of these concerns.

Without being pretentious, the fact is that the Quasiturbine corrects or improves each of these deficiencies.

Side by Side

Like the piston engine, the Quasiturbine is a volume modulator of high intensity, and acts as a positive displacement engine. Here is a diagram showing the Piston and the Quasiturbine side by side.

Click here for a 2000 pixels high resolution image 

Quasiturbine may compare 1 to 1 by displacement,
but 1 to 8 by total intake fuel-mixture volume and power,
because the chambers are used 8 times more often by revolution.

Better torque continuity and acceleration (exceeds even the 2-stroke engines): The crankshaft and the flywheel are the main obstacle to engine acceleration, and since the flywheel are unable to store energy at low rpm, the engine torque at idle is highly handicapped by the engine dead times. The piston of a 4-stroke engine works in power mode about 120 degrees / 720 degrees (2 turns), and thus constitutes a drag 80% of time, period during which the flywheel assumes a relative torque continuity. The Quasiturbine has jointed torque impulses, and presents a profile of almost flat torque characteristics, without the assistance of a flywheel (Quasiturbine torque continuity would compare to a 16 or more pistons conventional engine).

Low revolution - Reduction of gearbox ratio: The gear boxes are evils necessary (expensive, complicated, delicate, and energy consuming). The RPM required by the human activity are generally lower that the performance optimum speed of the engines (e.g.: an automobile wheel generally does not rotate to more than 800 or 1000 RPM, which is 4 to 5 times less than the engine RPM). As the Quasiturbine turns 4 to 5 times less quickly than the other engines (including the Wankel), the gear boxes can often be removed (amongst other things in the field of transport) with an increase in efficiency.

Continuous combustion with lower temperature: As the Quasiturbine strokes are jointed (what is not the case with the Wankel), the lighting is necessary only in launching, since the flame transfers itself from one chamber to the following. The thermalisation of the Quasiturbine by contacts with rollers (Model AC) is more effective, and prevents hot point. From the thermal point of view, the Quasiturbine does not contain any internal parts requiring coolant fluid (like oil).

Better overlaps: The intake and exhaust ports being at different ends of the combustion chamber, it is possible to do a better filling of the chamber by having a simultaneous open overlapping of the two ports, without risking that a portion of the intake gas goes into the exhaust, as it is the case with the piston engine.

Quasiturbine Rotor Dynamic

The eccentric crankshaft machines reach their maximum and minimum mechanical extension in synchronization with the pressure strokes, while in the Quasiturbine, the rotor reaches it maximum and minimum extension at half-stroke, producing a smooth kinetic transition near Top and Bottom pressure Dead Center. Le piston atteint ses positions extrêmes en coïncidence avec le début et la fin des cycles de pression, et comme lui, le vilebrequin du Wankel impose aussi cette synchronisation, qui favorise un cognement du rotor sur le stator près des points haut et bas. Dans la Quasiturbine, les positions extrêmes du rotor correspondent à l’élongation en losange, alors que les cycles de pressions débutent et terminent en configuration carrée, ce qui crée une situation particulièrement heureuse pour la continuité du mouvement de rotation et le balancement des efforts internes sur le rotor lors du passage (sans cognement) en configuration carrée, ce qui accentue la compatibilité avec la photo-détonation.
Une fois la déformation du rotor lancée depuis une élongation losange sur un axe vers une élongation sur un autre axe, le système des 4 pales présente une inertie qui assure la continuité (sans cognement) de la déformation lors du passage à la configuration carrée, là où sont les principales et violentes perturbations de pression. Notons que cette inertie de la déformation est freinée par l’action des joints de contour sur les parois internes du stator dans la région éloignée du centre, mais que l’effet de rappelle dynamique dû à la pression interne dans les chambres vient aider ce freinage, voir même le dominer à certain régime.

Power Density

Here is a table comparing engines (order of magnitude only) on the basis of same combustion chamber volume and same rpm.

Quasiturbine model of series AC (with carriages)
Same chamber displacement, same rpm.

High power density engine: The Wankel is already known as a high power density engine. At comparable power, the Quasiturbine presents an additional reduction of volume. Integrated into a use, the density factor is even more impressive (no flywheel, less gear box ratio, optional central shaft...). Because of its quasi-constant torque, the use factor of the intake and exhaust pipes is 100% (still better than the Wankel), implying tubes of smaller dimension, etc.

Same dynamic power range than piston engines: Just a word to recall that the conventional gas turbines are conceived for a precise aerodynamic flow, and do not offer a wide power range with reasonable efficiency. For its part, the Quasiturbine does not use aerodynamic flow characteristic on the blades, and keeps its excellent efficiency on a wide power range. It is the same when the Quasiturbine is propelled by steam, compressed air, or by fluid flow (Plastic Quasiturbine for hydro-electric centrals, etc).

Same range of nominal power: Like the piston engines, the Quasiturbines can be made tiny or huge. Due to concept simplicity and the absence of gears, the small units should be still more tiny than piston engines or Wankel. On the other hand, nothing limits the construction of huge Quasiturbines like for ship power, fix power plan stations, or large Quasiturbines for thermal power plan or nuclear, using steam or hydraulic.


More effective conversion into mechanical energy: Engines that use crankshaft generate sinusoidal volume impulses during which the piston stays a relatively long time at the top while it decelerates and reverses direction, and stays briefly at mid-course, which is contrary to the logic of a better engine (Compression impulses should be as short as possible, and the stay at mid-courses the longest possible for a better mechanical energy extraction). On the other hand, the Quasiturbine is more effective because it has less engine accessories  to operate (no valve, rocker, push rod, cam, oil pump...).

In addition, the piston engine suffers from the symmetry of the back and forth piston movement. Ideally, the piston should have a longer displacement for the expansion (extracting the most possible mechanical energy), and smaller for the admission, without reduction of volume. The Quasiturbine has this asymmetry by compressing the mixture in a smaller angular zone, and by using a greater angular displacement for the expansion. The admission stroke of the piston presents also a major defect in the sense that it is taking-in little volume initially and most at mid course, which does not leave much time to the mixture to enter the cylinders (The role of turbo is essentially to correct this default); for its part the Quasiturbine admits a significant volume initially and leaves much more time to flow for a better effective filling which can even be extended in the next cycle without flow back (In this case, the turbo would be a real improvement, and not a default correction). At the time of the expansion, this same defect of the piston stroke does prevent the piston to extract mechanical energy at the beginning of the stroke, which the Quasiturbine manages to do.

Also, with the Quasiturbine the gearbox can often be removed with an increase in efficiency, to which the reduction of weight can also contribute. An other fundamental improvement over the piston is the intake and expansion characteristics. Contrary to the piston which must release its residual pressure at the end of the expansion to avoid counter push, the Quasiturbine asymmetry defines a post-expansion confinement zone in which the residual pressure can be maintained without slowing down the rotation, and during which gas treatment can be done, and the residual energy can be extracted, either through a turbine or in building up a compress gas reserve.

Engine Exhaust Heat Recovery:
By placing a hot Quasiturbine into or around an engine exhaust pipe, and injecting pressurized hot water (steam keep in the liquid state for better heat transfer), some heat can be recovered into mechanical energy. Stirling and short steam circuit Quasiturbine could do similarly!


Less pollution and more fuel options: In all engines, the NOx results from three factors: high pressures, high temperatures, and prolonged times of confinement. As the Quasiturbine expansion starts quicker than in the other engines, the initial temperatures and pressures are less, as well as the time of confinement in the extreme conditions. Additionally, using high technology material (ceramic) for the seals would allow the Quasiturbine to run with no need of lubrication, nor maintenance. Piston mass injection (droplet density and inertia are greater that vapor and affected by valve flow perturbation) and exhaust valve cooling (rapid combustion is hotter) are two other vaporization piston limitations. However, fully pre-vaporized gasoline does improve combustion quality and is desirable from the environment point of view even if the piston engines do not stand it well... (conventional gas turbines prefer gaseous state or very rapid liquid fuel vaporization). The Quasiturbine engine has no valve, and continuous intake flow permits optimum mass injection. Furthermore, being able to produce early torque pass the top dead center, the Quasiturbine does support the fully vaporized gasoline in Beau de Rocha (Otto) cycle, for better combustion quality and environment.

Less noisy: For comparable power, the Quasiturbine is much quieter than the piston engine, since it splits each expansion in 4 per turn (or 8 by 2 turns for the 4-stroke engines), and evacuates the gases more gradually and on a greater angular displacement (in opposition to the piston which evacuates gases especially at mid course).

Zero Vibration: The foundation of the Dr. Raynaud syndrome in Chicago is dedicated to the preoccupant problem of vibration. The vibrating portable tools (of which the chainsaws) gave name to the " disease of the logger " which goes from insensitivity of the hands and the arms, until the back bone pain, and capillary vessels and blood bursting. The professional truck drivers generally suffer from the syndromes of vibration. The Quasiturbine is a perfectly balanced engine which turns without vibration, and generates less noise. This is the motive for our priority project of a therapeutic chainsaw with zero vibration to fully emphasize the characteristics of the Quasiturbine.

Free Green House Gas Internal Combustion Engine: Hydrocarbons contain only Carbon and Hydrogen which are separated by heat, and recombine with air's oxygen to make water and CO2. People are complaining of bad combustion when engine is making black carbon particles though the exhaust, but this may be good new for GHG? In fact, a way to have a GHG pollution free combustion engine (with somewhat less total power) is to burn only the hydrogen from the hydrocarbon fuel, and recover the <burnt> Carbon (...not dropping it in fine particles in the environment). This is in some way what fuelcell (reformer) are attempting to do, by <burning> only the hydrogen. Modern diesel engine captures carbon particle in after treatment filers - where burning it does not bring any energy, worse is producing pure CO2! So, not burning the carbon from the hydrocarbon fuel would be a way equivalent or better than the CO2 sequestration. The carbon in the fossil fuel would then only play the role of a hydrogen storage chemical bound, a simple way to go around hydrogen storage.

Multi-fuel and Multi-mode

The Quasiturbine can be fed (if adapted) by a whole fuel range going from methanol to  Diesel oils, including the kerosene, natural gas and possibly hydrogen. The Quasiturbine shows characteristics superior than the 2-stroke engine, with a quality of the exhausts better than the 4-stroke engine.

Not sensitive to detonation: The piston stroke does not allow a rapid increase in the volume of the expansion chamber in the vicinity of the T.D.C., and consequently badly supports detonation. The Quasiturbine reacts better to detonation thanks to an earlier expansion process (which means the end of additives to increase the octane rate of  gasoline). Moreover, since the detonation occurs at the time of the robust square configuration of the blades, and because there is no load transfer on a central shaft, the Quasiturbine is a candidate for the detonation driving mode.

Compatible with hydrogen: The high inflammability of hydrogen imposes on hydrogen engines (over 15% hydrogen) a stratified admission chamber distinct from the combustion chamber (which disqualifies somewhat the piston engines). The Wankel engine success for direct hydrogen combustion comes from its intake and combustion stratification, which results mainly from early intake (like Quasiturbine) and its excessive volume during expansion (with an efficiency lost). The Quasiturbine engine offers the same hydrogen advantage without the lost of efficiency. The Quasiturbine meets the fundamental  criteria imposed by the "hydrogen" engine of the future (cold intake area, stratified intake, reduced confinement time, low sensitivity to detonation, less polluant, robust and energy efficiency), and even surpasses the Wankel in this respect, since the intakes are separated by 3 strokes instead of two. Frequent instabilities in the combustion of hydrogen should not appreciably affect the Quasiturbine as it is not sensitive to detonation.


Robust and reliable construction: The Quasiturbine does not present the critical sealing problem of the Wankel where the 3 seals at the top of a triangle (Apex) meet the housing profile with a variable angle around the perpendicular (-60 degrees with +60 degrees). As the seals of the Quasiturbine are assembled on a swivel carrier, they are perfectly normal (perpendiculars) to the perimeter profile at all time. The rotary engines are generally acting between a robust external housing and a central shaft assembly mounted on good bearings, able to take the load on the shaft created by the pressure during combustion. For its part, the Quasiturbine requires only one robust external profile, on which is also applied the load created by the pressure during combustion; the central shaft is optional and is only needed to transfer the torque when necessary. Moreover, contrary to the Wankel, the Quasiturbine does not require any synchronization gears (fragile, complicated, expensive to build, and prone to lubrication and wear!), nor a lighting synchronization system (particularly if one makes use of the continuous combustion option). In addition, the average torque of a 4-stroke piston engine does not exceed 15% of the maximum instantaneous torque (which dictates the required engine strength), while for the Quasiturbine the average torque is equal at 90% of the maximum torque, thus illustrating the substantial   internal stress reduction and the unique homo-kinetic quality of the Quasiturbine.

Submersible, because no crankcase or lubricant coolant: Lighting (piezo electric) is necessary only in launching, since the transfer of flame is done from one chamber to the following. Consequently, the Quasiturbine engine can be immersed without fearing an electric lighting breakdown, nor a water infiltration in the crankcase (the Quasiturbine does not have one). The Quasiturbine is thus an ideal engine for use in hostile environment (for example, in boat propulsion, the blades of the propeller could be directly welded to the rotor, and the whole engine immersed, which also has the advantage of lowering the center of gravity). The use of high technology (ceramic) seals makes it possible to conceive a Quasiturbine without any lubrication, and without maintenance.

Electric integration: The Quasiturbine allows for the first time a real monolithic integration of the electric generator with fuel engines (highly in demand for the hybrid applications, and without vibration). Since the center of the Quasiturbine is free, the motionless electrical components can be located on the central core and the peripheral stator. Only the intermediate area is in rotation. Reciprocally, if the electrical components are part of a motor, the Quasiturbine becomes an integrated electric motor-driven pump, or a Bi-energy power group.

Differences in Short

Hard to summarize, but 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-stroke piston completes 4-stroke while the Quasiturbine completes 32! 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. Intake and exhaust ports being at opposite of the chamber, overlapping intake is more efficient in the Quasiturbine. Continuous intake and exit flows make better use of intake and exhaust manifold, and allow to reduce the weight and the volume of the engine by a factor 4.

More Technical

Methodology of Comparison: Diesel Piston versus Quasiturbine

Quasiturbine difference with the piston

Quasiturbine for vehicles

Why is the Quasiturbine exceptional?