Quasiturbine> Theory> Engine Problematic

 


Unless a single engine concept serves all applications well,
there will be a variety of engines, of modes, of energy sources...
Here is a short overview of them, with ideas for possible improvements...

Theory of Engine Core Issues


In their book about the Quasiturbine, the inventors have used a set of 14 engine parameters to show that none of the modern engines simultaneously meets all the optimum criteria. Engines fail to be simultaneously compact, light weight, low noise, zero vibration, high torque at low rpm, efficient on a wide power range... while having homogeneous clean combustion and being multi fuel capable... With today's Beau de Rocha (Otto) mode piston gas engine, about half the gasoline used in the transportation sector is literally wasted to fight the intake atmospheric vacuum depression generated by the carburetor or injector manifold butterfly-valve (the engine-braking effect). This is half the pollution of transportation activities.

Quasiturbine has no vane

Unlike vane pumps, which vane extension is important and against which the pressure acts to generate the rotation, the Quasiturbine contour seals have an imperceptible extension and the rotation does not result from pressure against these seals. The vane geometry does not allow high compression ratio at TDC (top dead center), while Quasiturbine does, and this is why QT is efficient (less pressure charging losses), and this is why there is no vane combustion engine. Quasiturbine publishes efficiency data while vane motor manufacturers don't. Premium on efficient equipment is rapidly recovered in operational cost...

Energy sources can be transformed from one into an other with unavoidable losses. Transformations must be minimized. Energy sources can be water dam, solar radiation, compressed air, conventional or nuclear steam, heat, fuel... and for each situation, a proper engine has to be selected. This is the reason for Quasiturbine!

Engine Displacement

Engine comparison can be made on different basis, each with their uses. Generally engine power goes up with displacement, but because of the way in which displacement has traditionally been defined, this is not always 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 only takes in this volume of air-fuel mixture 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 its PV diagram), is proportional to its air-fuel mixture intake capacity per revolution, and not its displacement. As an example, a Quasiturbine that has the same displacement as a given 4-stroke piston engine will take in 8 times as much air-fuel mixture and thus have roughly 8 times the power at the same rpm.

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


Combustion modes

Current Beau de Rocha (Otto) cycle piston engines use deflagration combustion, which is a relatively slow combustion driven by a thermal wave front initiated from the sparkplug, with the great advantage of being homogeneous and quite clean. In order for a fuel to burn in this mode, the ratio of fuel to air must be within certain critical limits. At reduced power, intake would admit too much air to sustain this mode, so a butterfly intake throttle valve is used to limit air intake. In doing so, the engine acts as a vacuum pump against the atmospheric pressure (the engine compression braking effect), with the result that in transportation vehicles, about half the fuel is wasted in removing this excess air. (Diesel, turbines, detonation engines and Hybrid systems, all aim to overcome this limitation).

Diesel cycle has no butterfly intake valve, and uses thermo-ignition combustion (not a detonation). It does not intake an air-fuel mixture, but only air, and produces a non homogeneous combustion very hard to control and keep clean...

Detonation is the enemy of the piston engines, and is referred to as knocking / pinging, and to prevent it, gas contains anti-detonation additives, which essentially act as photon radiation absorbents. Despite all efforts to avoid detonation in piston engine, this is a superior combustion mode which is not ruled out for the future engines. Detonation engines aim to achieve higher compression ratio while maintaining homogeneous fuel mixture, and hope the piston engine will stand it... The HCCI "Homogeneous Charge Compression Ignition" idea is to make thermo-ignition controlled threshold detonation in some regions of the chamber while some of the combustion will still progress under the slow deflagration combustion mode. Such a control with piston engines requires exhaust recycling which results in reduced efficiency and not so clean combustion...

Photo-detonation self-fires similarly to Diesel,
but burn homogeneously, faster and cleaner.
This mode uses a « detonation chamber »
instead of a « combustion chamber ».

Detonation combustion mode is driven by a supersonic shock wave. It is very fast, and is generally initiated by another combustion mode followed by an excessive compression level.

Photo-detonation is the fastest and the cleanest of combustion modes, driven by volumetric black body radiation density, like a powerful laser beam. It requires no anti-detonation fuel additive, and piston will likely never withstand. The HCCI process with piston engines is not quite pure photo-detonation, because in order to control somewhat the timing and the stress, the intake is contaminated with exhaust... which of course makes some people conclude that HCCI is not a pollution free combustion... while pure photo-detonation is (excepte for CO2)! The road to photo-detonation goes through some deflagration, some thermo-ignition auto lit, some threshold detonation and some supersonic detonation, all adding toward radiation process, and finally radiative combustion driven photo-detonation. This mode is almost independent of the shape of the combustion chamber and works with almost any type of fuel. Detonation will end the need for anti-detonation additives in gas.

Notice that detonation modes, just like Beau de Rocha (Otto) mode, compress a gas-air mixture, while the diesel mode compresses only pure air. However, Beau de Rocha mode is a near stochiometric combustion, while diesel and detonation are globally fuel lean modes...

Green-House-Gas-Free 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 exhaust contains carbon particles, but this may be good news for GHG. In fact, one way to have a GHG-pollution-free combustion engine (with somewhat reduced total power) is to burn only the hydrogen from the hydrocarbon fuel, and recover the “burnt” Carbon (...not dropping it in fine particles into the environment). This is similar to what fuel cell (reformer) are attempting to do, by “burning” only the hydrogen. But carbon is not the only atom suitable to link and store hydrogen. Ammonia NH3 is a simple molecule which combustion produces only nitrogen and water vapor, solving the CO2 problem at the user point (the carbon atom being replaced by nitrogen - and sequestrated - at the refining site). Sure Ammonia is toxic and harmful to handle, but still not as much a challenge - and a danger - as pure hydrogen anyway! Ammonia could eventually be a great fuel for internal combustion Quasiturbine.

Modern diesel engine captures carbon particle in after-treatment filters - where burning it does not bring any energy and worse produces pure CO2! So, not burning the carbon from the hydrocarbon fuel would be a way equivalent to or better than CO2 sequestration. The carbon in the fossil fuel would then only act as a hydrogen storage means through chemical bonds, a simple way to approach hydrogen storage.


Hydrogen and Water Doping

Water do not bring any net energy to an engine (the combustion camber already has plenty of dissociated hydrogen and oxygen from the fuel), but by efficiently heat absorption when evaporating, a lot of the engine heat switches from the engine block to the invisible steam in the exhaust, allowing to run harder the engine (extra power) generally for short period of time. This increase of power must not be confuse with efficiency, which does not increases significantly (water vapor taking room in the combustion chamber could make the compression ratio higher in regard to fuel, but heat absorption cancel such positive efficiency gain. Furthermore, fuel droplets do vaporized in the combustion chamber providing < fuel steam > effect, to which additional water is of no significant role.

Hydrogen brings some net energy, but its indirect benefit is better and elsewhere. Hydrogen is known to be a small molecule which can act somewhat like the thinner does in a gallon of paint: It does help homogenization. Because detonation has very unstable thresholds, adding 10 to 15% hydrogen help homogenization and better stabilized the detonation threshold, which allows to run with higher compression ratio, and consequently at higher efficiency (a step closer to full detonation!). Adding hydrogen to a standard fuel engine will not however provide that kind of benefit.


Present Engines

Pneumatic engines, steam and hydraulic engines all uses either pistons or turbines without internal fuel combustion. The source of power being initially the pressure, which generally transforms into kinetic energy within the engine, and then into mechanical energy on the engine shaft.

In internal combustion engines, the 4-stroke 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 valve inertia.

Piston engines also present a long list of conceptual deficiencies, such as :
(See the complete list at www.quasiturbine.com/ETheoryQTVersusPiston.htm )

•    The 4 engine strokes should not be of equal duration.
•    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 dwell time at top and bottom are unnecessarily long.
•    The proximity of the intake valve and the exhaust valve prevents a good mixture filling of the chamber and the open overlap lets some un-burnt mixture flow directly into the exhaust.
•    The average torque is only 15% of the peak torque, so many parts of the engine and drivetrain must be strong enough to withstand a peak load that is 7 times the average.
•    The connecting rod gives an oblique load 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 internal engine accessories (like the camshaft) use substantial power.
•    At low load factor, the intake depressurization of the Otto cycle dissipates power from the engine (vacuum pump against the atmospheric pressure).

The high RPM also imposes constraints which require a reduced piston stroke, which calls for a reduction of the crankshaft diameter and thus a reduction of the engine torque, and consequently a more severe need for the gearbox and the flywheel, which severely reduces engine acceleration. The modern conventional engine fitted with direct fuel injection (and three-way catalyst) can be seen as a very clean engine. But it suffers from poor part-load efficiency, mainly due to the throttling. Engines in passenger cars operate most of the time at light and part-load conditions. For some shorter periods of time, at overtaking and acceleration, they run at high loads, but they seldom run at high loads for any longer periods. This means that the overall efficiency in normal driving conditions becomes very low.

Specific engine power density is a major factor for which direct gas injection has been a major incremental improvement in piston engine in the 1980's. Since gas droplets are about 600 times as dense as gas vapor, any gas vapor takes the precious room competing with air during the intake stroke, and doing so, reduces the maximum engine power. Direct electronically controlled gas injection on the intake valve and some rpm increase have almost doubled the specific power of modern engines, leaving very little extra potential to harvest in that direction.

Diesel engine "non-homogeneous combustion challenge" is still subject to some potential improvements, which could lead to about the same extra efficiency as the Hybrid Concept tends to do. Europeans major manufacturers favor advanced diesel over hybrid vehicles. The Diesel engine has a much higher part load efficiency, but must deal with significant 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 particles and NOx simultaneously through combustion improvement. Today, there is no fully adequate exhaust after-treatment that takes away both soot and NOx, but further CO2 waste production.

Conventional gas turbines are most efficient in large power units. Micro-turbines have attracted some attention and hope lately, but because it does not offer the good power modulation of the piston (and costs more), interest is not steady, and no breakthrough is expected in that direction.

Detonation research effort in piston engine has been going on for years without yet any commercial potential (except at low power?). Research focus is on finding possibilities and limitations of the HCCI engine, and specially on how different parameters affect the engine performance and emissions, without seriously questioning the piston concept itself. Quasiturbine opens the door to such a development by providing a much shorter pressure pulse, quickly and linearly increasing to maximum pressure and falling from maximum pressure.


Issues with Future Engines

Detonation and hybrid are two different approaches to improve upon the low efficiency of piston engines at reduced power, and both are compatible with efficient electrical (in-wheel) power train. Detonation engine is however a more direct and efficient way, and because it depends on less energy conversions than hybrids where the chemical energy of fuel is degraded when restored chemically in batteries.

At low load factor, the intake depressurization of the Beau de Rocha (Otto) cycle dissipates power from the engine since the intake throttle valve is almost closed and the descending piston acts as a clogged vacuum pump against the atmospheric pressure, in which vacuum is subsequently partially destroyed by fuel vaporization during the compression. Due to this effect, the engine in Beau de Rocha (Otto) cycle opposes all RPM increases (well known as the engine compression braking) and this intrinsic resistance to speed augmentation is compensated by a constant and significant fuel consumption at all times, except at full power. The diesel engine does not have this limitation, but non-homogeneous combustion has adverse consequences.

Generally, the minimum residual engine combustion chamber is a undesirable parasite volume from the stand point of energy efficiency, since it must be pressurized with energy that cannot be recovered before the engine can produce strong forces on the piston and thus useful mechanical work. Ideally, the combustion chamber should be as small as possible, which implies, among other things, a high compression ratio.

Following the recent engine improvements, the issues of future engine are even more complex, and breakthroughs are required for significant improvement. Here is a summary of engine performance issues:

•    Efficiency increases with compression ratio, but so does pollution;
•    Specific engine power increases with rpm, but so does pollution;
•    Homogeneous gas mixture is highly desirable, but high compression ratio with this mixture leads to knocking / pinging;
•    The Beau de Rocha (Otto) combustion is clean, but its need for a stochiometric air-fuel mixture requires intake manifold vacuum wasting half the gas energy in transportation applications.
•    The Diesel does not have this intake vacuum drawback, but has a strongly non-homogeneous polluting combustion.

Much can still be done within this problematic, but the only way to escape its fundamental dilemma would be to considerer detonation, a mode which is very tough on piston engines:

•    The ideal model : The detonation engine, which would have a very high compression ratio while maintaining a homogeneous clean and efficient combustion – a mode unlikely to be compatible with piston engines.
•    Solution - The Quasiturbine (especially the AC model) with a volume pulse 15 to 30 times shorter near the tip, and with fast linear auto-synchronizing raising and falling ramps. – Without the efficiency penalty at reduced power, this engine could save up to 50 % of the gas used in transportation applications.

The detonation mode does not use any throttle valve and accepts without constraint all available air at atmospheric pressure (similarly to the Diesel, where the pressurization energy is recovered during expansion). For this reason, the efficiency at low load factor of the detonation engine is twice that of the conventional Beau de Rocha (Otto) cycle, and considering that the load factor of a vehicle is on average about 10 to 15%, this is not a small difference. The thermal and photonic ignition control in the piston is still an unsolved problem, and possibly a dead-end that the Quasiturbine overcomes!

Photo-detonation self-fires similarly to Diesel,
but burn homogeneously, faster and cleaner.
This mode uses a « detonation chamber »
instead of a « combustion chamber ».

There is no way to have "vacuum-free intake manifold, while having uniform low pollution combustion", except through detonation (which can intake uniform gas mixture at atmospheric pressure) ... and the Quasiturbine short pressure pulse device is designed specifically for that...


What Next?

A March 2003 - MIT study says : Improving gasoline and diesel engines is the way to go ! The hydrogen car is no environmental panacea. The hydrogen fuel-cell vehicle will not be better in terms of total energy use and greenhouse gas emissions by 2020. If we need to curb greenhouse gases, improving mainstream gasoline and diesel engines is the way to go. These results come from an assessment of a variety of engine and fuel technologies forecasting no real 'breakthroughs' (Note that the Quasiturbine has not been included in the study).

Considering recent engine developments, future engine breakthroughs are expected mainly in two area:

•    Diesel engine "non-homogeneous combustion challenge" is still subject to some potential improvements, which could lead to about the same extra efficiency as the Hybrid Concept. Europeans major manufacturers favor advanced diesels over hybrid vehicles.
•    Detonation engine, where research effort in piston engine goes on for years without yet any commercial potential (except at low power). Research focuses on finding possibilities and limitations of the HCCI engine, and specially on how different parameters affect the engine performance and emissions, without seriously questioning the piston concept itself.

Quasiturbine (especially the AC model) opens the door to detonation development by providing a much shorter pressure peak pulse, with pressure rising to and falling from the peak pressure linearly and rapidly.

The next step in world engine research is to make the gas engine as efficient as the diesel engine, and the diesel engine as clean as the gas engine. The photo-detonation Quasiturbine AC does that and more, by reconciling both gas (homogeneous) and diesel (non-homogeneous) engines in one extremely efficient and clean photo-detonation mode, leading the way to a major efficiency breakthrough! Photo-detonation permits 2 efficiency gain improvements: The removal of the butterfly intake vacuum valve (responsible for engine compression breaking - which exist at all time within gas engines), and the increase of the compression ratio (well over the knocking and the diesel level). Because the combustion is homogeneous and occurs in an excess of air, it is as clean as an external combustion.

Not to confuse the ignition process (the sparkplug and the diesel thermo ignition)
with the combustion mode (thermal wave or detonation)
Notice there is no detonation in diesel engine.

Photo-detonation self-fires similarly to Diesel,
but burns homogeneously, faster and cleaner.
This mode uses a « fast detonation chamber »
instead of a « combustion chamber ».

  www.photodetonation.com

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


Quasiturbine Solution

The Quasiturbine is a compact, robust, simple and highly efficient expander, which is necessary  in pneumatic, steam and Stirling applications. It has some advantages in Beau de Rocha (Otto) and Diesel cycle modes, and could make appreciable efficiency gains in vehicle applications, where weight, volume, vibration and noise are important. The Quasiturbine has great potential...


Quasiturbine Model SC for expander, or Beau de Rocha (Otto) and Diesel


The Quasiturbine can solve the modern engine development dilemma by two main unique characteristics, which are:

•    Firstly, by firing 8 times each two revolutions in a 4-stroke mode, which uses the combustion chambers much more often without having to increase the engine rpm, and without being limited by the fast gas flow problem, or by valve inertia since there are no valves.
•    Secondly, by reaching detonation mode with its shorter peak pressure impulses with linear pressure increases and decreases, it can self-trigger the thermal and photonic ignition and  overcome the obstacles limiting the high engine compression ratio, in both cases increasing the efficiency while maintaining the uniform combustion capability and thus simultaneously reducing pollutants.


Quasiturbine Model AC for expander or detonation mode

Unlike piston-crankshaft concepts which are limited to near-sinusoidal chamber volume pulses, the Quasiturbine is a family of engine concepts based on 7 geometrical parameters, which allows a multitude of designs quite different one from another. Because the Quasiturbine can accept carriages, it is possible to define sets of parameters which can give almost any desired variation of chamber volume with time. To withstand detonation, a Quasiturbine with a chamber volume pulse of 15 to 30 times shorter at the tip than piston, which rises to and falls from minimum volume linearly and rapidly, has been proposed. The QT-AC (With carriages) is intended for photo-detonation mode, where high surface-to-volume ratio is beneficial in attenuating the violence of detonation.

Photo-detonation self-fires similarly to Diesel,
but burn homogeneously, faster and cleaner.
This mode uses a « detonation chamber »
instead of a « combustion chamber ».

Detonation is an extremely rapid combustion, either supersonic or totally volumetric when photon driven. Many labs have been trying to make piston engines work in the detonation mode without serious success (except at low power). The Quasiturbine family of engine uses no sinusoidal crankshaft, and allows for carriages which permit it to shape the volume pulse more appropriately than the piston for detonation. Quasiturbine (Model AC with carriages) is intended for detonation mode, where high surface-to-volume ratio is a factor attenuating the violence of detonation. In photo-detonation mode, since the combustion is driven by the radiation and since the pressure pulse is much shorter, the shape of the combustion chamber and its surface to volume ratio has little negative effect. In fact, the high ratio Surface to Volume helps attenuate the violence of combustion. Because it was designed for thermal and photonic ignition, the Quasiturbine cannot be considered as a "rotary piston engine", nor be correctly characterized by piston paradigms.

With our current Beau de Rocha (Otto) mode piston gas engine, about half the gasoline used in the transportation sector is literally wasted to fight the intake atmospheric vacuum depression generated by the carburetor or injector manifold butterfly-valve (the engine-braking effect). This is half the pollution of transportation activities. A detonation Quasiturbine engine could save this fuel... Doesn't it deserve a try ?

Quasiturbine Uniflow Characteristic

In most reciprocating piston engines, the steam reverses its direction of flow at each stroke (counter-flow). By entering and exhausting the cylinder by the same port, the cylinder valve and walls are cooled by the passing exhaust steam, while the hotter incoming admission steam is wasting some of its energy in restoring the temperature. Some energy is further lost in reversing the motion momentum of the mass of steam within the piston. The aim of the piston uniflow is to remedy this defect by providing an exhaust port at the end of the stroke, making the steam flowing only in one direction, but has the inconvenience of recompressing some residual cylinder steam. Quasiturbine is a uniflow engine, with the further advantage of not recompressing any residual steam, resulting in superior energy efficiency.  Recompressing residual steam means some reversibility losses, and the pressure increases makes a substantial restriction to the initial steam flow into the chamber, not to ignore the truncated cycle near bottom dead center - None of this with the Quasiturbine.


More Technical

Photo-detonation engine

Methodology of Comparison: Diesel Piston versus Quasiturbine