The detonation combustion mode is
Theory - Detonation Engine
Present Engine Limitations
With our today Beau de Rocha (Otto) mode piston gas engine, about half the gasoline used in the transportation sector is literally wasted to fight the intake atmospheric vacuum depression generated by the carburetor or injector manifold butterfly-valve (The engine-braking effect). This is half the pollution of the transportation activities.
The high RPM also imposes constraints which require a reduced piston course, which calls for a reduction of the crankshaft diameter and a reduction of the engine torque, and consequently a more severe need for the gearbox and on the kinetic aspects like the flywheel, which severely reduces the engine accelerations. The modern conventional engine fitted with a three-way catalyst can be seen as a very clean engine. But it suffers from poor part load efficiency, mainly due to the throttling. Engines in passenger cars operate most of the time at light and part load conditions. For some shorter periods of time, at overtaking and acceleration, they run at high loads, but they seldom run at high loads for any longer periods. This means that the overall efficiency at normal driving conditions becomes very low.
Diesel engine "non-homogeneous combustion challenge" is still subject to some potential improvements, which could lead to harvest about the same extra efficiency as the Hybrid Concept tends to do. Europeans major manufacturers favor advanced diesel over hybrid vehicles. The Diesel engine has a much higher part load efficiency, but fights with great smoke and NOx problems. Soot is mainly formed in the fuel rich regions and NOx in the hot stoichiometric regions. Due to these mechanisms, it is difficult to reduce both smoke and NOx simultaneously through combustion improvement. Today, there is no well working exhaust after treatment that takes away both soot and NOx.
For over 50 years, researchers have been dreaming about the perfect engine, having uniform combustion, with a small combustion chamber (high compression ratio). This is what the Quasiturbine does by producing a much shorter pressure pulse (particularly QT-AC with carriages), and furthermore accepting detonation, because compression and relaxation slopes are very nearby in time.
Gas and Diesel versus Detonation
self-fires similarly to Diesel,
Beau de Rocha (Otto) cycle compresses fuel mixture (not pure air).
Intake air pressure is controlled by the throttle valve
making vacuum intake
to proper mix air with the small fuel quantity coming in... This is a near stochiometric
engine which cannot be made a detonation engine
because of low intake vacuum pressure (at low load factor),
which once compressed cannot generally provides the
amount of heat required for detonation. Making the intake vacuum requires
about 50% of the gas energy in vehicle applications.
Everyone probably recall using a lens to concentrate the sun light and burn papers. Amazingly, radiation in a cylinder acts quite like a gas and as the compression increases, the density of photons increases (like with the lens), and similarly the associated electric field which is ultimately responsible for sparks, combustion and detonation. Compression also increases the gas temperature, so does the combustion itself, further adding radiation into the cylinder, but very high compression ratio is dominant in getting the high photons density (in absence of anti-detonation additive photon absorbent molecules) needed to trigger a volumetric combustion (sort of a detonation not mainly driven by shockwave).
Contrary to popular belief, detonation is not a phenomenon that occurs when an air/fuel mixture is compressed to the point of thermo-self-ignition. The point of self-ignition is a highly irregular and non-homogeneous condition where ignition does not occur uniformly, but rather by patches. As pressure increases, the mixture reaches first the thermo-self-ignition, where the following combustion is still governed by conventional slow thermal waves between the patches (alike the sparkplug ignition). With additional pressure, the ignition patch can develop a shock wave, which can then drive a detonation (common detonation source). With still higher pressure (and mostly in absence of anti-detonation additive, which role is to absorb radiation), the radiative ionization is taking over the shock wave as photo-detonation becomes dominant. In Beau de Rocha (Otto) engine mode, shock waves are the dominant phenomena mainly because at the time of maximum compression ratio, a substantial part of the fuel is still in liquid state as micro-droplets, limiting the power and radiation production of the full photo-detonation (true detonation mode requires full evaporation at the time of maximum compression ratio). Because engineers have not yet succeeded in controlling the less demanding shock wave detonation phenomena, photo-detonation is today mainly a curiosity among scientists. To actually achieve photo-detonation, a fast and narrow pressure pulse like in the Quasiturbine AC is necessary to rapidly skip straight through the sequence of events, and rapidly access the photo-detonation mode. The Quasiturbine AC geometry is not especially attractive for ignition patches, not even for shock wave detonation, but quite indicated for the photo-detonation, the end of the combustion road! However, because of its short pressure pulse and rapid ramp near top dead center, the Quasiturbine AC handles all types of detonation, which the piston cannot.
Variation of detonation combustion studies are still limited to very few labs around the world, and a poor result with piston engine is fuelling exasperation and is quite confusing to the public. Similar radiation ignition and photo-detonation occur in high light intensity condition of chemical or nuclear bomb, and can be produced under control and study in confined chamber by modest power pulsed laser beam. See for example "Simultaneous Measurements of current and magnetic field in laser-produced plasma at variable pressure" Appl. Phys. Lett., 29, 469 (1976). Once photo-detonation gets engineering applications, Internet search engines will document it better! To find out about detonation driven by shockwaves, electrical sparks, microwaves, radioactive particles, thermal radiation (photons), laser light ... search for "trigger detonation" "radiative detonation" "optical detonation" and "triggering detonation". Quasiturbine research associates photo-detonation specifically to fuel mixture, a designation useful to dissipate confusion in the world of detonation.
Detonation is referred to as HCCI "Homogeneous Charge Compression Ignition" or SCCI Stratified Combustion, CTI - Controlled Auto Ignition or ATAC - Active Thermo-Atmosphere Combustion. Detonation is the enemy of the piston engine, and is referred to as knocking / pinking. Despite all effort done to avoid detonation in piston engine, this is a superior combustion mode which is not discarded for the future engines. Detonation threshold objective is to achieve higher compression ratio while maintaining homogeneous fuel mixture, hoping the piston engine will stand it... HCCI "Homogeneous Charge Compression Ignition" idea is to make thermo-ignition controlled threshold detonation in some piston areas while some of the combustion will still progress under the slow deflagration combustion mode. Such a control with piston engine required exhaust recycling which results in reduced efficiency and not so clean combustion...
self-fires similarly to Diesel,
Detonation combustion mode is driven by a supersonic choc wave. It is very fast, and is generally initiated by an other combustion mode followed by an excessive compression level.
Photo-detonation combustion mode is the fastest and the cleanest way, driven by volumetric black body radiation density, alike a powerful laser beam. Reference to laser light is a good way to see it; an other way is to remember burning a piece of paper at the sun focal point of a lens. It requires no anti-detonation fuel additive, and piston will likely never stand it ? The road to photo-detonation goes through some deflagration, some thermo-ignition auto lit, some threshold detonation and some supersonic detonation, all adding to radiation process, and finally radiative combustion driven photo-detonation. This mode is almost independent of the shape of the combustion chamber and accepts almost any type of fuel.
Notice that detonation modes, just like Beau de Rocha (Otto) mode, compress a gas-air mixture, while the diesel mode compresses only pure air. However, Beau de Rocha mode is a near stochiometric combustion, while diesel and detonation are globally fuel lean modes...
Thermo-lighting due to very high pressure is not an homogeneous effect and can depend upon the geometry of the combustion chamber and be distributed in time. On the other hand, the photo-detonation is a voluminal combustion due to the high radiation concentration ( as the paper which ignites at the focal of a lens directed towards the sun), which is homogeneous and independent of the shape of the combustion chamber. Additives added to the fuels to increase the octane rate are essentially photonic absorbents, which prevent the high density of radiation. Photo-detonation mode prefers the cheap fuels without such additives. In practice, thermo-lighting is initiating the first combustion which increases the pressure to the point of reach of photo-detonation. The photo-detonation is a very violent phenomenon that only the fast linear slopes of pressure and relaxation of the Quasiturbine can contain (preferably models QT-AC with carriages). The shorter Quasiturbine presses pulsates is self-timing. In experiments on photo-detonation with piston engines, the researchers attenuate the violence of the detonation by reducing the oxygen concentration in admission by mixing the air with exhaust. By doing so, combustion is not perfect and releases HC - unburn hydrocarbons (this is not however an intrinsic deficiency of detonation).
Advantages of Detonation
The HCCI engine is always un-throttled, a high compression ratio is used and the combustion is fast. This gives a high efficiency at low loads compared to a conventional engine that has low efficiency at part loads. If an HCCI engine is used instead of an ordinary gasoline engine in a car, the fuel consumption can be reduced to one half! Another advantage is that the HCCI engine produces low amount of nitrogen-oxides (NOx). The formation of nitrogen-oxides is strongly dependent on combustion temperature. Higher temperature gives higher amount of NOx. Since the combustion is homogeneous and a very lean mixture is used the combustion temperature becomes very low, which results in very low amounts of NOx. The HCCI engine does not produce the same levels of soot as the Diesel engine.
The HCCI engine has much higher part load efficiency than the conventional engine and comparable to the Diesel engine, and has no problem with NOx and soot formation like the Diesel engine. In summary, the HCCI engine beats the conventional engine regarding the efficiency and the Diesel engine regarding the emissions.
Over the Hybrid Concepts
The detonation engine suppresses all interest and need for hybrid vehicle concepts, since a powerful detonation engine would have a small low regime efficiency penalty, and the objective of hybrid is exactly to harvest the present low regime efficiency penalty of the piston engine!
A Must for Hydrogen
In order to do work on a piston, the fuel-air mixture needs to burn at a speed faster than the piston is moving. Low hydrogen flame speed is a disadvantage shared with most other gaseous fuels. For comparison, a gasoline-air mixture has a flame front speed that ranges typically from 70 up to 170 feet/second in IC engines, while an ideal hydrogen-air mixture has a flame front speed of about 8 feet/second. An average vehicle engine rotating at 2,000 rpm (33 revolutions per second) produces piston linear speed of 45 feet/second in the middle-stroke, which is already 5 times faster than the hydrogen flame front speed ! The fact that a hydrogen-air mixture has a flame front speed of about 1/10 that of a gasoline-air mixture, contributes to explain why hydrogen engines only run at reduced power and low rpm under load. However, the photo-detonation mode is extremely rapid and totally removes this limitation. This is why the detonation mode (not compatible with piston, but with the Quasiturbine) is critical for the future of the hydrogen engine.
Quasiturbine Detonation Solution
Contrary to piston-crankshaft concept confined to near sinusoidal chamber volume pulse, the Quasiturbine is a family of engine concepts based on 7 independent geometrical parameters, which allows a multitude of designs quite different one an other. Because the Quasiturbine can accept carriages, it is possible to define sets of parameters which can shape "almost at will" the chamber volume pressure pulse. To withstand the detonation, a Quasiturbine with a chamber volume pulse of 15 to 30 times shorter than piston, with rapid raising and falling linear ramps has been proposed. The QT-AC (With carriages) is intended for photo-detonation mode, where high surface-to-volume ratio is a factor attenuating the violence of detonation.
Most piston minded experts think the research work should go toward the thermal ignition "control", with several difficult considerations... However, this is not at all the way to go with the Quasiturbine. Because of its much shorter tip pressure pulse, the Quasiturbine does not care about ignition considerations since the temperature increases occur at the short pressure tip, and exceed by far all ignition parameters (does not care the engine wall temperature or otherwise...). The shorter Quasiturbine pressure pulse is self-timing.
Why does the Quasiturbine Stand It?
Because kinetics in the vicinity of the TDC of the "piston" and the "QT-blade" are diametrically opposed, both in volume and speed. In volume, because the piston passes at the TDC at almost constant volume, whereas QT-blade (specially Model QT-AC) passes the TDC with a discontinuous varying volume (volume vary quickly linear downward and ascending, where the tip is an abrupt turn around). In speed, because the piston passes at the TDC with one discontinuous speed (deceleration, stop, and acceleration in opposite piston), whereas the QT-blade passes the high point at constant speed (with moreover a null radial component). Two mechanical considerations rise directly from these physical characteristics. Firstly, the piston is in rise (kinetic ascending) when early photo-detonation comes to strike it (kinetic downward), and like two objects moving in opposite direction run up very violently, the piston resists badly, whereas the QT-blade passes the TDC at constant kinetic and null radial speed. Second, the short tip impulse of the Quasiturbine retains the pressure less longer than the long sinusoidal impulse of the piston, and consequently the QT-blade tires much less. Centrifugal force on the blades of Quasiturbine also helps to contain high pressure. Notice that because of its crankshaft, the Wankel behaves like piston near TDC.
The Best of Engines
The Quasiturbine detonation combustion is a combination of
the best elements of other internal combustion engines:
(5) The Quasiturbine is suitable for multi-fuel use, including hydrogen combustion. It can also be operated in a combine thermal cycle mode (including steam and Stirling mode hook-up on the same shaft) thereby increasing further the efficiency.
(6) Finally, the Quasiturbine can operate in the more conventional Otto mode, yet retains its added value characteristics when compared to the piston engine.
For all these reasons, and considering what it is intended to achieve, the Quasiturbine cannot be considered as a "rotary piston engine". Piston paradigms do not apply to the Quasiturbine!