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Dual Heat Recovery Engine

Improved thermal efficiency through better use of waste heat
  [vote for,

A typical internal combustion engine converts about 1/3 of it's fuel's energy to mechanical energy. Of the remainder, half is lost as heat that goes out the exhaust, and the other half is removed from the engine block via coolant, and dissipated through the radiator.

The internal combustion engine system described in this idea uses water to recover a portion of the exhaust gas heat, and engine block heat, and uses that recovered heat to produce additional mechanical energy.

The system consists of the following main components: The engine block, a steam condenser, a gas/liquid separator, an exhaust gas heat recovery device (aka a heat exchanger), a water recovery device, two compressors, and three manifolds.

Part of the system's operation is simple, part is complicated.

First, the simpler parts:

Air enters the system through an air filter, passes through the intake manifold to the engine block to the air exhaust manifold, then the heat recovery device, the water recovery device, the muffler, and leaves through the exhaust pipe.

There's a smaller flow of air from the steam condenser, through the gas/liquid separator, a compressor, and into the heat recovery device.

Water goes from a reservoir, to a pump, through the heat recovery device, to the engine block; it's injected into the engine block and converted to steam; the steam goes to the condenser, turns to water, passes through the gas/liquid separator, and is returned to the reservoir via a pump.

The water recovery device a simplified version of that described in patent 4725359. Specifically, engine exhaust gas flows across a hygroscopic membrane which is permeable to water, but mostly impermeable to air. The other side of the membrane is at sub-atmospheric pressure. Water vapor from the exhaust gas condenses on the membrane, diffuses through it, evaporates on the other side, and is removed by a compressor to the system's condenser. The membrane is coiled in such a way that the device contains a large surface area of that membrane in a small volume, and is shaped to minimize the amount of exhaust gas back-pressure the device produces.

Now, for the most complicated part of the system; namely the engine block.

The engine block resembles a six cylinder Cylindrical Energy Module engine invented by Eddie Paul, but with a several important differences.

The cam track's curve is of the form z=L*sin(3*phi), so there are three up strokes and three down strokes.

A derivative of the six stroke cycle invented by Leonard Dyer is used.

Each of the two heads of the engine has the following ports and injectors:

The air intake port has a variable geometry, allowing the first four strokes of the combustion cycle to be similar to an Otto cycle, or similar to an Atkinson cycle. The shape of the intake port controls the power the engine produces... a larger opening produces less power, a smaller opening more. The variable geometry ports eliminate the need for a throttle valve. Removing the throttle valve eliminates throttling loss.

Water injection will be used to lower peak air temperatures, prevent the formation of nitrous oxides, and prevent knocking. The water used for this will come directly from the water pump, bypassing the heat recovery device. Note that this is conventional water injection, and has nothing to do with the water injection that's used to make this a six stroke engine.

Fuel is supplied by means of an injector. Since this is, in effect, gasoline direct injection, it should be possible to supply a stratified fuel charge, and thus allows the engine to use a lean fuel mixture for all but the heaviest engine loads. The lean mixture reduces pollutants and increases fuel efficiency.

After the air exhaust port on the engine head, is a second water injector; this one does use the water from the heat recovery device. The amount of water injected is computer controlled, and is dynamically adjusted so that the piston surface and cylinder walls are at the optimal temperature at the end of the steam expansion stroke.

Note that, even once the engine reaches operating temperature, and the water entering the injector is very hot, it will still be capable of cooling off the cylinder and piston... this is because, as the water is injected, it will experience flash evaporation, and reach a cool enough temperature for the portion that remains liquid to cool the cylinder and piston.

After the water injector, is the steam exhaust port, and after the steam exhaust port is the air intake port.

goldbb, Jan 01 2011

Exhaust Gas Water Recovery http://www.freepate...ne.com/4725359.html
[goldbb, Jan 01 2011]

Cylindrical Energy Module http://www.animated...mpglos/cem_pump.htm
[goldbb, Jan 01 2011]

Conventional Water Injection http://en.wikipedia...injection_(engines)
[goldbb, Jan 01 2011]

Flash Evaporation http://en.wikipedia...i/Flash_evaporation
[goldbb, Jan 01 2011]

crower 6 cycle engine http://en.wikipedia...i/Crower_six_stroke
[metarinka, Jan 15 2011]

Bruce Crower's Patent application http://ip.com/patapp/US20070022977
[goldbb, Jan 25 2011]


       Questions, Comments, Criticism, Buns and Bones all gladly accepted. Of course, I'd prefer that bones be accompanied by (valid) criticisms, but anything's better than being Warnocked to death. :)   

       Hmm... considerations I forgot:   

       The compressor which moves steam from the water recovery device to the steam condenser is not needed if the condenser's pressure is sufficiently low. However, a low pressure condenser might be too big / heavy / costly to be practical (especially if this engine is in a car).   


       Ideally, this can be done by using high tech low friction ceramic bearing surfaces.   

       Alternatively, liquid lubricant (oil) could be sprayed into the cylinder along with the water, during the fifth stroke, and recovered by an oil/water separator at the condenser's output. There *do* exist oils suitable for this purpose, though they are not your typical automobile oils.   

       Corrosion protection: Since the engine is burning lean, it's inevitable that the exhaust will contain some free oxygen, and much CO2 (some of which will form carbonic acid later in the cycle). Since scavenging isn't perfect, it's inevitable that some exhaust will be in the cylinder when water is injected for cooling. Naturally, the steam that results will have some exhaust in it. Using chemicals to remove that oxygen or CO2 isn't practical. Instead, it's easier to just make all parts which will be exposed to steam or hot water out of plastic, stainless steel, or other corrosion resistant material in the first place.   

       Freeze protection: This is hardest...   

       We could mix some sort of alcohol into the water... as the engine runs, the alcohol will burn off from the water, though, and will need to be replenished. If the fuel is a suitable alcohol, then we have a ready source of antifreeze to regularly add to the water.   

       We could make the engine sturdy enough to not be damaged as the water freezes, and use electrical heating elements to thaw the engine each time we need to start it in cold weather.   

       We could use gasoline as a substitute for water, and eliminate both the water recovery device, and the conventional water injection. Back-of-the- envelope math suggests that the fifth-stroke injector, used for cooling, would need to squirt about 15x as much gasoline as the third-stroke injector supplying gasoline for combustion; a lot, but doable. If we *don't* do this, and use water for cooling, the volume of water needed for cooling is approximately twice the volume of gasoline used for combustion.   

       There're probably other solutions for the freeze protection problem, but I can't think of any offhand.
goldbb, Jan 03 2011

       //Warnocked// I'm afraid if I write anything the post will fall on me and I'll be crushed.   


       The exhaust-membrane sounds neat, won't that get clogged up ?   

       All throughout the post you say "goes into the engine block" without bothering to say if it's going into the cylinder or around the cylinder.
FlyingToaster, Jan 03 2011

       Whether the exhaust membrane will get clogged up depends whether the exhaust contains particulates, how many there are, and how prone those particles are to sticking to the membrane. Keep in mind, the exhaust is flowing across the membrane, not being forced through it, which should reduce the likelyhood of particles sticking.   

       Ok, air going "through the intake manifold to the engine block" is actually going into the two engine heads; specifically the air intake port of each engine head.   

       Water going "through the heat recovery device, to the engine block" is actually going to the two engine heads; specifically to the fifth-stroke water injector in each head.   

       Where water "is injected into the engine block"... I meant: goes to an injector in the engine head, is injected into each passing cylinder, moves from each cylinder to the steam exhaust port to... but wanted to simplify. Obviously I simplified a bit too much. Hope this clarifies things. [edit: removed "Will fix... tomorrow." ;)]
goldbb, Jan 03 2011

       Efficiency and power can be improved even further, by using a high (20:1 or so) compression ratio, little or no EGR, and homogeneous charge combustion ignition (HCC).   

       For the HCCI version of this idea, at low loads, the engine would use a very lean fuel/air mix, a minimal size air intake port, and cool the cylinder to a relatively low temperature on the 5th stroke. This results in the largest possible charge of air per cycle, which results in high pressures; the high pressure causes a high temperature, which causes the fuel/air mix to ignite.   

       As the engine load increases, the fuel/air mix would gradually be enriched (though not exceeding stoichiometric), the intake port kept open past bottom dead center, and less 5th stroke cooling would be done.   

       The richer mix produces more power, the extended intake stroke lets air get regurgitated into the intake manifold, reducing the total air charge and effective compression ratio (which prevents pre-ignition and keeps the engine from blowing up), and the reduced cooling results in higher cylinder and piston temperatures, which results in enough heat transfer from the cylinder and piston to the air/fuel mix that it ignites in spite of the lowered compression ratio.   

       In other words, the driver's accelerator pedal (or the governor, if this is in a generator instead of a vehicle) determines the fuel/air mix, and the engine management system simultaneously adjusts the compression ratio and cooling to achieve the appropriate combustion timing.   

       Note that compression ignition can be used for most of the engine's load range... since I've already explained how we avoid blowing up for a high load, and (since the engine already uses gasoline direct injection) we can use a stratified charge for extremely light loads.   

       Since the HCCI version of the system is no more mechanically complicated than the spark ignited version, we can think a switch to it as being basically "free." (Well, not free free; we will probably need to add in a catalytic converter, but at least we only need to use a 2-way cat, not a 3- way one, since the lean fuel mix results in few nitrous oxides).   

       Before anyone objects that switching the design to HCCI would require that the engine be made sturdier (to avoid blowing up due to the high air pressures), consider that we already need to make the engine quite sturdy, due to the need to avoid blowing up due to high 5th stroke steam pressures.   

       In other words, switching the design to HCCI might not necessitate an increase in the engine's weight... it just produces more power and higher efficiency.
goldbb, Jan 13 2011

       Sounds similar to a crower six cycle engine. While it may be more mechanically efficient, there would be a large increase in complexity.   

       The 6 cycle engine offers similar performance gains without a net gain in complexity, weight or size.
metarinka, Jan 15 2011


       It is indeed a form a six stroke cycle, but with the following important differences from Bruce Crower's design:   

       First, a CEM engine block has far, far, fewer moving parts than a conventional engine. There are no crankshafts, no connecting rods, no camshaft, no valves, no timing belt. This means less weight and less maintenance. A CEM engine is also more compact that a conventional engine with the same displacement.   

       This means that if we're comparing engine blocks alone, and not other parts of the system, mine wins on weight, cost, and maintenance.   


       Bruce Crower's six stroke engine will require a steam manifold which connects to the head of each cylinder. I can't visualize the fresh air, exhaust air, and exhaust steam manifolds in such a way that it doesn't resemble a mutant squid.   

       A CEM engine block has only two heads, so there would only be three pipes on each end, for a total of six for the entire engine... two fresh air, two exhaust air, two exhaust steam.   


       Even in his patent application (US20070022977), Bruce Crower's engine does not have an exhaust gas water recovery device.   

       Since a six stroke engine will inevitably lose a little bit of steam with every single cycle (steam will remain in the combustion chamber past the end of the steam exhaust stroke, and mix with the air during the air intake stroke), the water will inevitably need to be replenished.   

       Because my system includes an exhaust gas water recovery device, should never need additional water.   


       By preheating the water using the exhaust gas heat recovery device, before injecting it, the thermal efficiency and power are much greater than they are in Bruce Crower's six stroke engine.   

       In fact, if we were to pretend that the heat recovery device can be 100% efficient, or close to it, and assume the same engine displacement, number of working chambers, and number of combustion cycles per second: my engine will produce as much more mechanical power than a Crower Six Stroke engine, than a Crower Six Stroke engine produces compared a four stroke engine.   

       Of course, I'll freely admit that the heat recovery device is neither 100% efficient, nor weightless, nor tiny, but considering how much this one simple no-moving-parts component can boost power and efficiency, I'd posit that it's a worthwhile component to include in the system, in spite of it's weight and size.   

       Plus, it will lower the exhaust gas temperature... probably enough that no additional cooling is needed to pass the exhaust to the water recover device. And since the water recovery device is key to preventing this system from needing annoying regular water replenishment, well, enough said.   


       Since my engine is a CEM engine, one revolution of it's shaft will result in one complete six stroke cycle for all twelve of it's working chambers. For a Crower Six Stroke engine to produce those same twelve combustion strokes and twelve steam expansion strokes, it's crankshaft needs to make three complete rotations, and thus a much higher RPM.   

       Thus, my engine will run at a much lower speed while producing more power.   


       A six stroke six cylinder CEM is naturally dynamically balanced, and (if the two engine heads are 60, 180, or 300 degrees apart) produces very even torque. Furthermore, the spinning engine block will have enough angular mass to act as a flywheel, so no explicit flywheel will be needed.   

       This helps ensure low vibration, quite running, smooth power, and high maximum RPM.   

       What kind of cylinder layout would be needed to dynamically balance a Crower Six Stroke engine, and how big a flywheel would it need?   


       While the Crower six stroke engine could use variable valve timing for increased fuel economy, there is no mention of this in his patent application. Presumably, engine power is modulated purely through a throttle valve.   

       By varying the geometry of the intake port, my engine's power can be controlled just as fuel- efficiently as BMW's Valvetronic system, or Nissan's Variable Valve Event and Lift system.   

       This idea is not completely original -- several of Mazda's Wankel engines have variable geometry intakes, though I believe that they also use throttles.   

       It's also not exclusively beneficial to six stroke CEM engines ... any CEM engine could benefit from using variable port geometry instead of a throttle in order to control power.   


       Lastly, I'd be surprised if Bruce Crower has even considered combining the six stroke cycle with HCCI combustion.   


       Ok, this one's the real last difference: where I specify exhaust gas heat recovery happening in a separate component (that component being some type of heat exchanger), Bruce Crower's patent application suggests routing the exhaust gas through passages in the engine head!   

       While heating the engine head would result in slightly more heat available for the production of steam, much of that heat would just end up in the air of the engine bay, not in the water.   

       Furthermore, this would surely result in high exhaust gas back pressure.
goldbb, Jan 16 2011


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