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Variable Stroke Count Engine

Like a six stroke engine, but different
  [vote for,

This engine concept is derived from the six stroke steam hybrid engine concept [link], but should have more power when the engine is cool, and consume less water, and less fuel, when the engine is hot.

Each engine head contains the following components, all of which are computer controlled: A fuel injector, a water injector, an air intake valve, an air exhaust valve, and a steam exhaust valve. There might be a spark plug or a glow plug.

There are also a number of high-speed electronic thermometers which measure cylinder temperature, head temperature, and water temperature at the injector.

Near the end of every engine cycle, a weighted average of the temperatures is calculated, and compared to a threshold.

Whenever the temperature is below the threshold (which will always be true when the engine is starting), the cylinder will be operated with a conventional four stroke Otto cycle.

Whenever the temp is above the threshold, the cylinder will operate as two stroke steam engine.

In steam mode, water is injected into the cylinder, flash-boiled into steam by the hot piston, cylinder walls, and valves, expanded to produce power, then expelled through the steam exhaust valve into the steam manifold, which leads to a condenser.

Furthermore, the amount of water injected is precisely controlled, so that the average torque of the two stroke cycle exactly equals the average torque of the most recent four stroke cycle.

When the engine is cold, the engine will run just like a normal four stroke engine. At higher temperatures, each four stroke cycle will be followed by one or more two stroke cycles; the number of two stroke cycles which take place between adjacent four stroke cycles will vary... hence the idea's name.

The advantages of this idea over a regular four stroke engine are the same as those of a six stroke steam hybrid, namely:

The engine isn't water-cooled, thus the engine block can be lightened by eliminating the coolant passages through it.

Each steam cycle produces power without consuming extra fuel.

In-cylinder hot spots are reduced or eliminated, which reduces engine knocking, and allows higher compression ratios.

There are also advantages over a regular six stroke steam hybrid:

Because the amount of power that must be produced by the steam expansion stroke is approximately one half of the power produced by the Otto-cycle combustion stroke minus the power consumed by the Otto-cycle compression stroke, we don't need very high steam pressures.

Since the maximum steam pressure is less than the maximum compressed air pressure, the variable stroke engine engine doesn't need to be any sturdier than a regular internal combustion engine.

Compare this with Bruce Crower's 6 stroke steam hybrid, whose prototype he built out of a diesel engine block, in order to contain the high steam pressures.

In addition, by injecting less water at the beginning of each steam expansion cycle, the steam pressure at the end of the expansion cycle is lowered, implying that water is being used more efficiently.

Last but not least, when the engine is warming up, we don't lose any power due to "coasting" through an unused fifth and six stroke; instead the engine runs as a normal 4 stroke engine.

goldbb, Apr 05 2010

Six Stroke Steam Hybrid http://en.wikipedia...r_six-stroke_engine
[goldbb, Apr 05 2010]

Preheated six stroke engine Preheated_20six_20stroke_20engine
[goldbb, Apr 05 2010]

Atkinson cycle http://en.wikipedia...wiki/Atkinson_cycle
[goldbb, Apr 08 2010]

Using a leaner than stoichiometric air/fuel mix http://en.wikipedia.org/wiki/Lean_burn
[goldbb, Apr 08 2010]


       Although the engine I've described here gets the same amount of power, for a given amount of throttle, as a conventional engine, we *can*, if we choose, get even more power, by injecting more water... but to avoid losing efficiency, this should only be done when the engine is at full throttle already. And, we shouldn't inject so much water that the steam blows up the engine :)
goldbb, Apr 05 2010

       Oh, and of course, this concept could be easily combined with my "preheated six stroke engine" concept.
goldbb, Apr 05 2010

       //lightened by eliminating the coolant passages through it.// Wait, what? You lighten it by removing holes?
As far as the rest of it goes, I don't understand* well enough to have an opinion []

       *My limited understanding -- not an issue with your writing.
mouseposture, Apr 05 2010

       [+] but I don't understand why a six-stroke... a four-stroke with a long stroke could have water injected after the fuel has burned, and save complication
FlyingToaster, Apr 06 2010

       [+] Intriguing and practical - what website am I on again?
BunsenHoneydew, Apr 06 2010

       I'd love to see the study material for the smog techs who have to verify that it's running clean enough for California standards.
normzone, Apr 06 2010

       mouseposture, I'm assuming that part of the metal of the engine block is needed for structural strength, and part to contain the coolant. Eliminating the coolant passages doesn't mean filling them in, but removing the non-structural metal that is part of the block solely to contain the coolant.   

       FT, firstly, if water is injected after the fuel has burnt, then the entire exhaust system would need to be cooled if we wanted to recycle the water, requiring a really big cooling system. If the water is injected after the exhaust stroke, the steam can go through a separate exhaust valve and manifold, and then to a condenser, with a minimum of unwanted air, and thus a much smaller condenser/radiator.   

       Secondly, by injecting water when the piston is at top dead center, we can expand the resulting steam by the cylinder's full expansion ratio.   

       Thirdly, if water were injected halfway through the conventional expansion stroke, it wouldn't be able to reach the piston, which would be far away and quickly moving further away, and thus would be unable to cool the piston.   

       Normzone, each cylinder which is using a four stroke Otto cycle will produce the same emissions as a conventional engine. Each cylinder which is using a two stroke steam cycle won't produce any emissions, since all the steam goes to the condenser, turns into water, and is re-used.   

       All else being equal, the emissions per unit of fuel consumed will remain the same, but since the engine will be more fuel efficient, the emissions per unit of work produced will decrease.
goldbb, Apr 06 2010

       [+] excellent
afinehowdoyoudo, Apr 07 2010

       Fuel efficiency can be improved even more using the following two obvious methods:   

       First, since we've gone through the trouble of making the valves completely computer controlled, we can use an Atkinson cycle when less than full power is wanted, and of course inject less fuel. To do this, we simply delay the closing of the air intake valve until beyond bottom dead center.   

       Second, since we've got such a superb cooling method, we can use a lean air fuel ratio when the engine is lightly loaded, and stoichiometric when fully loaded.   

       In fact, we can use the above two techniques to fully control how much power the engine's four stroke combustion cycles produce, and eliminate the throttle valve, thus eliminating pumping losses.
goldbb, Apr 08 2010

       whoa.. easy now fella.. the partial vacuum created by the throttle valve is instrumental in converting droplets of liquid fuel into vapor. Only vapor burns quickly enough to contribute to the power stroke.
afinehowdoyoudo, Apr 08 2010

       Although, if you are recovering heat from the combustion cycle to drive the steam cycle, then maybe the heat from the 'second burn' isn't as wasted as it would be otherwise. Still though.
afinehowdoyoudo, Apr 09 2010

       You're suggesting that an engine running with the throttle fully open won't produce any power.   

       That doesn't sound quite right :)
goldbb, Apr 09 2010

       An engine with the throttle fully open still has some pumping losses and maintains an amount of vacuum.
RayfordSteele, Apr 10 2010

       I am suggesting that an internal-combustion engine in which the fuel is delivered as a contiguous mass will not produce much power. Even with the throttle valve wide-open or absent, liquid fuel is still converted to vapor, but the fuel-efficiency drops. But that is not to say that vacuum is the only, or best, way to convert fuel liquid to fuel vapor.
afinehowdoyoudo, Apr 13 2010

       I've often thought that waste heat is a squandered resource in the ICE
simonj, Apr 13 2010

       Sorry, I'd like to correct my anno: I meant to say throttling loss, not pumping loss.   

       simonj, a company called "Transonic" is developing an engine that uses heat pipes to move heat from the exhaust valves to the fuel injectors, where that heat helps boil the fuel just prior to injection. Injection is just before top dead center, as on a diesel engine, but is able to work at a wider range of pressures, and a wider range of fuels.
goldbb, Apr 13 2010


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