It's pretty easy to convert a two-stroke engine into a "uniflow" steam engine: you just need some sort of valve in place of the spark plug that allows steam into the cylinder at top-dead-center. The steam expands, pushes the piston downward, and exits out the exhaust port.
This valve can be something as simple as a "bash valve," which is basically just a one-way check valve that is opened when the piston slams into it.
My idea is to add a bash valve onto a two-stroke motor, so that it can be powered either by steam, internal combustion, or some combination of both. If you start with a water-cooled engine, you won't need a large boiler, since the water coming out of the engine will be near boiling anyway. You could even add a water jacket around the exhaust pipe and get even more heat out. Then you'll just need to heat it up a bit more in the boiler so that it has more pressure than the combustion gasses at TDC.
You would have to start this engine like a normal two- stroke until it warms up and the boiler reaches a certain pressure. Then you could either switch to combined combustion/steam power, or shut off the gasoline to the carb and go to steam completely. If you're doing this you'll need a separate oil injector rather than running premix. And you'll want to run it on gasoline only for a minute or two before you turn it off, so that the piston rings don't rust.
When running on both steam and internal combustion, there will be an upper limit to the amount of steam you can inject per revolution before it "quenches" the combustion in the cylinder and you get less power. Ideally, you will get slightly more power than a regular two- stroke, slightly better efficiency, much better emissions (the condensing steam will trap soot and unburned oil/fuel), and a slightly heavier, costlier, and more complex engine.
Most two-stroke engines fire the spark plug about 15 to 20 degrees before TDC, and if the bash valve opens at, say, 10 deg. before TDC, I don't think it would interfere with combustion. A more sophisticated steam inlet valve would allow for more fine-tuning in this area. If you can time it correctly, then the incoming steam would also pressurize the fuel/air charge, giving it a higher effective compression ratio without causing pre-ignition. And if the steam was hotter than the ignition temperature for gasoline (about 500F, IIRC), you might even be able to ditch the spark plug and just use the steam to ignite the charge.
Of course this idea would probably work with a four- stroke engine as well. I'm just thinking of what I know best.
I'm sure there's some issues with the idea, and I haven't done the math to see if it would be worth it, but I thought I'd put it out there. One issue I can think of right now is that combustion pressures can reach as high as 2,300 psi in some engines (not sure what it is for a typical two- stroke), so you would need a strong boiler (maybe made from stainless-steel tubes) and a high-pressure water pump (maybe from a pressure washer) to overcome the combustion pressure.-- discontinuuity, Jan 04 2013 Uniflow Steam Engine http://en.wikipedia...niflow_steam_enginewithout the two-stroke part [discontinuuity, Jan 04 2013] video of a steam-powered moped http://www.youtube....edded&v=6elzt0TN3mQwith its stock two stroke engine converted into a uniflow steam engine [discontinuuity, Jan 04 2013] Bash Valve description http://opensourceec...e_Design/Bump_Valve [discontinuuity, Jan 04 2013] more on bash valves http://whitlox.net/including info on converting two stroke engines to steam [discontinuuity, Jan 04 2013] my illustration of the whole assembly http://i.imgur.com/MHLD5.jpg?1 [discontinuuity, Jan 04 2013] displacement steam oiler http://www.southern...ual/lubricators.htmno moving parts! [discontinuuity, Jan 04 2013] Crower six-stroke http://www.autoweek...0227/free/302270007 [ytk, Jan 04 2013] Water Injection http://en.wikipedia...injection_(engines)cools the intake charge to prevent detonation in turbocharged or high compression engines [discontinuuity, Jan 04 2013] steam diesel hybrid locomotive http://en.wikipedia...l_hybrid_locomotiveSort of baked, although alternating and not at the same time. Also I don't know if this was 4 stroke or 2 stroke. [discontinuuity, Jan 06 2013] (?) Turbo two stroke diesel, not even slightly baked, vaguely preheated... Maizechinegun [normzone, Jan 08 2013] Four-stroke steam engine http://www.flashste..._Engine_Project.htmQuite long-winded, but a good demonstration on how superheated and pressurized water can flash into steam after being injected into a hot cylinder. [discontinuuity, Jan 08 2013] Sounds a bit like the Crower six-stroke engine (link).-- ytk, Jan 04 2013 Don't you hate that when you have a great idea, just to find out that someone like Crower built it already! I like the way your mind works. I have heard a bit about Large ocean liners reusing exhaust etc.. But never thought you could "burn" your own coolant! bun for you.-- Brian the Painter, Jan 04 2013 Yes, I was thinking a bit of the Crower six-stroke when I came up with this. The problem with the six- stroke engine is it has 3 times as many strokes as it needs!
But seriously, I think that a two-stroke engine would benefit from steam injection, and it has the benefit of fewer "coasting" strokes.-- discontinuuity, Jan 04 2013 Do they inject water vapor into internal combustion engines? I've seen some YouTube videos but I don't believe everything I see-- Brian the Painter, Jan 04 2013 Yes, lots of turbocharged cars have water injection (in the intake manifold). This is meant to cool down the intake charge and prevent detonation. As far as I know, the Crower engine is the only internal combustion engine in which water is injected directly into the cylinder.-- discontinuuity, Jan 04 2013 Why not just use port timing? Suzuki has used rotary-valve 2 strokes in the 70s. Use a conventional reed-valve on start up, then when switching to steam power, physically block the reeds. Then use a rotary valve for steam injection in the head? But then again, I don't know jack about engines. Also: is there much fact behind the idea of injecting steam into the combustion chamber during two-cycle operation could really increasing power or efficiency? Water-injection is common practice in high performance turbo applications to try and reduce the temperature of your intake charge in a bid to effect its density. Why not just make a V-twin powerplant and keep one cylinder a conventional two-stroke and the other a steam/compression style cylinder and blend their use?-- Letsbuildafort, Jan 04 2013 I was also thinking about blocking off the transfer ports between the crankcase and cylinder during the steam cycle. You could do this with a rotating cylinder sleeve, maybe even diverting the exhaust into a condenser rather than a conventional exhaust pipe. You could even use the sleeve valve to open and close the steam inlet, although it might leak at the 2,300 psi pressure I was thinking of.
Rotary valves might work for the steam inlet, but they couldn't be driven off the crankshaft like in a two stroke, since you would want the steam to come in through the head. You could have a separate shaft above the head for this, similar to a camshaft, but driven at the same speed as the crank. If not bash valves, I was thinking of using high-pressure diesel injectors for the steam, as long as they would hold up to the high temperatures.
Steam injection during combustion would definitely add some power, since the expanding steam would impart more force to the piston and crankshaft. The only question is how much more power, and at what point would there be diminishing returns as the steam began to put out the fire in the cylinder.
If both the steam and fuel were directly injected into the cylinder, you could alternate between combustion and steam power, so as to avoid any "quenching" of the combustion by the steam. The combustion cycles would also keep the cylinder walls and piston hot so that any water droplets in the steam would flash into vapor.
A twin-cylinder engine would work with steam in one cylinder and combustion in the other, but you would still be wasting much of the combustion cylinder's heat. Not to mention the uneven power outputs would make vibration and smoothness an issue. But it would definitely be an easier way to do things, and you could still use some of the waste heat from the combustion engine to pre- heat the boiler water. If I remember correctly, BMW was recently testing something along those lines.-- discontinuuity, Jan 05 2013 or you could make the combustion-stroke and steam-stroke interchangeable: one or the other. If there's enough of a head of steam that a steam-stroke would be equivalent to a combustion stroke in power, then the steam stroke is used until the pressure backs off a bit.-- FlyingToaster, Jan 05 2013 Yes, that's what I was thinking. One combustion stroke to heat up the cylinder, and then a steam stroke. Or maybe several combustion strokes followed by several steam strokes.
One advantage to using steam is that the engine will potentially last longer, since pressure is applied to the piston more gradually than the "bang" in a combustion engine.
It also seems that something like this has been tried, with a hybrid steam/diesel locomotive. Check out the link. Although in this case the engine switched between combustion and steam based on its speed, in order to take advantage of the high starting torque of the steam. This might have applications for my engine, in that you could eliminate the clutch and low gears and start the vehicle on steam. Of course, you would need to wait for the boiler to heat up first.-- discontinuuity, Jan 06 2013 bellauk65 read it again,this time a little slower, let it sink in a bit... Its actually a good idea, good enough that its (partially) baked by crower-- Brian the Painter, Jan 08 2013 bellauk65, you could inject superheated water and have it flash into steam inside the cylinder, but any large temperature difference between the water and the cylinder would cause metal fatigue over time.
Can you tell me more about this nozzle?-- discontinuuity, Jan 08 2013 //metal fatigue over time// don't use metal. try porcelain or some high heat plastic.-- Brian the Painter, Jan 08 2013 Porcelain would be even more fragile than metal, and I don't know of any plastic that will stay intact at temperatures of up to 400C like aluminum will.
There are some ceramic materials that would work for the cylinder liner and piston, but from what I understand they are quite expensive or difficult to machine.
It would be possible to inject steam (or superheated water) at roughly the same temperature as the combustion chamber while still transferring heat from the combustion chamber to the steam. Since the steam would be undergoing expansion (and also a phase change), it would be absorbing energy even while everything remains mostly the same temperature, and thus avoid thermal stress and metal fatigue from rapid heating cycles. Check out the "four-stroke steam engine" link for (lots) more info on this subject.-- discontinuuity, Jan 08 2013 random, halfbakery