An internal combustion steam engines

[Scania]

the stoke:
1.intake very few fuel (H2) & air
2.combustion, but not too much power provide because too less fuel
3.intake water
4.water changh to steam because of the high temp
5.the volume of steam go big, push the piston down

http://hk.youtube.com/watch?v=E1OWDcWoXHs
http://www.lfsforum.net/attachment.php?attachmentid=58840&d=1213590427

[Scania]

the stoke:
1.intake very few fuel (H2) & air
2.combustion, but not too much power provide because too less fuel
3.intake water
4.water changh to steam because of the high temp
5.the volume of steam go big, push the piston down

http://hk.youtube.com/watch?v=E1OWDcWoXHs
http://www.lfsforum.net/attachment.php?attachmentid=58840&d=1213590427

[VFR750R]

I've heard of this, using a cam turning 1/3 the speed of the crank instead of 1/2. (6-cycle engine) Steam engines are noted for huge torque(peak cylinder pressures are low, but they can maintain them throuhout most of power stroke), but RPM was always a limitation (therefore power).

The 6-cycle engine uses water in the 4th cycle to absorb heat that would normally be wasted in cooling systems. Arguement is less weight in cooling system, and recovered energy. For high rpm engines the heat transfer back from aluminum to the water to create the steam to build pressure and force the piston down isn't fast enough. Steam engines were limited in RPM when the steam was already made, how slow would you have to go when you inject water instead and wait for it to turn to steam?
Additonally, the water screws with the normal combustion process and leaves you with an engine that for its displacement makes less total power due to 6-cycles per firing vs 4, meaning in most cases a larger required engine.
About the only benefit is the reduced cooling system requirement, but since 6 cycles produce 50% less power then 4, it would take less cooling anyways.

Also, it's hard to tell in the pictures what's going on since the piston is in the same position in every picture but the one the steam is forcing it down. It almost looks like it's showing 5 figures for a more traditional 4 cycle (different from the 6-cycle mentioned above). I feel in this case, the water's heat capacity and heat of vaporization will cool the burned charge(which isn't done burning when you start injecting water) and leave you with less cylinder pressure then your orginal ~1400psi charge which...
will leave you with less power.

ADDITIONALLY, how hot does water have to be at 1400psi to turn to steam. Anyone? You'll likely quench combustion and get no steam until the exhaust valve opens. Meaning no additional power but more pumping losses in the exhaust.

They say water-injection for boosted cars actually reduces power, but because of the reduced charge temps and peak cylinder temps(due to heat capacity of the water), you can run additional boost which offsets the losses and some, meaning additional power. So I like water injection for racing, but it isn't going to make cars get 60mpg.