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Old 08-18-2012, 02:33 PM   #111 (permalink)
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Originally Posted by Old Mechanic View Post
I checked the exhaust on my old Nissan Z car engine once. At idle it was not even 200 degrees. I think the amount of heat you need to "instantly" turn water into steam just isn't there after expansion of the combustion gasses.
I'm not sure that's right either... but drain the water from your old Z car, rendering the cooling system useless, and as the temperature continues to rise. You WILL melt the ring lands off the pistons, eventually ruin the temper of the aluminum that the head is made from and loosen the valve seats, then drop a seat and valve. The exhaust temp might be a lot hotter at idle, if your Z car didn't have a cooling system.

If in a conventional 4 stroke engine, 30% of the BTUs from a unit of gasoline are turning into work, the other 70% turned into heat, but you find a way to turn say, half of that heat into work within the combustion chamber... you have much less waste heat to get rid of. You might not need a conventional cooling system at all.

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Old 08-18-2012, 03:26 PM   #112 (permalink)
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Will somebody actually up and build an engine that actually takes advantage of direct water injection into the combustion chamber, already? And have it power a production car down the road?
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Old 11-29-2012, 07:06 AM   #113 (permalink)
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Consider this possibility. 4cyl engine. Substitute radiator with heat exchanger. Fabricate waterjacket around exhaust system. Run two cylinders in conventional manner. Control steam flow in remaining cylinders using exhaust valve as steam inlet, intake valve now becomes steam exhaust. Condense post power producing steam back to a liquid. Pump liquid back into heat exchanger.
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Old 11-29-2012, 07:21 AM   #114 (permalink)
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Originally Posted by smokey442 View Post
Consider this possibility. 4cyl engine. Substitute radiator with heat exchanger. Fabricate waterjacket around exhaust system. Run two cylinders in conventional manner. Control steam flow in remaining cylinders using exhaust valve as steam inlet, intake valve now becomes steam exhaust. Condense post power producing steam back to a liquid. Pump liquid back into heat exchanger.
Needs unconventional valve timing to pull off and increased piston clearance, but sounds plausible. You might want more cylinders for NVH reduction, maybe like, a V6 with each bank running like an inline 3 in terms of "firing order", one side fired by gasoline the other steam driven, rather than having 2 gasoline powered cylinders which is not very smooth.

Doing it this way would have higher peak thermal efficiency than for example BMW turbosteamer, since you are using a piston and not a turbine, but it would have much lower specific power.
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Old 11-29-2012, 09:22 PM   #115 (permalink)
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I don't think steam works so well in high speed piston setups like a gas engine.
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Old 11-29-2012, 11:03 PM   #116 (permalink)
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I don't think steam works so well in high speed piston setups like a gas engine.
That's probably true, it would incur higher pumping losses as a proportion of total work due to the low pressure nature of steam.

Compact steam turbine would have the same issue to a lesser degree, and I have the feeling that small steam turbines would suffer pretty big efficiency penalties.

SMA band engines and thermoelectric generators have inherently lower efficiency but if the technology brings them up to around the same efficiency (as a percentage of ideal cycle efficiency) as mechanical engines, it's a no brainer since they are much simpler and lighter.

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