thoughts on Crower 6-stroke?

[user removed]

I guess what a lot of people may not understand about steam is it really needs to be superheated to become even remotely efficient. That being understood the Titanic had both turbines and a triple or quadruple expansion engines, The turbines were for speed and the piston engine was for economy.

regards
Mech

[JackMcCornack]

Roger that, Mech, and looking at the 6-stroke as a steam engine I'd guess it has 10% efficiency...but since the first four strokes convert, say, 30% of the combustion energy into work, if strokes 5 and 6 can extract 10% of the 70% left over, that's another 7% to add to the 30% efficiency, total 37%. In concept.

There's some extra heat energy in the combustion exhaust; if there were two exhaust ports (one for stroke #4, one for stroke #6) the combustion exhaust could be heat-exchanged to preheat the injection water (600f, maybe?) you could get a 1500 psi hit right off the starting blocks--a brief but significant boost to BMEP.

[Bicycle Bob]

Modern people somehow miss the significance of the general appearance of a RR steam engine. The boiler is what you see. The cylinders they feed look tiny. The classic texts all specify 10 to 12 sq. ft of boiler area per HP, and that's not on waste heat.

[oil pan 4]

Those steam piston engines were real low speed too, they typically turned a few hundred rotations per mile.
I don't know how well steam works in high speed piston setups.

[serialk11r]

Originally Posted by Bicycle Bob

Modern people somehow miss the significance of the general appearance of a RR steam engine. The boiler is what you see. The cylinders they feed look tiny. The classic texts all specify 10 to 12 sq. ft of boiler area per HP, and that's not on waste heat.

Thanks for pointing that out. I wonder how the BMW Turbosteamer fares then, since they claim pretty significant amounts of power.

[payne171]

I have wondered about hybrids using engines as a generator in one of the earlier posts, instead of as a power source. Imagine a Chevy Volt. You enter your destination into the trip computer. The computer calculates how much electricity it will take to get there. Instead of running to maintain a charge level, it runs only enough to get you there. The point is, not only would it save fuel by only maintaining the minimum charge required, but it would also allow a downsizing of the engine because it would basically only need to supply the mean power needed for the trip, rather than for a worst case scenario.

Also, check this out:
Green Car Congress: TIGERS: Exhaust Gas to Electricity for Reductions in Fuel Consumption
We don't need to convert to steam from the exhaust to gain efficiency; let the exhaust side of a turbocharger spin a generator (or at least that's the general idea).

[oil pan 4]

An exhaust driven turbine is still going to create back pressure which will lower MPGs.

[payne171]

Yes but an exhaust will have some back pressure regardless or it won't muffle anything. In addition, turbochargers muffle the exhaust, to the point that the dodge neon srt4 came from the factory without a muffler. If a turbo created so much back pressure as to make a turbo driven generator unfeasible, how is it possible that a smaller turbo engine could be more efficient than a larger engine?

[serialk11r]

A turbo is good, an impulse turbine can collect the exhaust pulse pressure (not sure if there's a term for this) without much restriction and will muffle the exhaust without wasting as much energy as a muffler. The only problem is under part load operation there isn't much energy to collect, and because it arrives in pulses you can't collect as much of it.

That's where the steam generation comes in. An ideal gasoline engine that has no cooling losses, no friction, and has full expansion of the burnt charge will still dump 30% of the energy as heat into the exhaust. Even under full load, the leftover pressure that is being blown out only accounts for a small amount of the total energy that can be extracted from the fuel. As the exhaust blows through the restriction of the exhaust valves, it loses energy, and what's left can only be converted at less than 50% (?) efficiency in an impulse turbine.

If you can generate electricity with steam heated by exhaust at just 10% efficiency, you can recover 3% of the overall fuel energy. If you consider that good engines are running in the high 30s (percent efficient), this is a pretty good amount of power.

I think in Formula 1 they are thinking of using turbocompounding (using a turbine to fully expand exhaust gases as you describe), and someone told me they saw a 7% efficiency gain. This means the turbocompound makes the same amount of power as a 10% efficient steam generator at full load, except street cars rarely run full load.

[payne171]

The TIGERS link I gave earlier implies that there is enough power there to replace ALL of the belt driven ancillaries with electric ones, essentially freeing up 20 hp on the average engine. Electric storage of exhaust gas energy must be doable, and soon; Subaru is ready to replace the turbo on the next WRX with such a setup that transfers the exhaust energy to boost via electricity.
All-New Subaru WRX: What to Expect - Motor Trend