Is Crower's Six-Stroke Engine a Practical Solution for Improved Efficiency?

[magi]

Hi.

I was thinking of a engine with a extra stroke and get the energy from heat in that stroke but some one have already done it.

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But what do you Physics think about it?

Do you think it is a good idea?

Will it work in a car or truck?

Magi

 

[Mech_Engineer]

I've read about this engine and it is a very cool idea.

Only problems I can think of are:

- the water has to be pure to avoid mineral deposits
- It could be a better fluid needs to be found for the second power stroke, since water would freeze in cold environments
- have a tank of gas, and a tank of distilled water to carry around

 

[DrClapeyron]

This almost seems like a no-no to add water in the cylinder where it can blow by and then reach the crankcase, hell it'll strip the cylinder walls of oil and make the next round of combustion unlubed. The big issue I have is concerned wtih how powerful and productive the expansion of any quantity of water in an engine cylinder can possibly be. I am guessing not much.

 

[mgb_phys]

If all they are trying to do is recover waste heat from the coolant why not just mount peltier stacks to the radiator. I thought combined power heavy diesels already did this?

 

[russ_watters]

I also don't see how this can be better than a waste-heat boiler. It has some big potential practical problems.

 

[JLobes]

This almost seems like a no-no to add water in the cylinder where it can blow by and then reach the crankcase, hell it'll strip the cylinder walls of oil and make the next round of combustion unlubed. The big issue I have is concerned with how powerful and productive the expansion of any quantity of water in an engine cylinder can possibly be. I am guessing not much.

I read something in, I think, Popular Science a while back about this. He thinks the power will be unaffected, but obviously it will run significantly more efficiently since its using water to power half of its strokes. He acknowledged the problem of water mixing with oil, citing development of new oils that could be used in the engine derived from steam turbine oil.

As for the amount of energy created from flash-boiling water, water expands to ~1600 times its original volume when turned to steam. I'm not sure of the expansion of gases which happens during the combustion of gasoline, but I'm sure it's greater than that. But adding power isn't the point, it's about increasing the efficiency of the engine, by turning energy once lost in heat into energy usable by the engine. Also, the steam stroke doesn't have to be as powerful as the combustion stroke to make up the energy lost by the added stroke, since 2/6 of the engines strokes are powered, as opposed to 1/4 in a traditional 4 stroke gasoline or diesel engine.

 

[DrClapeyron]

Come to think of it, this is just a radiator using a thermosiphon inplace of a pump. So what are the troubles associated with such a system: maintaining convection current rates with heat transfer rate, location of radiator tank (must be seated high) and a large amount of coolant which retards the engine's warm up.

 

[rethunk]

Sorry to re-animate this old thread, but any idea how much extra work the steam cycle would add? A previous poster has suggested not a lot and this was my gut feeling when I googled it, but can we throw together any rough figures for it?

 

[c0re]

Holy thread resurrection batman! I've also been thinking about 6 stroke engines for a few years now in this manner. Injecting water every other power stroke to turn what used to be called "waste" heat just makes so much sense in so many ways.

As for rethunk's question, when you think of this from an energy perspective, it should be pretty simple to answer what energy you have to play with...

For starters, I got this from Wikipedia (not always the most reliable source, but from what I remember in high school about thermodynamics it sounds reasonably ballpark: "Most steel engines have a thermodynamic limit of 37%. Even when aided with turbochargers and stock efficiency aids, most engines retain an average efficiency of about 18%-20%."

Now consider you start with 100% potential energy in your fuel, so chemical energy. That 100% then gets divided up into three major forms: thermal energy, useful mechanical energy and mechanical energy that constitutes sound and vibration. For the sake of argument, let's say that 10% of all your energy is converted to sound. It's probably less, but let's go with that...

That means that at 20% efficiency in conversion to useful work and 10% losses to sound & vibration, you have about 70% "wasted" as thermal energy AKA heat.

In an engine that produces 100 HP (roughly 75KW) that means that you are converting about (75 KW * (100 / 20)) = 375 KW from chemical energy to get your 100 HP.

We know that about 70% of that ends up as thermal energy, so 75KW * 70% = 263 KW

If you were to perfectly insulate an engine from all thermal losses to the ambient environment (e.g. consider it a closed system) then you are producing 263 KW of power that you would be allowed to recover by turning water into steam.

Now whether you can build some form of water injection system that can allow the water to work its endothermic magic quickly enough will determine whether you have a winner on your hands. If it is possible then clearly you could *substantially* increase the operating efficiency of any heat engine.

Now there will of course be problems with this, namely corrosion issues, the fact that in places where temperatures go below 0 you'll need to find a way to keep water from freezing. There is also the fact that this process will be useless until an engine is warm so for short trips an engine would need to run as a regular 4 stroke.

That said, in the warm-up period you can probably recover a lot of water condensing from combustion and then start using it once you are up to temperature. That is getting down to the nitty gritty of actually building a comercial system though and goes beyond the simple question of "is there really a useful amount of energy there for me to recover?"

 

[fredric21]

Oh dear, as if four strokes aren't enough, we now have to use six! That's four friction strokes instead of three.
If water is used to cool the surfaces of the combustion chamber (which it will do most effectively) then I hate to think of the effect it will have on the air/fuel mixture when it hits those cold walls. I think the fuel will condense to droplets which will only partially combust and be ejected into the exhaust as UHC's.
It will be like running a cold engine all the time, and I'm not sure what effect that would have on Volumetric Efficiency.
I would prefer water injection and a higher C/R to increase efficiency, but this is added complexity and cost.
Just give me an advanced two-stroke anytime!