High efficiency ICE (exhaust heat recovery)

[bwarchitect]

One of the companies competing in the Progressive Auto X Prize, Enginer,
is working on a steam system to use waste heat. In addition to using it for the competition, their website indicates that they're hoping to get a system to market for retrofitting existing vehicles. They're already selling a plug-in conversion for the Prius.

[jdgFirefly]

Using the spark plug wires to signal the water injection might be a good idea because the water will not boil instantaneously, like advancing timing for combustion it may prove advantages to start the process just before top dead center. I wouldn't worry about needing a diesel engine, the steam pressure will be lower than typical combustion pressure.

Something I didn't mention is that a part of the 35% of the wasted exhaust energy is pressure, what part I don't know. But if its going to be expand a second time you might as well expand it fully. So maybe you should bore and stroke the two middle cylinders to allow for more expansion of the exhaust and the steam.

As for the steam compression stroke I don't think it works the same as what your thinking (assuming I know what your thinking). Compressing the steam isn't actually adding any heat. Yes the temperature rises along with the pressure but the boiling point of the steam also rises with the pressure. Also the gain in pressure and temp costs energy from the crank. So its hard to say if compressing the steam and exhaust has any advantages. It might just be a wasted stroke but I'm not exactly sure. If it is just a wasted stroke it will add a lot of heat and fricion loss.

A different configuration that you can think about is to have the steam expansion stroke during the the exhaust transfer. Say cylinder 2 & 3 are connected, while cyl 1 is pushing the exhaust into cyl 2 & 3 expansion occurs because of the diff in displacements. If there is any pressure in the exhaust than the force on cyl 2 & 3 will be double the force pushing on cyl 1 so there will be a net gain in torque. The water could be added in the transfer port as needed to maintain steady pressure. Then cyl 2 & 3 exhaust the steam and are ready for a steam stroke from cyl 4. If the expansion stroke of 2 & 3 is to large that you could bore and stroke or super charge cyl 1&4 to help get it balanced right.

[user removed]

The Museum of RetroTechnology

Look through this interesting site for ideas.

Biggest problem I see:

Oil contamination from steam blow by.

Most steam systems require superheated steam, and steam engines are much less efficient than IC.

That may not be true if modern insulating technology was applied, but in general making things more complex means less overall efficiency as well as greater cost and complexity.

It will take a lot of water to run you engine and I don't see any practical way to recirculate and re use the water.

One nice thing about external combustion engines is they do not have the emissions issues of high compression IC engines.

regards
Mech

[amnonholland]

Just to clarify the idea

In the steam cylinders
Compression stroke
Exhaust gas from the combustion cylinders enters steam cylinders
In compression T(final at end of compression)= 600K(tinitial)*(9(compression ratio))^(1-(1/1.3)), 1.3 = adiabatic index
=~1000K (very hot). Assuming exhaust from combustion cylinders is 600K
(Pumping losses will be high on the compression stroke(having to compress a hot gas), but would be more than made up for on the expansion stroke)
When the spark plug would normally fire, say 10BTDC the water injector injects a tiny amount of water which instantly becomes superheated, creating really high pressures.
Cylinder pressure can be controlled by amount of water injected.
Could a petrol engine withstand these pressures? or could the water injector be controlled well enough so that pressures don't exceed.....
Not much water will need to be injected/ used at those high temps/pressures, and hence open loop water system should be ok
Expansion stroke
The superheated stream expands over the 9:1 compression ratio. Sterling and steam engine generally have low compression ratios anyway there for i assume the majority of the pressure energy will be extracted by the expansion stroke.
"As for the steam compression stroke I don't think..."
I wouldn't be compressing any steam, steam gets injected at end of compression stroke

"Oil contamination from steam blow by."
Will this be problem if steam is superheated? At the bottom of the expansion stroke the steam may be wet steam. Pressures shouldn't be really be large enough at bottom of stroke to blow steam past piston seals and contaminate oil.

I like the idea or being able to supercharge the combustion cylinders to balance steam cylinder torque against combustion cylinder. Or this could be also achieved by venting some of the exhaust, but this results in lower efficiencies.

[Phantom]

the issue of Oil contamination from steam blow by would most likely be solved/helped by tighter piston rings or even a vacuum pump on the crank case with a seperator. That is if it is an issue.

If there is an issue with how easily the water boils alcohol could be added as ethanol boils at 78C and water boils as 100C you could drop the temp some what.

[mpgx2]

The best link that I've been able to find is this:

water injection

I've admit I've been somewhat inspired by it.

I'm in the middle of implementing it myself so I can't comment
if it works or not. If my car was simpler it would have been done
some time ago.

Also, water boils at lower temperatures if it is in a vacuum.

Boiling Tempetrature of Water in Vacuum - Engineers Edge

In my vehicle I get a vacuum of 10-20Hg on the vacuum
gauge on the manifold which suggests the water only needs
158-194F to boil.

[amnonholland]

water/steam injection into the intake isn't all that effective. Problems are that will can quench the combustion flame. i.e. cool the flame temp and hence reduce pressure. On the other hand it could also increase the pressure (if there were enough heat generated (high compression ratios)). The will be some optimum amount of water depending one the engine.

Also injecting water/steam into the intake increases pumping losses. This is the energy required to compress the warm/hot steam air mixture. We would want to avoid this to maximize efficiency.

The otto cycle efficiency is depends on maximum and minimum pressure and compression ratio. hence to improve the efficiency we seek to raise the maximum pressure. Superheated steam can generate higher pressures from the combustion temperatures of fuels than hot air.

[jdgFirefly]

I did understand your Idea, I'm just not convinced that compressing the exhaust will gain you anything but extra losses. However while compression doesn't add any heat maybe it is necessary for operating the engine at higher rpm's due to the water instantaneous conversion into steam. Admittedly I need to find and read my thermodynamics text book before debating my point anymore, I don't remember much about steam. Even if I do find my text I probably would not fully understand this particular setup because its not a normal steam cycle. The heat for making the steam comes from a gas that is also mixed with the steam during expansion. This complicates it because the water heats and turns to steam as the exhaust gas cools and contracts.

[Piwoslaw]

Originally Posted by mpgx2

Also, water boils at lower temperatures if it is in a vacuum.

Boiling Tempetrature of Water in Vacuum -* Engineers Edge

In my vehicle I get a vacuum of 10-20Hg on the vacuum
gauge on the manifold which suggests the water only needs
158-194F to boil.

But the pressure in the cylinder where water gets injected will be far from a vacuum. Is it possible that at that high pressure the temperature will be too low for water to instantly vaporize?

BTW: Here's a similar exhaust-utilizing engine (without the water injection) prototype:
5 stroke engine could increase FE by 5%-20%

[amnonholland]

According to my steam tables at highest temp and pressure reading displayed
T(sat vapour)=374C for 220Bar. Temps will definitely be exceeding this. I doubt pressures will. Therefore steam would be superheated