Steam-powered prius

So does the Prius, starting with gen 3. The one in gen 4 gets posted about here when it springs leaks. (For whatever reason, the gen 3 one didn't seem to do that as much.)

 

Is it an actual air (exhaust gas) to water(coolant) located in the actual exhaust system or an EGR type system? The Niro actually uses both.

I am not familiar with the newer generation Prius.

 

If it weren't, I wouldn't have mentioned it.

 

It would be interesting to see if Toyota could democratize that tech, but I still maintain that even a real-world measurable gain in fuel economy for an equal gain in price would only be attractive for people that suck at math.

 

I wonder if "BMW is" ought to be "BMW was". The Wikipedia article that quote comes from is based on one publication in Motortechnische Zeitschrift in 2008, describing research conducted over several years past, and the Wikipedia article also says "the technology didn't reach production."

 

I found two relevant BMW press releases, both quite old:

More efficiency instead of power loss: BMW Group Research and Engineering is using combined heat and power in a car for the first timenhancing efficiency by up to 15 percent feasible+++1.5 litres of petrol less consumption realistic in mid-range car+++Basis: The principle of the steam engine

Looking for the next gram.

Note the "up too" words attached to the claim here, but "up to" was dropped by all the third-party articles. Too often, I find "up too" as a marker of figures selected from the high end of test results, greater than typical or average.

Also: "Under these conditions the developers are sure that the average driver will be able to reduce fuel consumption by up to 10 percent on long-distance journeys. " I take that as suggesting that average drivers will be seeing less than 15% on those long journeys, possibly because average conditions not allowing that high a gain, or the steam system taking a while to get sufficiently heated up, e.g. longer than can fit into the EPA test cycles. Fuggetabout getting similar results from short trips and city driving.

How do you see this boosting a Prius to 70 MPG average? From EPA, that is a lot more improvement than BMW's "up to" 15% and 10% claims.

The press items make no mention of Atkinson-cycle engines, so they almost certainly used traditional Otto-cycle engines. I will claim that the Prius family, with its HSD and Atkinsonized engines, will have a cooler exhaust than was used in BMW's tests, so will have less exhaust heat and a lower exhaust stream temperature, so simply won't be able to reclaim as much energy.

I strongly suspect that the Toyota HSD gains and the BMW Turbosteamer gains, have some significant overlap in their energy gains, such that you cannot add the two systems together and get a total gain equal to the sum of their separate gains. I.e. Conservation of Energy does not allow double-counting any of the energy portions.

 

I remember hearing about this six stroke engine.
https://www.autoweek.com/news/a2063201/inside-bruce-crowers-six-stroke-engine/
It injects water into the cylinder at the top of the exhaust stroke. It flashes to steam to drive another power stroke. The engine no longer needs a cooling system, but does need to also refill the distilled water tank when refueling.

Water will be the issue for any steam system. Not only will it require refilling with a pure source to prevent mineral deposits, it is heavy, and freezing will need to be addressed.

There are other six stroke engine designs. Some use air instead of water as the medium to put the excess heat to more work.
Six-stroke engine - Wikipedia

The simple answer is to just put a turbine in the exhaust. It doesn't have to spin a charger. It could directly add to the engine output. Turbo-compound engine - Wikipedia With hybrids, the turbine can directly drive a generator, which could be coming to production cars soon.

Going by past gains, 60 to 65 mpg was more likely for an efficiency focused Prius design.

Care needs to be taken when drawing heat from the exhaust. The gases slow down as they cool. High efficiency boilers and furnaces have blowers on the exhaust to keep it flowing out. Without it, the exhaust, and CO, flows back into the house as it isn't hot enough to get out the chimney on its own. While engines are already air pumps, the cooling exhaust will create back pressure that has an effect on the engine's performance.

The emission controls also need to reach certain temperatures in order to work.

It warmed up coolant to speed up engine warm up. The gen5 may not have it, but then earlier Prius with it in the US didn't have it in other markets. Depended on the region's emission regulations.

 

I would think that any practical 'steam' system would need to be a closed system, with a condenser recovering the working fluid. A condenser also allows for the possibility of a 'vacuum', or lower than atmospheric back pressure, on the turbine exhaust, improving efficiency.

And being closed cycle, the working fluid no longer needs to be water, but can be other gases/fluids selected for appropriate boiling / condensing temperatures and heat contents. Similar issues as refrigerants and heat pump working fluids.

 

And now we are adding all the mechanicals for that. With the move to higher degree of hybridization, and PHEVs, engine designs will be moving towards ones to be better packaged in the car. That's what Toyota did with their upcoming models. For PHEVs, that could be more important than over all efficiency of the engine when it is only being fired up once a week or so. These proposed systems all add the space needed in the car.

They could be worth it in other applications, like commercial trucks, though solid oxide fuel cells might be better proposition by that point.

 

Sure, just harvest less of it. Leave more meat on the table. That's the cleanest easiest way.

That's quite difficult when they are two expressions of the same thing.

 

My gas furnace also has a heat exchanger that is made partly of aluminized steel tubes, then partly of smaller, stainless steel tubes. It has a variable firing rate, and it very carefully coordinates the gas valve opening, the draft blower speed, and the circulating blower speed, to make sure the point in the heat exchanger where water vapor starts condensing to liquid water is always about where the stainless tubes start, while keeping the aluminized part too hot for liquid to condense.