Steam-powered prius

With a stationary system, you certainly could get some gain. The best combined-cycle steam power plants, burning natural gas, are now in the 62-64% efficiency range.

But in a mobile system, the extra efficiency needs to offset the energy cost of carrying along the additional weight. That will be difficult, especially considering that the Prius's exhaust ought to be cooler than the exhaust of a traditional ICE engine, thus any energy scavenging will have both less energy to work with, and can't reach the same thermal conversion efficiency.

The Prius engine is already at about 40%, and should be spending far more of its operating time somewhat near its peak efficiency than any traditional non-hybrid propulsion power plant.

 

gen 5 probably could have achieved 75mpg if they had put efficiency ahead of power and big wheels. but would it sell?

 

I don't believe that will ever exist as a gasoline vehicle. By the time the tech advances to the point of achieving it, the EV mandates will have already removed fossil fuel vehicles from the new car market. Some instead of talking about 75 mpg, you'll be talking about 500+ miles of battery range.

 

How do you boil water to make steam when your proposed heat source is cooler than the boiling point of water? I mean, there are ways... but they all cost additional energy and it may be enough to spoil the results.

You might not want to steal the heat from the coolant anyway. A gasoline engine gets its best fuel efficiency when 'hot,' and the only time the coolant in a Prius has a real surplus of heat is during continuous high-speed drives in summer weather.

Given all that, I'd concentrate on using the exhaust system as the heat source for this project. A Prius exhaust already runs much cooler than most cars due to Toyota's use of the Atkinson cycle- they are already directly recovering a lot of that waste heat (as pressure) directly into the crankshaft.

You could recover still-more heat out of the Prius exhaust, but again that only has surplus heat during extended highway driving.

During an extended freeway drive you aren't exactly in EV mode, and your battery is still small so you can't exactly save that energy for later any better than you could before.

So if your setup only works during sustained freeway travel in warm weather, you'd have to work out whether these part-time gains were worth the cost, weight & reliability concerns of adding the extra hardware.

 

As nice as the G5 looks on paper it's still a $35,000 hatchback cosplaying a $25,000 Corolla with better gas mileage.
Convert it to steam and you'd get - what.....
A $75,000 Prius?

I do not think that the market is ready.

 

You are thinking the right way, commonly called a 'topper system.' To simplify the design:

• small turbo charger
• replace compressor with alternator
  • interface to traction battery buss
• water injection system
  • exhaust temperature and pressure sensor(s)
  • insulate the exhaust and muffler behind the catalytic converters
  • freezing temperature 'system'

This will take the remaining heat from the exhaust (when there is hot gas flow) to convert water into steam. The steam drives a turbo-alternator to a battery buss interface to add charge. Special attention to water system to deal with freezing temperatures.

Bob Wilson

 

Prius exhaust is below 100 °C / 212 °F?

 

My understanding:

Normal operating temperatures of a converter are 500-800°F, and up to 1200°F when the vehicle is under heavy load. ​

I believe the exit temperature of the catalytic converter would be in these ranges. With water injection, the amount should be regulated by the exit temperature, ~120-150 F.

LATE THOUGHT - the turbine may reduce the muffler noise requirement . . . perhaps a glass pac. AAAHHHH!!! turbine whine from a PRIUS!! LOL!

Bob Wilson

 

if i were buying a hybrid, no. but i'm not your average driver. prius has proved over 20+ years that 99% of the american public has mpg's way down on their list of wants and needs, except when gas prices spike. then it drops to 98%

 

Always payed cash here; I'm looking for a car, not a debt.

One really effective way to improve gas consumption, and this works with any car: change your lifestyle, drive less. When you do have to drive, consolidate driving chores if possible.

 

Re-read 1st post. OP wanted to use the coolant as the primary heat source.

 

The figures I see indicate that 80-ish % of new cars are initially acquired through financing, down from mid- and high-80s over recent years. But only 40-ish % used cars are now financed, down from 50-ish a few years back.

A separate news item indicates around 40% of Americans have car payments, though it was from a not-so-large poll that included people who don't own a car at all, so likely somewhat understates the portion of car owners making finance payments.

 

That could be done using a different working fluid than water. It is really a question of the Carnot efficiency formula:

efficiency = 1 - (K_cold / K_hot)​

There are technical problems:

• Typical coolant temperatures are just over 373 K
• Typical air temperature up to 313 K
  • 1 - (313 / 373) ~= 16%

Seems impractical even before adding the mechanical weight and internal losses. The higher exhaust temperatures are more practical for waste heat, energy capture.

At lower temperature differences, I would look for a Stirling engine. One advantage, no loss of working fluid or gas.

Bob Wilson

 

The Prius brand had three major downsides when I was thrown into this community in 2010.
They were unattractive AND drove that way, their drivers were combatively smug, and they were expensive.

In 2024 most of the automotive activism clubbed up to BEVs, and the G5 looks and actually drives like a car that a young adult would not be ashamed to be seen in....but they're still expensive - more than $5k base-to-base over a wireless Corolla for a 20-something MPG delta.
(The real-world differences actually start out closer to 10k in most states)

As our former POTUS would say:
"Here's the thing...."
Toyota doesn't NEED to develop a steam powered Prius.
Their wireless model already gets 55+ mpg - and they're already waaaay out to the right on the cost/benefit curve with these things.
If 'steam' really worked, the Big Three would be doing it to keep CAFE regs from further savaging their lineup.
THEY are the ones who would benefit more from a non-theoretical mpg gain.

That and a lot of boomers taking mandatory disbursements from their 401s and getting new wheels.

The average new car payment is over $730 and used ones are well over $500 - up from a few years ago probably because money now costs more.

 

I would recommend sharing Prius optimization here: Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com



That advice also goes for alternate battery chemistries.

Bob Wilson

 

The Niro which is a Hybrid like the Prius has a Heat exchanger in the exhaust as you suggest :

 

I read "coolant or exhaust." I guess that's not very specific, and the coolant of course won't usually get over the boiling point. But if we go by the second option, which is better, then exhaust it is.