We're going to see a lot of organic Rankine cycle this century - and not just on cars!

part of the problem with a turbo, and any form of heat exchanger is that it requires energy to push air/gas/water through the exchager.
even with a downsided, tubro driven, highly effiencet engine, there is still alot of waste heat. Why not make a very simple Stirling where the chamber is passivly heated by the exhasust?? the head pipes in an exhaust glow very hot at idel or at load!! With a stirling, the output would simply increase with laod/heat. surely a simpe stirling would be lighter and simpler and more robubst that a complex steam cycle rankine?

Obviously your assertion was not found to be true by Honda.

Even a series hybrid without a battery would be a much more efficient use of petroleum - small 500 - 1000cc generator (turbine preferably) to power the motor, yes like a diesel electric locomotive. That would be cost effective to produce, simple and fuel efficient.

The more efficient and so far more successful Stirlings that I have seen are those used in concentrated solar thermal conversion to electricity. They have a large temperature difference between the hot and cold sides, use expensive materials and cost quite a bit.

Maybe this was a cost benefit decision. There have been stirlings created for home CHP that claim to be cost effective, but I have not seen them in general usage, nor seen any high efficiency numbers for them.

In CHP, what you do not get in efficiency generating electricity becomes heating for the home and hot water. Here you have some heat going out the cooling system and some heat going out the exhaust system. If you study the turbo steamer, you can see how they dealt with that.

Emphyrio,

You would still want to have a battery. People don't typically drive at essentially the same power so either you have a too big generator and waste power when not accelerating or you have a too small generator and nobody buys the product due to extremely sluggish acceleration.

Instead couple a small generator with a small battery pack which is designed to handle typical acceleration duties with the generator supplying enough power to drive the vehicle at highway speeds and a little more to slowly recharge the battery.

Also, how will you reclaim braking energy without a battery? You are just throwing away energy if you don't have some type of energy recapture system.

"Passenger car turbos are less efficient because the engines operate in part load much of the time."

rafael, how much can VGT's help with this inefficiency?

@ Eric -

the twin objectives for a variable geometry turbine is to reduce turbo lag when spooling up and, increase feasible boost in part load. Turbo efficiency does go up, but not by much - the more expensive dual stage systems do a better job of that.

However, it's really the system of (diesel) engine plus turbo that you have to look at: a VTG enables higher torque at low RPM. This generally means you can deliver adequate accelerator response with a smaller engine. Combine this downsizing with taller gear ratios and modified shift points (downspeeding) and you end up with an overall fuel economy gain.

More importantly, a VTG increases the fun-to-drive factor and hence, the attractiveness of the diesel option to those customers who would otherwise only consider a gasoline engine.

Unfortunately, the high exhaust gas temperatures of those gasoline engines means that so far, only Porsche has applied VTGs to one - and they are made from very expensive high-temperature alloys.

Meanwhile, Ricardo - one of the major engineering consultancies in drivetrain R&D - has developed a demonstrator for its EGR-boost concept. This leverages low-pressure cooled EGR to reduce both throttling losses in part load and exhaust gas temperatures at high load. The latter enables the use of a VTG made from affordable materials.

thanks rafael, i'm always impressed by your informative and in-depth replies. hopefully my next car will be a mini cooper D, which I believe is equipped with a vgt.

To put it perspective, an advanced gasoline engine typically has a peak efficiency of about 35%. The same engine using Atkinson cycle by delaying closure of intake valve can achieve nearly 40% efficiency, a higher gain than using RAnkine bottoming cycle without any additional complicated hardware. The drawback is that Atkinson-cycle engine is less powerful than a equivalent gasoline engine, requiring a hybrid drive train for power boost during acceleration.

A good hybrid drive train will allow the engine to run near at its peak efficiency for most of the time, hence boosting the overall thermal efficiency of a typical car from little above 20% (due to low-efficiency part-load operation) to nearly 40%. Full-hybridization will yield far more real-life efficiency gain for the amount of hardware cost and complexity than any waste-heat bottoming cycle scheme. For a big-rig turbo-diesel engine, turbo-compounding can further enhance efficiency of the engine without major increase in cost or complexity.

It seems to me that they've ignored a large source of waste heat for the Rankine engine: the diesel engine coolant. By incorporating a heat exchanger to move heat from the coolant to the high pressure water out of the feed pump, they could probably double the energy output from the steam engine. That would also allow for a smaller (or maybe non-existent) radiator.

A more aggressive variant on this theme would be to use the diesel engine's coolant as the steam engine's working fluid. Of course, it would present a few more engineering challenges. The main ones I can think of are: making the diesel engine happy with a higher-temp and pressure coolant and making sure the coolant doesn't boil within the diesel. Besides the higher efficiency, a big advantage would be reduction in parts: only one radiator and coolant pump for example. It's probably still too complicated but it's fun to think about.

Also, assuming sufficient engineering resources, there's no reason why this couldn't be done with a gasoline engine. Even a higher efficiency engine like the Atkinson would benefit.

Kevin, your suggestion was discussed several posts up. The coolant temperature is low-grade heat, difficult to make effective use of it other than interior heating. Raising the temperature of the cooling jacket requires considering the extra heat load effect on the engine's internal components.

Perhaps, if the technology is not so expensive and if the solid state devices can work hot enough, something like the power chips could help to obtain more energy from waste heat from the exhaust gases, or at least from the coolan.
http://www.powerchips.gi/

One of Toyota's hybrids in Japan is already using a waste exhaust heat recapture system.

Nice to see Honda still putting effort into hybrids.

The way BMW does it in the TurboSteamer is a lower to higher temperature fluid routing as I recall. The engine coolant can be used to pre heat the fluid that has condensed and is to be reheated.

http://www.gizmag.com/go/4936/

An exhaust heat exchanger is next and then the catalytic converter, you heat the fluid more and the last route might be the exhaust manifold where there is the highest temperature.
(you can see by the IR photos)

I may not have all the details totally accurate, but that seemed to be the gist of it. This makes sense, you want to heat the fluid using the various heat sources that you have.

Again, to further putting this issue in perspective, waste heat recycling is too complicated, too expensive and too heavy for the modest gain in fuel efficiency of 10-15%, as shown by both efforts of BMW turbosteamer and now Honda. BMW's project is a very sophisticated and comprehensive effort using an organic rankine cycle to capture the coolant heat on top of a water-rankine cycle to capture the exhaust heat, and still, the gain in efficiency is still modest at 10-15%.

Until all new car sold will be full HEV's, it would not be practical to divert precious engineering and manufacturing resources in making low-yield waste heat recycling scheme.
Toyota's concept ultra-light carbon fiber re-enforced plastic car, couple with an HEV drive train, can easily double the Prius's fuel efficiency without any additional complication of a waste heat recycling system.

BMW and Honda must see something in this or they would not be doing it. If you can get 15 hp, like the turbosteamer and drive an alternator, you might get close to 10 kw. That is one nice mileage extender. BMW used it as mechanical energy, perhaps because they are not all that far along with hybrids.

Honda has done hybrids, but may have chosen the wrong design for the expander. Sometimes you have to think outside the box to come up with a solution that not only works, but is cost effective. If you can use elements of the cooling system and combine costs, it might be more practical. We are going to need everything we can get to help out. I have no problem trading hardware for efficiency in a reasonable balance.

Brian,

I disagree that the heat from the engine block coolant is too "low grade" to be of use in a waste heat steam engine system. A low grade heat source is one of insufficient temperature to provide efficient conversion via a heat engine. If one were trying to use only the heat imparted to the engine block, that would be true. But in Honda's system, they're using exhaust gas to boost the steam engine's working temperature. So the engine block coolant would exit @ 200-300 degrees F and the exhaust would heat it the rest of the way to a temperature that gives good efficiency. Since an engine's coolant and exhaust heats are roughly equal, the available output energy could be approximately double that of the exhaust-only system. Maybe even better since the working temperature might turn out to be higher.

The efficiency boost from a system like this has great potential. For example, imagine a diesel engine of 40% efficiency coupled to a waste heat engine that can achieve 50% of Carnot efficiency. If the working fluid is heated to 600F and cooled in the condenser to 100F, then the output is (600-100)/(600+459)*0.6*0.5 = 14% of the input fuel energy giving a total efficiency of 54%. Another way to say it is that the power output is increased by 14/40 = 35%. You might argue with the specific numbers but the potential is there.

Like I said before, I grant that the engineering to get there would be considerable and, in the end, the added cost and complexity might still not be worth it.

If the engine coolant is 250f+ with glycol water under pressure, it would make a good bulk heater for the water that has been condensed from steam and is now under 200f on its way back up to be heated again. Coolant heat exchanger, converter heat exchanger and then manifold, by the time you enter the expander the fluid is 400f under 200 psi pressure and has lot of steam energy ready to drive something.

Considering that a typical Gas engine only converts 15-20% of its energy into mechanical energy, that leaves about 80% of the energy lost in the form of heat. Just think if we started to tap into that 80% what would happen.

Hi, For more information on steam cars have a look at.... www.steamcar.net regards, Jeff.

This development exemplifies a big part of the problem in today's automotive industry: its reliance on complexity as a problem solving tool.

Twelve years ago, Greenpeace doubled the fuel economy of the already stingy Renault Twingo with their SMILE concept car. They did it by simplifying: reducing the weight primarily by replacing the stock engine with a pressure-wave supercharged one having half as many cylinders and one-third the displacement; improving the aerodynamics while keeping the same essential body form; using lighter seats and half the fuel tank volume.

The Twingo SMILE achieved 78 g/km CO2 while retaining the original's performance and utility.

I think that it has potential. Hybrids are good around town with stop and go driving, but do very little at highway speeds. This offers more efficiency at highway speeds by reclaiming some of the waste heat energy. Hybrids are the way to go here, because whether you use IR PV, turbines, expanders or whatever, you can always make some electricity.

Thanks to all the posts. This is a great blog to review the concepts out there. It's good to know that steam is being revisted for cars. There has to be a way to flash steam by an energy-efficient method. What about microwave, gigawave, or other energy to flash-steam water vapor 625 times a minute?

It is good to see this remake of the hundred year old Still engine combination of internal combustion and steam. They were used mostly in stationary engines but also in ships.

The most interesting example of the Still concept was the Kitson-Still locomotive. Eight pistons with steam acting on one side of the piston and diesel on the other. The boiler was intially heated by a small oil flame so that there would be enough steam to start both the locomotive engine and the train.

The engine was coupled directly to the wheels of the locomotive. The waste heat from both the exhaust and cylinder cooling was used to heat the boiler between stops. Fuel was not fed to the diesel end of the cylinder until the train was moving more than 2 miles an hour, and the steam was cut off until required again for starting or a steep grade. Only one locomotive was built but it was tested for years in actual use.

This locomotive had the misfortune to be built in England where there was little or no oil production at the time and world wide major monetary difficulties, so the locomotive company went bankrupt. And the railroad returned the experimental locomotive to the creditors. The locomotive used one eighth(1/8) the weight of fuel as the coal burners with the same performance.

The US Southern Pacific railroads was burning oil in most of its steam locomotives at the time, and it is likely if they had invented the locomotive in 1915 when they had a lot of money that they would still be using newer versions of it.

England should have built and China should build a producer gas engine version that runs on gas made from coke in a tender. The heat from making the producer gas can also heat the boiler water. Modern computers and electric motors make a producer gas generator easy to operate. Electric fans and modern materials make water condensors easier to build and run. The coal or coke is delivered as powder in suspension for convenience.

The diesel electric system is mostly less efficient than direct coupled engine and wheels, but with large enough motors, it can give very high torque and very flexible operating conditions.

A car, that used modern materials and a vacuum insulated reservoir that could hold steam pressure for days, could be a very cheap and convenient car. No gearshifting, no clutch, high torque at zero speed and no starter motor. For short trips, no fuel would need to be burnt. Electricity or a small natural gas flame could keep the water hot enough for starting during long periods of no use. Or if parked in a garage with a high power electrical outlet, a very high power electric heater could be activated to make enough steam for operation in a few minutes if not seconds.

One company makes an electric heater that keeps steam locomotives ready for instant use or heats them up just prior to use. This company also has made diesel burning steam locomotives that are more economical to operate than diesel locomotives.

In a car, an additional tiny gas engine, also coupled to the steam system, could keep the battery charged for electric air conditioning during traffic jams. The battery should be very large so that it can be charged while parked from the grid for most of the cars electrical use.

Cars are mostly bought for beauty or art including size and horse-power not for economical transportation. High volume production has made them cheap enough. It is almost impossible for alterations to be made to the standard concept of cars. The TATA Nano proves this with its continued announcing of a horse power rating that will never appear at the wheels. The actual average horsepower of a car is related to miles per gallon.

The body of all highway vehicles should be rated, like light bulbs, with the drive shaft horsepower required to move the car in still air at various speeds on the motorway. Most people would be surprised at how low this is. With all the electronics and computers available, no manufacturer would provide a read out that showed wheel horse-power. The engine advertised at 300 hp would seldom show more than 20.

..HG..