Why not forget about the ICE and go steam-only?

How often would water need to be added to this sort of system to keep it operating?

1 litre of water = 1 kg of water = 2.2 pounds ~= 1700 litres of water vapour at atmospheric pressure.

That and if intelligently designed will have a condenser to change the vapour back to a liquid state to reduce the need to keep recharging it.

This isn't a steam engine. It's an energy recovery system that uses water/steam.

Why add new hardware? I think Bruce Crower and his 6 Stroke engine are a good option. This is a low cost, simple and efficient way of capuring waste heat. I think this one has merit. Inject water to make a steam stroke in the same cylinder after the exhaust stroke. This captures the waste heat to create cylinder pressure and gets rid of the radiator at the same time for thermal and aerodynamic gains. Internal combustion engine and waste heat powered steam engine in one package.

http://en.wikipedia.org/wiki/Steam-O-Lene

http://www.autoweek.com/apps/pbcs.dll/article?AID=/20060227/FREE/302270007/1023/THISWEEKSISSUE

http://www.popsci.com/scitech/article/2007-05/invention-awards-six-strokes-genius

Cyclone Power's WHE is being considered for powering big truck hotel loads. But then again, why not go steam all the way.

http://www.cyclonepower.com

A neat approach to further increase the overall efficiency of hybrids such as the Prius, specially on long trips, where the Prius efficiency needs to be improved. The Volts could also benefit by with free battery (partial) recharge, specially on highways where it is realy needed.

Large long distance trucks could save a bundle in fuel each day.

Could turbo-prop airplanes use a similar approach (if not already done) to further increase their efficiency and reduce fuel consumption. Extra tons of fuel in the air is very expensive these days.

That might sound ridiculous but...

So they used steam engine as a heat recovery...how the piston steam engine work .. well on one approach it used series of extenders, usually up to 2-4 pistons with progressively bigger diameter). The working fluid temperature and pressure decrees so in order to capture most of the energy from presure bigger piston diameter have to be used.
So why not add additional pistol to each cylinder that will act as a expander only.
The exhaust will act as working fluid.

By the way returning to moder steam engine with 35-40% efficiency (Cyclone Power) will not be bad idea at all.
Steam engine toque and power characteristics are much more suitable for modern car then ICE. You probably will get at list 34 time more millage then ICE.

@Anne, dogood;

The efficiency of a stand-alone Rankine cycle is poor by comparison to, say, a decent modern diesel engine. This is one of many reasons why steam-only is not a good plan (and why they disappeared from the automotive scene decades ago and have never come back). The maximum theoretical efficiency of a Rankine cycle can be calculated using charts in any common thermodynamics text. Hint; it's rather dismal. (@mki - 35% efficiency of a Rankine cycle is a pipe dream unless multiple stages of expansion, reheat, and feedwater preheat are used - but that's only practical on a utility-power-generation scale.) But if you are using it to do something with heat that you would otherwise be throwing away, that's where the attraction is.

@Tonychill and mulad,

A Rankine cycle of this type would most likely use a boiler with very small and thin-wall pipes with the working fluid inside the pipes (opposite of an old steam locomotive), to keep the "thermal inertia" low, and to maximize surface area for heat transfer relative to the amount of steel used to construct the boiler. An additional benefit is that the amount of fluid contained in the boiler becomes very small - so little that it is scarcely an explosion hazard. Also, note that I have been saying "fluid". Water is not a particularly good choice, in an engine that has to survive use in a below-freezing environment - most likely the working fluid would be something other than water. And that, in turn, means the working cycle (boiler, expander, condenser, feed pump) has to be hermetically sealed - like your average refrigerator. No fluid fill-ups needed.

SJC - got a better link?

A better link? That is the link for the company sited here. What are you referring to?

There's a limit to how much exhaust waste heat can be used. For one thing, all exhaust gas aftertreatment systems only work above a certain light-off temperature. For another, the waste heat from a secondary steam cycle must be shed through a radiator, possibly creating a major packaging headache.

A better option is to simply apply turbocharging to a large number of engines - with high unit volume, even modest improvements add up to major gains. Variations include turbine gensets such as TIGERS or turbos with integrated motor/generator such as proposed by Honeywell for commercial vehicles.

Note that VTG turbines made from affordable materials can be applied to spark ignition engines if 20-30% low pressure EGR is applied (cp. Ricardo EGR-boost)

"The recovery of waste heat on an ICE is not a good idea, since it will result on a complex and heavy machinery on an already complex engine."

I do not agree with this assessment when it comes to large trucks. The truck is already very expensive and with $4+ fuel, the cost of operating it is getting higher.

I do not know what mileage 18 wheelers get, but we were talking about city buses and 3 mpg. I big rig with all the weight and lack of aerodynamics might get about that on the open highway at 60 mph. Filling 220 gallon tanks could cost $1000 and be used up in one day on a long haul trip.

So, even a 10% improvement in mileage could save the operator $10,000 to $20,000 per year on fuel. Obviously you go for the lowest cost best return improvements, but when so much goes out as waste heat, it might be worthwhile to recover some of it.

BMW has the turbosteamer on a 1.8l I4 engine. The cost and complexity is a problem, but with big rig tractors and huge expensive turbo diesel engines, it might be real cost effective.