HydroICE project developing a solar-powered combustion engine


November 22, 2012

A cut-away view of the prototype HydroICE engine, with cotton batten indicating how steam would be used to drive the piston down

A cut-away view of the prototype HydroICE engine, with cotton batten indicating how steam would be used to drive the piston down

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OK, first things first – stop picturing a car with solar panels connected to its engine. What Missouri-based inventors Matt Bellue and Ben Cooper are working on is something a little different than that. They want to take an internal combustion engine, and run it on water and solar-heated oil instead of gasoline. That engine could then be hooked up to a generator, to provide clean electricity. While that may sound a little iffy to some, Bellue and Cooper have already built a small-scale prototype.

The duo have labelled the system HydroICE, which is short for Hydro Internal Clean Engine. Here’s how they envision it working ...

To begin, mirrored parabolic solar collectors would be used to heat oil to a temperature of at least 400 to 700ºF (204 to 371ºC). This hot oil would then be injected into the cylinder chamber of the engine, just like gasoline ordinarily is. A few microdroplets of water would then also be introduced, which would turn to steam immediately upon contact with the hot oil.

The rapidly-expanding steam would serve the same purpose as exploding gas, driving the piston downward and turning the driveshaft. As the piston reached the bottom of its stroke, the spent steam and oil would exit the cylinder and be run through an oil/steam separator. They could then each be returned to their respective reservoirs, for re-use within the closed-loop system.

Hot oil would be injected into the cylinder (Fig 1/Port A), water droplets would then be introduced to that oil (Fig 2/Port B), then the resulting steam would force the piston down (Fig 3)

In order to test the technology, Bellue and Cooper have converted a 31cc 2-stroke gas engine to run as a HydroICE engine. While it isn’t clear if they’ve actually had the thing running yet, they have partnered with Missouri State University and the Missouri University of Science and Technology to develop all the necessary peripheral hardware (such as the solar collectors), and to test the engine’s efficiency.

That efficiency is currently estimated at being at least 15 percent – about the same as the maximum efficiency of existing photovoltaic panels. The technology's big advantage, however, would be price. They’re projecting that a HydroICE system would cost about a quarter of what an equivalent-output photovoltaic system would go for ... obviously, though, that’s still looking some distance down the road.

For now, they’re trying to raise research and development funds via Indiegogo. More information is available in their pitch video below.

Source: HydroICE

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

That's a clever combination. Sort of like a 2 stroke ICE meets steam engine. I guess normally you'd do the heat exchange externally and inject the steam to drive the piston. Is there greater efficiency in doing the heat exchange within the cylinder? Worth exploring due to the similarity between the engine and existing ICE engines. That would allow, presumably, car part manufacturers to turn their spare capacity to making power generators.


Even if it is more efficient than using a Sterling Cycle engine the additional complication of the mechanisms make it less practical.


From your description, that's no longer a combustion engine, as there is no ignition and burning of the oil.

Matthew Harrison

@Slowburn - it is Stirling, not Sterling. Also, I doubt it will be more efficient than a Stirling or Ericsson cycle engine. The only major problem with Stirling engines is their low power density, but that is a non-issue for stationary power plants.


@Scion: generating the steam where it is needed follows the KISS parameters; @slowburn: although the concept is novel, the 2-stroke ICE fits like goldylocks to implement it; @matthew: the article says "internal Clean engine"; @flame_can AND slowburn: no matter the current efficiency, if this thing runs without fossil fuel then it is a blessing.

Eron Silva

What will happen at night when there is no sun?

Henry Franken

Since there is a waste heat in ICE, why not combining 2+2 (or any other combo) 2 cylinders work on fossil fuels, 2 on steam/oil ICE develops much higher temperatures then those from solar collectors and thus more efficiency (more water at once, more steam)

Wolf War

This won't go anywhere. What benefit does it have over electrical energy storage systems.

Siegfried Gust

Wondering: Why not the water meats up with air heated well above 212 deg F? Why oil?If air not hot enough, would not heat of compression be the ticket?


No particular reason why it should not work but it's going to take a really big solar panel or multiples to get enough hot oil to run more than just a few minutes at a time.

Lee Bell

Why not just make it a steam engine, with closed system that uses water, oil, graphite, and gunk to make the steam and a rotary valve as the injector.


It would nice if the person writing the article knew the difference between a driveshaft and a crankshaft.

While this is pretty interesting I'm wondering if the temperature range of the heated oil would sustain during the night. No much use if it doesn't though I guess an auxiliary heat source could be used as a backup.

Mike Siesel

air is not dense enough to carry a significant amount of heat. and even if it was, it doesn't work to expend energy on the upstroke just to drive the downstroke. that's called a spring, and that's not how an engine works.


This reminds me of the Skinner Uniflow engine, except it didn't have oil injection. I've thought of similar concepts in the past, but was always stymied by the age-old steam engine problem; namely oil separation in the returns. In this case where the oil and water/steam are both injected, and boiling occurs in the cylinder, complete sparation is not as big an issue. It seems like a good idea. Dark hours operation could be accomplished through a traditional combustion system, or as mentioned earlier battery storage.


Come on, Gizmag.. this is not a combustion engine.. or Stirling Cycle.. it is a Rankine cycle engine... commonly known as a steam engine... the oil is merely a heat transfer medium.. not sure why they use oil at all, as the system could run without it.. perhaps it is to help lubicate the pistons and maybe have a smoother running solar collector .. a boiling collector can be tricky because of pressure surges, like popping popcorn.

Dan Moser


You hit the nail on the head. Oil-water separation is perhaps the biggest practical difficulty that this concept would have to overcome. Also, if they are to run it with any sort of reasonable efficiency (and power density), there will be condensation inside the cylinder.

I wonder, too, if they've thought at all about where the steam blow-by goes? Directly into the lubrication sump, it looks like.

Interesting concept, but there's some nasty difficulties with this particular design.


Danger, superheated water coming from the solar collector is subject to explosion upon loss of pressure.


Henry Darwin Franken and Mike Siesel: If it feeds batteries (for stored electricity) I don't understand why the lack of constant sunlight would be a deal killer.

Come on everyone, who hasn't wondered how we could harness focused/magnified sunlight to multiply its potential power? These guys seem to have finally figured it out!

Please keep us informed on this one, gizmag.

Fritz Menzel

Another failed hairbrained idea. It's been proven that the sterling engine is far superior to any steam engine for these solar collectors.

Bala Bafoofkit
In order to condense the steam and separate the oil in a closed loop system there will surely be a need for either a very long or large loop or a source of cool water to extract heat from the system. I suppose that in theory one could take the condensed side just below the steam point just before re-entry into the cylinder but the ability to control steam and pressure has always been a very thorny problem that resisted good solutions. Maybe they have some technology involved that is not being mentioned. That is why when we see steam engines they tend to be open rather than closed loop systems. Jim Sadler

i didn't see any proof. and why not divert the hot oil right to the cylinder.


Who's job is it to keep the mirrors clean ? I know how about a water powered dehumidifier, distilled water works great for cleaning mirrors or was it oil from the oil separator ? although the oily film on the water will will keep the mosquito's from hatching that's a plus.

Jay Finke

Gosh, I remember Popular Mechanics magazine back in the mid-1960's with an article on how to build a solar-powered piston engine using only air heated by a solar collector.

Terry Kepner

re; flame_can

The energy density of a Stirling Cycle engine can be increased by putting it in a pressurized environment.


PV prices have dropped drastically to a quarter of what they were 4 years ago. They have no moving parts and will last 25+ years, if this is to produce an equivalent amount of energy of +/- 16% efficiency, but with the additional maintenance and consumable costs, I do not see the attraction. I am working on a similar concept, with far less moving parts and related losses, the efficiency target is North of 30%.

Eric Rae

First of all, heartiest congratulations for making it possible. You have perhaps opened up a great opportunity for the energy sector incidentally proving that solar is the answer for future.

I have been eagerly waiting for something of this kind for my own house under construction. BUT, I am not sure as to how long it would take for the technology to reach India.

I would appreciate it very much if you could guide me to a few contacts for making it faster, please.

Congrats once again.

Asoor Shyam

I can see the principle working, but a drop of water seems too little to provide enough power. Moreover, the engine has to work with other types of fuel as well. Reason being the fact that sun doesn't always shine. Furthermore, the oil would have to circulate constantly while keeping the engine fully operational under all weather. And all that assuming the end design won't include a ridiculously huge parabolic mirror. That's because it would be impractical. I'd prefer if there was no need for a parabolic mirror, but this isn't how physics would have it.

My opinion on solar energy? Engineers are approaching from the wrong angle. They are trying to harvest the sun's energy directly. This is bound to be impossible or impractical. The only way engineers can harvest the sun's energy without doing the impossible or the impractical, would be to avoid conventional or straight-forward methods. Thinking like an engineer is really working against them.

Nitrozzy Seven

It'd work... I don't see why not but I struggle to think of a single thing this concept could do that some other proven technology can't do better.

Demian Alcazar

Hey folks, thanks for all of your comments and for checking out our project! I was asked to put together an FAQ to answer many of the questions and concerns brought up here, check out our blog for some more reading. Thanks, -Matt

Facebook User

I'm curious as to how this would be superior to using a turbine. Wouldn't it make more sense to simply heat water using an oil/water heat exchanger into steam and spinning a highly efficient turbine, which can of course then generate electricity. Given that this technology is ubiquitous and highly refined it would seem difficult to achieve higher efficiency with the inherently far less mechanically efficient reciprocating motion of the proposed solution.

Of course existing solar thermal plants work in exactly this way. Substituting a high temperature molten salt for the oil can also provide for a considerable amount of thermal storage, allowing operation during hours of darkness etc. (net efficiency is lower but load factor is much improved, on the whole it is net even sans any heat loss).


I have read their FAQ, as I too wondered what the advantage would be compared to say a Stirling heat engine powered by solar. I think the answer might simply be that the equipment could be cheaper on a per installed watt basis. They are shooting for 30% efficiency so that is not too far off from a good Stirling at 40%. There are conceivably a number of mass produced 2-stroke engines that could be readily adapted to make this, or possible even a 4-stroke engine could be adapted using a modified or replacement head. Whereas a Stirling engine is just too different from a common combustion engine, it has to be purpose built from the ground up. I have never seen a Stirling made from standard comubstion engine parts.

I have often wondered if there weren't some way that a home mechanic or engine shop could build some kind of solar generator using standard engine, mechanical, electrical, plumbing components, rather than more exotic solid state solar cells which have to be made in elaborate factories. Realize that you can build a very simple and effective solar hot water and space heating system using little more than pumps and plumbing and insulated tanks. But when it comes to solar electrical, you need fairly exotic parts. With this concept, it's conceivable someone could take standard readily available parts like an old engine, mirrors, oil and water reservoirs and pumps, and make something very practical. It could be reasonably simple, safe, reliable, long lasting, and generate significant power. Possibly you could run it on daytime solar and natural gas at night . . . Or store hot oil in insulated tanks . . . It potentially could be much cheaper than solar cells with storage batteries which though cheaper now, remain fairly expensive and exotic. It's really very interesting from that point of view.

Of course this is very early stage and experimental, but worth keeping an eye on and encouraging.


re; Seilertechco

Reread the article. It is very hot oil that come from the solar collector. The only high pressure steam is in the cylinder.


If this was self running, and could charge a battery, maybe i could eliminate my electricity usage here in Dallas?

Mark Ryan

I donated a concept a year ago to Advanced Research Projects Agency-Energy for a hybrid diesel-steam-Stirling piston engine. Don't know if they are working on the concept. Details are available at: Origo


Interesting idea you've got going here, kudos folks! My 2 cents: I know you've considered this, but why must you inject the heated oil directly into the cylinder? Why not simply pump it through a jacket/chamber surrounding the cylinder head (such as current water cooling systems do on an ICE 2-stroker - thinking a 125cc dirtbike, here)? In this way, the cylinder is appropriately heated, you can inject the water as before, but you wouldn't have to be concerned with separating the two again (which, as has been commented here already, will be quite a challenge, particularly when dealing with contaminates resulting from natural engine wear.) Keeping these separated, you will only then have to deal with engine lubrication separately (along with the water that would infiltrate it), for which more conventional systems already exist.


I love it. A few people have wondered in the comments section why not just build a steam engine and use water instead of oil? By using oil they do not have to worry about water converting to steam in the heat collectors or lines. They could have a heat exchange and keep the oil out of the cylinder (just inject steam), but the oil probably lubricates the cylinder and greatly extends its life. Its benefit over a sterling engine is they will be using engines that are already mass produced and low cost.

re; origo1

Diesel/steam hybrids have been used and found wanting; water in the oil is a mess. Matching a Stirling's output with the diesel's would be problematic as well but using a Stirling to drive secondary functions (coolant pump, alternator, and such) Should work well. Steam is an unnecessary complication Stirling works at high temperatures as well.


Stirling engines are large and expensive to produce for high power output. This is because the higher the power output you want the greater the heat difference you need between the hot and cold parts. The higher the heat, the harder to find a material that doesn't break down. Also you need to keep the hot and cold parts separate so you end up with large machines that are expensive and temperamental when producing decent power. The arrangement above would reuse existing manufacturing equipment to produce a compact power plant cheaply that could theoretically produce good power per price unit. I imagine the power output would not be utility scale, but surely useful in smaller applications.


re; Scion

The material problems of Stirling engines have been solved decades ago.


@acorn you have it right.. I just calculated that to get a temp of 371 deg Celsius, compression ratio required would only be 14.59 (with plain air) why is then the oil and solar heater required?

Mohamed Pallipurath

This concept has some potential. Think for a moment about the function. Oil was mentioned but consider a liquid heat transfer medium that has high heat transfer and is more friendly in separating from water. A modest vacuum assist on the return line could deal with the water which will boil off anyway. Check valves will keep the cylinder's high pressure from pressurizing the system. Even though the medium is recycled, it must still retain a lot of heat and they are talking about micro droplets of water. This means the burden on the solar heater is reduced (conserved). The idea is to flash the water which looks to me more like impulse energy driving the piston. You do not want to input any energy except the solar or what's the point, so do not compress any air for heat.

I am confident the University will look at the balance of energy input-output considering solar flux, thermodynamics and masses of the system to arrive at a theoretical potential. The real problem is the mechanical efficiency loss of the crankshaft which is approximately 50%. However, by using a linear piston constant torque mechanism such as the CV Engine they can recover this loss which will double whatever efficiency they can now get (you can Google CV Engine). Remember they are only trying to beat the photovoltaic in kW/dollar which also must include life cycle and maintenance.

David Haley

The last I heard, it's Mixing oil and water that's hard. Separating Oils and water need nothing more technial than a bucket.

Matthew Bailey

While this system might be made to work, I can't help but think that the technology to convert the suns heat to electrical power can probably be done in a more simple and efficient manner. I'll be watching the news to see if this takes off... Storing the energy can be done in a variety of ways, which is a whole separate issue.

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