“Water as a Fuel” by Dr. Paul Erickson
As there has recently been a rash of publicity regarding water as a fuel (see for example http://www.dpccars.com/car-movies/05-15-06pageWaterasfuel.htm) I thought it expedient to post a brief explanation of the technical considerations about the idea. Note that water is not a fuel of any sort but can be used as molecular supply of hydrogen and oxygen with a significant energy penalty. Along with the rash of publicity there have been comments like “…4 ounces of water propels the vehicle 100 miles…” and “…the car can be configured to run exclusively from water…” Such comments made by anyone are complete nonsense but that does not mean that hydrogen cannot be used to enhance the combustion of a primary, energy-bearing fuel.
Let us first discuss the claim that “4 ounces of water propel the vehicle for 100 miles.” Taken at face value this is perpetual motion or in other words, plain impossible. If you draw a box around the vehicle and call that a control volume, fill the vehicle up with water (no battery power, no gasoline or other chemical energy) and claim that useful power comes out of the control volume you have a clear violation of the 1st law of thermodynamics. No energy in = No energy out! No matter how complex the system is. Note that along with friction from the engine, transmission, tires etc which results in heat, that steam from the recombination of hydrogen and oxygen will also exit the control volume. Now where did that energy come from? Energy is conserved and cannot be destroyed nor created, which is the first law of thermodynamics. Try taking a power splitter and plugging it into itself… just because you have power outlets available does not mean that the outlets are energized… the power has to come from somewhere else. If we throw a battery into the circuit the power will last as long as the battery energy and no longer. Take your UPS and plug it into itself … It will work until the battery runs down… it isn’t perpetual motion!
Some might argue that the input energy crosses the control volume boundary from the ambient surroundings. This argument does not violate the principle of energy conservation, as heat is potentially absorbed from the surroundings, but this does violate the second law of thermodynamics. If you leave a cup of hot cider in a cold room and wait a while, the cold room gets a little warmer and the hot cider eventually reaches that same temperature which is cooler than the starting condition. Under no conditions (unless of course work is being added from another source) will the hot cider get hotter and the cold room colder. Energy only flows downhill unless work is input to the system. Water is about as downhill as you can get when referring to energy content. So we either have violation of the 1st law or a violation of the 2nd law when we talk about water as a fuel. Now some have said that if we could just get the efficiencies of the electrolysis process up high enough perhaps we can get the system to work by itself. Remember that if you don’t put energy in you don’t get energy out. Period!
So should we dismiss the water fuel concept altogether then? Before we throw the baby out with the bath water because of what I suspect is some misquotations by the media let me explain why hydrogen-enriched combustion could be beneficial. I am not saying that perpetual motion exists but hydrogen combustion can be used to enhance combustion of another fuel and thus boost overall efficiency as long as one takes into account the energy required to produce the hydrogen. First understand that hydrogen combustion is a weird animal. Hydrogen combustion can be sustained in an extremely lean or air filled environment. The lean limit of typical fuels like gasoline is much higher than that of hydrogen. Also, hydrogen has a very fast flame speed and diffuses rapidly. This implies that hydrogen can potentially boost the combustion of other fuels. There are documented increases in efficiency when using hydrogen fuel blends and if the hydrogen is produced from a waste stream such as the exhaust heat the hydrogen can come with minimal energy penalty.
Now the million dollar question is whether or not the benefits of using the hydrogen with another fuel outweigh the energy penalty of making the hydrogen. It is easy to see how well meaning enthusiasts in the media might misquote the sources because they do not understand the implications of saying “the vehicle can run exclusively from water.” It is a much different quote if one says “the vehicle can run exclusively from hydrogen once it is produced.” As I check through the HHO web site (See http://www.hytechapps.com/applications/HHOS.htm ) I think that the hydrogen enriched combustion is what they are really talking about here rather than perpetual motion (I could be wrong though- I have not had any direct interaction with them). Let me also say that the implications of hydrogen-oxygen enriched combustion are not completely understood at this point in time but that is what research is all about. There are several companies claiming that electrolyzed water aids the combustion process (see H2 innovations and others) but usually these people are not using nearly enough hydrogen to make any difference.
Based on my experience you need about 10% hydrogen fuel before one can see any difference and the optimal level is closer to 30% +. I do not know how much hydrogen HHO uses in their process but 4 ounces of water every 100 miles seems too low. Potential benefits of hydrogen enriched combustion are lower lean limit, flame stability, potential for low temperature combustion (with high amounts of Exhaust Gas Recirculation (EGR) or air dilution), potential for simultaneous emissions reductions (NOx and Hydrocarbons) and efficiency increases due to lower losses from lower temperatures. Potential drawbacks are the de-rating of engine power for a given size, potential flashback in the intake, Efficiency decreases due to a high energy penalty in making the hydrogen, and difficulty in maintaining an optimal air to fuel ratio.
I hope that clears things up.
Dr. Paul Erickson
Director, Hydrogen Production and Utilization Laboratory
Mechanical and Aeronautical Engineering Department
University of California, Davis