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Examining the science behind "HHO" systems

August 2008

It's been two months since I wrote my original articles on the subject of these "run your car on water" (RYCOW) schemes and I've been constantly researching the subject to get a better understanding of all the issues involved.

Let's see what the science says about these systems, even when we take into account the very real effect that hydrogen/oxygen enrichment can have on the efficiency of an internal combustion engine.

Scientific proof

By passing an electrical current through water, you can break the bonds that hold the atoms of hydrogen and oxygen together in the form of a water molecule.

This is good science and is a process that has been known since the 1800s.

To break these bonds however, requires a significant amount of electrical energy that must come from somewhere. In the case of the RYCOW systems, this energy has to come from the vehicle's alternator and in most cases, that limits the amount of available power to around 0.75-1.0KW.

Of course that 1KW or so also has to recharge the vehicle's battery, power the ignition, headlights etc, and run the various other accessories that abound in a modern car or truck.

So it's safer to assume that only around 600W is always available for the electrolysis cell, which is a maximum of around 50 amps.

Now if we delve into some more good science we find this formula for Faraday's First Law:

Vtheoretical (in m3) = (R I T t) / (F p z)

Where R=8.3414 Joule/(mol Kelvin), I=current(in amps), T=temp in Kelvin, t=time (in seconds) F=Faraday's constant = 96485 Coulombs per mol, p=ambient pressure (pascals), z=num of excess electrons.

If we plug some numbers into this formula and do some simple conversions then the following results appear:

  • 237.1KJ is required to convert 1 Mole of water (18g) to H2/O2

  • To convert 1 Mole of water to gas via electrolysis will reuire 237.1KJ of energy

  • 1 litre of H2O produces 55.55 Moles of H2 (1,358.3l) and 27.775 Moles (679.15l) of O2 (for a total volume of 2037.45l of H2/O2)

  • To convert 1 litre of H2O to H2 and O2 by electrolysis will require 3.658KWH

Of course all the above assumes a 100% efficiency and as we know this is simply not attainable with current materials and technology.

To get an idea as to how efficient the electrolysis process is when performed in a home-made electrolyser I found plenty of videos on YouTube where people proudly share their results.

This example is pretty typical so let's do the math:

12V x 40A ==> 480W

If we plug Faraday's First law into this figure, it suggest that in a 100% efficient cell we should be generating around 4.5 liters per minute of H2/O2 from 480W of electrical energy.

The cell in the YouTube video produces just 2.0 liters per minute, indicating an actual efficiency of around 44% - so we'll assume 50% efficiency for the rest of our calculations.

Now we need to take a look at some of the scientific research that demonstrates how hydrogen/oxygen enrichment can improve engine efficiency. This report (PDF) suggests a best-case improvement in thermal efficiency of around 14.8%-15% so we'll use the higher figure.

Now let's plug in some other figures and see if we can get a net-gain.

The engine in that paper was producing around 6.5HP at 1,500RPMs and needed 240 liters per hour (4 liters per minute) of H2/O2 gas.

An average auto engine will be capable of around 200HP and so a simple scaling would indicate that 30 times the 4lpm figure (or 120lpm) would be required to see the same 15% increase at full throttle. Of course we don't drive around at full throttle all the time so a safer figure to use would be the 20HP or so that an average-sized car requires to cruise at highway speeds.

20HP / 6.5HP = 3 times the horsepower so we'll need 3 times the fuel and three times the H2/O2 gas to see the same effect. That brings our H2/O2 requirement to 12.0 lpm.

Actually, at this stage we must also take into consideration that the engine in the paper was as diesel which uses significantly less fuel to create the same HP (due to the higher compression ratios and naturally more efficient cycle) -- that's why diesel vehicles get better MPGs than gasoline-powered ones. So we'll allow a very conservative additional 20% to account for the greater mass of gasoline required to produce the same power.

That lifts the H2/O2 gas requirement to 14.4 lpm.

Now we see that the addition of 14.4 lpm of H2/O2 should (according to the scientific reports) increase our engine's horsepower by 14.8%-15% (we already decided to use the latter figure).

We're assuming a 20HP requirement for cruise speed so once we add the 14.4 lpm of H2/O2 the engine will output an additional 20 x 0.15 = three horsepower.

So far so good.

Next we have to work out how much energy we'll be taking back in order to create those 14.4lpm of H2/O2.

If we use Faraday's First Law again to calculate that figure we discover that we need around 1,536 watts - but that's only if our electrolysis cell was 100% efficient, which it's not.

We've assumed an efficiency (based on real-world figures) of just 50% for the electrolysis process so we need to double that figure -- which gives us 3,072W of electrical energy required to generate sufficient H2/O2 to give us the maximum fuel-efficiency improvement at cruise speeds.

That 3,072W is 4.1 horsepower.

Uh-oh, it looks like we're spending 4.1 horsepower creating H2/O2 gas but only getting 3 horsepower back. That's a net *loss* of 1.1hp which mean's we'll actually burn *more* fuel than if we hadn't gone to all this trouble.

But wait... it gets worse...

That 4.1hp assumes that our alternator is 100% efficient in turning mechanical energy into electrical energy -- which it certainly is not.

An auto-style alternator is actually only around 60% efficient so the actual amount of horsepower we'll be sucking from the engine to power our cell is going to be around 6.8hp.

Now we find that the net energy return from these "HHO" systems is an even bigger. We're spending 6.8 horsepower to boost the engine's output by just 3 horsepower.

That missing 3.8 horsepower will have to come from burning *MORE* not less gasoline.

I'm sorry -- but those are the facts, there is the science.

I invite anyone to pick holes in my science or my math.

Please feel free to air your views in the forums.

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