Jeff's Lunchbreak

A friend of mine sent me a link to an interesting device, known as an HHO Generator. HHO stands for 'hybrid hydrogen oxygen'. It's basically an electrolysis unit that runs off your car's electrical system, and sends the hydrogen and oxygen into the engine's air intake. The company selling the device claims gas mileage improvements on the order of 30% to 90%!

I'm skeptical. This seems too much like a perpetual motion machine. For example, you can't hook up an electric motor to an electric generator, and then have the generator power the motor. Resistance in the wires and friction in the moving parts will rob energy from the system and dissipate it as heat into the environment. In fact, if you just had a flywheel of the same inertia on low friction bearings, it would spin longer.

I drew up two quick diagrams to illustrate what I'm getting at with this HHO generator. The first diagram below is a normal car - it burns gasoline to power the engine to turn the wheels. Below that is a car with the HHO setup.

That extra loop resembles a perpetual motion machine too much. You're taking energy from the engine to split water, then trying to use that as fuel to turn the engine, and hoping to get more energy out than you're putting in. But remember, there's friction in the alternator and resistance in the wires running from the alternator to the HHO generator; when you run current through the water, only some of it goes into splitting the molecules while the rest heats up the water; and then there's also friction in the lines from the HHO generator to the intake. You're losing energy to heat in every step of that process.

Still, my friend bought that system and installed it in his car, and he insists that he's getting better gas mileage than before. So, I've tried to think of reasons why this may be the case. Here are my thoughts.

1) The hydrogen makes the combustion process more efficient, so that the engine converts more thermal energy into kinetic energy. This really seems pretty unlikely, though, especially without doing any additional modifications to the engine. First of all, the increase in efficiency would have to more than offset all the lost energy from the HHO generator. And internal combustion engines are already really efficient, especially modern engines with oxygen sensors and fuel injection that can tailor the air fuel ratio. And automotive companies are under pressure from government regulations (not to mention market forces) to make the engines as efficient as possible. Given the number of engineers working on these engines, and the amount of money manufacturers spend on development, I can't imagine that there's much room for improvement in efficiency.

2) He hasn't done enough tests. Fuel mileage is strongly dependent on driving style and other variables. A lead foot burns a whole lot more fuel than driving conservatively. Sitting at stops signs and traffic lights hurts fuel economy (even though the engine's at idle, you're getting zero miles per gallon during those times). A head wind will hurt you, while a tail wind helps. Properly inflated tires have a noticeable effect. I don't think a few tanks of gas driving around town is enough to smooth out all those variables. You either need to do some really controlled testing (an external fuel tank you can weigh on a closed course), or run thousands of miles with and without the HHO generator for comparison.

3) The hydrogen and oxygen are messing up the oxygen sensors. Engines are usually tuned to run at lower power at a stoichiometric air fuel ratio (AFR). This is when the amount of gasoline and oxygen are matched up perfectly, so there's no fuel left unburnt, and no free oxygen left. However, as the engine's power output increases, if it continued to operate at the stoichiometric AFR, it would burn hot enough to damage engine components. That's why the AFR needs to be enrichened - the extra fuel lowers the combustion temperature, keeping the engine from getting damaged. I've got some first hand experience with that - at work, we hired an 'expert' consultant to help us tune an engine, and he let the exhaust gas temperatures (EGTs) get up to 1750ºF (we usually tried to keep them below 1550º), and it literally burnt the ends off of the spark plugs.

The other problem with running too lean is that the engine could start knocking (when the fuel air mixture explodes instead of burning smoothly). That's another reason the AFR gets enrichened. I've got some first hand experience with that, too. We were tuning the engine another time (at a different shop), and we had a laptop hooked up to the engine computer that gave us real time feedback on all the variables the engine computer was monitoring. We kept advancing the timing (another variable that strongly influences knocking) to try to get the engine operating as efficiently as possible. The guy operating the dyno had run plenty of engines, so he had a good ear for it. The laptop was telling us that the engine was sensing knocking, but the guy running the dyno couldn't hear it, so we figured it was a false signal. After a few more dyno runs, we basically destroyed the engine. When we took it apart and inspected it, it had all the signs of knocking. The moral being - your ear isn't sensitive enough to reliably detect knocking at levels that are still high enough to damage your engine.

If the hydrogen and oxygen are messing up the oxygen sensors, it may be tricking the computer into running the engine leaner. This would improve fuel economy, but at the cost of higher EGTs and increased chance of knocking - both of which will reduce the life of your engine. Unfortunately, there's no way of telling on a more or less stock system. Block temperature is not a reliable indicator of exhaust temperature, because there's plenty of capacity in the cooling system to keep the block temperature low enough. And knocking isn't something you can always catch by ear.

My gut feel is that it's probably option two above. I think that with more testing, my friend will find that the HHO generator is actually hurting his gas mileage. If it turns out to be option three, though, it could be causing some serious damage to the engine. I recommended to him that he at least pull the plugs periodically to see what they look like, and that it might not be a bad idea to invest in some EGT probes and a knock sensor, either.

Anyway, after a little bit of research, I did find a few other sites discussing this (the first link below is the best). It looks like my second option above is the most likely.

• http://www.consumeraffairs.com/news04/2008/07/water4gas.html
• http://en.wikipedia.org/wiki/Hydrogen_fuel_enhancement
• http://www.popularmechanics.com/cars/alternative-fuel/gas-mileage/4276846?series=19
• http://www.wyff4.com/news/17036761/detail.html

It looks like maybe there could be something to these HHO generators in an engine specifically designed for them, but nowhere near as much as many of the scam artists are claiming. Plus it's analagous to octane. High octane fuel doesn't explode as easily, so some of those things that cause knocking (advanced timing & leaner mixture which I already discussed, plus higher compression ratios which I didn't mention) can be pushed harder if you have high octane fuel. So, if you have an engine designed to take advantage of high octane fuel, you can get better efficiencies. But, if you simply run high octane fuel in an engine designed for low octanes, you won't see any difference. Some of the stuff I've seen for hydrogen says that it might allow you to run leaner than with pure gasoline, but your engine and sensors would have to be designed accordingly. Simply pumping it into a stock engine wouldn't give you those benefits.