Why on-board hydrogen generators won't boost your mileage
Historically whenever gas prices have gone up, charlatans have come out of the woodwork offering drivers all manner of devices that are claimed to provide dramatic reductions in fuel consumption. From magnets that are clamped to fuel lines, to assorted vacuum advance devices, and intake vortex generators and magical carburetors none of these have actually been demonstrated to work. Many of these old school devices can still be found, but one of the most popular new devices is the on-board hydrogen generator and injection system. The basic premise is that injecting hydrogen into the intake stream will displace some of the gasoline required, reducing both gasoline consumption and emissions. Just have hydrogen and injecting it will actually achieve this result since the hydrogen burns and produces only water and trace amounts of NOx (although much lower than gasoline or diesel engines). Burning more hydrogen means less gasoline is consumed. Easy right? Not so fast there buddy! Where does that hydrogen come from? The marketers out there are selling on-board hydrogen generators which are claimed to provide enough hydrogen to reduce gas consumption by 30-40 percent or more. Is this plausible? Not even close. Read on after the jump to find out why.
[Sources: Wikipedia, Hypertextbook.com, answers.com]
Electrolysis of water is a process that's been known for over two centuries. It's not complicated, just stick a pair of electrodes into water and pass a current through them. Oxygen bubbles will be produced on one electrode and hydrogen on the other. Unfortunately as with all such processes it isn't 100 percent efficient. Some of the electrical energy put into the system is lost as heat. The process has gotten better over the years but it is still about 70 percent efficient at best.
If you convert 1 US gallon of water to hydrogen by electrolysis it will yield 420.6 g of hydrogen (H2 gas). If the electrolysis is 100% efficient it will take 16.821 kWh of electricity to crack 1 gallon of water. That 420 g of H2 only has an energy density of 14 kWh (33.3 kWh/kg * .4206). That's 16% more energy to crack the water than you get out of it. At 70 percent efficiency that means it would take about 24 kWh of input energy to produce hydrogen with 14 kWh of energy output.
To electrolyze water on the fly means the energy has to come from the engine via the alternator. Whatever electricity the alternator produces has to come from mechanical energy to drive it via the belt from the engine. That means the 24 kWh of energy will ultimately come from the engine while only 14 kWh will get put back in. As a result of this parasitic loss, on board hydrogen generation is an energy negative process that will actually reduce the total fuel efficiency of the vehicle because the load on the engine will be increased.
The only way that the fuel consumption of the vehicle can be reduced by hydrogen injection is to produce the hydrogen outside of the vehicle and store it as a gas on board. The total energy requirement doesn't change but off board generation opens up the possibility of using renewable sources like solar and wind to power the electrolysis.
With all of those companies selling on board electrolysis systems claiming to reduce fuel consumption there have even been news reports claiming these systems work. The answer to this is cheating. Ask any veteran NASCAR mechanic about places to store extra fuel on board a car. The same thing is being done by these scam artists. They are using stored hydrogen somewhere on board to make it seem as though their systems are beneficial.
Hydrogen injection is fine as a stop-gap but the hydrogen must be produced outside the vehicle. If home electrolysis systems or hydrogen filling stations are readily available, existing cars could fairly easily be retro-fitted with injection systems to reduce gasoline consumption. In India they are already experimenting with vehicles fueled by hythane (a blend of natural gas and hydrogen) but that is produced and sold that way.
The bottom line is don't waste your money on these devices. Want to save money and use less fuel? Drive less, consolidate trips, drive less aggressively.
If you convert 1 US gallon of water to hydrogen by electrolysis it will yield 420.6 g of hydrogen (H2 gas). If the electrolysis is 100% efficient it will take 16.821 kWh of electricity to crack 1 gallon of water. That 420 g of H2 only has an energy density of 14 kWh (33.3 kWh/kg * .4206). That's 16% more energy to crack the water than you get out of it. At 70 percent efficiency that means it would take about 24 kWh of input energy to produce hydrogen with 14 kWh of energy output.
To electrolyze water on the fly means the energy has to come from the engine via the alternator. Whatever electricity the alternator produces has to come from mechanical energy to drive it via the belt from the engine. That means the 24 kWh of energy will ultimately come from the engine while only 14 kWh will get put back in. As a result of this parasitic loss, on board hydrogen generation is an energy negative process that will actually reduce the total fuel efficiency of the vehicle because the load on the engine will be increased.
The only way that the fuel consumption of the vehicle can be reduced by hydrogen injection is to produce the hydrogen outside of the vehicle and store it as a gas on board. The total energy requirement doesn't change but off board generation opens up the possibility of using renewable sources like solar and wind to power the electrolysis.
With all of those companies selling on board electrolysis systems claiming to reduce fuel consumption there have even been news reports claiming these systems work. The answer to this is cheating. Ask any veteran NASCAR mechanic about places to store extra fuel on board a car. The same thing is being done by these scam artists. They are using stored hydrogen somewhere on board to make it seem as though their systems are beneficial.
Hydrogen injection is fine as a stop-gap but the hydrogen must be produced outside the vehicle. If home electrolysis systems or hydrogen filling stations are readily available, existing cars could fairly easily be retro-fitted with injection systems to reduce gasoline consumption. In India they are already experimenting with vehicles fueled by hythane (a blend of natural gas and hydrogen) but that is produced and sold that way.
The bottom line is don't waste your money on these devices. Want to save money and use less fuel? Drive less, consolidate trips, drive less aggressively.
Reader Comments (Page 1 of 7)
rj 12:13PM (8/04/2008)
ok - how bout regenerative braking hydrogen production?
yeah I know you wouldn't get much - I'm just looking for a hole in your article.
Reply
JSacharuk 12:24PM (8/04/2008)
Well, the real hole in the argument is that you can get energy from something like a solar panel mounted on the car. This kit is a retro-fit onto your current car, though, so regenerative braking and solar panels don't really fit into the equation.
If you've already got a regenerative braking system, you can probably get better gains by storing that energy some other way than creating some hydrogen. That unit is going to weigh something, so it's not worth tacking on extra parts if that power is being generated and going somewhere anyway.
why not the LS2LS7? 1:22PM (8/04/2008)
JSacharuk:
A solar cell on the roof of your car might make about 250W peak power production if you park it in direct sunlight on a clear day. That'd be maybe 2.5KWh of energy. This is about equivalent to 1/12th of a gallon of gas.
Chris M 8:01PM (8/04/2008)
Well, doing regenerative braking via a generator, electrolysis cell, then burning the resulting gas would have an overall efficiency of 8% - or maybe less, if a poorly designed electrolysis unit was used. Considering the added cost and weight, plus the difficulty of storing the very low density gas, it would hardly be worthwhile.
On the other hand, regenerative braking as used on hybrids and EVs would have an efficiency of around 75%, considerably better.
HHOFuel.net 2:54PM (8/07/2008)
The person that wrote this article is obviously blurting out uneducated opinions.
Personally, I'm more concerned with our environment than anyone I know, and I've been producing and using HHO gas or Brown's Gas for at least a year. I also own a website called HHOFuel.net with videos that prove the viability of this gas that is produced ON BOARD.
The author is a liar here, claiming that hydrogen is stored ON BOARD. This is wrong as you can produce it on demand, along with more oxygen, which increases the octane value of the gasoline, So why store hydrogen??
The fact that this author claims that the energy used from the alternator will reduce fuel efficiency is moronic to say the least. Does this guy even think or research before he writes?? Of course not. There's no way. If he did, he wouldn't write such garbage.
It's true that HHO is only on average about 80% efficient, meaning you'll get 80% of the electrical energy out of it, that's put into it. However, with new cells, we are able to use "neutral" plates in between the energy fields to cut the electricity used and produce MORE gas for LESS energy. Not to mention, gasoline is less that 25% efficient, so when you add fuel that's 80% efficient, the overall efficiency increases.
PLEASE educate yourself on HHO gas before writing it off as BS just because you read some idiot blogger who's obviously never done anything in the field, has done ZERO research, and is creating bullshit opinions based on his own lack of success.
Rob 2:40AM (8/09/2008)
The author is well informed, well researched, and quite right on all points covered. All of these hydrogen kits are outright scams, or at the absolute least, do not function at anywhere near as advertised.
The only thing she did not cover was if the presence of the generated hydrogen in the chamber can help create better combustion overall.
cptierney6 9:18AM (8/09/2008)
the article says its a negative proccess but its not. the energy to power electrolysis comes from the belt on the engine. the friction from the belt can be stored as energy. with or without the injector there will be energy coming from the belt along with all the other moving parts. so the hydrogen injecter is using energy thats already there.
Chris M 4:48PM (8/09/2008)
Sorry, cptierney6, but "friction from the belt" turns useful mechanical power into useless waste heat, it does not store energy. The belt is simply a convenient way to transfer mechanical power from the crankshaft to the alternator (and several other devices), it doesn't store energy either.
There is no way around it, the extra electrical power an electrolysis cell needs to operate comes from the alternator, which in turn requires extra power from the engine. The only fig leaf the HHO promoters have left is to claim it somehow improves combustion efficiency, and that improvement more than compensates for the additional power required.
al mintz 11:53AM (8/30/2008)
I have been testing the HHO gas generator in my truck for months. This nit-wit who wrote this has no idea what he/she is talking about. It works I am not trying to sell you anything. I went from 20 mpg. to 48mpg. I have helped several of my friends place units in their car and trucks they work some more than double some not as much but all get incress.
I know that coming soon is a company called HydroMiles. has a system that will put all of these nutcases to rest. They are building a web site now I think it is ging to be www.hydromiles.me . I have had the privilege of seeing their proto type's they will blow you away just wait and see.
Pick 1:51AM (9/25/2008)
The base argument here is wrong. It doesn't put an extra load on the engine by hooking a couple of wires to the alternator. The math is right on the electrical side but the alternator is already spinning regardless; it doesn't make it harder turn than it would be without the extra draw. When you put an extra load on an engine it means to make it harder to crank around like an a/c compressor that has a neutral and engaged pulley. It physically makes it harder for the engine to turn making your fuel economy go down. Whoever wrote this may be good at doing conversions with a calculator but knows nothing about how engines work/what makes fuel mileage go up or down
Chris M 10:47PM (9/27/2008)
Pick: Alternators are regulated to produce only as much power as needed to operate the electrical devices and recharge the battery. When power output is increased, the mechanical power needed is also increased.
It would be wasteful for an alternator to produce more power than is needed, especially since doing so would overcharge and damage the battery!
meme 12:14PM (8/04/2008)
There are other tricks besides stored hydrogen that can be used. For example, tweaking the engine to burn a richer fuel-air mixture can yet you better mileage, but it'll worsen your emissions. The average driver won't know any better.
Then there's the invariably common human trait of attributing random fluctuations to whatever actions they took most recently that they think might affect them, combined with the human trait of remembering the "hits" and forgetting the "misses" in a random process.
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Ryan 12:55PM (8/04/2008)
Wouldn't *leaning* the fuel-air mixture be the solution which provided better fuel economy? Leaning would give you better mileage, but will increase the operating temperature of the engine and could cause premature wear, depending on how hot you run it.
rumour 12:43PM (8/04/2008)
Good article. I agree that these are mostly scams, but you haven't disproven one of the claims I see made about HHO.
Rather than displacing gasoline, the claim is that by injecting hydrogen, it is somehow changing the nature of the combustion process within the cylinder, resulting in more complete combustion or more energetic combustion, thus wasting less fuel or heat out the tailpipe. At a high level, the claim is that the parasitic loss of the hydrogen generator is offset by an increase in overall engine efficiency during acceleration (much like how a hybrid car's heavy batteries still help it achieve an overall higher efficiency in the city).
That's the argument I've heard. As you've argued, at a thermodynamic level, HHO systems are fundamentally flawed. However, if they are increasing the efficiency of the engine, then they might have something to stand on. That said, all the articles I've read where a skeptic got it installed resulted in failure, so I imagine this is not the case.
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Serge 6:23PM (8/04/2008)
A properly tuned ICE is already fairly efficient at burning fuel completely -- there is very little unburned fuel (and corresponding unused energy) in the exhaust. Low overall efficiency of an ICE is due to its inability (inherent in design) to convert a large amount of thermal energy produced by combustion into mechanical energy.
If the ICE engine is not operating properly, introduction of hydrogen into gas-air-mix may result in more efficient combustion, leading to lower gas consumption, however better results are to be expected by making the engine operate properly.
The only way that hydrogen injection can reduce fuel consumption is by using externally supplied hydrogen. No system or device known to man is able to output more energy than it takes in.
Neil 4:33PM (8/09/2008)
If this system does not work why did my milage go from 29 to 41mpg? Now it's back to 33 but when I fool the air sensors it will go back up. Darn car makers!
Serge 10:09AM (8/11/2008)
Neil: you haven't posted any details of modifications you've actually done. My guess is that "improvement" in mileage that you saw is due to leaning of combustion. Word is quoted, because doing so usually comes at a price, like increased NOx emissions and engine wear.
Vishva 12:49PM (8/04/2008)
Hi Sam,
I do not agree with you completely. Using your logic, I can also say that even the hybrid cars should give less mileage since the process of storing energy in batteries and using it later when required cannot be 100% efficient and so actually that should also be energy negative.
Vishva
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Sam Abuelsamid 1:04PM (8/04/2008)
That would be true if the engine were doing all the charging of the battery. Most of the energy going into the battery is kinetic energy of the vehicle being recaptured during deceleration. The parasitic losses would outweigh the benefits with out the regenerative braking
srue 6:21PM (8/04/2008)
Sam:
A hybrid does not get most of its battery-charging energy from regenerative braking. Once you consider all the losses from converting battery energy to mechanical energy and back, plus air drag and rolling friction, regenerative braking only charges the battery a small percentage compared to the engine.
The reason a hybrid works (and why hybrids don't cause a problem for your argument) is that it charges the battery the most when the engine is running at its most efficient, i.e. in higher gears (highway). It saves that energy and uses it later when the engine is running less efficiently - lower gears (city).
As to the claim that hybrids weaken your argument, a closed (non-plug-in) hybrid can never be more efficient than its engine's most efficient state. It just makes that higher efficiency available to the car for greater periods of time.