Hydrogen as an additive to diesel fuel?

[Shahil]

Hey...Interesting topic ... I did some googling and came up with this from the Mythbusters forum.

http://community.discovery.com/eve/forums/a/tpc/f/9551919888/m/2321969559

Every step of all these schemes consumes far more energy than it could possibly release. There is no magic way to get such phenomenal gains in fuel efficiency out of your existing car.

Check out the article though ... I guess that closes the topic here :/

 

[utimmer43]

No mention of diesel engines in that article. The statement that 99% of gasoline does go through combustion doesn't hold true for diesel. Even if it's close to that, not all of the combustion of diesel fuel happens in the chamber. Diesel fuel burns slowly, and some combustion happens after the exhaust valve opens, but by then it's too late to be useful. The hydrogen isn't supposed to add any valuable energy to the driveshaft, rather, it is supposed to cause the diesel to burn more completely before the exhaust valve opens. I think there is something to that, but perhaps not with hydrogen.

As mentioned earlier in this forum, hydrogen tends to preignite. So what if something a little more stable, methane (also mentioned earlier), were used in a similar fashion. Obviously not produced onboard, like the hydrogen (I don't even know where to get methane). Isn't it plausible that adding just a little bit of methane to the intake air might possibly cause the diesel fuel to complete its combustion sooner, when it counts?

 

[schreiz375]

The reason why using hydrogen or HHO gas as they call it makes an engine more efficient is because the oxygen for the hydrogen to react with is all right there in the combustion chamber. The burning of the hydrogen is rather explosive, and ignites more of the diesel fuel rapidly, allowing more diesel fuel to burn with the oxygen in the engine. It speeds up the reaction of the diesel. Typically new Tier 3 and 4 engines are losing about 30% of the stored energy to heat and friction. This is why radiators must be used to cool engines. If an engine ran at 100% efficiency, it would be as cold as the air outside. This is why the hydrogen helps to increase the efficiency of diesel or gasoline engines.

 

[Ulysees]

Diesel fuel burns slowly, and some combustion happens after the exhaust valve opens, but by then it's too late to be useful.

One thing that needs to be considered too, is that the burning does not propagate from molecule to molecule, but all molecules ignite at the same time. It's not like gasoline where the burn starts at the spark, in diesel engines the burn starts everywhere where the pressure is high enough.

Therefore combustion outside the chamber must only be an issue at high revs. Is it?

 

[Ulysees]

And I wonder what role hydrogen might play if all molecules ignite at approximately the same pressure. Maybe not much.

 

[pantaz]

One thing that needs to be considered too, is that the burning does not propagate from molecule to molecule, but all molecules ignite at the same time. It's not like gasoline where the burn starts at the spark, in diesel engines the burn starts everywhere where the pressure is high enough.

Diesel combustion is a great deal more complicated than you describe. This presentation deals with the subject in some detail -- http://egweb.mines.edu/faculty/TParker-Primary/Recent%20Presentations/Wyoming.pdf"

The simplest example I can find is on the following web page -- http://public.ca.sandia.gov/crf/research/combustionEngines/AF.php" -- You will find a series of photographs, (as a GIF animation), showing the actual combustion inside a diesel engine. The flame propagation is clearly visible.

Copy of image is attached for convenience...

 

[schreiz375]

I understand that diesel combustion is complicated, even so. The basic concept of why the hydrogen is beneficial remains the same. Even in newer diesel engines, it is beneficial. In newer engines you can have up to 5 injections per cycle. The diesel fuel that is ignited due to the high pressures will ignite the hydrogen. Since the hydrogen is explosive, its ignition instantly ignites the entire combustion chamber, which in theory will help the diesel fuel more completely burn. In a gasoline engine, it is very beneficial because gasoline engines are on average not even 50% efficient users of gasoline, the hydrogen helps the gasoline burn more completely, and when you buirn mnore completely, you have lower exhaust temperatures, which also helps reduce emissions. Same with diesel engines. Just a thought.

 

[Ulysees]

But it's not obvious at all why diesel wouldn't burn completely at low revs. Probably completeness of combustion is only an issue at high revs.

 

[russ_watters]

The reason why using hydrogen or HHO gas as they call it makes an engine more efficient is because the oxygen for the hydrogen to react with is all right there in the combustion chamber.

No, when people say hydrogen here, they really mean hydrogen. H2. "HHO" is a hoax. It's water by a different name, meant to confuse people about what it really is.

 

[jeffmoss1]

HHO isn't a hoax...it's an H2 and O2 gaseous mixture.

The reason why the presence of hydrogen in small amounts would speed up the combusion process is because it supplies more H and O radicals, sooner, to react with the decomposing hydrocarbons and helps trigger the chain branching reactions sooner.

Combustion is way more complicated than they way you guys are referring to it. There are 1000's of reactions happening all at once and going back and forth until the mixture is finally at a stable equilibrium. Modeling this process is extremely difficult and its part of what my research involves for my graduate degree. Usually there are some critical reactions that one can say dominates the process and you can get a good idea of reaction rates from that and they all involve H2 O2 H O and H2O significantly.

While I haven't yet tried this myself yet (and I am too still very skeptical about it) you can't prohibit it without years of experiments. Trace amounts of hydrogen and oxygen in the intake air can very plausibly make a big difference in allowing for a more complete combustion.

(not making any absolute statements, just providing what I think I know)

 

[TVP45]

HHO isn't a hoax...it's an H2 and O2 gaseous mixture.

But then we'd call it H2, O2 or 57%H2, 43%O2 or something like that. "HHO" is deceptive.

 

[jeffmoss1]

"oxyhydrogen" is what I've read in literature

I agree, HHO is a dumb name.

 

[gambrinus]

existing H2/Diesel engine research

interesting discussion; a couple more link's

(i can't post full URLs on here yet; sorry)

abc.net.au/ra/innovations/stories/s1499183.htm

eprints.utas.edu.au/2781/

 

[kl2345]

I would like to know three things:

Does adding hydrogen into a gasoline engine makes it more efficient?

If you were to use a electrolyzer does the extra load from the altenator decrease the engine efiiciency so that there is no benefit?

And if the electrolyzer load does effect the engine can you then just add another plug in battery to offset the power load.

thank you

 

[mgb_phys]

Does adding hydrogen into a gasoline engine makes it more efficient?

Unlikely, there is an argument for diesel, but only because diesels are pretty efficent at burning aything.

If you were to use a electrolyzer does the extra load from the altenator decrease the engine efiiciency so that there is no benefit?

Yes, we obey the laws of thermodynamics in this house

And if the electrolyzer load does effect the engine can you then just add another plug in battery to offset the power load.

Which would be charged up by?

 

[kl2345]

Which would be charged up by?

I would have a battery that is charged in the house then put it in the car and run the electrolyzer solely from this battery.

 

[mgb_phys]

I would have a battery that is charged in the house then put it in the car and run the electrolyzer solely from this battery.

Is it likely that battery->electrolyzer->hydrogen+gasoline->engine is more efficient than battery->electric motor? And a regular car battery running an electirc motor might run a golf cart but isn't going to do much for a car.

 

[kl2345]

Thank you, i will definitely not buy one.

 

[russ_watters]

Does adding hydrogen into a gasoline engine makes it more efficient?

There is evidence of a very small (under 10%) improvement in combustion and thermodynamic efficiency.

If you were to use a electrolyzer does the extra load from the altenator decrease the engine efiiciency so that there is no benefit?

Yes.

And if the electrolyzer load does effect the engine can you then just add another plug in battery to offset the power load.

Another plug?? I don't know what you mean. Regardless, the first law of thermodynamics applies. That's conservation of energy. You can't get more energy out of a system than you put in. And there are enough sources of inefficiency in the process of electrolysis that you lose a lot of energy.

The hoax in these devices is easy to spot. The people who adverties them directly claim a violation of the first law of thermodynamics that is transparent: they claim that they can get more energy out of a car's alternator without putting more energy into it. But of course, if that were true, you could just couple the alternator to an electric motor and generate electricity that way.

 

[kl2345]

Good point.

i guess i should have explained it better; i understand that i cannot get more energy out of a system than i put in, but it does matter where the energy comes from.

In this situation i want to charge a battery from my power grid and use it to power a electrolyzer to get better gas millage from a gas powered el camino. While i am still putting in the same amount of energy. The cost of charging the battery at home can offset the current cost of gasoline prices. But i only want to do this if it make my engine considerably more efficient.

So in this case the deciding factor is not just science but economics.

 

[CRGreathouse]

In this situation i want to charge a battery from my power grid and use it to power a electrolyzer to get better gas millage from a gas powered el camino. While i am still putting in the same amount of energy. The cost of charging the battery at home can offset the current cost of gasoline prices. But i only want to do this if it make my engine considerably more efficient.

Alright. Electricity might cost $0.10 per kilowatt-hour, and gas $4 a gallon. Given an 80% recharge efficiency, every 32 kilowatt-hours would need to save a gallon of gas to break even. Can any of the physics gurus give advice here on how much energy it would take to save a gallon of gas?

Of course this neglects the weight of the battery and additional equipment...

 

[mgb_phys]

every 32 kilowatt-hours would need to save a gallon of gas to break even. Can any of the physics gurus give advice here on how much energy it would take to save a gallon of gas?

A litre of gas contains 35MJ of energy that's about 10KWH. Electricity is cheaper than gas/petrol, otherwise power companies would use gas/petrol powered powerstations!
The problem with electricity as many threads here point out is storing the stuff.
1Litre of gas/petrol fits in a large cup, 10KWH of batteries don't.

 

[CRGreathouse]

I meant using the battery to power an electrolyzer as kl2345 suggests, not to run the whol car. If this would exhibit a "very small (under 10%) improvement in combustion and thermodynamic efficiency", at what watt cost and for what %age savings?

 

[mgb_phys]

It doesn't matter how you use it - the laws of thermodynamics still apply.
The problem is that a car battery (12V 80AH) only contains about 1KWH of energy, the same as half a wine glass of gasoline.
The reason for the whole hydrogen addition industry/scam is the idea that because you are supposedly unlocking extra hidden energy in the fossil fuel somehow the law of conservation of energy doesn't apply.

 

[CRGreathouse]

I'm a fan of the laws of thermodynamics. I'm not looking for a 'way around'; I'm trying to disprove as large a fraction of these systems as possible.

Any system claiming, for example, to burn hydrogen obtained from onboard electrolysis is trivially impossible by the second law of thermodynamics. But a system claiming to increase the efficiency of an engine is harder to disprove, since car engines are typically inefficient -- I typically see figures around 20%, I don't know what the experts around here think of as a typical efficiency.

So since I couldn't rule it out a priori, I thought I'd go with the next step: find reasonable figures for the efficiency of a system, find the additional load on the system of carrying the extra weight, and show that it fails. This seemed the best path to me, since batteries are (as you point out!) much larger/heavier than gasoline for the same energy.

But as I'm not an engineer, I hoped to get some information from those around here who are (or know reasonable figures, regardless). I have no idea what an electrolyzer would even do in the system, let alone how much efficiency it might cause...

 

[russ_watters]

The numbers are there, just not in a good form. It actually works out nicely, though:

Gasoline has an energy content of about 36 kwh and costs about $3.60, or $.1 per kWh.
Electricity costs about $.1 per kWh (that can vary though - it can be as much as $.15.

That should set off the warning bells - unless the hydrogen can improve the efficiency of the car by more than the loss from creating the hydrogen, you'll lose money on the deal.

According to this paper, using a 7% mixture of hydrogen in gas (by mass) yields a 7% improvement in efficiency (from 30% to 32%). http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770016170_1977016170.pdf

Now since hydrogen actually has 3x the energy density of gas, that's actually replacing 21% of the gas's energy with hydrogen energy. In other words:

1kW gas = .30 kW of output mechanical energy
.79 kW gas + .21 kW hydrogen = .32 kW output mechanical energy

That's a 7% efficiency improvement for zero extra energy (or money) input.

But since your electrolyzer efficiency will be around 50%, you actually need .42 kW of electricity to realize that 7% efficiency improvment and .21 kW hydrogen input. Now your input energy is greater than your improvement in performance: .21 kW of extra energy input for .02 kW of extra energy output.

 

[russ_watters]

But a system claiming to increase the efficiency of an engine is harder to disprove, since car engines are typically inefficient -- I typically see figures around 20%, I don't know what the experts around here think of as a typical efficiency.

Car engines are inefficient, which makes such a belief easy to swallow. But the problem is that, car engines are inefficient for a reason: the laws of thermodynamics dictate how efficient they can be. In reality, if a car's thermodynamic efficiency is, say, 30%, it's theoretical maximum efficiency is likely only to be perhaps 35%. If there was more efficiency to be sqeezed-out, that would simply mean that car engines were poorly designed.

 

[russ_watters]

Electricity is cheaper than gas/petrol, otherwise power companies would use gas/petrol powered powerstations!

I don't understand this statement. Electricity is not cheaper than petrol (on a per btu basis) precisely because the power companies do use petrol (actually oil and natural gas, mostly) powered power stations.

Even after you take out mark-ups for the oil company profit (the power company pays less for oil than you do), a power company still has to deal with the efficiency of the power plant. They top out at about 60%, so on a per kWh basis, 1 kWh of electricity requires 1.67 kWh of oil to produce. So that means that the power company would have to be paying only 60% of what you pay for oil for this scenario to break even.

Now when it comes to your car, though, what you want out is mechanical energy. That's why it's better to use the power plant's far superior thermodynamic efficiency to drive your car with electricity instead of gas. For heating your home, on the other hand, gas is much cheaper than electricity (resistance heating anyway) because the efficiency is 80-95% instead of the 30% in your car.

 

[russ_watters]

Heh - I just realized this thread was locked. Sorry, but after spending an hour on those posts, I'm leaving them. In any case, hope they were helpful.