OK, I think we are on the same page here. When I was referring to it violating the 1st and 2nd Law (I’ll assume they still think the entropy of a perfect crystal at 0K is inviolate…and the 0th Law as well), I meant with respect to the performance/economy gains of 10% they promised. I’m not convinced at all that, in the thought experiement above, adding the assumed 5.6 Btu of hydrogen will allow the assumed 10 Btu of additional energy recovery. However, I agree that that may not be impossible - I believe that it would be impossible, on that point, but belief is not proof, of course. Without knowing exactly what is going on, I’m just not convinced, especially given the earlier 10% claim by them.
The problem is that a catalyst isn’t simply regnerated at another location at some future date by some other reaction, as hydrogen is in this instance. A catalyst takes no direct part in the reaction and emerges from it unchanged whiel at the same time altering the reaction speed. There’s no way that hydrogen is going into a diesel cylinder and emerging from it as unoxidised.
I know we are talking hydrogen here, but this is pretty closely related.
Propane and natural gas injection has been a more or less standard “hot rodding” technique for diesels for a number of years. Burlington Northern even experimented with train engines that ran mainly on NG using only a small amount of diesel fuel as a “pilot” charge.
Careful measurements indicate that the total fuel consumption does decrease on such dual-fueled engines. Propane cost per BTU is somewhat higher than diesel, so there is seldom any econmic gain. Propane injection is done mainly for the substantial (>30%) power gains possible.
Remember that energy isn’t the same as power (power is energy-per-time). Also, neither “fuel economy” nor “combustion efficiency” is the same as “thermal efficiency”. To claim that 100% combustion efficiency maximizes the engine’s thermodynamic performance is a red herring. Combustion efficiency is just a way to measure one of the many mechanisms that lower thermal efficiency, which is the only parameter that really matters if you’re trying to figure out whether this thing violates thermodynamic laws.
Also, “fuel economy” and “combustion efficiency” aren’t strictly linked here. The fuel economy of a pure diesel engine is linked to its combustion efficiency through the expected horsepower of the reaction. As long as you burn diesel in air (with no other additives) you can expect horsepower, as well as all of the following parameters to stay the same, or vary predictably:
- maximum temperature
- maximum pressure
- rate-of-increase of P and T
- maximum expected fuel economy
- volume and temperature of reaction products
- chemical composition of reaction products
…but when you add hydrogen to the air intake, you’re redefining what “100%” is. It’s a different reaction with different products. Those long J-shaped loop diagrams (what are they called?) from thermodynamics will have different endpoints, so your maximum thermal efficiency will change.
The website for the manufacturer claims that losses are recovered through the following mechanisms:
- higher flame velocity yields higher horsepower for the same RPMs
- hotter reaction cleans carbon deposits from inside the engine, reducing friction
- combustion efficiency increases
I guess I just don’t find it very hard to believe that the additional power generated by this (fundamentally different) reaction has enough overhead to pay for the electrolysis.
Argh…ya beat me to it.
A heavy fuel like diesel injected and combustedheterogeneously in a cylinder can never achieve true stoichiometric combustion efficiency: there will always be smoke and soot production beyond a certain level of throttle.
A light, clean fuel like propane injected into the intake can take advantage of the unused oxygen otherwise left over from heavy diesel throttle applications.
(btw, propane fumigation is an on/off affair, triggered by at- or near-full-throttle power levels)
A lighter, cleaner fuel like hydrogen would do even better.
Fair enough, but in this situation the hydrogen can’t be acting as a fuel - it’s made by electrolysis, using power generated by the engine itself. Closed loop - best you can ever hope to do with the hydrogen is break even, and in the real world you won’t even do that.
Now, if the hydrogen modifies the combustion characterisics of the engine so as to get better thermodynamic efficiency, then it may be worth doing. I can’t see how it might do that, but it doesn’t have to break the laws of physics.
I did manage to pick that up in all my IC engine graduate classes and time in the lab… In this case we were trying to assume that adding hydrogen to the fuel was not changing the other components of the IC engine cycle; that is, I was going along the lines of the earlier example put forward in this thread, which was that any alleged differential relative benefit should come about just from the increase in combustion efficiency. I didn’t even need to address the conversion of combustion heat into power (maybe 40% or so) because it just doesn’t work even if you assume 100% conversion. In fact, I did note the latent heat loss factor as well, so I already deviated from pure combustion efficiency.
But someone show me the math. Work it out and show me how changing that 2% in lost efficiency (assuming 100% combustion efficiency of the diesel component, which has not been proven at all, as there would be in essence zero soot and zero HC and CO emissions, as well as zero NOx emissions, something even they aren’t claiming) results in a 10% fuel economy increase. In fact, based on the emissions results, I’d say maybe even saying they boost it to 99% might be a stretch, but I won’t assert that as a “cite” either way, just relying on my emissions testing experience. The hydrogen component I’ve already proven doesn’t pay for itself alone, due to having to generate power at 40-some percent efficiency, going into an alternator at 70% efficiency, to be used in a process with 80% efficiency. Even if you ignore the power conversion it still doesn’t work. So how does this cover the energy cost of producing the hydrogen, plus end up in a “10%” fuel economy increase?
Right.
How exactly does “higher flame velocity” contribute to that “10% increase”? Remember, we’re talking just 2% combustion ineffciency. And no, let’s not get into the red herring of chaning the peak cylinder pressure - in a cycle, you have to look at the brake mean effective pressure, not just the peak. And I want to see the math as to how a 2% change in combustion efficiency results in substantially “more horsepower” to the level of 10%.
Cleaning carbon deposits reduces friction? I suppose, in theory, at some microscopic level. How much? Where is the testing on this? And woe to anyone who has so much in the way of carbon deposits that it actually impacts piston friction beyond couple percentage points or so.
And here again, the third item - “combustion efficiency increases”. It sounds to me like they’re double-dipping on this with point 1 and 3.
On inspection, their claims simply appear to be invalid. Unless I’m not finding it on their website, they present exactly 0 independent, scientific tests conducted by known testing laboratories showing the changes in bmep and bsfc as a function of hydrogen injection. They do not show the efficiency of their electrolysis process. They instead seem to be engaging in engine mumbo-jumbo hoping most people will just assume “hey, it could work, why not?” and go for it. Remember all the pseudoscientific bullshit that goes on with fuel line magnets, air cleaner vortex coils, “platinum gas savers”, and even outside of automotive apps, the “Quadro Tracker”? Like Muldur, people just plain want to believe.
There’s no point in going around on this. Show me the tests, or in absence of that, the hard math, using a simulated diesel engine.
You could start with Houseman & Cerini’s paper on hydrogen injection in internal combustion engines (SAE 740600), researched at JPL and peer-reviewed for SAE. I can only find the abstracts online – the papers themselves have to be ordered at $12/per. I realize that the existence of those papers (without having read them) is not proof, and respect your skepticism on this point, but there’s a whole list of research papers on this topic. I can’t think of any other MPG scams that bothered to cite peer-reviewed journals.
This PDF is written by the manufacturers (therefore much less independent) but it does go into slightly more detail about how it works:
and
The second-to-last slide even shows the energy usage of the electrolyzer, so we don’t have to guess – it draws 266 Watts of power. Even if it only resulted in a 1HP increase, that would be 745 Watts of payback. I know, all of this information is from their mouth; it’s not proof. But surely it makes more intuitive sense to you than the pseudoscience of the magnetic stickers and cyclone intakes?
I think your assumption above, that “any alleged differential relative benefit should come about just from the increase in combustion efficiency,” falls apart. Hydrogen fuel injection doesn’t just increase the percentage of fuel burned (combustion efficiency); it also shortens the time over which that fuel burns to completion (power = energy/time, smaller time => larger power).
Page 7 of the PDF above actually has a chart showing the “weighted, corrected BSFC” before and after, as tested by a CARB-certified and EPA-recognized laboratory. I’m not sure what it takes to get CARB-certified or recognized by the EPA, and the lab looks like they do a lot of studies on other MPG devices and additives. Again – I recognize that it’s not proof, but if it’s a fake, they went to an awful lot of trouble to fake it.
Jurph, thank you for sticking with me on this.
I’ve gone and looked at their Powerpoint you linked, but I’m afraid that while answering a couple of items, and backing me up on one point, it also raises further questions which are troubling.
Slide 6: “The high flame speed of the hydrogen causes the crank angle duration of combustion to be reduced by several degrees, resulting in an increase in torque, a 5-15 HP increase and a more complete combustion of the fuel.”
This isn’t entirely correct. Decreasing the crank angle duration does not in itself cause torque to increase except in terms of instantaneous torque. But engines are not measured on an instantaneous basis, they are cyclic devices which deal in the brake mean effective torque. Their statement is neither true nor false, it’s indeterminate. And I’m afraid that your point at the end of your post which I quoted, also has a problem in this standpoint. The math you post is true, however, that’s not really what determines if the net mean effective torque increases or not. One could argue that more pressure applied at a better position of crank angle makes for more torque, and that very well may be the case, but the statement alone cannot stand without qualifications. And there are some serious limits as well to the minimum crank duration, due to bearing loads on the wristpin and main bearing, which could impact longevity. Also, rapid rises in peak cylinder pressure is not necesssarily a good thing for other reasons, as even a diesel engine can suffer from destructive detonation (it’s true, I’ve seen the scalloped-out heads…).
Also note that they claim the hydrogen in one gallon of water will result in a 5-15 hp increase over 12,000 km. Does that sound correct to you, considering the actual energy available from a gallon of electrolyzed water, then taking out the energy from the cycle needed to produce it? It doesn’t to me, I fear.
Slide 7: They show a 4.5% decrease in “weighted corrected brake specific fuel consumption”. Weighted and corrected how, and for what? They also seem to show much lower emissions reductions than previously claimed too. Oddly, I can believe the emissions reductions on a couple of standpoints. The source study is not available to me for some reason, I do not know why.
Slide 8: Why do they guarantee a “minimum 10% improvement” in fuel economy, when in Slide 7 they list 4.5%? They then go on to claim savings of “30-35%” as being “quite normal”. Can anyone defend a 30-35% increase in economy? I’m afraid that makes this whole thing sound even more suspicious than I thought at first. An increase of 30-35% is groundshaking, and the sort of thing that would be grabbed up by every diesel manufacturer in the world. And yet…there’s not much interest in it, for some reason. This perceived lack of interest does not prove anything in itself, however.
Slide 9: “Recent Ontario Drive Clean tests showed a 38% decrease in opacitty immediately after…(opacity was reduced from 2.1% to 1.7%)” - maybe, but in terms of opacity measurement, those two numbers are not nearly as different as they think. For a power plant, the error in opacity measurement is such that 2.1% and 1.7% are not really statistically significant. I wonder that automotive opacity meters are that much better than ones which are used in power plants. Of course, a power plant has its own stratification issues and all, that a automobile may not suffer from.
Slide 10: How does a 10% decrease in a cost which is “7-15%” of the total operating costs result in a “50 to 100% increase in industry profits”? That’s saying that the industry profit margin right now is less than 1.5%? I’m not sure I get that, but I really don’t want to argue economics with anyone.
Slide 11: They say the efficiency of the “complete device” is 68.5%. That sounds possible, at least. But it also biases the equations more against them than before.
Overall, I think their paper raises more questions than it answers.
Happy to oblige.
I understand, mostly – it’s been almost ten years since I got a B in thermo! – you’re saying that just because the energy is higher for a shorter rotation, the real measure of the engine’s power is the area under the “torque vs. radians” curve. To really get the benefit they’re claiming, you would need to run much hotter than spec, but you’d be doing it for a shorter period… not sure if that creates a net hotter or cooler engine. I agree with you that to really buy this, we need to see numbers. I guess you saw their mileage charts already? Not a controlled experiment, but it does demonstrate a solid gain in efficiency.
I agree with you completely on this point. The energy has to come from somewhere, and I suspect that adding hydrogen to the mix is equivalent to “overclocking” the engine. Are they overclocking within the safety margin? Probably. Are commercial diesel engines maintained aggressively? Absolutely. If this were marketed for civilian use (and it has been; Googling earlier I saw a system being marketed for private vehicles) I would be worried about seeing a few car-becues on the side of the road from overzealous drivers. As it is, I hope they’ve done the math.
Back-of-the-(Google-calculator)-envelope, I get 1600 MJ, assuming a mean speed of 60mph, for the tractor-trailer. In a gallon of water, there should be 210 moles of H[sub]2[/sub], which has a mass of about 423g. Earlier I cited a source that listed hydrogen as having 120kJ/g of energy available; so I get about 50MJ out of the hydrogen. That leaves me with 1550 MJ of energy that I have to account for. Maybe I left it in my other pants? :eek:
That slide states that these are the “immediate” reductions, and that running the system for a sustained period results in a slow increase in efficiency, which plateaus near their higher numbers.
It’s possible this is running into market inefficiencies – the company claims that their device is installed on over 100 fleets. I know that in weather satellite production (where you build maybe a dozen of anything, tops) there’s no way to set up production for the next order of magnitude. Maybe these boxes are still being made as one-offs in an assembly-by-hand fashion?
It’s possible that opacity is measured more precisely for automobiles. If the legal limit is near 2% then the state would have to be able to measure it to enough precision, hundreds of times a day, to fail unsuitable cars and still pass suitable ones. I can’t really do much more than speculate on this, though.
I can see profit margin being thin on that business – not many barriers to entry, lots of people able to do the work, high volume of business, and little to distinguish competitors. Again, speculation. It’s also possible they’re talking out their asses on this; it sounds a lot like a “business development” kind of pitch rather than one based on engineering reasoning.
Actually, that 1550 MJ isn’t as much energy as I though. It’s not terribly hard to account for… given the energy content of diesel fuel (as above) you’re gaining the equivalent of 34.9kg of diesel fuel over 120 hours, or 291g/hr of diesel fuel. That’s about a tenth of a gallon per hour. Given my earlier assumptions (100km/hr ~ 60mph, 5HP increase) the 5HP boost doesn’t cost more than 5g of fuel per mile – does that amount square with an increase in combustion efficiency from 98% to 99%?
Regardless, it doesn’t answer the mail on how they get a mileage boost, unless that additional marginal horsepower (at the same throttle setting) saves them double-digit percentages of fuel. Since it’s only about a 1% increase in overall HP (assuming a 340 HP standard), I can’t see where the efficiency comes from.
I still think the answer lies in the shape of the pressure/volume/temperature curve for diesel fuel burned in hydrogen+air mixtures, vs. the same curve for diesel in air. I suspect they’re getting the extra energy by running the engine up to higher temperatures and stresses than the factory default values – or running to the same pressure, but faster; or to a higher temperature, but for not as long, so that steady-state temp stays the same.
Jurph
At this point, my good man, I’m not certain what more I can say about their process without more hard facts from the company about how exactly they are accounting for the efficiency increase in the engine. Most aspects of it seem suspicious to me, along the lines of what I’ve posted earlier. One of my many jobs is to evaluate potential “too good to be true” devices or processes, and so much about this just screams this to me.
To try to get a more concrete answer, one which I could point to as a “cite”, I tried doing some calculations last night to see if I could come up with a “reasonable” scenario where their system would work, and I was unable to do so. In absolute fairness, that by no means disproves their claims, it only means except that I was unable to determine an obvious mathematical solution that falls in line with the automotive engineering principles I was taught in grad school. I do have a call in to an old friend at Daimler who works on diesel engine R&D and maybe I can get some info from him on what he knows about this process and claims. It’s possible, since he’s into biodiesel and all sorts of renewable diesel projects…
That’s the only way it could work. You’d have to extract more energy from the expanding combustion products before they get out the exhaust pipe. Which is certainly possible in principle.
A little factoid I remember from thermodynamics class is that for the same compression ratio, Otto cycle (gas) engines are more efficient than diesel! The main reason diesels beat gas engines for efficiency is that you can build diesels with much higher compression ratios, since diesels don’t have to worry about pre-ignition. (A lesser reason is that diesels don’t suffer from pumping losses since they don’t control power by throttling.)
Looking at the ideal pV diagrams for the Otto and Diesel cycles, the main difference is that the Otto cycle has virtually instant combustion - the pressure “jumps” at constant volume, giving a vertical line. Which is a reasonable model of reality because the spark-ignited, pre-mixed charge burns very fast. The diesel cycle O.T.O.H has slow combustion over time, because the fuel is injected and has to mix as it burns. This is modelled as constant pressure over increasing volume - a horizontal line on the cycle. Not actually that close to reality, but it does for a start.
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/diesel.html
Now it seems to me that if you could make that injected fuel in a diesel mix instantly and burn as fast as a pre-mixed charge, you’d effectively have an Otto cycle but without having to worry about pre-ignition. And that should net you more bang for the buck.
Problems are, firstly real diesels operate somewhere between the ideal diesel cycle and the Otto cycle anyway - they already have some pressure elevation during combustion. So there’s fewer gains to be had by burning faster then there appear to be at first glance. Secondly, the thing that limits the burning rate in diesels is the mixing rate of the fuel and air, and making that physical process go faster isn’t easy. I can’t see how having a few vol. percent hydrogen in the air is going to help.
Having said that, if it works, it works, the truth will out and we’ll figure out how it works later. But I’m not going to get excited yet - Una’s forgotten more about IC engines than I’ll ever know.
Just the other day, I forgot where my car was parked, and had to walk around like the Statue of Liberty, holding my remote high and clicking it to try to get my car to honk at me…so I guess from that standpoint you’re right. 
Sorry to hijack with a tangent, but this is one of the reasons I proposed creating a diesel engine with multiple injectors per cylinder.
http://biodiesel.infopop.cc/groupee/forums/a/tpc/f/869605551/m/148601261/r/148601261#148601261
But it is exactly the injection rate limited burn that permits diesels to work.
“bang for the buck” is an apt choice of words. Because diesels have high compression ratios, and thier fuel would have a very low octain rating if it were measured, it won’t burn as fast as a gasoline-air mix…it will burn much faster, in fact it will detonate.
This in fact happens do a small extent in most diesels. There is a delay between the start of injection, and the start of combustion. During this time fuel accumulates and mixes with air. Once combustion starts, this fuel-air mix. detonates. This creates the characteristic knocking sound of a diesel engine. Utilizing high cetane rated fuel minimizes this. Department of Energy testing has identified at least one fuel additive that measurably decreases the igniton delay, resulting in more power and decreased stress on the engine. It is not unreasonable to suppose that adding some flamable gas to the the air could give similar benifits.
Well, there’s two factors at play here. I’ve always felt the more important one was that you don’t have a pre-mixed charge - no combustion can take place until the fuel is injected, so you can compress the simple air charge as much as you like. True, if you pre-vaporised diesel fuel, premixed it with air and used this as a charge for your engine it would knock like crazy, but that isn’t what happens in a diesel.
When the fuel is injected, you have a non-mixed charge. Droplets distributed in air. The air in between the droplets can’t burn, since there’s no fuel there. The fuel in the middle of the droplets can’t burn, since there’s no air there. Only at the interface between the droplet surfaces and the air can combustion take place. So you have a relatively slow combustion over time, limited by the mixing rate of the air and fuel at the droplet surfaces. This would be true even if your fuel were gasoline. The octane/cetane rating is secondary.
My understanding is that it doesn’t “detonate”, at least, not in the explosive sense of the word. Are you using “detonate” as a synonym for “ignite”? Diesels aren’t throttled - their fuel-air proportion varies enormously from idle to full power. The only reason this works is because the fuel and air aren’t homogeneously mixed - the fuel-to-air ratio varies from zero in the pure air to infinity in the pure fuel, so somewhere in between there has to be a mixture that can burn. A detonation would require homogenous mixing and a relatively narrow fuel-air ratio.
I can accept that the knocking sound is caused by a rapid pressure elevation in the already-high-pressure diesel cylinders, but not that a detonation takes place.
Fair enough. As I understand it, the delay is due to the necessary heat transfer from the hot air to the fuel droplets, and the necessary mixing of fuel and air at the droplet surfaces. Using a fuel with a wider flammability range, or one that can burn with a richer mixture, will decrease the delay. Then again, so will using a finer fuel spray, and/or getting more swirl in the cylinder.
Agreed, but we are talking about a really small quantity of hydrogen here! If it works, I think we’ll be needing a flame physicist to tell us why.
Of course it must be so. Didn’t you follow all of the links to find NO Hard Date to substatiate their case. IMHO HFI is 99.44% pure bs, hokum, or snake oil. It is written up in “Wired,” without reference to any creditable scientific publications. Yeah I ‘rely’ on Popular Mechanics/Science for all the up to date accomplishements of 10 years ago and the sci-fi products of today
Where’s the beef err scientific journal references?
I heard a bit more on this hydrogen system. and yet have found a diagram on it. I suspect even more that it is just a water injector with some electronics that convert water into O2 and H2 (and bubbles), but it is the cooling effect of the water vapor, and it’s expansion into steam which is the real benefit, the electrolysis is just a way of creating bubbles and to justify it’s multi thousand dollar price.
Here is a link to a simple (homemade) water injection system:
http://journeytoforever.org/biofuel_library/ethanol_motherearth/me3.html
Which claims a 6% improvment in mpg (unfortunalty w/ another modification), on a gasoline engine, I haven’t found anything on using it w/ diesel though, but water injectors work better w/ turbos and aren’t most trucks turbo’s?