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Last week we ignited some healthy discussion in the comments with my post on the (de)merits of on-board hydrogen generators and injectors. While few could argue with my basic thermodynamic analysis of the process, defenders repeated the claim from producers of these systems that something magical happens when you add hydrogen to the air fuel mixture of an engine. We've looked into this a little further in recent days including with a powertrain engineer that actually understands combustion processes. In the comments on the previous article a number of readers repeated claims that adding H2 gas or the H2/O2 blend has a catalytic effect on the combustion properties. While there is no evidence of this being true, the addition of hydrogen to the mix can have some beneficial effects in certain circumstances.

Hydrogen does indeed have a faster burn rate than gasoline. Blending even a little bit of it with gasoline will indeed increase the burn rate of the mixture. The idea that was put forward in at least one of the comments is that this would faster burn would trigger knocking in the engine that would be detected by the engine management system resulting in retarding of the spark and more of the explosive force pushing the piston down during the power stroke. This is nominally true, but it only applies to newer engines that have knock sensors. There are however a number of problems with this. Read on after the jump for the rest of this discussion.

[Source: Fuel Cell Insider, Popular Mechanics]

As I said, only newer engines equipped with knock sensors will be able to automatically compensate for the knocking that can generated by hydrogen injection. Those hoping to benefit from hydrogen injection on older engines will be out of luck unless they go in and start manually adjusting spark management calibrations. For those with older carburated engines even more manual adjustments will be required. There is another problem with this whole theory however, Hydrogen increases the effective octane rating of the fuel mixture, increasing knock resistance. Therefore knocking may not even be detected and thus no automatic adjustment.

Another potential benefit of injecting hydrogen is the ability to lean out the air fuel mixture. Again here there are limitations on how much can be achieved here. The engine management systems are calibrated in order to minimize fuel consumption while still meeting all emissions standards. Again, an engine with a carburetor would not be able to adjust itself and would have to be manually adjusted. Other engines may not have enough compensation range in their controls to make a measurable difference. Regardless, recalibration of the engine management system will be required to allow the system to run lean enough to get any benefit.

If the spark can be sufficiently retarded with hydrogen injection, one way that efficiency can be improved is by increasing the use of late intake valve closing, essentially creating an Atkinson cycle as used on hybrid vehicles.

All of these potential benefits are unlikely to be realized on any retrofitted engine without significant recalibration and potential mechanical changes. If H2 injection is designed in, the increased knock resistance and faster burn rate could be utilized to achieve some benefits through higher compression ratios, optimized spark and valve timing and fuel management. All of this requires system level changes that are not a part of any of the kits being sold.

The combination of running lean and the higher temperatures resulting from the hydrogen burn rate on retrofitted engines can increase production of NOx which means that the engine might not pass a smog test. Tampering with the emissions control systems actually poses a problem in states like California. Such a system may have to be removed or disabled before a smog test. It's also not clear that even with an engine designed for hydrogen injection, that the benefits would be significant to overcome the thermodynamic losses inherent in generating hydrogen on the fly. Also note that hydrogen has no magical catalytic effect on burning the gasoline. Modern engines, especially direct injected units have relatively little unburned fuel that will be influenced by the hydrogen.

While we haven't actually tried out a hydrogen injection system ourselves, Popular Mechanics has. Mike Allen at PM installed a hydrogen generating and injection system in a test vehicle and used a data logging system to record the fuel flow. The hydrogen system had a switch to enable and disable the system. By monitoring the fuel injection pulses, the most direct measure of how much fuel was being delivered to the engine, he found absolutely no change in fuel consumption. The one change Allen did see was a drop of a couple of tenths of a volt in the vehicle system voltage when the electrolyzer was turned on indicating the load it was putting on the electrical system.

We've also learned about about a column at Fuel Cell Insider pointing out that some of the electrolyzer systems being sold are labeled as fuel cells. This is a misnomer, since a fuel cell consumes hydrogen and oxygen to produce electricity. An electrolyzer is essentially the opposite of a fuel cell, consuming electricity to produce the hydrogen and oxygen.


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  • 14 Comments
      • 6 Years Ago
      You really need a Pulse Width Modulator with any HHO System. They obviously didn't use one.

      This company makes custom PWM's specifically for HHO and there not expensive.

      http://www.extremehho.com
      • 1 Year Ago
      https://independent.academia.edu/hydrogen check the link it has been tested and verified by NASA twice
      • 6 Years Ago
      I do not think this is a serious article. I do not see the evidences of failing a test as it says the title.

      A part of that, what about diesels engines, do they have the same issues?

      I would like to see how a current ICE could improve injecting small quantities of pure hidrogen. This would prove the point, and after it could be investigated the generation of HHO on board.
      If the mixture of pure Hidrogen could improve the eficiency of the current ICE it could be a new market for Hidrogen distribution.

      • 6 Years Ago
      It might be different if you were injecting hydrogen from a compressed tank of hydrogen filled beforehand.

      But the HHO kits sold can't generate any meaningful quantity of hydrogen.

      "on-the-fly" hydrogen production is meaningless.
      • 6 Years Ago

      The naysayers can think what they like. There are none so
      deaf as those that don't want to hear.

      Alternator doesn't generate unused power? No it doesn't
      but just a small alteration of the voltage in the field coils
      will give a large decrease or increase in output. There is
      no extra work done by the engine or anything else.
      The voltage regulator does the work at no cost.

      I personally wouldn't put one on a petrol engined vehicle,
      but my Smack's booster gives me 40mpg round town
      on my 2.5tdi VW, and 50+ on a motorway trip, book figures
      are 27 and 36 respectively.

      I know, I put the diesel in, and pay for it!

      I should mention that the Smack booster is serious kit,
      and not for the inexperienced in HHO.





      • 6 Years Ago
      I met a gentleman with a c.1930 model A Ford with 4 bottles attached in front of the radiator. He reports his milage went from 15 to 18mpg. He was part of a rally, and not seeking 'converts' . Unfortunately I neglected to obtain further details, as it was a chance encounter.

      Unfortunately, the method of marketing and dissemination does not offer the best model for technical clarity and comparison over a variety of applications, which the consumer/government agencies are loath to/unable to test.
      • 6 Years Ago
      My primary argument to people that espouse this crap is this; if these devices actually worked, we would see them on production cars. If there was a way to increase mileage that was as simple as these hucksters like to claim, every automaker in the world would have some variation of the technology on their vehicles today.
      • 6 Years Ago
      That H2/O2 mix is a bulky gas with low energy value, fed into the air intake it displaces air, so less air goes in, leaving less atmospheric oxygen available to burn the fuel. That in turn means adjusting it to inject less fuel, which improves fuel economy - and decreases performance.

      It would be simpler, cheaper, and more effective to just go light on the gas pedal. But then, what would the hucksters sell?
      • 6 Years Ago
      I'd like to see someone test the unit that is being used on one of the X-Prize cars. It's a little pricey and comes with a warranty. It's hard to believe that someone trying for a $10,000,000 prize would use something that did not work.

      http://www.hydrorunner.com/products.html
      • 6 Years Ago
      Wouldn't it be more productive to figure out how it can work rather wasting time debunking folks who are just trying to get off oil. The folks working on this do not have multi-million dollar engineering departments, they work out of their garages.
        • 6 Years Ago
        If it were free, it would be no problem. Unfortunately, lots of these tinkerers are also attempting to sell their miracle machines to an unsuspecting/uneducated public.
      • 6 Years Ago
      Yes they work - and are erratic in computer controlled cars.

      Get an old carb engine and add a Smacks booster ( or two )
      Plans are free - parts about $60 to 80 -

      About .1 and 1/2 liters per minute on 20 amps ( 260 watts )

      Lots of adjustments possible, but the emissions go down.

      Yes I have -
      25% increase in mileage on my ford 460
      30 % on the Subaru wagon -

      ( that is about 2000 mile average on the ford
      and about 1500 on the Subaru )

      Reccomended - TEST it YOURSELF

      If the person telling you it does not work has not tested on two or three cars - they do not know -

      Testing - Testing - Testing

      Richard
        • 6 Years Ago
        I agree. I have been testing testing and more testing. Building building and building. I have experienced incredible positive results. Some negative as well. Do to the fact that the computer needs manipulation. There is so much to learn. I find it entertaining to read how the skeptics easily and quickly flap their gums with nothing but negativity. They are quitters. And lot's of them. Just want turn key, handed to them. Good for them. It's easier that way. They are plenty, and easy to spot in society. Same old, same old. Good day.
      • 6 Years Ago
      This technoligy has been available since the Hindenburg. There are hundreds of thousands of success stories. You have to want to report the truth of the matter. Look a little broader. There are whole countries operating on Hydrogen primarily. Let's give those who have the spirit to bring this to the next level credit for their efforts.
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