Your post peaked my interest due to your engineering background and project.
Quote:
Originally Posted by
Andre
Hello I'm new and looking forward to being part of this forum.
I am doing a project on converting an engine to run on hydrogen and oxygen for my senior year engineering independent study and I was hoping you could help me out. let me make this clear, I AM NOT ATTEMPTING TO BREAK THE LAWS OF THERMODYNAMICS. I am very good with physics and chemistry and the amount of garbage information I have found out there on this topic is incredible. What I am trying to do is build a split cell hydrogen-oxygen generator that will collect the gasses separately and then run a small 3.5 horsepower horizontal shaft 4 stoke engine off of the mixture. The split cell will be powered by a variable output dc power supply that plugs into the wall . The purpose of doing the split cell is so that I can collect and temporarily store the gasses if I don't have enough output to run the engine on demand and so that I can adjust the h2 to o2 mixture as it enters the cylinder. I have been a small engine mechanic for 3 years and I have a ton of experience working with these machines so I am very comfortable modifying and adjusting whatever needs to be done. Please spare your time telling me that this wont work, its an engineering challenge for a reason and I will be building the setup no matter what. I have unlimited funding and quite a lot of time so those are issues either. I was hoping that some of you would have advice on split cell designs, they are hard to find. Also if anyone who has done a hydrogen or propane conversion can give me some insight on the problems I am going to run into so that I can start to plan and possibly avoid them that would be awesome. Any knowledge you can share pertinent to this project would be greatly appreciated. Thanks :cool:
Practically all the design goals on this and other forums are to use the electrolysis gasses immediately without storage. Thus, there have been only a few designs that separate the hydrogen and oxygen. The classic Hoffman Apparatus can and does separate the gasses. These can be seen in a Google search and are a simple U configuration that can be made with ABS or PVC pipe. These are similar to what is used in chemistry lab demonstration units.
Alternately, you can produce the gasses and separate them later using semi-permeable membranes or ceramics that take advantage of the large size difference between H2 and O2 molecules. I have used the ceramic separators but it can take a long period of time to get relatively pure gas content on both sides. There is always some mix.
As far as engine design, I am not sure what your goals will be, but using a single cylinder engine to start with is very good since you can maximize your efforts. Also, it is very easy to find a large alternator to attach to the engine to use as a variable absorber and, with the addition of some instrumentation, provides a good dynamometer.
The Hoffman Apparatus is no less efficient than any of the other designs.
Quote:
Originally Posted by
Andre
I would like to avoid the Hoffman design if at all possible, I know those are inefficient and have minimal output. I was hoping to make something similar to a normal hho dry cell but put a semipermeable material between the positive and negative plates so that the ions can travel through the barrier but the gas will not. The gas would rise straight up from their separated compartments and I could collect the two individually. I probably would still need to do some filtering but not nearly as much is if I mixed them and then attempted to separate the gas. You can see some pictures of that I am trying to describe here ---->
http://hho4free.com/hydrogen_separator_cell.htm <------. Do any of you have experience with these type of separator cells?
Electrolysis proceeds based on voltage and output is based on current. I have seen Hoffman Cells powered by a high voltage, high amperage power supply. They produced on the order of 10 liters of gas per minute. You can use much smaller amperage and string the Hoffman cells in series with super saturated electrolyte. You seem to think the "Dry Cell" designs are inherently more efficient when in truth they are not. Most have plates with holes through them to provide for electrolyte flow and gas flow. Those holes provide a current "short". No matter how they try to hide that fact, they can only design to reduce that short but can never eliminate it. The middle "neutral" plates are not able to produce to their intended potentials. Many on this forum tout their efficiency by quoting the milli-liter per milli-watt output of their cells forgetting to let the gas cool back to room temperature and then drying the gas to eliminate the volume taken up by water vapor. When measured correctly, the "dry cells" are less efficient than a well executed classic Faraday cell. In electrolysis systems I build I simply use a series connected collection of Faraday cells so that the EXACT amount of hydrogen is easily measured by the CURRENT passed through the cells. One electron is needed for every hydrogen proton, so the math is easy. The Hoffman Apparatus has much the same advantage.
As for using the ion membrane you linked to, you will find that there will be some mixing of the gasses as the membrane is not a true ion membrane like the solid nafion types which pass only the protons. At high rates of production, there is also an imbalance of gas flows and fluid displacements that you will have to deal with.
If you want to make a gas separating system, go ahead and use most any fine weave synthetic fabric and it will work as well as the nylon mesh they are using in the link. Just make sure it is unaffected by your electrolyte.
Your project is quite ambitious.
Quote:
Originally Posted by
Andre
As far as the engine is concerned I would like to get it running and have the ability to throttle up and down but if i can only manage running at idle speed I will still consider that a success. I will need to measure the hydrogen/oxygen consumption somehow and also the efficiency of combustion with an oxygen sensor on the exhaust. temperature will be monitored to prevent overheating and blowing the motor. I plan on adjusting many variables such as ignition timing, fuel mixture, valve clearance, and cam lobe shape and seeing how they affect the performance. Please share ideas on how I could improve and streamline this experiment/ project, I really would enjoy some input from you hho veterans. :)
Almost none of the HHO veterans on this site or any other site for that matter are true engineers or scientists and thus, what you are proposing to do is beyond what anyone else has done. You truly are stepping out to the edge.
I have done much of what you are proposing to do. I have worked on single cylinder gasoline engines in a well equipped university lab. As such, our instrumentation was largely provided for. However, the research was not specifically about HHO. If money truly is no object to you, you can purchase ready made dynamometer cells for a few hundred thousand and the training to use it. If that is not an option, you can build your own dyno cell.
I suggest starting out with an L-head air cooled engine as that is an easy one to modify as you move on. The diffusion rate of hydrogen is so high, mixture stratification is not an issue. An electronic ignition system with full ignition timing control is imperative along with an electronic injector for your hydrogen. You can use natural gas solenoids as they work quite well in this application. You will find that because of the wide range of combustibility of hydrogen, you can run your engine without a throttle over a wide load band and only apply the closed throttle at idle. Look up College of the Dessert and their work on hydrogen engines.
I will look for diagrams or create some.
Quote:
Originally Posted by
Andre
Oh okay maybe the Hoffman design is the way to go then.... that makes sense. Do you have any diagrams or examples of a system similar to the one described? I will be purchasing a power supply that best fits my needs so I'm not restricted in that manor. Do you I suggest I string a bunch of the Hoffman cells together in series or make one large one and run a ton of amps through it? am I correct in my understanding that 1.6 and 2.2 volts are ideal to maximize efficiency? wouldn't a high voltage setup (without neutral electrodes to step voltage down) have serious overheating issues?
I am looking into getting my hands on a loner dyno but otherwise I will have to build one, my funds are not quite unlimited. Also are you referring to stratification as the separation of the gases due to their inherent density difference? If so I was worried about that and I'm relieved to hear that will not be a problem. I Don't think I understand what you were talking about with the throttle. Are you saying the flow rate of fuel will not affect the engine's speed? Thanks again for the reply this was exactly what I was hoping for
Using stainless steel as your electrodes, you will need between 2.3-3 volts to get adequate production. I use a super saturated electrolyte to minimize electrolyte resistance so the overvoltage of the stainless steel is the greatest loss above that of the Faraday voltage for electrolysis (~1.4v).
Use the Hoffman Apparatus (HA) in series so they each drop about 3 volts. This will get you several amperes through each unit. This will be good for several milliliter per minute output. But, multiply that by the number of HA units you have in the series string and it can become significant. Since you are using wall power, I would suggest a custom power supply that takes advantage of the 170+ volts peak to peak. You can string 50 HA units in series and make several liters per minute of gas for only a few amperes of input. If you heat the electrolyte, the Faraday voltage will drop allowing more amperes. I use hot water at ~85 degrees C to increase my gas output. This goes against what the "experts" on this and other sites say, but hey, their cell designs cannot run at 4 atm without leakage. The higher the pressure you run your cells, the less steam will be produced. Electrolysis output is unaffected by pressure so your containment vessel is your limiting factor. Good quality 2 inch ABS drain pipes with 1/4 inch walls will hold 8 atm at 85 deg C, so I run at 4 atm with 100% safety factor.
Since hydrogen burns at 4% -70% you can simply change the hydrogen percentage as a way to change your engine output. It is surprising how lean you can run a hydrogen engine. Consequently, you can dispense with a throttle for a large part of your engine load map.
