Relatively Compact Power Generation Using Fuel

[rshayes]

It sounds like your previous attempt was pretty close except for the lack of a torque control. A switching regulator designed to control current instead of voltage would eliminate the problem with stripping gears. It should be possible to keep the efficiency of the controller above 90 percent so the impact on battery life would not be too bad. Added weight would probably be around a pound.

[dacflyer]

Joseph>>
quoted "dacflyer, the Cox .15 later became made by K&B and now by RJL. The regulation would be done by altering the engine speed."<p>
Even if you had the engine going as slow as possible,,this small emgine would still be turning thousands of rpm's also theres no way in the world that this engine could provide 250 watts of power @12 volts.. there is simply not enough horse power or torque.<p>i tried many years ago to make a gas powered bike.. i had found me a 6hp chain saw motor , but i quickly learned that horse power does not match the same for each kind of engine.. i found out that the 6 hp chain saw engine had much less torque than a 6 hp go cart engine..
your best bet if possible is to couple a small 4 cycle engine to a small alternator and a battery.<p>best of luck to you..
i have 2 of these .15 engines practally brand new.
interested in them? they are for CL planes. i got biggerones too as big as 45 i think

[Joseph]

I did finally add non-feedback PWM control. Even though that way is simplest, since it does not use feedback, it needs to rely on the parasitic resistances in the circuit from things like brushes, wires, and MOSFET channels, I think. In fact, I would monitor the voltage drop across the on-state MOSFET channels if I get to doing the current limiting, or current mode, way. I do it that way on power supply circuits I actually design since I do not like the power consumed by sense resistors.<p>dacflyer, thanks. Theoretically, the .15 can produce .86hp at 26k rpm. The problems I think we have thought of are noise and the inability of electric motors to survive turning so fast since they are not constantly fed lubricant. Since the goal would basically be a hybrid electric bicycle, that double-duty electric motor would also need to have enough torque to start the .15 when the battery needs charging. But higher torque electric motors are not designed to turn fast.<p>[ June 10, 2005: Message edited by: Joseph ]</p>

[rshayes]

If the peak voltage is kept down to the 100 millivolt range, the power loss due to the current sampling resistor will be about 1 percent with a 12 volt supply. At this level, careful layout will be necessary to avoid noise problems, but this is a workable level. Assume that any circuit near a switching supply will see some noise, the only question is "how much ?".<p>The channel resistance of a MOSFET is not very predictable or reliable. It varies from part to part, with gate drive voltage, and with temperature. This is the die temperature, which wll be a function of the load and the duty cycle.<p>There are sensing methods, such as saturating magnetic cores, that would work with less voltage drop and power dissipation, but the additional complexity probably wouldn't be worthwhile in this case.<p>An automobile engine usually idles around 600 RPM and red lines around 6000 RPM. This is about a 10 to 1 range. The gear ratios in a manual transmission are in the 2:1 range, and starting requires slipping the clutch in the lowest gear.<p>For the model aircraft engine, I would expect reasonable output between 13,000 and 27,000 RPM, with a minimum speed around 3000 RPM. A propeller is a fairly low inertia load, and the torque required to drive it is probably proportion to the square of its speed. This is probably a fairly good match to the engine characteristics.<p>An electric motor used as a generator may have problems when operated above 3000 or 4000 RPM. The bearings may not be designed for it, and the windings tend to come off the armature. Small motors can go faster, but 10,000 RPM is probably near the limit. There are faster generator designs, such as the Alexanderson alternator (once used to generate power in the 10 kilohertz range), but you really don't want to go there. A larger displacement, lower speed engine than the model aircraft engine would seem to be more appropriate.<p>The high inertia of the generator relative to a propeller may make it difficult for a model airplane engine to start and accellerate the load to its operating speed.<p>The model airplane engine may also have a short operating life, possibly under 100 hours. This would be adequate for a model airplane, where flights are a few minutes each, but it might be too short for a bicycle, since this may be only 100 trips or so.<p>These engines are also designed to be cooled by the air from the propeller, and they may overheat driving a generator.<p>A larger, slower speed engine might be a reasonable solution.<p>[ June 11, 2005: Message edited by: stephen ]</p>

[Joseph]

I maybe would try to obtain a Honda GX31 if dealers were still allowed to sell them by online form. They are a bit big and heavy though. I do have a 25cc 2 stroke which I am still considering using. The first power assisted bike I tried to make years ago used this engine with a poorly functioning pressure roller drive. After about a half mile, the drive wheel, not being knurled metal but rubber, was toast.<p>I think I will continue the search for now to try to find a small electrical source. Until then, I think I will use a small on board charger made out of a switching supply.

[rshayes]

The 25 cc engine sounds like a better prospect than the model aircraft engine. It should be capable of reasonable output in the 2000 to 3000 RPM range, and this is more compatible with any generator that you are likely to find. This could replace most of your battery pack. You might wind up with about a 5 ampere-hour battery that would supply the energy for starting and accelleration and that would be recharged by the engine and generator running at constant speed.

[peter-f]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by stephen:
Hydrogen peroxide decomposes into water and oxygen. In the presence of a catalyst, this decomposition can be very rapid. The reaction releases enough energy to raise the temperature of the water and oxygen to several hundred degrees centigrade. In rockets such as the V-2 and its successors this is used to drive a steam turbine which runs the fuel pumps.<p>This is not an explosion, but if a sufficient amount is released in a closed container such that pressure can build up, the difference may be academic. Many people have been killed by boiler explosions with no explosive involved at all.<p>It is certainly more pleasant than some of the other possibilities, such as hydrazine or nitric acid. These will kill or injure you in vapor form at room temperature.<p>Using an engine to drive a generator to drive a motor does work in diesel locomotives, but it may mot be particularly efficient. Diesel locomotives are efficient in comparison to steam locomotives, but that may not be saying much.<p>Hydrogen peroxide is not readily available. Unless cars start using it, it probably won't be. One of the alcohols might be a possibility. There may be fuel cells that can use it to directly generate electricity.<p>A reciprocating steam engine powered by hydrogen peroxide would be an interesting possibility. It would have good starting torque and clean exhaust. Direct injection of the fuel into the cylinder over a catalyst would avoid the need for a boiler or an ignition system. The lack of readily available fuel would still be a problem.<hr></blockquote><p>Thanks, Stephen... The H2O2 was, as you said, used for steam... but that was Nearly PURE H2O2, not the 3-5% dilution commonly available.<p>While I'm not sure what the fuels are, the fuels used in space maneuvering rockets, I'm sure You know, are reactive- as the hydrazine fuel is... and are caustic. Most people arent aware of the skin burns they'd cause on contact... and that's one reason that the shuttle (upon landing) always sat for about an hour (while draining fuels) before anyone was allowed to approach it.<p>Then, there's also the WWII version of a still... I beleive Opel used it to get wood-alcohol (from chips and sawdust) to power an Internal-combustion engine... attache it to the side of the auto to use engine heat in the process.<p>This thread has been a good bit more amusing than most!

[rshayes]

The hydrazine group of fuels are quite toxic as I understand it. The oxidizer used with monomethyl hydrazine is either nitric acid or nitrogen tetroxide. I wouldn't want to deal with any of them, but nitric acid is probably the "safest". That isn't saying much.<p>I tried a few searches on "hydrogen peroxide" and found that a 35 percent solution is apparently used in large quantities for food processing. It appears to be reasonably safe if handled with a little care. You don't read about many food processing plants blowing up.<p>One of my professors in college once mentioned running cars on methane in Australia during World War II. I'm not sure what the feedstock for that was, but I suspect that it involved livestock and a shovel.

[Joseph]

I am also considering a parallel hybrid set-up. The mechanical output of the engine and electric motor would be in series with the rest of the drive system. It may be a little trickier to implement, but it would save the weight of a separate generator.

[Joseph]

The link is to a picture of the original idea I had in mind to generate power in a small package. Could it work? Its operation would depend on a combination of fluid dynamics and wave propagation. One important question is whether the energy required for ignition is greater than the return from the combustion. The size and intensity of the process would need to be great enough. Also, it would need to be configured so that the wave propagation and gas expansion from combustion function together. A computer program to simulate it would help.<p>Image hosted by ImageShack:<p>It needs electronic circuitry for its operation. The frequency of the resonating tweeter, fuel and air flow, as well as spark timing are essential considerations. The special tweeter would have to be predriven during startup.<p>[ June 18, 2005: Message edited by: Joseph ]</p>

[Gary]

I was looking at US Army (DARPA) research projects a few months ago and ran accross a small electric generator they were trying to develop. It was to use a ceramic high speed impeller to work in a little turbine for powering electrical things in the field. In the order of hundreds of watts I think. Maybe something like this could power your motor.<p>BTW, the Wankel engine is not a true rotary engine IMHO as it wobbles around a center point, it doesn't just rotate.<p>Another option for a bike is one of the new small scale jet engines they are using on model planes. They can run thousands of dollars, but burn kerosene and come in small packages. I wasn't sure how to measure their power as they are measured in pounds of thrust. 10 pounds if I remember correctly. Some use impeller blades from turbo car engines.