Quote:
Originally Posted by chuckm
Until God repeals the laws of thermodynamics, I won't buy an on-board hydrogen generator system.
Let me offer this again: I'll help someone design a safe and effective way to meter in H2 from a bottle free of charge. If practical, I'll help you test the results. If it shows a net power output that is equal to more than the fuel value of the hydrogen (ie, hydrogen injected alongside gasoline), then I'd say you had something worthwhile. I'll even assign all rights to the design over to you.
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There is no violations of the laws of thermodynamics. The total energy doesn't change. It is a matter of kinetics (time). This is taken from the document I indicated previously.
Listed are the basic constituents of modern pump gasoline, their vapor (boiling) points, and their burn times:
Petrochemical Vapor Point (degrees F. 1 BAR/2BAR) Burn Time
Hexane 156/199 <1 ms
Heptane 207/257
Octane 258/307
Nonane 303/350
Decane 345/400
Undecane 384/440
Dodecane 425/481 >33 ms
Consider a typical modern engine (2.0 liter with a 90mm stroke) at cruise conditions whereas the ignition event begins at approximately 30˚ BTDC. The 2% to 10% burn rate (the amount of time required for approximately 2% to 10% of the total air/fuel charge to be consumed by the combustion process) takes 16 to 17 Crank Angle Degrees (CAD).
This equates to 1.3 to 1.4 ms [(60 seconds / 2000 RPM)/360 degrees • CAD]. The 10% to 90% burn time takes another 80 CAD. This still is only another 6.6 ms. 80 + 17 CAD after spark event begins places the engine at approximately 67˚ ATDC in the combustion cycle. Considering the flame speed of gasoline is 41.5 cm/sec, and the piston will average a mean velocity of 180 cm/sec from TDC to BDC, with peak velocity around the 90˚ ATDC point of approximately 6666.67 cm/sec (6.7 m/s), it becomes easy to see
that the piston rapidly begins to outrun the pressure wave created by the expanding gasses activated by the thermal-to-mechanical conversion expansion pressure process.
It is so incredibly pronounced, even at cruise speeds, that the piston exceeds the typical speed of sound! Although pressure transducers may register positive (above ambient) pressure in and around the cylinder head within the combustion chamber, there would have to be a slight vacuum at the surface of the piston. This negates the possibility of the pressure within the cylinder to further contribute to useful work.
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Even though as much as 90% of the fuel may be burned by 65˚ ATDC, the piston speed is already walking away from the pressure wave and rendering any Chemical-to-Thermal or Thermal-to-Pressure conversions ineffective in the engine (as far as productive work done). It therefore becomes evident that expediency in the rate of vaporization, initiation of combustion, completion of combustion, and conversion from thermal to pressure
energies are very time sensitive. The engine’s ability to harness “pressure” forces and convert them to kinetic energy occurs in a very small window of time limited to approximately 14˚ ATDC to about 30˚ ATDC (or 1.328 ms for our theoretical 2.0 liter engine at 2000 RPM).
Effectively, any fuel not vaporized and initiated in the combustion process early in the combustion cycle cannot contribute effectively in the conversion to kinetic energy at the crankshaft. Its contribution, if burned at all inside the engine, is simply thermal energy released to the coolant and exhaust systems.
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Hydrogen has a flame speed more than five times greater than [gasoline]. Also, it has a lean limit (mixture at which flame will not propagate due to excess air) of φ = 0.1, much lower than the theoretical limit of gasoline (φ = 0.6). Theoretically, it is possible to extend the lean limit of the mixture, by adding a small amount of hydrogen to a liquid or gaseous hydrocarbon fuel. Operating with abundant excess air ensures more complete combustion, improves efficiency and results in a decrease in peak temperatures, which aids in lowering NOx, while eliminating problems commonly associated with operating on lean mixtures. Secondly, the higher flame speed increases the rate of combustion of the mixture and lowers cycle-to-cycle variations.
Hydrogen has a higher diffusivity compared to HC fuels, which improves mixing, enhances turbulence and increases homogeneity in the charge.
Thanks for reading.