I drive a Mazda RX-8, and ever since I heard about the RX-8 Hydrogen RE, I’ve wished it had made it into production in the United States. Every once in a while, I’ve googled to see if there’s anybody who converts RX-8’s to dual-fuel hydrogen, but I’ve not found any yet.
It was this recent thought which prompted the electrolysis experiment, ostensibly with my kids.
And here’s some raw notes to myself that I made when trying to figure out what mileage I might get (comparing combustion numbers on gasoline [octane] and hydrogen).
octane: 114.23g/mol 0.703g/cm3 255.68J/K/mol hydrogen: 2.0162g/mol 14.3kJ/K/kg .703g/cm^3 * 1cm^3/0.001L = 703g/L = 2661.14448g/gal 1 gal => 23.2963712 mol From GasolineVsHyFuelCell: 2 mol of octane combusted -> 10224kJ released -> 5112kJ/mol. 23.296 => 119 MJ 1 gallon of gasoline produces around 119MJ, and gets me 18miles 2 mol of hydrogen releases 486kJ, so 243kJ/mol To combust 119MJ of Hydrogen, at 119MJ / 243kJ/mol, need 490mol of H2. At 2.0162g/mol, Plug (0.703g/cm^3) * (1gal) / (114.23g/mol) * (5112kJ/mol) / (243kJ/mol) * (2.0162g/mol) into google search, which handles unit conversions for you 988.1g -- or about 1kg of H2 will produce as much energy as 1gal of gas
So, assuming it’s purely energy that causes the rotation, I would use about 1kg of hydrogen per day
OTOH, assume it’s really pressure (of PV=nRT fame) that causes the pushing. I’d need the specific heat to be able to convert the energy (assuming all heat) into a change in temperature… which would then change the pressure, causing the pushing.
But, I was able to find the DOE Hydrogen and Fuel Cells Program Record PDF, which says that 1kg of H2 is approximately 1 gallon-gasoline-equivalent on an energy content basis. Which means my calculations were reasonably accurate.
Some of my original links:
- L.David Roper’s Comparison of Water Produced by Gasoline Combustion and by Hydrogen Fuel Cells, which did a great job of explaining the reactions involved.
- Yahoo! Answers has this incorrect answer, which I desparately want to correct, even though it’s five years old. I list it because it was the first link I found that came even close to describing what I was looking for. I used it as a starting point, and Roper’s PDF to help me complete my analysis.