Wednesday, May 21, 2008
The plug-in hydrogen hybrid, Part 1
But what if you powered it with a battery you'd charged from your home and recharged every night? Let's run a few calculations and spec out a system for a car. First, let's define what we want this system to accomplish. Suppose we are starting with a big SUV that gets 20 miles to the gallon when driven at a steady 60 miles per hour. And let's suppose we want it to get 50% better mileage, to 30 miles to the gallon of gas. Running a little bit of math shows that it would originally be burning 3 gallons per hour, and the improved version would be burning 2 gallons per hour. So this makes the math a bit easier to follow, at least up until this part. And let's add that this car will see 1 hour of use on a single battery charge.
The first question is, "How much hydrogen do we need?" Well, we'll need to supply the equivalent of 1 gallon of gasoline in hydrogen, per hour. Now the math gets hard: We need to figure out how much hydrogen that is. And we'll also figure out the device's water consumption. We'll start with a couple key numbers pulled from around the Web.
Energy density of hydrogen: 142 MJ/kg (most optimistic value from this source)
Energy density of gasoline: 46.9 MJ/kg (from Wikipedia)
Ratio of hydrogen to gasoline energy by weight: Hydrogen has 3.03 time the energy of gas.
Fraction of water that is hydrogen, by weight: 1/9
Ratio of gasoline's density to that of water: 0.739 (source)
Using these ratios, we find that you'd have to break down 2.2 gallons of water to get enough hydrogen to replace one gallon of gas. The calculations for this are pretty long, so I'm taking a break now. Next up, we'll see how much energy is needed to do this, how much power this thing is going to consumer, and what you'd spend on batteries. And why you shouldn't call it an HHO generator...
1942-1947 Buick Shop Manuals
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