Designing a Car
There are over one billion cars operating on earth. In about fifteen years, there will be over two billion. Cars and trucks already contribute over one-third of the global warming gases, and consume about three-quarters of the oil. What can we do to accommodate the new drivers in the developing world?
The good old gasoline internal combustion engine cannot be tweaked much more. About 35% of gasoline's energy finds its way to the wheels. Diesel is only slightly better. Every gallon of gasoline, though, creates twenty pounds of carbon dioxide. The only way to reduce this is to burn less.
We can return to small and light cars with small engines, but safety and convenience may suffer. We can drive less, but all too often, especially in suburban areas, the alternatives are sadly lacking.
Our choices for new kinds of engines are:
Hybrid - Eeks a bit more energy out of the gasoline by capturing about 25% of the braking energy, and by turning off while stopped. Also, the gasoline engine can run at a more optimum speed, with the extra energy going into batteries. More advantageous in stop and go city traffic, and less of a benefit on the highway. Adds at least $5000 to the cost of the car because of the extra drive train and the batteries. It can take a long time to get the financial benefit back, but has a bit of the 'At least I'm doing something' panache.
Electric - Batteries only. You plug it in at night, or plug it in wherever you can during the day, and hope for the best. The catch is the batteries. Lithium-ion are the best so far, but they're still heavy and expensive, and can only stand so many charges. If you happen to live in an area with a non-carbon electrical source (wind, sun, nuclear, hydro) you're doing a good thing for the planet. If your electrons come from burning oil, coal or natural gas, you might actually be better off running your old gasoline engine.
Plug-in Electric Hybrid - The Chevy Volt, if it ever arrives on the market, gives us a small gasoline engine to charge the batteries if they happen to run low during our trip. More expensive again than Hybrids because the batteries are larger, and the benefit again depends on the electrical source. The gasoline engine can run at an optimum speed, though, which keeps efficiency high and pollutants low.
Hydrogen Combustion - Burn hydrogen in your tank instead of gasoline and you get water out the tail pipe. You get some nasty nitrous oxides too, but engineers are working on that. Efficiency is about the same as gasoline - 35%.
Hydrogen Fuel Cells - A chemical process to change hydrgen to electricity. Works well and very efficient, but the cells are expensive, and still need refinements to go prime time.
Both hydrogen combustion and fuel cells suffer from several problems. Hydrogen just loves to burn, so it tends to pre-ignite in the cylinder causing poor efficiency and knocking. Hydrogen is a very light molecule, so it's difficult to store a lot of energy in a small space. You need high pressure, requiring expensive tanks, or liquid at a low temperature, causing large losses over time. The worst, though, is that it's not an easy thing to make. The two main ways to make hydrogen are from processing methane, creating - you guessed it - greenhouse gases, or from electrolysis, where you apply lots of electric current to water. Neither are very efficient, and the benefit from electrolysis again depends on where the electrons come from.
The best solution appears to be get all of us to drive very small and light cars with optimized plug-in electric hybrid engines, and get the freight out of the trucks and onto the railroads.
What a shame that hundreds of million of SUVs still have at least ten years of life in them. We'll be burning a lot of gasoline for a long time still.
Next post: What should we be buying - cars and fuel, or services to get us from one place to another. Personally, I don't want a litre of gasoline - I want to get to where I'm going!