In a few years, we may have many more options about what to put in the "gas" tank of our cars. Some of the fuel won't work with current cars, but some just might work better than what we have now. There are variations on many of the proposals as well, ranging from hydrogen to ethanol to gasoline to diesel. Which is best? That is a very complex question.

Hydrogen isn't cheap to produce, but burns completely without pollution. Bad news and good news, it seems. Fuel cells only work with hydrogen. Normal internal combustion engines can work with hydrogen as BMW demonstrates with their limited-production Hydrogen-7 cars. A real problem with hydrogen is where to get it. Today, there are very few locations anywhere, but our Gov. Schwarzenegger is working to get a chain of hydrogen stations established from the Mexican to Canadian borders. Think a chain of stations along highway 5.

Storing hydrogen is another problem. It can be stored as a liquid, but that must be done at -420 degrees F. It can be contained that way, but eventually it heats up and becomes a gas that must be vented. Could you accept the concept that you fill your car up with hydrogen in the morning, but park it in the sun all day and some of your fuel is gone at the end of the day? Okay, so store it as a gas. That requires high-pressure tanks that are heavy. A final option is to use a "hydride" which captures hydrogen chemically. It can be freed with heat. This is technology that needs to be developed.

Ethanol seems to be popular politically these days. The farming lobby is working on Congress with money. That means that Congress likes ethanol. The problem is that today it comes from corn. If we "burn" corn in our vehicles, then demand rises as do prices. The farmers love that, but poor people worldwide who eat corn don't like it. With today's technology, burning ethanol in cars is much more expensive than gasoline, let alone that it doesn't have as much energy content, so mileage is poorer by about 25%. Also pure ethanol isn't very practical because it makes cars very hard to start in cold weather. E85 is the result of that problem, which is 85% ethanol and the rest gasoline. Still there are very few E85 stations, only about 1000 in all of the United States, and in fact just one in Southern California -- in San Diego.

Gasoline is a fuel we know a lot about. Right? Maybe there is still some life left in gasoline. Using imported oil is a problem, as is the fact that China and India will be competing with us for oil on the world market. Gasoline prices will be going up. But what about the possibilities of using a ethanol and gasoline differently than E85?

Ford is proposing a fuel called Ethanol Boosting Systems or EBS. This approach would take advantage of ethanol's inherent higher octane number than gasoline as well as its better engine cooling ability. This would facilitate a high-boost supercharged engine that would develop huge horsepower and torque -- or a smaller engine with similar horsepower and torque but better fuel economy without sacrificing performance.

This would work by starting with a strong modern gasoline engine with port fuel injection and high compression ratio. That would be about 12 or 13 to one rather than the "normal" 10:1 used today. Then add a turbocharger or supercharger with an intercooler to make about 20 to 25 psi of boost across a broad rpm range. With standard gasoline, this would produce an engine with massive detonation immediately. With the EBS system, gasoline would be injected using the port injection system and then E85 would be injected using a separate direct injection system. The amount of E85 would depend on what the knock sensors tell the engine computer about detonation. This would allow the engine to behave if it had 150 octane fuel when power is needed, but cruise along on just regular gasoline when lots of power isn't needed. The idea is to use E85 only when it is needed to prevent detonation.

The use of E85 would depend on how heavy the driver's foot was, but for a normal driver, the use of the E85 would be modest. The estimate would be about 5 to 10 gallons of E85 to every 100 gallons of gasoline. Since the E85 tank and gasoline tank would be separate, it could be filled at every other gasoline fillup or maybe even less than that. Of course, the car would run without any E85 in the tank at all, just at a lower maximum power level.

An average V-6 of 3.5-liters produces about 250 horsepower and 270 ft-lb of torque. A 1.8-liter EBS engine with 22 psi of boost would make about the same power and torque. It would be lighter and smaller. When the driver requests 25 to 50 horsepower, the EBS engine would run with no boost and produce far better fuel economy than the V-6 producing the same power.

The EBS engine is usually compared to a turbo-diesel. It would be about 25% more fuel efficient than the gasoline engine, whereas the turbo-diesel would be about 30% better. For the green types, the CO₂ emissions would be about the same because of the higher energy content of diesel fuel. The big difference between the EBS engine and turbo-diesel would be initial cost -- about $2000 less, in fact. The EBS engine uses a 1000 psi direct injection system, the turbo-diesel's direct injection uses 20,000 psi. There also is no urea-based NO_x catalyst system or particulate trap either. Also the EBS engine would produce lower emission levels more easily than the equivalent turbo-diesel.

Doing the math, the EBS system would save about three gallons of gasoline for every gallon of ethanol used. Compared to E85-burning engine and gasoline-only-burning engines, there is about 2/3 of a gallon of gas saved for each gallon of ethanol consumed.

Also the EBS engine looks good because there is no real high-technology stuff used. The addition of the E85 tank in the car probably would negate the lower weight of the engine. The only negative might be a lag in power deliver off idle. Given modern turbo and supercharged engines, that problem may well not exist. I would assume that manufacturers are giving this approach a very close look.

So what do the diesel advocates have up their sleeves? You may not know, but there is diesel fuel and there is diesel fuel. Hmmm... They don't look different do they? All the diesel fuel available in the United States comes directly from a barrel of oil. But diesel also can be made using a gas-to-diesel process -- or more properly gas-to-liquid (GTL). This may well be the future of diesel. GTL diesel may well be the answer for the upcoming emission problems from diesel engines. GTL burns much more cleanly than normal diesel which means less pollution, but also more power. The question is whether there is more natural gas available than oil in the world.

The rapid increase in the cost of oil and political concerns about relying on oil-producing countries has led to interest in these "synthetic" fuels. Last year, Sasol-Chevron opened a $1 billion plant in Qatar producing around eight million barrels a year of GTL diesel. The company will open a second, similarly sized plant in Nigeria in 2009. Shell has operated a GTL plant in Malaysia since 1993 and will open another one in Qatar by 2010. By 2015, it's estimated that GTL will account for around 4% of the world's diesel.

GTL diesel is already available in Europe. It is blended with normal diesel in Shell V-power, a performance-branded diesel. Because it burns more efficiently, it can improve the performance of diesel engines.

It also has a higher cetane rating (that's the equivalent of octane and gasoline) than normal diesel. The cetane rating tells you how quickly the fuel ignites and how evenly it burns. The higher the number, the better the performance. GTL's cetane rating is 70. Normal diesel's rating is 50.

Initial tests show that GTL is carbon neutral, but another environmental advantage is that it is virtually free of sulfur that causes particulate emissions. A car running on pure GTL reduces particulate emissions by between 25% and 40%. This will be most appealing to urban public transport systems. Sasol-Chevron people are talking to officials in Tokyo, Singapore, Berlin and London -- and surprise -- the state of California.

Of course, to get the most advantage from GTL diesel, the engine needs to be modified, just like a gasoline engine needs to be modified to take advantage of high octane gasoline. The problem for Europe right now is that there is no distribution system for GTL diesel, so manufacturers aren't all that interested in making cars that run on GTL diesel.

These systems mean that we have near-term possibilities for better gasoline and diesel engines. Maybe I shouldn't quite say it that way since we really don't have diesel cars in the United States today at all.