If you wanted to buy an internal-combustion car today that delivers better than 40 mpg, you could do it--the VW Golf featuring the TDI turbo diesel. Actually, you couldn't buy it in New York, Massachusetts, or California, because it doesn't meet their smog standards on currently available U.S. diesel fuel. Using low-sulfur European diesel, it beats all U.S. smog standards.
A diesel engine gets its best mileage on the open road. Yet hybrids shine in stop-and-go city driving. So, expect to start hearing more about diesel hybrids. GM Daimler's Astra concept car has a 125-hp (92-kW), 1.7-liter turbo-injected engine and two electric motors (30 and 40 kW). It's supposed to do 0 to 60 mph in under eight seconds, which is brisker than the diesel Golf, while delivering around 60 mpg. Remember, then, that anything you can engineer for a gas hybrid, you can engineer for a diesel hybrid. The only difference is where the fuel comes from.
And what could be greener than biodiesel? Vehicular users of biodiesel say it lubricates better than petrodiesel, has much lower emissions, and doesn't make their exhaust stink. The stuff is made from new or used vegetable oils and animal fats. Interestingly, Rudy Diesel designed his engine to run on peanut oil.
Today's non-recycled biodiesel comes mostly from soy beans and canola (rapeseed). Mixed with ethanol and a catalyst, these sources produce biodiesel methyl esters, which we call biodiesel, and glycerol. A bio-oil refinery industry already is in place, serving a range of industries. Every year, it transforms 2.6 billion pounds of biomass oils into about 4 billion pounds of bio-based chemicals, fuel additives, and biodiesel.
Commercial biodiesel comes in mixed with various percentages of petrodiesel. B100, B50, and B20 are typical designations; the numbers represent the percentage of biofuel. The reason for the mixtures is that unlike petrodiesel, biodiesel gels when it gets cold. B100 gels at around 30° F and B20 at around -15° F. So when it's cold out, you buy the stuff with the lower number.
Alternatively, you can tinker with the vehicle fuel system. There's an $800 vegetable-oil kit for the Golf that adds a second fuel tank with a switch and fuel warmer. As a result, a properly equipped Golf can even run used cooking oil from restaurants. (Electronic Design contributing editor Roger Allan, who once owned a fried-chicken joint, says he used to pay a recycling service to take away several 55-gallon drums of chicken drippings and french-fry oil every week. Lately, he's wondering whether he got out of the restaurant business too early.)