You’ve probably heard about diesel engines, and you may have seen cars with a “Diesel” or “TDI” badge. Here in the US, the diesels are often associated with trucks and buses where their longevity and strong pulling power make them optimal choices. But diesel engines are also much more fuel efficient than gas engines, which has made them wildly popular in Europe. As fuel prices continue to fluctuate, more and more automakers are offering diesel engines in their US-market cars and SUVs.
How diesels differ from gasoline engines
Gasoline engines are spark-ignition engines. They draw in a mixture of gasoline and air, compress it, then ignite it with an electric spark; the resulting explosion produces power. Diesel engines, on the other hand, are compression-ignition engines. Diesels draw in a charge of air, compress it to increase its pressure and temperature, and then spray in diesel fuel (a less-refined and less-volatile form of petroleum).
The hot compressed air ignites the diesel fuel, and the resulting combustion and expansion produces power.
Advantages of diesel engines
Fuel economy: Diesel cars can easily approach the fuel economy of a hybrid, without the need for mileage-boosting devices such as auto shut-off systems and low rolling resistance tires.
Range: Most cars that offer a diesel version use the same fuel tank for both diesel and gas engines, but since the diesel is more fuel efficient, it will drive much further on a full tank. Gasoline cars typically have a range of 300 to 400 miles; diesels usually have a range of 600 to 700 miles, which means less frequent fill-ups.