Turbocharged Direct Injection (TDI) is a trademarked term that refers to a turbocharged diesel engines made by Volkswagen (VW). The first TDI engine was introduced in 1989 in the Audi 100, according to FreeDictionary.com.
Fuel injectors spray fuel into the main combustion chamber of the cylinders, a turbocharger increases airflow into the cylinders and an intercooler lowers the air temperature. This allows more fuel to be combusted, more complete combustion, better engine performance and lower emissions.
VW recommends No. 2 diesel fuel with a cetane number of at least 51 for optimum performance and lowest emissions. A TDI engine can achieve more than 40 miles per gallon.
A direct injection engine also is easier to start when cold, unlike older diesel engines. TDIs are noisier. Other manufacturers also use direct injection diesel engines with turbochargers, but do market them as TDIs. VW diesel engines without a turbocharger are called Suction Diesel Injection (SDI) engines.
