| Turbocharged Direct Injection (acronym: TDI) is the technology used to describe and name modern turbocharged direct injection diesel engines produced by Volkswagen Group and widely used in all marques of passenger cars and light commercial vehicles produced by the company. The engine uses direct injection, where a fuel injector sprays atomised fuel directly into the main combustion chamber of each cylinder, rather than the pre-combustion chamber prevalent in older diesels which used indirect injection. The engine is coupled with a turbocharger to increase the amount of air going into the engine cylinders, and an intercooler to lower the temperature (and therefore increase the density) of the air from the turbo, thereby increasing the amount of fuel that can be injected and combusted. These, in combination, allow for greater engine performance (from a more complete combustion process compared to indirect injection), while also decreasing emissions and providing more torque than its petrol engined counterpart. Similar technology has been used by other companies but "TDI" refers to these Volkswagen Group engines. Naturally-aspirated engines (those without a turbocharger) made by Volkswagen Group use the label Suction Diesel Injection (SDI). The reduced material volume of the direct injection diesel engine reduces heat losses, and thereby increases engine efficiency, at the expense of increased combustion noise. A direct injection engine is also easier to start when cold, due to more efficient placing and usage of glowplugs. |
