What does 1.5TDI mean in car engines?

1.5TDI refers to a 1.5-litre turbocharged direct injection engine. The '1.5' indicates engine displacement, 'T' stands for turbocharger, and 'DI' means direct injection. This technology combines forced induction with precise fuel delivery for improved performance and efficiency. Modern engines increasingly use turbocharging and direct injection, evolving from carburettors to sequential port injection and now direct injection. Direct injection sprays fuel directly into the combustion chamber at high pressure (typically 100-300 bar), creating better fuel atomisation and more complete combustion than port injection systems. This allows for increased power output and improved fuel economy. Many manufacturers including Audi use direct injection to achieve stratified combustion. However, these engines can be prone to carbon buildup, requiring periodic cleaning - walnut shell blasting is considered the most effective method. Some advanced engines now use dual injection systems (combining port and direct injection) to optimise performance across different driving conditions while reducing emissions. Turbochargers continue to evolve with technologies like low-inertia turbos and electric compressors helping reduce turbo lag - the delay in boost pressure when accelerating.