Turbo direct injection vs common rail

Both common rail and electronic unit injectors are better than the 12 years old technology found in the US as TDI.

Both common rail and electronic injectors are better than TDI because of much higher injection pressure. which results in better atomisation of fuel and giving more power with the lower emission.

Here are some technical difference between TDI, CRDI, and Pressurized injector.

TDI : 

TDi uses a mechanical rotary injection pump its fueling and timing controlled by a computer rather than mechanically. The rotary distributor that distributes the pressure to each injector. A metal pipe feeds the pressure to each injector which opens when the pressure is high enough to overcome a spring mechanism.


A single pump which develops a high pressure feeds to each injector through a strong pipe (the rail).
The pressure in a pipe is relatively constant.
Each injector opened individually and electronically.

PI :

This type of engine feeds fuel to each injector.
Each injector is pressed by a cam lobe in the cylinder head, which pumps each injector individually and giving very high pressure.

Common rail and high-pressure unit injector are both improvements over our system.
Common rail uses a single fuel rail that is under enormous pressure. The ECU controls the injector individually.

Which one is better Technology for a Diesel Engine?

Yes the TDI is inferior to CRDI because you get more horsepower for same displacement engine size with CRDI. But emission wise, CRDI is much better. Moreover, with CRDI less fuel plumbing is required from the pump to the injectors.

Verdict :

Moving to a verdict about CRDI and TDI.
we come to know CRDI has better performance & efficiency as well due to a reason it is technologically ahead. 
But, CRDI costs more than TDI & CRDI are also bigger in size. 
On the contrary, TDI's are also good engines they offer you value for money and durability with a decent performance & efficiency as well. Moreover, TDI also needs lesser maintenance than CRDI.