Turbocharged Direct Injection VS Common Rail Diesel Injection (TDI VS CRDI)

TDI    was ( turbocharged diesel intercooler) or (turbocharged direct injection) and CRDI was ( common rail diesel injection.)

TDI ENGINE:it had 2 variants VGT(variable geometric turbo) and (non variable) normal TDI engine had a fixed turbine.

The TDI 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 also uses forced induction by way of a turbocharger to increase the amount of air which was able to enter the engine cylinders,and most TDI engines also feature an intercooler to lower the temperature (and therefore increase the density) of the 'charged', or compressed air from the turbo, thereby increasing the amount of fuel that can be injected and combusted.

(VGTs) slightly different design to avoid turbo lag causing by low speed, usually designed to allow the effective aspect ratio (A:R) of the turbo to be altered as conditions change. This was done because optimum aspect ratio at low engine speeds was very different from that at high engine speeds. 

If the aspect ratio was too large, the turbo will fail to create boost at low speeds; if the aspect ratio was too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output.

By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum

A CRDi engine had rails that inject the fuel into the engine, which was designed to handle higher pressure than an ordinary diesel engine "thereby having results in fuller combustion and efficiency. Since the development of the diesel engine almost a century ago, the focus had been on increasing the fuel injection pressure.In CRDi, the high fuel injection pressure was generated by a supply pump storing in a reservoir the fuel under high pressure in a central container (rail) and delivering to the individual injection valves (injectors) on demand