How is a common rail diesel better than a normal diesel?

Answer 1

First you need to understand what each of these systems is.

"Normal" diesel. In this method, a mechanical fuel pump gear driven directly from the engine crankshaft, both pressurises the fuel system and controls the firing order mechanically or electronically, depending on the age of the engine. Both work on the same principle.

Common rail on the other hand, works by a single (smaller) pump, working at much higher pressures to maintain high fuel pressure within a single large fuel line (a common rail). Each fuel injector is fed via a separate fuel line from the common rail. The Injection timing is solenoid controlled via an electronic signal from the ECU.

Common rail allows MUCH more accurate injection timings due to having constant high pressure maintained in the rail prior to injection, along with controlled pre-injections to allow for reduced diesel "knock". The pressures involved are also significantly higher, allowing for a much finer atomisation of the fuel. This finer spray means the fuel can burn much more efficiently, resulting in reduced soot emissions and increased power output per unit of fuel combusted.