Sure thing, Gary.
My mechanical injection engine, and all the older ones build pressure with a plunger pump for each cylinder. Once this pressure reaches a certain threshhold, the injector "Pops" open. This is referred to as the "pop" pressure and is one of the things done at a mechanical injector overhaul.
The injection event continues till the pressure falls below the pop pressure, the injector closes. One event.
On the newer electronically controlled common rail engines, the Rail pressure is constant and available at all injectors, all the time. they are all hooked together, hence the term "common rail".
All the timing is now done electronically. So instead of picking the best average place for all conditions, IE accelerating, light loads, decelerating, the common rail engine can change both the timing, duration, and even the number of injection events per cycle.
Instead of one big squirt, it can deliver the fuel in three or more distinct pulses, spreading the combustion event out for maximum efficiency.
One of the big things you notice right off is the lack of diesel "rattle" or noisiness. The new cars you can hardly tell are diesel, it is because of this. Noise is just another form of wasted energy.
The 305/555 Cummins Common Rail is a 3 event engine.
