The solenoid-controlled injector does three "squirts" per power stroke, the first small "pilot" squirt just B4 top dead to heat up the combustion chamber even more than the natural compression-ignition principle. This speeds up the main burning when the main squirt comes slightly later, enabling the DIRECT injection system AND reasonable revs AND a better fuel economy than the older indirect systems with lossy swirl chambers in cylinder head. The third squirt after main-burn is to deal with NOX emissions

Piezoelectric injectors as fitted to your diesel Jag. are quite different, although they achieve the same objective in a better way. Instead of solenoids with their inertia, there is a stack of piezoelectric elements like a stack of very small coins inside each injector. A voltage of about 400 volt is applied across the stack, controlled by the ECU, and the stack gets ever so slightly longer.

This change is applied to an hydraulic amplifier (like a jack in reverse) which opens a valve allowing fuel to squirt. The force this can apply is truly enormous. This is all contained in the body of the injector. This system has virtually NO inertia, and is therefore extremely fast, so much so that there can be FIVE squirts per power stroke, resulting in even better fuel efficiency and even less combustion noise. The piezoelectric elements are well proved and tested, they have been around a long time in other common applications.

Fuel filter is next on my list, I like to change fluids and filters, when I get a "new" car, even that the previous owner and servicing Citroen garage, say it's been changed.