As a secondary question, though...

If you crank the injection timing forward on a diesel engine, you end up with a very audible rapping noise, above and beyond the normal combustion noise, which should be crisp sounding but not a hammering sound. In this way, the fuel is being injected before the ideal time, and starting to ignite before the proper time.

Similarly, when you back off on the injection timing, a diesel engine becomes very quiet, and the combustion clatter becomes almost muffled. The engine also doesn't run well, and smokes white (unburned).

Improper (advanced) injection timing was what killed a good share of VW/AUdi (Volvo) diesels in the mid-eighties.