Diesel engine combustion phenomena, structures, and evolution in burning modes are studied based on anomalous and normal group combustion theories and numerical simulation, with updated KIVA-3V code, which is implemented with the droplet state criteria, laws of interacting droplet, models of droplet breakup, and gas-phase ignition. The predicted diesel combustion processes occur in a remarkable well-ordered sequence: (1) spray formation, (2) autoignition; (3) flame propagating premixed combustion, which consumes the combustible mixture created during the preignition period (4) partially premixed combustion and droplet combustion in the downstream of the liquid jet due to air entrainment in the lifted flame configuration; and (5) primary mixing controlled, external or internal group flame (stabilized by the recirculating flow, induced by the vortices produced by injection and piston motion in the compression or expansion phase). The temporal variation of the extent of collective interaction, expressed by the instantaneous global Chiu number G. is also predicted to explain the evolutional variation of the diesel anomalous group combustion field structure. The G(c) value exhibits a dramatic reduction during the flame-propagating premixed combustion, reflecting rapid weakening of the collective behavior of the spray. The ratio of the G(c) value at the beginning, and after the premixed combustion, is found to be 6.4 for the Caterpillar engine, and 15.6 for the Cummins engine. The latter is caused by intense premixed combustion. The mean group combustion number during the mixing controlled burn period is of the order of 0.5-1.5, thus, the sprays burn globally with external group combustion. The effects of fuel injection time, initial values of orifice radius, and group combustion ratio on the ignition delay, time of the onset of mixing controlled external combustion, are examined. Areas of future research are also discussed.