A simple single injection scheme is used to understand the fundamental processes of diesel engine ignition. Two different combustion regimes, partially premixed combustion (PPC), and conventional direct injection compression ignition (DICI), are computationally achieved with the single injection scheme in a 3-D CFD program. An ignition phase curve covering the two combustion regimes is proposed and verified by numerical simulation. The ignition phase curve is used to reveal the underlying physics of each regime. It is found that the interaction among piston motion, chemical kinetics, fuel-air mixing, and injection event differs the two combustion regimes. The conventional DICI mode ignition is dominated by injection timing and affected by the mixture pressure and temperature during the flame induction period. In the PPC mode, the over-mixing effect of the fuel affects largely the ignition process. The variations of the moment of cool flame onset and high temperature ignition are discussed in detail. The differences between the proposed and calculated ignition phase curve are due to the specific piston and injector design of the test engine for which calculations are done. Finally, the effects of intake temperature on the ignition phase curve are explained based on numerical results.

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