Premixed charge compression ignition (PCCI) combustion is effective in reducing harmful exhaust gas and improving the fuel consumption of diesel engines [1]. However, PCCI combustion has a problem of exhibiting lower combustion stability than diffusive combustion [2, 3], which makes it challenging to apply to mass production engines. Its low combustion stability problem can be overcome by implementing complicated injection control strategies that account for variations in environmental and engine operating conditions as well as transient engine conditions, such as turbocharging delay, exhaust gas recirculation (EGR) delay, and intake air temperature delay. Although there is an example where the combustion mode is switched according to the intake O2 fraction [4], it requires a significant number of engineering-hours to calibrate multiple combustion modes. And besides, such switching combustion modes tends to have a risk of discontinuous combustion noise and torque. In this study, a physical model of PCCI combustion is developed and applied to calculate the cycle-by-cycle ignitability of the cylinder to control the ignition delay, thereby eliminating the need for switching multiple combustion modes. Applying continuous control improves the combustion reliability where the target ignition delay is continuously updated by the physical model’s ignitability calculation. The lower the ignitability, the longer the target ignition delay, and the higher the ignitability, the shorter the target ignition delay. As a result, it was demonstrated that even if there are variations in the intake and transient engine conditions, consistent and stable rate of heat release (ROHR) can be achieved.