Improving the trade-off between NOx, soot, efficiency, durability in a PPCI engine: optimal design of the injection pattern via CFD simulations

Literature on CFD validation of PPCI combustion are mainly conducted with automatic mesh refinement and detailed chemical kinetics for combustion. These features constraint the user to adopt supercomputers or computing clusters to fit standard simulation time, even though their accuracy in literature results is in line or below the average of conventional combustions simulation. After validation, these works approach the optimization of PPCI mainly focusing on fuel properties and piston bowl while implementing a single fuel injection. However, this choice cuts out the complexity of reproducing premixed-diffusive combustion stages typical of multiple injection with charge-temperature stratification. Few works have simulated the latter, but analyses are oriented towards the fuel mass split rather than on the design of the injection pattern. This work presents a validated CFD method based on fixed mesh and Progress Variable Model combustion model to design the injection pattern aiming at a solid efficiency, emissions and durability trade-off in a light-duty PPCI engine at mid-high load (10 bar, 14 bar Indicated Mean Effective Pressure). Considering a reference three-events pattern, the shift of the two early events is simulated. Simulations are run o affordable modern-workstations and completed within standard time. An improved configuration has been discovered, resulting in reduced soot and (–22 %) and Pressure Rise Rate (−25 %), moderate NOx reduction (−4%) and decent efficiency increase (+3%). The new pattern is spaced as: 41 deg BTDC; 15 deg BTDC; 1.7 deg BTDC. Overall, the improving shift direction is along anticipated 1st and delayed 2nd events.