IMPROVEMENT OF IC ENGINES COMBUSTION

The oncoming stringent emission regulations require development or improvement of land vehicle engine combustion systems. In this research activity two of the most promising combustion systems were studied. The first one is Gasoline Direct Injection (GDI) in spark ignition engines; the second is Homogeneous Charge Compression Ignition (HCCI) combustion in Diesel engines. The first part of the research activity involved both 2 and 4 stroke GDI engines. In the 2 stroke activity, a numerical and experimental research was conducted on the influence of throttling in stratified charge operation, in a single-cylinder 50 cm3 engine. The research proved that some throttling lessens HC and NOx emissions. Besides, throttling decreases pumping loss and increases exhaust gas temperature at light loads, with evident advantage for catalytic converter efficiency. The 4 stroke activity concerned the applicability of Gasoline Direct Injection in a high performance engine. By means of a 3-dimensional CFD code, indirect and direct injections were compared and the benefits coming from the GDI system were quantitatively predicted. The second part of the research activity pertained homogenous combustion in Diesel engines. A new combustion concept called HCPC (Homogeneous Charge Progressive Combustion) was studied by means of a CFD code with detailed chemistry. This study demonstrated the validity of the idea and identified the key parameters which control and influence HCPC combustion. With the aim of improving the calculation methodology in Diesel and HCCI engine, a study on the effects of initialization and geometrical details on the results of CFD engine simulations was conducted. The study pointed out that the swirl number decreases when the piston and head geometrical details are included in the CFD model, affecting combustion and pollutant emission numerical predictions.