• Split-cycle
• HCPC
• HCCI
• Diesel
• Combustion

Due to concerns regarding the greenhouse effect and limitations on carbon dioxide emissions, the possibility of a next-generation combustion mode for internal combustion engines that can simultaneously reduce exhaust emissions and substantially improve thermal efficiency has drawn increasing attention.
The presented research activity was focused on the design and development of an innovative combustion system for Diesel engines. A new approach for a low emission – high efficiency Diesel combustion was conceived: the basic idea is to control the heat release rate by a gradual supply of an almost homogeneous charge in the combustion chamber, without relying on exhaust gas recirculation or extremely diluted mixtures to moderate the combustion reactions. This new approach was defined Homogenous Charge Progressive Combustion (HCPC).
HCPC is based on the split-cycle principle. The intake and compression phases are performed in a reciprocating external compressor, which drives the air into the combustor cylinder during the combustion process, through a transfer duct. A transfer valve is placed between the compressor cylinder and the transfer duct. The compressor piston has a fixed delay, in terms of crank-angle degrees, with respect to the combustor piston. The combustion takes place after combustor TDC, thus, during the combustion process, the combustor piston moves downwards whereas the compressor piston moves upwards. As a consequence, the air moves from the compressor cylinder to the combustor cylinder. Contemporary with the air transfer, fuel is injected into the transfer duct, evaporates and mixes with the air, bringing about the conditions needed for a nearly homogeneous combustion.

The research activity carried out during the PhD course was focused on the CFD study of the HCPC engine, both for Light-Duty and Heavy-Duty applications. Preliminary results were the concept validity was tested are presented, followed by further studies and development of the engine geometry. A light duty version of the engine is firstly presented, which can run at the even better ISFC of Diesel engines at speeds that are typical of SI engines for passenger cars, maintaining a low soot emission combustion. Next a validation activity on Heavy-Duty engines is presented, where the CFD model was tested, both for performance and emission behavior. Finally two versions of an Heavy-Duty HCPC engine are presented, the latter delivering a Diesel-like indicated thermal efficiency, with ultra-clean combustion. As a matter of fact the HCPC Heavy-Duty engine can comply with EURO 6 regulations, without needing complicated and expensive aftertreatment system (i.e. SCR, LNT and/or DPF).