Abstract
A new Diesel combustion concept has been developed, which allows reducing both soot and NOx emissions, even at high load and engine speed, with benefits for thermal efficiency as well.
The concept consists in forming a pre-compressed homogeneous charge outside the cylinder and in gradually admitting it into the cylinder during the combustion process. In this way, combustion can be controlled by the transfer flow rate and high pressure rise rates, typical of standard HCCI combustion, can be avoided. This new combustion concept has been called Homogenous Charge Progressive Combustion (HCPC).
HCPC is based on 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 positioned 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 homogeneous combustion.
Keywords: HCPC, Diesel, HCCI, split-cycle, soot