Improvements to Premixed Diesel Combustion with Ignition Inhibitor Effects of Premixed Ethanol by Intake Port Injection

摘要

Premixed diesel combustion modes including low temperature combustion and MK combustion are expected to realize smokeless and low NO_x emissions. As ignition must be delayed until after the end of fuel injection to establish these combustion modes, methods for active ignition control are being actively pursued. It is reported that alcohols including methanol and ethanol strongly inhibit low temperature oxidation in HCCI combustion offering the possibility to control ignition with alcohol induction. In this research improvement of diesel combustion and emissions by ethanol intake port injection for the promotion of premixing of the in-cylinder injected diesel fuel, and by increased EGR for the reduction of combustion temperature. The smoke emission was reduced with promotion of premixing due to longer ignition delay and shorter injection period of diesel fuel with ethanol port injection, and the NO_x was reduced with decreases in intake oxygen content by EGR regardless of ethanol quantity. When ethanol quantity was set to 20% of the total energy supply and intake oxygen was reduced to 15% with EGR, smokeless and low NO_x operation was established over a wide load range. It was revealed that the compression ratio should be reduced to promote premixing of the diesel fuel with ethanol as long as misfiring and knocking do not occur. The combination of premixed ethanol and EGR can achieve smokeless and ultra-low NO_x combustion even with the fuel injection pressure of 60 MPa. Although a high concentration of acetaldehyde is emitted with the ethanol port injection, an oxidation catalyst in the exhaust system can remove the emissions for all but extremely light engine load conditions.