Effects of Premixed Low Temperature Combustion of Fuel Blends with high Resistance to Auto-ignition on Performances and Emissions in a High Speed Diesel Engine

This paper reports results of an experimental investigation to demonstrate the potential to employ blends of fuels having low cetane numbers that can provide high resistance to auto-ignition to reduce simultaneously NOx and smoke. Because of the higher resistance to auto-ignition, blends of diesel and gasoline at different volume fraction may provide more time for the mixture preparation by increasing the ignition delay. The result produces the potential to operate under partially premixed low temperature combustion with lower levels of EGR without excessive penalties on fuel efficiency. In addition to the diesel fuel, the tested blends were mixed by the baseline diesel with 20% and 40% of commercial EURO IV 98 octane gasoline by volume, denoted G20 and G40. The experimental activity has been performed on a turbocharged, water cooled, DI diesel engine, equipped with a common rail injection system. The engine equipment includes an exhaust gas recirculation system controlled by an external driver, a piezo-quartz pressure transducer to detect the in-cylinder pressure signal and a current probe to acquire the energizing current to the injectors. Engine tests have been carried out at the engine speeds of 2500 rpm and a BMEP of 0.8 MPa exploring the effect of the start of injection, exhaust gas recirculation, injection pressure on combustion behavior and engine out emissions. The main results of the investigation have provided to realize a premixed low temperature combustion by the management of EGR rate, injection pressure and the longer ignition delay induced jointly by the higher resistance to auto ignition of fuel blends and their higher volatility. Results of smoke emissions have been cut down to zero for G20 and G40 blends at moderate level of injection pressure and oxygen concentration at the intake.