Experimental study of pollutant emission reduction for near-stoichiometric diesel combustion in a three-way catalyst

Abstract

An experimental study was performed to examine the possibility of simultaneous reductions of NO x, hydrocarbons (HC), CO, and soot emissions for near-stoichiometric diesel combustion using a three-way catalyst and a diesel particulate filter (DPF). The DPF was deactivated in order to ensure the non-regeneration state and was just used as a soot filter trap upstream of the three-way catalyst. The goal of the research was to investigate the efficiency of emission conversion for an automotive diesel engine with a general three-way catalyst normally used for gasoline-powered vehicles under near-stoichiometric combustion operation. A modified single-cylinder engine was used for the experiments that considered throttled diesel combustion at 65–90 kPa intake pressure to achieve near-stoichiometric conditions, and a common rail injection system with 90 MPa injection pressure was used for mixture preparation and to avoid spray wall impingement. The results showed that the three-way catalyst was able to reduce NO x and CO emissions by up to nearly 98 per cent, and the DPF trapped soot emissions up to 99.6 per cent for near-stoichiometric operation. However, the particular palladium/rhodium catalyst formulation used in the study was less effective for HC emissions, which were only reduced by up to 57 per cent. It is concluded that the use of the present proposed three-way catalyst/DPF aftertreatment system provides significant promise for future efficient, low emission diesel engines.