Analysis of the influence of pre-DPF water injection technique on pollutants emission

Abstract

The pressure drop across DPFs directly affects the exhaust back-pressure and fuel economy of compression ignition engines. Pressure drop is related to the soot trapped inside the DPF, increasing exhaust back-pressure as the soot mass loading does. Consequently, regeneration strategies are required to remove the soot collected in the DPF. However, these processes usually involve additional fuel consumption. Considering this context, control techniques to reduce the exhaust back-pressure dependence on DPF soot loading are arising. One technique is based on the pre-DPF water injection events to get an optimum redistribution of the soot layer leading to a reduction of DPF pressure drop. This paper is focused to establish a comprehensive analysis of the change in pollutants emitted due to this technique application. The effects of this technique on filtration efficiency and particle size distribution are also analysed during and after a DPF loading test. Results have shown a dilution effect on gaseous compounds and a negligible particle emission during the pre-DPF water injection event (<2 mg), increasing PSD mode downstream the DPF to the mode of the raw emission. Nevertheless, there are not relevant effects on overall filtration efficiency, which keeps value comparable to baseline operation clearly higher than 99%.