Fuel economy benefits in internal combustion engines due to soot restructuring in the particulate filter by water injection

Abstract

Wall-flow particulate filters are key elements to control particulate matter emissions. The stricter emission standards also for non-road mobility machinery makes this device essential to improve the air quality in the short to medium term. However, their high filtration efficiency brings with it an increase in backpressure. This effect becomes more damaging as particles get accumulated in the filter and in hybrid vehicles where exhaust temperature are lower due to more frequent cold starts. Pre-filter water injection is a proven method to reduce the impact of soot load on the pressure drop avoiding the fuel consumption increase. In this paper, the effect of pre-filter water injections is analysed in engine and flow test rig environments. After verifying the impact of consecutive injection events on fuel consumption, the filter was loaded and divided into quarters. These were studied one at a time in flow test rig to separate soot mal-distribution from water drag effects. A wide range of conditions were tested to assess the change in pressure drop generated by a single injection. With this reference, the soot restructuring pattern was analysed employing optical techniques. These provided evidences of the way the soot fragments got released from the particulate layer and moved towards the inlet channels rear end. Additionally, a closer look into the porous wall micro-structure provided insights explaining the lack of effect on filtration efficiency. These results provide a basis for synergistic removal of vehicle condensates for use in fuel consumption reduction.