A numerical investigation of the regeneration characteristics of diesel particulate filters under simulated transient exhaust conditions

Abstract

Particulate emissions from diesel engines, which have hazardous effects on living beings and environment, can be controlled by employing diesel particulate filters (DPFs). The DPF cleans the exhaust by physical trapping of the particulates. A major challenge in developing a DPF with wider applications is its lower durability. The filter durability may be increased by careful design of regeneration (soot oxidation) strategies, which restrict the peak filter temperature to below 900–1000°C. The regeneration characteristics of a DPF under steady state conditions are well known. However, during a typical driving cycle, a DPF is subjected to various transient conditions owing to changes in driving modes. These transients result in fluctuations of exhaust flowrate, gas composition, and temperature, which strongly influence the DPF performance and regeneration characteristics. The objective of this paper is to investigate the thermal and catalytic fuel additive-assisted regeneration characteristics of a DPF computationally under simulated time-varying exhaust conditions. The time-varying conditions were simulated by considering sinusoidal modulations in exhaust gas temperature and the mass flowrate at the filter inlet. The study employed a one-dimensional mathematical model, which was validated with experimental measurements under different operating conditions. The results showed that the filter dynamic behaviour is different from that under steady state conditions, and it is strongly influenced by the soot loading and the exhaust flow characteristics. The imposed modulation is found to initiate soot oxidation at a lower mean temperature and thus to have a positive effect on the filter regeneration efficiency (soot oxidation rate) for both thermal and catalytic fuel additive-assisted regeneration mechanisms. The modulation effects are found to be important at low frequencies, which gradually disappear at higher frequencies.