Regeneration of diesel particulate filter using sliding discharge
Diesel particulate filter (DPF) is widely used to trap fine soot particles emitted from diesel engines. It can collect particles as small as submicron but it is necessary to oxidize accumulated particles by heating the filter. Temperatures of 600 degree C or higher is required to oxidize the soot but it is difficult to maintain stable reaction because this is exoergic reaction. The filter is sometimes damaged due to thermal runaway of the reaction. To address this trade-off problem, we have studied low temperature regeneration of DPF using sliding discharge, which can be generated on the surface of DPF and produces oxidative species at room temperature. Diesel soot collected by DPF was used. Simulated air consisting of N2 and O2 and not including CO2 or CO was used and CO and CO2 concentration was monitored by real time FTIR to estimate the soot oxidation. All the experiment was carried out at temperatures between 100 and 190 degree C to simulate exhaust temperature under low load. Experimental results show that soot was oxidized by generating sliding discharge on the DPF. No thermal damage of the DPF was found. Energy efficiency, denoted by the amount of oxidized soot per electric energy dissipated in the sliding discharge, increased with increasing the temperature as well as oxygen concentration in the test gas. Small amount of Ag2O supported by the DPF significantly increase the energy efficiency of soot oxidation. On the contrary, excessive amount of Ag2O resulted in energy efficiency lower than that of DPF without Ag2O probably because the sliding discharge was not generated favorably due to high conductivity resulted from metal Ag. These results suggest that sliding discharge can induce soot oxidation and that Ag2O possibly catalyzes soot oxidation.
Continuous Regeneration of Ceramics Particulate Filter in Stationary Diesel Engine Using Nonthermal Plasma-Induced Ozone Injection
The regulation for the diesel engine emission becomes stringent every year, and it is difficult to meet the requirement only by the combustion improvement techniques in the near future. More effective post-processing technology is desired especially on particulate matter (PM), such as carbon soots. Although the use of ceramic diesel particulate filter (DPF) is now a leading technology for PM removal, the problem exists on the soot removal or regeneration at low temperature, especially at the cold start. In the present study, a pilot scale experiments on nonthermal plasma regeneration of diesel particulate filter in stationary diesel engine generator is carried out using the low temperature atmospheric pressure nonthermal plasma induced ozone injection. In the method, the NO2 and ozone induced by the plasma reactor is used to burn carbon soots deposited on DPF. Regeneration experiment is carried out with a small diesel engine and a surface discharge type plasma ozonizer. The amount of injected ozone required for the regeneration is determined under various operation conditions of the engine, It is confirmed that the pressure difference decreased only when the plasma is turned on and the regeneration of DPF is realized approximately at 250degC. The required plasma energy is only 0.25% of the generated power of the engine.
On the characteristics of the corona discharge in a wire-duct reactor
The aim of this paper is to study the effects of the magnitude and direction of air flow rate on the characteristics of the corona discharge generated in a wire-duct reactor. Two air flow directions were attempted: one parallel to, and the other normal to the discharge wire in the reactor. The corona current-voltage characteristics correlative with ozone generation were studied under different modes of applied voltage. The results have shown that dc and ac corona current-voltage characteristics depend significantly on the magnitude of the air flow rate in the reactor, whatever the direction of the air flow. The ozone concentration generated by either dc, ac or pulsed coronas with parallel flow is higher than that generated with normal flow with the same discharge conditions. The ozone concentration generated by pulsed coronas is higher than that generated by either dc or ac coronas with the same discharge conditions irrespective of the polarity of the pulsed corona.