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.
Pilot-Scale Experiments of Continuous Regeneration of Ceramic Diesel Particulate Filter in Marine Diesel Engine Using Nonthermal Plasma-Induced Radicals
As the regulations governing diesel engine emissions have become more stringent, it has become difficult to fulfill these new requirements by only using techniques that improve combustion. Therefore, more effective aftertreatment technology is needed, particularly for particulate matter. Although ceramic diesel particulate filter (DPF) is a leading technology in automobiles, their implementation in marine diesel engines operated with marine diesel oil (A-heavy fuel oil) containing sulfur presents a problem, in terms of soot removal or regeneration. In this study, a pilot-scale experiment is performed to establish a method implementing nonthermal-plasma-induced radicals for DPF regeneration of marine diesel engines. The pressure difference decreases only when plasma is turned on, and DPF regeneration is realized at 320 °C. The amount of ozone required for regeneration is determined under various engine operating conditions, and the basic characteristics of regeneration are elucidated. The plasma energy required for emission control of the entire gas is approximately 5% of the generated power of the marine engine.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.