Innovative Emission Aftertreatment System for Super Clean Diesel Engine Using Nonequilibrium Plasma Process

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A new type plasma exhaust cleanup system for super clean diesel engine in near future is developed and basic study on it is carried out. This research is characterized by utilizing low-temperature nonthermal and nonequilibrium plasma. Research and development of "1. Nonequilibrium plasma DPF (Diesel particulate filter) regeneration" and "2. Nonequilibrium plasma desorption and reduction of NOx" are made. The following results are obtained.1.Nonequilibrium plasma DPF regeneration : A new incineration regeneration system of the diesel particulates trapped by the DPF is demonstrated and the performance is optimized using the atmospheric-pressure nonthermal plasma. In this system, NO_2, ozone and negative ion radical clusters excited with the nonthermal plasma are introduced into the DPF to realize the removal of the diesel particulate nearly at the room temperature. Using a small diesel engine, continues regeneration during the engine operation is performed nearly at the exhaust gas of 20 … More 0℃. Energy consumption is further decreased down to 1 Wh/m^3.2.Nonequilibrium plasma desorption and reduction of NOx : In the exhaust gas of diesel engines, the oxygen of approximately 2〜10vol.% is usually contained. Applying the plasma to such exhaust gas, the total NOx (= NO + NO_2) amount hardly decreases because most of NO contained in the exhaust gas is only oxidized to NO_2, This process is not considered to be a real pollution control process. Therefore, the following new process is proposed : In the oxygen rich state, the exhaust gas containing NOx is first adsorbed to the adsorbent in the reactor. After the NOx adsorption reaches saturation, either N_2 gas or the exhaust gas containing much HC, CO and less O_2 obtained by changing the engine operation mode is introduced into the reactor with the small flow rate, applying the plasma. As a result, the desorption and reduction of NOx, and oxidization of HC and CO are carried out simultaneously. More than 85% removal with the energy efficiency of 22Wh/m^3 for 250 ppm NOx is achieved in the laboratory test. Furthermore, the examination of the present system treating the whole exhaust gas of a small diesel engine (200cc) is carried out. The operation procedure and validity of the system are confirmed.3.The numerical simulation of nonequilibrium plasma chemistry is performed and the detailed mechanisms (chemical reactions) of the plasma exhaust gas processing are clarified. Less