F2008-09-055
Diesel Aftertreatment System Using Non-Thermal Plasma for Light-Duty Vehicle
A Non-Thermal Plasma (NTP) system is expected to be one of the alternative technologies for diesel emissions control. In electric discharge plasma, it is known that reactive species such as electrons, ions and radicals are generated. These highly reactive species can oxidize particulate matters (PM) in diesel exhaust gases. The advantages of a NTP system are a successive removal for PM emission irrespective of ambient temperature and not using precious metals. Since the NTP system doesn't need full trapping PM such as a conventional diesel particulate filter (DPF) system, the pressure loss can be reduced. In addition, PM removal efficiency is controllable by power management in accordance to the increase and decrease of PM emission in exhaust gases. We have investigated a NTP system using 2-cycle diesel engine (under developments by Daihatsu Motor). The fuel penalty and pressure loss for our NTP system has been targeted below 2.5 % and under 10 kPa, respectively. And PM emission has been targeted below 0.005 g/km to achieve Euro5 and 2009 Japanese Emission Standard in the new transient modal test (JC08). However, in order to develop a practical NTP system, there are several hurdles to overcome such as designing of the novel plasma reactor, reduction of energy consumption and improvement of the power supply system. The elucidation of PM removal mechanism is also required. In our NTP system, a dielectric barrier discharge (DBD) reactor driven by high-voltage pulses has been investigated. This DBD reactor mainly consists of some pairs of dielectric plates and electrodes. A newly developed electrode shows wide discharge space and has function of temporary trap different from full trap such as DPF. This function is very important for the purpose of extending reaction time between plasma and PM because the expected life span of plasma is extremely short and flow velocity of exhaust gases including PM is very rapid. A virtual vehicle simulator using a 2-cycle diesel engine with diesel oxidation catalyst (DOC) and an engine dynamometer, aiming to evaluate PM removal properties of the DBD reactor in various modal driving schedules, was also designed and developed by ourselves. In the JC08 Japanese modal test, PM emission was reduced below 2009 Japanese Emission Standard level (Euro5 level) with discharge power of only 210 W. It was confirmed that PM removal by our DBD reactor had selectivity in soot and soot removal rate was above 90%. However, there are still problems about the removal properties for soluble organic fraction (SOF). On the other hand, maximum pressure loss of this DBD reactor was 3.2 kPa during transient modal test. The DBD reactor with newly developed electrode showed the excellent PM removal properties and low pressure loss in transient mode. Above mentioned our NTP system is expected to be promising technology for diesel emission control.
Session: Exhaust Gas Aftertreatment