Non Thermal Plasma Aftertreatment of Particulates - Theoretical Limits and Impact on Reactor Design

Increasingly stringent emissions legislation has resulted in a requirement for aftertreatment technologies capable of removing nitrogenous oxides (NOx) and particulate matter (PM) from lean exhaust environments.

Non-thermal plasma (NTP) has been studied previously as a potential candidate for lean exhaust aftertreatment. Both experimental and theoretical work, however, has suggested that the energy cost for the complete gas-phase oxidation of particulates and hydrocarbons is too large for practical consideration in vehicle applications.

It is shown that, by introducing a packing material into a NTP reactor, it is possible to increase the residence time of species within the plasma region. By increasing the residence time selectively, the level of oxidation of species may be decoupled from the energy deposition into the exhaust gas, thus allowing complete oxidation to be achieved more economically than previously predicted. An upper limit to the energy required for the NTP low temperature oxidation of carbonaceous PM in diesel exhaust is determined as 0·34 kW -hr/g.