Interaction between soot particles and NOx during dielectric barrier discharge plasma remediation of simulated diesel exhaust

Abstract

Plasma remediation is being investigated as a means to remove NOx from combustion effluent and from diesel exhausts in particular. Soot particles are inevitably present in actual exhausts and may, through heterogeneous chemistry, affect the remediation process. In this article, a computational investigation of the effect of soot on the plasma chemistry of NOx removal in a simulated diesel exhaust processed in a dielectric barrier discharge reactor is presented using a zero-dimensional global-kinetics simulation. A surface chemistry model is employed to describe soot oxidation by O and OH radicals, and soot-NOx interactions. The NOx chemistry may be substantially affected by the reactions at the soot surface. In particular, for soot particles having densities of 108 cm−3 and diameters of 100 nm, significant increases of NO are obtained when taking into account NO2→NO conversion on the soot surface. Heterogeneous reaction of NO2 also results in an increase in the gas-phase OH density which results in the increased formation of HNO2, thereby adding to the NOx remediation. NO2→NO heterogeneous conversion also results in an increase of CO and a subsequent reduction of the soot mass. The mechanism for soot-NOx interactions depends on the deactivation of active hydrocarbon radicals on the soot.

Experimental investigation on diesel PM removal using uneven DBD reactors

“…4 They found that PM size and mass fraction are reduced in the pulsed corona discharges (energy density 38 J/L), respectively, from 100 to 60 nm and 1.0 to 0.21 after 0.2-s discharge times. The PM mass fraction loss is initiated by reactions with NO 2 which accounts for about 99.9% of the loss.…”

“…4 However, it is still unknown how PM is removed under plasma discharge conditions. In this study, we measure PM size changes and PM oxidation products due to plasma discharges generated using an uneven DBD reactor installed in the tail pipe of a diesel engine and using a model DBD reactor.…”

O 2 ( Δ 1 ) production in He∕O2 mixtures in flowing low pressure plasmas

“…Ideally the gases are cooled to around 140 K as they flow through the laser cavity and are drawn into the exhaust system. 23 GlobalKin, a global plasma kinetics model, 24 was modified to simulate steady-state plug flow for this investigation. GlobalKin consists of three main modules: a reaction chemistry and transport module, a Boltzmann equation solver for the electron energy distribution (EED), and an ordinary differential equation (ODE) solver module.…”

Plasma-Based Depollution of Exhausts: Principles, State of the Art and Future Prospects

“…When only hydrocarbons have been used as catalysts, the NOx reduction above 70 % has been achieved in temperature range of 170°C to 260°C with BaY zeolite (space velocity 12,000 h -1 ) and by using both BaY and γ-Al 2 O 3 the temperature range has been extended to 500 °C (Kwak et al, 2004). For real diesel exhaust gases, the reduction efficiencies are usually smaller because of the presence of particles which reduce NO 2 back to NO (Dorai et al, 2000). Diesel exhaust gas of an Multicar M25-10 engine (1,997 cm 3 , without catalyst) having gas flow of 10 sl/min (space velocity 20,000 h -1 ) and typically 434 ppm NOx was treated with plasma-enhanced catalysis where catalyst was placed downstream from the plasma reactor (Miessner et al, 2002).…”