A Self regenerating diesel emissions particulate trap using a non-thermal plasma

There is great concern about the adverse effects associated with exposure to diesel exhaust. There is increasing evidence that diesel exhaust particulate matter (PM) is carcinogenic and may cause cancer. Non-cancerous lung damage and respiratory problems are also associated with exposure to diesel exhaust as well as acid rain and smog. Diesel exhaust PM is very easily respirable once emitted into the atmosphere and therefore poses a significant health problem. A diesel engine emissions particle removal system which utilizes Electrostatic Precipitation (ESP) and Non Thermal Plasma (NTP) technologies was studied for trapping and oxidizing micron sized particles (0.01 to 10 microns) in the exhaust. Particles are first charged in a mono polar manner in a NTP in the diesel exhaust stream, and then collected on an electrically grounded precipitation surface. Gaseous radicals produced in the NTP oxidize the precipitated particles to provide a continuously regenerating system. This device is targeted to help meet recently instituted US Environmental Protection Agency (EPA) Tier II as well as upcoming European (Euro 4, 5) and Japanese diesel particulate emissions standards. This system can be coupled with a suitable catalyst or other emissions treatment technologies to produce a complete exhaust aftertreatment system. Analytical and empirical methods were used to model the proposed Self Regenerating Diesel Emissions Particulate Trap. The analysis showed that a total particle precipitation efficiency of greater than 95% could be obtained using less than 0.5% of total engine energy output at a vehicle speed of 120 km/hr for a compact diesel powered vehicle. It was determined that the energy requirement for producing gaseous radicals in the exhaust stream is higher than is needed for particle charging and precipitation. It was also determined that the conversion of radicals can be accomplished using less than 2% of the total engine output. The results of the model developed shows that the proposed device would be effective reducing diesel PM emissions on a heavy-duty vehicle

Plasma Processes for Renewable Energy Technologies

The use of renewable energy is an effective solution for the prevention of global warming. On the other hand, environmental plasmas are one of powerful means to solve global environmental problems on nitrogen oxides, (NOx), sulfur oxides (SOx), particulate matter (PM), volatile organic compounds (VOC), and carbon dioxides (CO2) in the atmosphere. By combining both technologies, we can develop an extremely effective environmental improvement technology. Based on this background, a Special Issue of the journal Energies on plasma processes for renewable energy technologies is planned. On the issue, we focus on environment plasma technologies that can effectively utilize renewable electric energy sources, such as photovoltaic power generation, biofuel power generation, wind turbine power generation, etc. However, any latest research results on plasma environmental improvement processes are welcome for submission. We are looking, among others, for papers on the following technical subjects in which either plasma can use renewable energy sources or can be used for renewable energy technologies: Plasma decomposition technology of harmful gases, such as the plasma denitrification method; Plasma removal technology of harmful particles, such as electrostatic precipitation; Plasma decomposition technology of harmful substances in liquid, such as gas–liquid interfacial plasma; Plasma-enhanced flow induction and heat transfer enhancement technologies, such as ionic wind device and plasma actuator; Plasma-enhanced combustion and fuel reforming; Other environment plasma technologies

Electrocatalytic control of exhaust soot

The feasibility of combining electrostatic precipitation and use of a catalytic wall in a straight tube reactor as a means of destroying soot particles was investigated. Enhanced particle diffusion to the wall by an applied electric field provided the means of particle capture for subsequent catalytic oxidation at the active surface in a small length tube. Soot particles flowing in a gas stream are influenced by the following transport mechanisms: convective flux as a result of bulk flow, diffusion flux as a result of particle concentration or number density gradient, and an electrostatic flux from the coulombic attraction as charged particles move to an electrically grounded wall. When an external electric field is applied, the resulting electrostatic flux dominates the particle transport mechanism. Soot capture on a catalyst wall is by adsorption onto a catalytically active site. With sufficient oxygen present and surface temperatures near 400 °C, catalytic oxidation of soot is evident by heat released due to exothermic reactions, and increased CO and CO2 (COx) concentrations. The experimental results indicated increased catalytic activity under light sooting conditions by raising the applied voltage in stepwise increments. A voltage of -2.5 kV was found to yield the maximum COx levels and highest catalytic surface temperatures (30-60 °C). Increased oxygen concentration (\u3e 0.40 mole fraction) was the most important factor in promoting soot oxidation. Heavy sooting conditions, or a high voltage quickly applied caused rapid accumulation of particle deposition on the surface resulting in fouling the catalyst and decreasing the catalytic activity. The particle size fraction of soot flowing into the catalytic reactor from the combustor indicated a bimodal distribution. The largest peak occurred at 1.4 μm, while a smaller peak was found at 3.0 μm. A mathematical model to simulate electrostatic precipitation was developed to incorporate the use of a distribution of particle size fractions. The predicted penetration from modeling was compared with experimental results of reactor outlet soot loadings for increased voltage. Under light sooting conditions, model predictions agreed well with the trends exhibited by the experimental data for a particle satuation charge level of 35%. Additionally, the mathematical model was able to predict particle penetration along the axial tube length. The modeling was found to be in good agreement with the experimental results

Three-Dimensional Modeling of Electrostatic Precipitator Using Hybrid Finite Element - Flux Corrected Transport Technique

This thesis presents the results of a three-dimensional simulation of the entire precipitation process inside a single-electrode one-stage electrostatic precipitator (ESP). The model was designed to predict the motion of ions, gas and solid particles. The precipitator consists of two parallel grounded collecting plates with a corona electrode mounted at the center, parallel to the plates and excited with a high dc voltage. The complex mutual interaction between the three coexisting phenomena of electrostatic field, fluid dynamics and the particulate transport, which affect the ESP process, were taken into account in all the simulations. The electrostatic field and ionic space charge density due to corona discharge were computed by numerically solving Poisson and current continuity equations, using a hybrid Finite Element (FEM) - Flux Corrected Transport (FCT) method. The detailed numerical approach and simulation procedure is discussed and applied throughout the thesis. Calculations of the gas flow were carried out by solving the Reynolds-averaged Navier-Stokes equations using the commercial FLUENT 6.2 software, which is based on the Finite Volume Method (FVM). The turbulence effect was included by using the k-ε model included in FLUENT. An additional source term was added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations, using the User-Defined-Function (UDF) feature of FLUENT. The particle phase was simulated using a Lagrangian-type Discrete Random Walk (DRW) model, where a large number of particles charged by combined field and diffusion charging mechanisms was traced with their motion affected by electrostatic and aerodynamic forces in turbulent flow using the Discrete Phase Model (DPM) and programming UDFs in FLUENT. The airflow patterns under the influence of electrohydrodynamic (EHD) secondary flow and external flows, particle charging and deposition along the channel, and ESP performance in removal of submicron particulates were compared for smooth and spiked discharge electrode configurations in the parallel plate precipitator assuming various particle concentrations at the inlet. Finally, a laboratory scale wire-cylinder ESP to collect conductive submicron diesel particles was modeled. The influence of different inlet gas velocities and excitation voltages on the particle migration velocity and precipitation performance were investigated. In some cases, the simulation results were compared with the existing experimental data published in literature

Nano-particle deposition in the presence of electric field

The dispersion and deposition of nano-particles in laminar flows in the presence of an electric field were studied. The Eulerian-Lagrangian particle tracking method was used to simulate nano-particle motions under the one-way coupling assumption. For nano-particles in the size range of 5–200 nm, in addition to the Brownian excitation, the electrostatic and gravitational forces were included in the analysis. Different charging mechanisms including field and diffusion charging as well as the Boltzmann charge distributions were investigated. The simulation methodology was first validated for Brownian and electrostatic forces. For the combined field and diffusion charging, the simulation results showed that in the presence of an electric field of 10 kV/m, the electrostatic force dominates the Brownian effects. However, when the electric field was 1 kV/m, the Brownian motion strongly affected the particle dispersion and deposition processes. For the electric field intensity of 1 kV/m, for 10 nm and 100 nm particles, the deposition efficiencies for the combined effects of electrostatic and Brownian motion were, respectively, about 27% and 161.2% higher than the case in the absence of electric field. Furthermore, particles with the Boltzmann charge distribution had the maximum deposition for 20 nm particles

The Impact of Delhi's CNG Program on Air Quality

This paper estimates the impact on Delhi’s air quality of a number of policy measures recently implemented in the city to curb air pollution using monthly time-series data from 1990 to 2005. The best known of these measures is the court-mandated conversion of all commercial passenger vehicles—buses, three-wheelers, and taxis—to compressed natural gas (CNG). Broadly, the results point to the success of a number of policies implemented in Delhi but also to a number of areas of growing concern. For example, the results suggest that the conversion of buses from diesel to CNG has helped to reduce PM10, CO, and SO2 concentrations in the city and has not, contrary to conventional wisdom, led to the recent increase in NO2. At the same time, however, the conversion of three-wheelers from petrol to CNG has not had the same benefit, possibly because of poor technology. Another policy measure that appears to have had a positive impact on air quality is the reduction in the sulfur content of diesel and petrol. This has led to a decrease in SO2 levels and, because of conversion of SO2 to sulfates (a fine particle), a decrease in PM10 concentrations. Some of these gains from fuel switching and fuel-quality improvements are, however, being negated by the increase in the proportion of diesel-fueled cars, which is leading to an increase in PM10 and NO2 levels, and by the sheer increase in the number of vehicles.air pollution, compressed natural gas, low-sulfur diesel, diesel-fueled cars, Delhi

Modeling of diesel particulate emissions aftertreatment system using non-thermal plasma

There is a growing demand for energy usage in the world, primarily due to increasing economic activity. This need can be met by pursuing increased power generation. However the impact of emissions from power generation sources on the health of human beings and environmental continues to be a major concern. In order to maintain and enhance environmental quality there is a need for the development of clean energy products. A diesel aftertreatment device was developed at RIT to reduce particulate matter (PM) in the emissions of generators and diesel engines by using the combination of non-thermal plasma oxidation and emission catalyst technologies. The non-thermal plasma (corona discharge) created by a high voltage electrode produces ionized gas or plasma in the charging section of the device. Simultaneously gas atoms are excited, producing highly reactive O, OH, and NO2 radicals. These radicals oxidize PM to gaseous products including CO, and CO2. The device has a low pressure drop compared with other diesel aftertreatment devices since it selfregenerates and there is no accumulation of PM in the system. The scope of this thesis is to develop a numerical model to simulate the performance of this diesel aftertreatment device. The model calculates the diesel exhaust conditions, plasma generation condition, electric field, power consumption, particulate collection, and particle removal. The model results agree with the experimental data, which proves that the model can be used for system performance prediction. Based on keeping the same PM removal efficiency and back pressure effects on diesel engine, a method was developed for system scale-up or scale-down