A Two Dimensional Numerical Soot Model for Advanced Design and Control of Diesel Particulate Filters

One of the most effective methods to control diesel particulate matter (PM) emissions from heavy duty diesel engines is to use wall flow diesel particulate filters (DPF). It is still a major challenge to get an accurate estimation of soot loading, which is crucial for the engine afterteratment assembly optimization. In the recent past, several advanced computational models of DPF filtration and regeneration have been presented to assess the cost effective optimization of future particulate trap systems. They are characterized by different degree of detail and computational costs, depending on the specific application (i.e diagnostics, control, system design, component design etc).;The objective of this study is to compare in detail a two dimensional (2-D) approach with a one dimensional (1-D) approach, thus giving a better insight of the variation of properties over the DPF length. This task has been archived by extending an in-house developed 1-D numerical soot model to the next dimension to understand the impact of 2-D representation to predict both steady state and transient behavior of a catalyzed diesel particulate filter (CDPF). Performance of the model was evaluated using three key parameters: pressure drop, filter outlet temperature and soot mass retained in the filter during both active and continuous regeneration events. Quasi-steady state conservation of mass, momentum and energy equations were solved numerically using finite difference methods adopting a spatially uniform mesh. The results obtained from the current model were compared with the 1-D code to evaluate the general validity of assumptions made in the latter, especially DPF loading status prediction.;The model was validated using the data gathered at the West Virginia University Engine and Emissions Research Laboratory (WVU-EERL) using a model year 2004 Mack MP7-355E Diesel engine coupled to a Johnson Matthey catalyzed diesel particulate filter (CDPF) exercised over a 13 mode European stationary cycle (ESC) followed by two federal transient cycles (FTP). A constant set of model tuning parameters were maintained for the sake of general validation of simplifying assumptions of the 1-D code.;The analysis shows that the predicted pressure drop across the DPF is in good agreement with the data obtained at EERL in both steady state and transient cycles. It is also shown that the soot accumulates mainly in the frontal and rear parts across the filter length under given soot concentrations. The model is capable of tracking DPF soot mass satisfactorily with a maximum discrepancy of 3.47g during steady state cycle. A 7.95% decrease in soot layer thickness can be seen in the front portion of the DPF during the transient cycle mainly due to O2 assisted regeneration at elevated temperatures. Both 1-D and 2-D models produce similar results during the loading phase. However, the current model is able to capture regeneration phase of the FTP cycle more descriptively than the 1-D model. The discrepancy of the reported total soot mass estimation between two models was 2.12%. The distribution corresponding to the 1-D model is representative of soot layer distribution given by the 2-D model at one tenth distance away from the DPF front face. 1-D model representation is effective towards PM prediction, although presenting considerable axial effects at higher DPF temperatures

On Soot Sampling: Considerations when Sampling for TEM Imaging and Differential Mobility Spectrometer

Particulate matter (PM) has been sampled from a compression ignition engine using a differential mobility spectrometer (Cambustion DMS 500) and for imaging in a transmission electron microscope (TEM) with the aim of coupling these two measuring techniques. A known issue when coupling these two methods is that a devise like the DMS samples all PM, and the TEM only soot. To help resolve this issue, a thermal denuder was designed and built to remove all volatile organic compounds (VOC) from the sample prior to entering the DMS. For TEM imaging, soot was either collected directly onto a TEM grid using the thermophoretic effect or collected onto quartz filters with the soot then transferred onto the TEM grids. The direct to grid technique did not work after the denuder due to the gas temperature being too low for the thermophoretic effect; hence the reason to collect some soot using the quartz filters. Soot was removed from the filters using an ethanol wash/sonication technique. Morphology; diameter of gyration, projected area, primary particle size and fractal dimension have been compared between the two TEM sampling techniques, with or without the denuder. Denuder effectiveness has been assessed using TGA analysis of sampled soot. Issues concerning the sampling process itself are outlined. A comparison between the TEM and the DMS results is conducted with the discrepancies between them discussed. Direct and filter sampling gave similar results as long as the sonication process and grid prep is done properly, otherwise the filter wash technique results in a number of clusters of agglomerates which distorts the post processing and morphological data

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

Influence of a thermal denuder on diesel exhaust particle size distributions

Particle size distributions in diesel exhaust were studied using a thermal desorption technique to determine the volatile and non-volatile fractions. A thermal denuder was designed and characterized for optimal operating parameters and its influence on the exhaust chemistries studied using diesel engine exhaust. The study was conducted on a 1992 DDC Series 60 engine mounted on a heavy-duty direct current dynamometer and exercised over steady state and transient cycles. The particle size distributions were recorded upstream and downstream of the denuder maintained at different temperatures to determine the behavior of the volatile fraction. The volatilization technique was also applied to the crankcase emissions in light of the 2007/2010 EPA regulations. The SMPS was used to obtain the particle size distributions from the sample gases diluted by an ejector diluter system. With the removal of the volatile fraction from the sample exhaust a shift in the size distribution towards the lower end of the spectrum was observed. (Abstract shortened by UMI.)

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

Numerical Simulation of a Wall-Flow Particulate Filter Made of Biomorphic Silicon Carbide Able to Fit Different Fuel/Biofuel Inputs

To meet the increasingly strict emission limits imposed by regulations, internal combustion engines for transport applications require the urgent development of novel emission abatement systems. The introduction of biodiesel or other biofuels in the engine operation is considered to reduce greenhouse gas emissions. However, these alternative fuels can affect the performance of the post-combustion systems due to the variability they introduce in the exhaust particle distribution and their particular physical properties. Bioceramic materials made from vegetal waste are characterized by having an orthotropic hierarchical microstructure, which can be tailored in some way to optimize the filtration mechanisms as a function of the particle distribution of the combustion gases. Consequently, they can be good candidates to cope with the variability that new biofuel blends introduce in the engine operation. The objective of this work is to predict the filtration performance of a wall-flow particulate filter (DPF) made of biomorphic silicon carbide (bioSiC) with a systematic procedure that allows to eventually fit different fuel inputs. For this purpose; a well-validated DPF model available as commercial software has been chosen and adapted to the specific microstructural features of bioSiC. Fitting the specific filtration and permeability parameters of this biomaterial into the model; the filtration efficiency and pressure drop of the filter are predicted with sufficient accuracy during the loading test. The results obtained through this study show the potential of this novel DPF substrate; the material/microstructural design of which can be adapted through the selection of an optimum precursor.Ministerio de Economía y Competitividad de España (MINECO) MAT2013-41233-RMinisterio de Economía y Competitividad de España (MINECO) BES-2014-069023Ministerio de Economía y Competitividad de España (MINECO) EEBB-I-17-1233

Nanoparticle measurement methods in internal combustion engines

The primary objective of this study is to investigate the characteristics of nanoparticle formation in dilute exhaust streams from diesel engines. Nanoparticle formation may be due to condensation, homogenous nucleation, coagulation and adsorption from low temperature, sulfate and water in exhaust system. After being released from the tail pipe, new nanoparticles also might be formed due to nucleation growth from low dilution ratio and long residence time. On the other hand, nanoparticles might be formed from dilution tunnels themselves. The artifact formation in dilution tunnels is due to specific problems that may occur in a dilution device, such as dilution ratio, dilution air temperature, dilution air pressure, residence time and critical flow orifice. The experimental apparatus consists of a variable residence time, micro dilution system for exhaust dilution. Particle detection instruments consist of a scanning mobility particle sizer (SMPS), a condensation particle counter (CPC), and a NOx analyzer. Exhaust from modern diesel and gasoline engines was analyzed. Two dilution devices were designed to simulate the process of engine exhaust into the atmosphere. For high dilution ratio from 5 to 10,000:1 and variable long residence time of 50 to 2000 ms, a first dilutor, Dilutor I, was used. For low dilution ratio from 5 to 300:1 and short fixed residence time of 50 ms, a second dilutor, Dilutor II, was used. Temperature, dilution ratio, and residence time were controllable. A NOx analyzer was used to check dilution ratio. A series of experiments was done to calibrate the dilutors. The results showed that the dilution devices alter particle size if particles were not solid. Particle size measurements were taken upstream and downstream of a diesel particulate filter (DPF) with residence time changing from 50 ms to 700 ms, which increased nanoparticle concentrations by up to two orders of magnitude. Nanoparticles below about 20 nm in diameter were higher than in Microwave Regeneration Particulate Filter (MRPF) exhaust engine out during DPF regeneration. The research should help for any future measurements of nanoparticles. The nanoparticle formation and growth under different dilution conditions needs to be investigated further. A nanoparticle formation model could be built to understand homogenous nucleation. Due to the complex nature of the atmospheric dilution process, a dilution system could be developed in the laboratory to imitate the atmospheric processes. The University of Tennessee, Knoxville (UTK) and the Oak Ridge National Laboratory have joined in this research. The Graduate Automotive Technology Education (GATE) Center of UTK, sponsored by U.S. Department of Energy (DOE), was the main participant, and the research was be conducted at Advanced Propulsion Technology Center (APTC), a research and evaluation laboratory for new internal combustion engines and emissions controls technologies. The DOE Office of Heavy Vehicle Technologies sponsored the research

Measurement of particulate matter size, concentration and mass emissions from in-use heavy duty vehicles

As technological advancements lower heavy duty vehicle particulate matter (PM) mass emission rates, there is concern that these improvements are increasing the toxicity of the PM by virtue of a subsequent reduction in particle size. These ultrafine particles are able to better penetrate the alveolar region where they can cause serious lung disorders. Alternative fuels such as compressed and liquefied natural gas (CNG and LNG) and the synthetic diesel fuel Mossgas are attractive in that they reduce the levels of total PM. However, use of natural gas in internal combustion engines may produce a larger number of smaller particles than commercial diesel fuel, and little particle size information is available on Mossgas combustion.;The tests showed the effectiveness of the measurement system while returning mass and size data for the various fleets. The particulate measurement system allowed this full description of particle emissions to be performed quantitatively rather than mathematically

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