Diesel Exhaust Gas Research Articles

DPFの初期PM捕集性能に対する表面粗さの影響(熱工学,内燃機関,動力など)

In recent years, environmental regulation tends to become strict rapidly, and the further highly performance of DPF is demanded, which mainly consists of surface filtration and depth filtration. Generally, if the wall thickness is thin, the soot in diesel exhaust gas may break through and leak the filter, because the depth filtration doesn't work enough. However, most of filtration efficiency depends on surface filtration, because the soot cake forms on the surface of ceramic filter, and the soot cake takes part in highly performance of the filter. Therefore, the most important thing is how to make the soot cake rapidly. In this study, we pay attention to the surface roughness of ceramic filter. We observed the micro-porous structure of the filter based on SEM images. Also, we measured soot diameter and particle number concentration using different filters. Results show that, when too big open and too deep pore exist on the filter surface, the soot leakage occurs easily. In this case, it's hard to make soot layer rapidly and the soot leaks during initial DPF usage. Once the soot layer is formed, the filtration efficiency becomes high, and small particulates called SPM are caught effectively. Thus, it is important to control surface roughness for making soot layer rapidly.

Automatic Control Method of NO Removal by a Combination of Ozone Injection and Exhaust Gas Recirculation

NOx from diesel exhaust gases can efficiently be removed by a combination of ozone injection and exhaust gas recirculation (EGR). To industrialize the system, it is necessary to develop a NO control system because the NO concentration largely changes by an engine output power. In this paper, we constructed a NO control system without using any sensor. As for the control method, we adopted two control methods: 1) an ozone control under a predetermined rate of the EGR and 2) an energy minimum control. The details of the automatic control methods are introduced in this paper. NO control experiments were carried out using a 2.4-kVA diesel engine generator, and the NO emissions were successfully controlled by the system.

307 SEM観察と初期PM捕集過程の検討(大気環境保全・改善技術(2))

In recent years, environmental regulation tends to become strict rapidly, and the further highly performance of DPF is demanded, which mainly consists of surface filtration and depth filtration. Generally, if the wall thickness is thin, the soot in diesel exhaust gas may break through and leak the filter, because the depth filtration doesn't work enough. However, most of filtration efficiency depends on surface filtration, because the soot layer forms on the surface of ceramic filter, and the soot layer takes part in highly performance of the filter. In this study, we pay attention to the surface roughness of ceramic filter with soot layer forming. We observed the micro-porous structure of the filter based on SEM images, and measured surface roughness of initial PM filtration of DPF. Also, we measured particle number concentration and particle size distribution at the DPF exit. Results show that, as the soot layer is formed on the filter surface, the filtration efficiency becomes high and the surface roughness becomes smooth. Thus, it is confirmed that there is a relationship between filtration efficiency and surface roughness.

Preparation and Characterization of Cu<sub>1-x</sub>K<sub>x</sub>Fe<sub>2</sub>O<sub>4</sub> Fibers and the Catalytic Activity for Diesel Engine Exhaust Removal

A series of complex oxide Cu1-xKxFe2O4 fibers have been prepared via a sol-gel process related electron-spinning procedure, in which x is among 0, 0.05, 0.1 and 0.2 corresponding to the quantity of Cu2+ partial substitution by K+. The average diameter of the fiber was 500 nm. The catalytic activity of the catalysts in removal of NOx and carbon black from diesel exhaust gases were examined in detail using temperature-programmed reaction technique. The results show that after partial substitution of Cu2+ with K+, the catalytic activities have been improved. Cu0.95K0.05Fe2O4 as an optimal catalyst can significantly decrease the ignition temperature (Tig) of the PM, and has high catalytic activity on the removal of NOx.

連続再生式ディーゼルフィルターにおけるすすの燃焼と堆積の数値解析(熱工学,内燃機関,動力など)

Since particulate matters (PM) emissions including soot from diesel cars do harm to our health, a diesel particulate filter (DPF) has been used in the after-treatment of exhaust gas. It is reported that DPF filling with PM causes higher back-pressure and more fuel consumption, and continuously regenerating PM trap system is needed. Then, we have focused on the diesel exhaust gas perfect burning system (DEGPBS) developed by COTEC, Ltd., where soot is trapped and burned by the heater. However, the phenomena in the system are not well understood, because it is difficult to conduct the measurement inside the filter. In this study, we simulated soot combustion and deposition by the lattice Boltzmann method to observe the combustion field in the filter. The inner structure of the filter was obtained by a 3D X-ray CT technique. Results show that the heat and mass transport in DEGPBS are well visualized. It is found that temperature of the filter and oxygen concentration are important factors to burn soot in exhaust gas.

Comparison of the effect of soot deposition on the flow and thermal characteristics of finned-plate-type and shell-and-tube-type exhaust gas recirculation cooling devices

Experiments were conducted to characterize the effect that diesel soot deposition has on the operational characteristics of a finned-plate-type compact exhaust gas recirculation (EGR) cooling device for Reynolds numbers from approximately 900 to 1200, typical of the values used in EGR applications. The results show that the Colburn j factor did not change significantly during diesel exhaust gas exposure for 5h at the lower Reynolds number, but the j factor and friction factor changed by 30–40 per cent during exposure for 5h at the Reynolds number of 1200. The Colburn j factor and friction factor for the plate-type device changed more slowly than those results for shell-and-tube heat exchangers at Reynolds numbers of 7000–9000, typical of the values used for these devices in EGR applications. Thus, the results show that the finned-plate-type compact heat exchanger operational characteristics should be less affected by soot deposition than the shell-and-tube devices in EGR applications.

A Novel Approach to Catalysis for NO x Reduction in Diesel Exhaust Gas

With the introduction of stringent emission standards in the US in 2007 (Tier II Bin8, 5) an exhaust aftertreatment for NOx reduction is required for compliance with the emission regulations. A new approach consists in the synergetic combination of existing technologies NSC (NOx Storage Catalyst) and SCR (Selective Catalytic Reduction) with onboard generation of ammonia as the reducing agent for the SCR. It is shown in this work that the performance of the combined system exceeds those of each one considered separately, especially after ageing. The generation of ammonia is correlated to the ammonia selectivity during the regeneration of the NSC. The selectivity is primarily dependent on the temperature, A/F ratio (Air/Fuel) and the rich time. It is shown that the development of a suitable control strategy leads to a high level of NOx reduction under transient conditions in an FTP driving cycle. Due to the complexity and high development costs of current exhaust aftertreatment systems, modelling and simulation were identified as an important aspect in the development process. A system simulation tool named ExACT (Exhaust Gas Aftertreatment Components Toolbox) developed at Daimler is presented. By using the simulation already at an early stage, specific development work can be carried out prior to the experimental work on an engine test bench.

Re-evaluation and Modeling of a Commercial Diesel Oxidation Catalyst

A modeling approach to predict the performance of a commercial diesel oxidation catalyst (DOC) under actual vehicle operating conditions is presented in this study. Prior to completing this prediction, the performance characteristics of DOCs, as previously published, are examined to validate the currently developed in-house computational code. Steady-state experiments with DOCs mounted on a light-duty four-cylinder 2.0-L turbocharged diesel engine then are performed, using an engine-dynamometer system to calibrate the kinetic parameters such as activation energies and pre-exponential factors of heterogeneous reactions. The reaction rates for CO, HC, and NO oxidations over a fresh Pt/Al2O3 catalyst are determined in conjunction with a transient one-dimensional (1D) heterogeneous plug-flow reactor (PFR) model with diesel exhaust gas temperatures in the range of 150−450 °C and space velocities in the range of (1−5) × 105 h−1. To determine the kinetic parameters that best fit the experimental data, a two-step...

Towards practical application of lanthanum ferrite catalysts for NO reduction with H 2

A series of perovskite-type catalysts (LaFeO 3, La 0.8Sr 0.2FeO 3, Pd/La 0.8Sr 0.2FeO 3, La 0.8Sr 0.2Fe 0.9Pd 0.1O 3, La 0.7Sr 0.2Ce 0.1FeO 3, Pd/La 0.7Sr 0.2Ce 0.1FeO 3 and La 0.7Sr 0.2Ce 0.1Fe 0.9Pd 0.1O 3) has been prepared by the solution combustion synthesis method and fully characterized by XRD, BET, FESEM and TPD/R analyses. The performance of these catalysts towards the NO reduction mechanism by H 2 has been evaluated in a temperature-programmed reaction apparatus (TPRe) in the absence and in the presence of oxygen. The catalysts have been studied in the 25–350 °C temperature range, and significant catalytic activities were measured at 150–250 °C. Among the catalysts screened, La 0.8Sr 0.2Fe 0.9Pd 0.1O 3, showed the best performance. Hence, it was deposited directly over a ceramic honeycomb monolith by in situ SCS, tested in a lab-scale test rig, then submitted to the specific ageing protocol (thermal treatment at 500 °C for 96 h) in the presence of water vapour and sulfur dioxide, two potentially deactivating species present in diesel exhaust gases, and it showed a good compromise between satisfactory catalytic activity and stability. A mechanistic analysis is presented concerning the relationship between the observed activity and the reducibility of the B site, determined through TPR experiments. Some final conclusions are drawn on the perspective of the practical application of the investigated aftertreatment route for diesel exhaust gases.

NO SCR reduction by hydrogen generated in line on perovskite-type catalysts for automotive diesel exhaust gas treatment

This paper deals with the preparation (by solution combustion synthesis, SCS), characterization (by XRD, BET, FESEM and TPD/R analyses), catalytic activity evaluation (in a temperature-programmed reaction—TPRe apparatus), and the assessment of the reaction mechanism of NO reduction by H 2 in the presence of oxygen on a series of perovskite-type catalysts belonging to the LaFeO 3 family (LaFeO 3, La 0.8Sr 0.2FeO 3, Pd/La 0.8Sr 0.2FeO 3, La 0.8Sr 0.2Fe 0.9Pd 0.1O 3, La 0.7Sr 0.2Ce 0.1FeO 3, Pd/La 0.7Sr 0.2Ce 0.1FeO 3, La 0.7Sr 0.2Ce 0.1Fe 0.9Pd 0.1O 3). The catalysts have been studied in the 25–350 °C temperature range. Significant catalytic activities were measured at 150–250 °C. Among the catalysts screened, La 0.8Sr 0.2Fe 0.9Pd 0.1O 3, showed the best performance. Hence, it was deposited directly over a ceramic honeycomb monolith by in situ SCS and then tested in a lab-scale test rig. A mechanistic analysis is presented concerning the relationship between the observed activity and the reducibility of the B site, determined from TPR experiments, as well as the correlation between the observed oxygen inhibition and the proposed NO x reduction mechanism. Some final conclusions are drawn on the perspective of the practical application of the investigated after-treatment route for diesel exhaust gases.

Electrical effect of soot depositions in a co-axial wire pipe flow

An investigation was performed to study the electrical effects on the soot deposition in a co-axial wire cylinder with cooled walls. Experiments were performed for applied voltages from 0 to −5 kV or +5 kV and a diesel exhaust mass flow rate of 20 kg/h or Reynolds number of approximately 9000. The outer wall was cooled using water with a temperature of approximately 40 °C, and the experiments were performed for exposure times of 2 h. The soot deposition layer thickness was measured using a non-destructive neutron radiography technique at the end of each experiment. The results show that the electric field had a significant effect on the soot deposition and increases it by a factor of approximately 4 at the applied voltage of 5 kV before spark on-set. The soot thickness was similar for the positive and negative polarities and the results show that there was significant deposition on the wire as well as the outer wall for both polarities. Since soot deposition even occurs on both corona wire and grounded pipe below corona on-set voltages of the clean system, there may be a significant pre-charging of the diesel soot with both polarities in the diesel exhaust gas as has been observed by the recent measurements of Marieq [On the electrical charge of motor vehicle exhaust particles, Journal of Aerosol Science 37 (7) (2006) 858–874].

Basic Characteristics of Dielectric Barrier Discharge Reactor Using Anodic Porous Alumina for NOx Removal

Dielectric barrier discharge (DBD), properly combined with porous ceramics and/or catalysts, is a promising technology for diesel exhaust gas treatment. In this study, anodic porous alumina, which has numerous pores with nanometer-order diameter and a high aspect ratio, has been examined for use as a barrier in a DBD reactor. The anodic porous alumina greatly improves the DBD reactor. Nevertheless, few reports describe DBD using the anodic porous alumina barrier. As described herein, the DBD reactor’s basic characteristics and NOx removal in atmospheric pressure air were studied to support its future development. Results were compared with those of a typical DBD to clarify the influence of anodic porous alumina on those characteristics.The electropolished 99.99% pure Al substrate was anodized in 1.0 M sulfuric acid of 10°C for 5 h at dc 24 V. The Al substrate and anodic porous alumina respectively act as the electrode and dielectric barrier of the DBD. The dry gas mixture of NO (several hundred ppm) / O2 (20%) / N2 was supplied into the DBD reactor at 1.0 L/min. The resultant voltage and current waveforms resembled those of a typical DBD. Results revealed that NO was mostly oxidized to NO2 ; about 20 ppm N2O was detected. Different from a typical DBD the NO2 increased characteristically as a function of operation time.

Effect of Fuel and Lube Oil Sulfur on the Performance of a Diesel Exhaust Gas Continuously Regenerating Trap

The continuously regenerating trap (CRT) is a diesel exhaust emission control that removes nearly all diesel particulate matter on a mass basis, but under some circumstances oxidation of sulfur leads to the formation of nanoparticles. The objective of the four year study was to determine CRT performance under controlled, real-world, on-road conditions, and to develop quantitative relationships between fuel and lubrication oil sulfur concentration and particle number exhaust emissions. It was shown that nanoparticle emissions are minimized by the use of ultralow sulfur fuels and specially formulated low sulfur lubrication oil. Nanoparticle emissions increased with higher exhaust temperatures. Fuel and lubrication oil sulfur increased the particle concentration by, on average, 36 x 10(6) and 0.14 x 10(6) part/cm3 for each 1 ppm increase in sulfur. On the other hand there was a decrease in nanoparticle emissions by the CRT as the system aged.

디젤 NOx후처리 장치에 있어서 암모니아 SCR 시스템 혼합영역 내 가스유동의 유입열 수치모델링에 관한 연구

Selective catalytic reduction(SCR) is known as one of promising methods for reducing emissions in diesel exhaust gases. emissions react with ammonia in the catalyst surface of SCR system at working temperature of catalyst. In this study, to raise the reacting temperature when the exhaust gas temperature is too low, a heater is located at the bottom of SCR reactor. At an ambient temperature, ammonia is radially injected perpendicular to the exhaust gas flow at inlet pipe and uniformly mixed in the mixing area after being impinged against the wall. To predict the turbulent model inside the mixing area of SCR system, the standard model is applied. This work investigates numerically the effects of induced heat on the gaseous flow. The results show that the Taylor- type vortex is generated after the gaseous flow impinges the wall in which these vortices influence the temperature distribution. The addition of heat disturbs the flow structure in bottom area and then stretching flow occurs. Vorticity strand is also formed when heat is continuously increased. Constriction process takes place, however, when a further heat input over a critical temperature is increased and finally forms shed vortex which is disconnected from the vorticity strand. The strong vortex restricts the heat transport in the gaseous flow.

The Effect of Sulphur on the Activity of Pd/Al2O3, Pd/CeO2 and Pd/ZrO2 Diesel Exhaust Gas Catalysts

Pd/Al2O3, Pd/CeO2 and Pd/ZrO2 diesel oxidation catalysts and their washcoat materials were studied after sulphur treatment. The catalytic activities were analysed in simplified diesel exhaust gas composition by FT-IR technique. ICP-OES or XRF, physisorption and CO chemisorption was used to catalyst characterisation. The result shows that the sulphur treatment clearly deactivates the studied catalysts.

A model gas study of ammonium formate, methanamide and guanidinium formate as alternative ammonia precursor compounds for the selective catalytic reduction of nitrogen oxides in diesel exhaust gas

Ammonium formate, methanamide and guanidinium salts were investigated in model gas experiments and found to be suitable ammonia precursor compounds for the selective catalytic reduction (SCR) of nitrogen oxides since they decompose to ammonia over different metal oxide catalysts.The decomposition of ammonium formate started with thermolysis to formic acid and ammonia. Formic acid reacted further, mainly to water and CO (decarbonylation), but CO2 formation (decarboxylation) was also observed. Under unsuitable reaction conditions, methanamide may be formed from ammonia and formic acid in an amidation reaction, and HCN may be formed from methanamide by dehydration.When methanamide was used as a reducing agent, it was emitted undecomposed at temperatures below 250°C and formed HCN as a side-product at temperatures above 350°C.Among the tested guanidinium salts, guanidinium formate best met the requirements for a reducing agent in the SCR process, i.e., it decomposed at moderate temperatures with high selectivity, and it is highly water-soluble and stable when heated to 100°C.For guanidinium formate, a similar decomposition mechanism is proposed as that for ammonium formate. First, guanidinium formate thermolyzes to guanidine and formic acid. Then, formic acid is decarbonylated and guanidine is assumed to hydrolyze in three steps, proceeding through urea and isocyanic acid (HNCO) as intermediates to the final product, ammonia.The formation of side-products was avoided for all three reducing agents when the reactor was filled with TiO2 (anatase) as a catalyst and operated at 275–350°C at low space velocities.

Hydrogen Promotion of Low-Temperature Passive Hydrocarbon-Selective Catalytic Reduction (SCR) over a Silver Catalyst

Relatively small amounts of H2 (500−3000 ppm) have been added to a real diesel exhaust gas during passive hydrocarbon-selective catalytic reduction (SCR) over a silver catalyst. The added H2 is very effective at promoting low-temperature activity and at sustaining it by removing carbon-rich poisoning species from the catalyst surface. NO2 production by the catalyst appears to be a key step in the self-cleaning process, but it is highly dependent upon the gas-phase concentrations of H2, total NOx, and hydrocarbons and the exhaust-gas temperature. Careful control of H2 addition is therefore required in response to changes in conditions, to maintain suppression of the carbon-rich species without releasing NO2 from the tailpipe. The highest overall NOx reduction can be achieved by operating the engine with exhaust gas recirculation in combination with H2-promoted passive hydrocarbon-SCR as an aftertreatment.

Measurement of soot oxidation with No2-O2-H2O in a flow reactor simulating diesel engine DPF

Understanding the mechanism of carbon oxidation is important for the successful modeling of diesel particulate filter regeneration. Characteristics of soot oxidation were investigated with carbon black (Printex-U). A flow reactor system that could simulate the condition of a diesel particulate filter and diesel exhaust gas was designed. Kinetic constants were derived and the reaction mechanisms were proposed using the experimental results and a simple reaction scheme, which approximated the overall oxidation process in TPO as well as CTO. From the experiments, the apparent activation energy for carbon oxidation with NO2-O2-H2O was determined to be 40±2 kJ/mol, with the first order of carbon in the range of 10∼90% oxidation and a temperature range of 250∼500°C. This value was exceedingly lower than the activation energy of NO2-O2 oxidation, which was 60±3 kJ/mol. When NO2 exists with O2 and H2O, the reaction rate increases in proportion to NO2. It increases nonlinearly with O2 or H2O concentration when the other two oxidants are fixed.

Removal of diesel soot particules using an esp supplied by a hybrid voltage

Electrostatic filtration is a process that has been studied for more than a century. One of the most recent applications is Diesel exhaust gas aftertreatment. More specifically, car manufacturers are very interested in using electrical discharge phenomena to remove the soot particles from exhaust gases. This process could be a feasible alternative to the Diesel particulate filter used at the present time. The aim of this paper is to investigate the effects of repetitive voltage impulses on the treatment efficiency on soot particles and to compare results with those achieved when a DC supply is used. The study was divided into two steps: in the first, a study of the modes of discharge which develop in an electrostatic precipitator allows us to optimize both the geometry of an ESP and a hybrid pulsed power/direct voltage supply. This study was performed without gas flow. In the second step, investigations concerning treatment efficiency were carried out under practical conditions using an engine test bench. Results show that the combination of direct voltage (–7 kV) and pulsed voltage (–14 kV, 3 kHz) provides treatment efficiency close to 75% using electrical power three times lower than that required using a DC supply.

Soot Measurement and Application on Diesel Exhaust Gas Using Laser-Induced Incandescence

In this study, we measured soot concentration by laser induced incandescence (LII). To obtain absolute soot volume fraction, laminar diffusion flames stabilized on a co-annual burner were used in calibration process. Our experimental conditions such as fuel and air flow rate were the same as those reported in the data base by National Institute of Standards and Technology (NIST). We used two types of Nd : YAG laser. One has powerful laser beam intensity, usually used in two-dimensional measurement. The other is small and portable, applicable for measurement in outer field. These systems are called system 1 and 2, respectively. For both cases, the LII signals were recorded by a ICCD camera. We applied this compact system to the soot measurement in diesel exhaust gas. For laminar diffusion flames, the measured instantaneous distributions of LII signals exhibit the similar profile of NIST data base. Since the calibrated soot volume fraction is the same as that measured by Artium LII 200, the reliability of our system is confirmed. In system 2, using the laser beam, the signal has enough S/N ratio. Results for diesel exhaust gas show that the monitored back pressure is larger when the engine speed (rpm) is increased, resulting in higher soot concentration. Additionally, the reduced soot concentration is recorded due to soot trap by a diesel particulate filer (DPF).