Reduce System Size Research Articles

SVM Strategies for Common-Mode Current Reduction in Transformerless Current-Source Drives at Low Modulation Index

In transformerless high-power pulse width modulation (PWM) current-source drives, common-mode inductor is implemented to attenuate the common-mode voltage (CMV). However, the common-mode inductor is bulky and costly, so that scaling down the size of the common-mode inductor can achieve the system size reduction and efficiency enhancement. The size of the common-mode inductor is mainly related to the maximum common-mode current, which occurs at the resonant frequency of the common-mode circuit when motor speed is low. Previous research demonstrates that 3-segment average-value-reduction (AVR) space vector modulation (SVM) has good common-mode resonance suppression performance by attenuating the third-order CMV from the inverter. However, as studied in this paper, when modulation index of the inverter is lower than 0.4, the performance of 3-segment AVR SVM is affected as the dwell time of zero vector becomes too long to effectively compensate the CMV introduced by the active vectors. To overcome this problem, three modified AVR SVM schemes are proposed in this paper, where the single long zero vector is separated into two segments in the PWM sequence. The working principles, CMV reduction performance, harmonic performance, and switching frequency analysis of the proposed SVM methods are presented in detailed. Experiments are conducted to verify the effectiveness of the proposed methods.

用于目标识别的紧凑型仿生复眼光学系统设计

The large-aperture bionic compound eye optical system can have a large field of view, it overcomes the defects that the aperture of biological compound eyes is small while the vision distance is short. The relationship between the actual array period and theoretical calculated period number was researched through analyzing the field stitching method of bionic compound eye, the method called padding sub eye method was proposed to reduce sub eye configuration density. By studying the geometry relationship of the fixed spherical body design, the mathematical connection between the main body vertical radius d and the curvature R was established, the design method of fixed spherical body was proposed, and the proposed bionic compound eye field stitching theory was perfected. Finally, the correctness of the design method through the actual alignment experiments was verified. This method can improve the integration of the bionic compound eye system, reduce system size, and promote the practical application of bionic compound eye optical system.

Performance analysis of diesel engine heat pump incorporated with heat recovery

This paper presents experimental study of diesel engine heat pump (DEHP) system to find potential as retrofit technology in off-gas or weak electricity network area to replace existing gas/oil/electric heating system in domestic sector. Test set-up of diesel engine driven water-to-water heat pump system was built which included heat recovery arrangement from the engine coolant & exhaust gas. The system was designed to meet typical house heating demand in Northern Ireland. Performance of DEHP was evaluated to meet house-heating demand at different flow temperature (35, 45, 55 & 65°C), a typical requirement of underfloor space heating, medium/high temperature radiators and domestic hot water. The performance was evaluated against four-evaporator water inlet temperature (0, 5, 10 & 15°C) and at three different engine speed 1600, 2000 & 2400rpm. Experiment results were analysed in terms of heating/cooling capacity, heat recovery, total heat output, primary energy ratio (PER), isentropic efficiency, etc. Test results showed that DEHP is able to meet house-heating demand with help of heat recovery with reduced system size. Heat recovery contributed in a range of 22–39% in total heat output. It is possible to achieve high flow temperature in a range of 74°C with help of heat recovery. Overall system PER varied in a range of 0.93–1.33. Speed increment and flow temperature has significant impact on heat recovery, total heat output and PER. A case scenario with different flow temperature to match house-heating demand has been presented to show working potential with different heat distribution system. In addition, DEHP shows good potential to save primary energy consumption and CO2 emissions, a helpful technology to achieve national emission reduction target.

Performance comparisons of two system sizing approaches for net zero energy building clusters under uncertainties

Uncertainties have significant impacts on system sizing in net zero energy building (NZEB) clusters and they have to be well considered. Through Monte Carlo simulation and statistical analysis, the impacts of three typical types of parameter uncertainties have been investigated in the study. Considering the uncertainty impacts, this study aims to compare the multi-criteria performance of two design approaches for system sizing of a NZEB cluster. The first one is the conventional separated design in which dedicated systems are separately designed in individual buildings. The second one is the integrated design in which integrated systems are designed to provide services to all buildings. The study results show that the integrated design approach can achieve significant system size reductions and large initial cost savings as compared with the conventional separated design. The initial costs of the air-conditioning, PV and wind turbine systems can be reduced by 14.4%, 13.7% and 11.8% respectively. The integrated design also achieves improved grid friendliness and equivalently good indoor thermal comfort in comparison with the conventional separated design. With such improved performance, the integrated design should replace the conventional separated design for system sizing in NZEB clusters as uncertainties considered.

High Pressure Mass Spectrometry: The Generation of Mass Spectra at Operating Pressures Exceeding 1 Torr in a Microscale Cylindrical Ion Trap.

We present the first demonstration of high pressure mass spectrometry (HPMS), which we define as mass spectrometry performed at pressures greater than 100 mTorr. Mass analysis is shown at operational pressures exceeding 1 Torr of helium buffer gas. A differentially pumped MS system was constructed for HPMS development consisting of two chambers. The first chamber (mass analysis chamber) was operated at pressures up to 1.2 Torr and contained the ionization source and a microscale cylindrical ion trap (CIT) mass analyzer. The CIT had critical dimensions of r0 = 500 μm and z0 = 650 μm. The second chamber was held at a lower pressure (≤10 mTorr) and contained an electron multiplier for detection. Mass spectra for xenon, 2-chloroethyl ethyl sulfide (CEES), and octane were acquired with helium buffer gas pressures ranging from 0.04 to 1.2 Torr in the mass analysis chamber. Full-width at half-maximum of mass spectral peaks was found to increase 143% for xenon, 40% for CEES, and 77% for octane over this pressure range, with maximum peak widths of 1.19, 1.26, and 0.82 Da, respectively. Data were fitted with an algebraic model that factors in ion-neutral collision peak broadening effects at high pressures. Experimental and theoretical peak broadening slopes showed good agreement at buffer gas pressures greater than 0.2 Torr. Experiments presented here demonstrate mass spectrometry at pressures orders of magnitude higher than conventionally practiced with any type of mass analyzer. The use of HPMS provides a way to eliminate turbo pumping requirements, leading to significant reduction in MS system size, weight, and power and facilitating a path toward compact/hand-held mass spectrometers with numerous potential applications.

PARSECSs

In this work, we show how parallel applications can be implemented efficiently using task parallelism. We also evaluate the benefits of such parallel paradigm with respect to other approaches. We use the PARSEC benchmark suite as our test bed, which includes applications representative of a wide range of domains from HPC to desktop and server applications. We adopt different parallelization techniques, tailored to the needs of each application, to fully exploit the task-based model. Our evaluation shows that task parallelism achieves better performance than thread-based parallelization models, such as Pthreads. Our experimental results show that we can obtain scalability improvements up to 42% on a 16-core system and code size reductions up to 81%. Such reductions are achieved by removing from the source code application specific schedulers or thread pooling systems and transferring these responsibilities to the runtime system software.

Development of a SPECT System for Industrial Process Flow Measurement Using Diverging Collimators

In industrial processes where multiphase flows are frequently encountered, it is important to examine the phase distribution and flow pattern to optimize process efficiency, safe operation, and cost savings. One of the most suitable techniques of industrial-process flow-dynamics visualization is the single photon emission computed tomography (SPECT) system, which provides, by means of a process-system-injected radioisotope source, cross-sectional images of the process flow. Obtaining reliable SPECT imaging results for a multiphase flow system, however, remains a significant challenge. In the present study, the use of a diverging collimator for improvement of industrial SPECT system performance is proposed. The advantages of the diverging-collimation industrial SPECT system as compared with a previous parallel-collimation version can be summarized as follows: (a) significant reduction of edge artifacts on a detection-efficiency map, and 19% improvement of average detection efficiency; (b) 36% improvement of image resolution; (c) accurate source region reconstruction even with the source positioned farther from the object’s center; and (d) a reduced system size.

Advanced Catalytic Igniters Technology for Small Compact Engine Applications

Development of technologies that allow small, high power density engines such as unmanned aerial vehicles (UAV), unmanned marine vehicles (UMV), and unmanned ground vehicles (UGV) to operate on single logistic fuel such as JP-8 is one of government goals. To advance this goal, a lightweight, compact, and retrofit capable ignition source is critical. Compared to standard spark igniters and noncatalytic glow plugs, the use of catalytic glow plugs will provide benefits of lower required compression ratio, improved igniter life, reduced electrical energy requirements, and overall reduction in system weight and size. Experimental testing demonstrated a significant increase in surface temperature (160+ °C) with impingement of a fuel spray compared to a conventional glow plug with engine testing demonstrating the use of catalyst allows stable engine operation at reduced power requirements. Computational analysis was performed to provide insight into the catalyst behavior. Analytical studies suggested increased stability due to both heat release due to exothermic catalytic reaction and production of reactive species. This technology would allow high power density engines to use heavy fuels, while potentially reducing electric power supply and engine complexity and weight, both of which would allow greater range and/or payload capacity. This paper discusses the feasibility of advanced igniters technology as an enabling component for the use of heavy fuels in small, high power density internal combustion engines. The paper presents and discusses analytical investigation, experimental test results, and durability testing data in an internal combustion engine environment.

Performance ranking of refrigerants with low global warming potential

This article is an evaluation of the cycle performance of 39 refrigerants identified in the AHRI Low Global Warming Potential Alternative Refrigerants Evaluation Program in a typical air conditioner. This program was initiated in response to environmental concerns raised by the use of high global warming potential refrigerants with the intent to identify and evaluate promising alternative refrigerants. The cycle performance of each refrigerant is calculated assuming the same evaporator heat duty and sink temperatures for the condenser. The evaluation included the effects of heat transfer and pressure drop in the evaporator and the condenser. Four performance variables were investigated: (1) the coefficient of performance, (2) the required volumetric displacement of the compressor, (3) the mean temperature difference of the evaporator, and (4) the compressor discharge superheat. Ratios of the above four parameters relative to the refrigerants that are intended to be replaced are provided for each replacement refrigerant. In addition, a methodology was developed using weighting factors to rank the alternative refrigerants either emphasizing the importance of a large coefficient of performance or the importance of reduced system size. The two ranking methodologies produced different rankings of the alternative refrigerants, although the top three ranked refrigerants had at least two refrigerants in common with each other. Both ranking methodologies identified R1234yf, R32, and R1270 as having ranking factors within those of the best three alternative refrigerants.

Analytical reduction of combinatorial complexity arising from multiple protein modification sites.

Combinatorial complexity is a major obstacle to ordinary differential equation (ODE) modelling of biochemical networks. For example, a protein with 10 sites that can each be unphosphorylated, phosphorylated or bound to adaptor protein requires 3(10) ODEs. This problem is often dealt with by making ad hoc assumptions which have unclear validity and disallow modelling of site-specific dynamics. Such site-specific dynamics, however, are important in many biological systems. We show here that for a common biological situation where adaptors bind modified sites, binding is slow relative to modification/demodification, and binding to one modified site hinders binding to other sites, for a protein with n modification sites and m adaptor proteins the number of ODEs needed to simulate the site-specific dynamics of biologically relevant, lumped bound adaptor states is independent of the number of modification sites and equal to m + 1, giving a significant reduction in system size. These considerations can be relaxed considerably while retaining reasonably accurate descriptions of the true system dynamics. We apply the theory to model, using only 11 ODEs, the dynamics of ligand-induced phosphorylation of nine tyrosines on epidermal growth factor receptor (EGFR) and primary recruitment of six signalling proteins (Grb2, PI3K, PLCγ1, SHP2, RasA1 and Shc1). The model quantitatively accounts for experimentally determined site-specific phosphorylation and dephosphorylation rates, differential affinities of binding proteins for the phosphorylated sites and binding protein expression levels. Analysis suggests that local concentration of site-specific phosphatases such as SHP2 in membrane subdomains by a factor of approximately 10(7) is critical for effective site-specific regulation. We further show how our framework can be extended with minimal effort to consider binding cooperativity between Grb2 and c-Cbl, which is important for receptor trafficking. Our theory has potentially broad application to reduce combinatorial complexity and allow practical simulation of a variety ODE models relevant to systems biology and pharmacology applications to allow exploration of key aspects of complexity that control signal flux.

ワンショットデジタルホログラフィによる赤血球の三次元計測

In these years, because of applications for medical analysis, such as biopsy, demand of 3D microscope is arising. Typical existing 3D microscopes are Scanning Electron Microscope (SEM) and confocal laser scanning microscopy (CLSM). SEM is a type of electron microscope that produces images of an object by scanning it with a focused beam of electrons. The electrons interact with atoms in the object, producing various signals that can be detected and that contain information about the sample’s surface topography and composition. However, SEM needs a vacuum system during measurement, and it is big size and price high. CLSM is a technique for obtaining high-resolution optical images with depth selectivity. It is its ability to acquire in-focus images from selected depths, a process known as optical sectioning. Images are acquired point-by-point and reconstructed with a computer, allowing 3D reconstructions of topologically complex objects. However, 3D measurement using CLSM is time consuming because it has to scan an object point-by-point, and 3D measurement accuracy of CLSM is about 1μm which is difficult to measure nano-structure objects. To resolve problems in existing 3D microscopes, 3D microscope using single-shot phase-shift digital holography is proposed in this paper. In proposal 3D microscope, at first, a Michelson interferometer and general optical components are used, so reduction in system size and price-down can be realized easily. Second, the proposal 3D measurement method, single-shot phase-shift digital holography, uses Fourier-transform method of fringe-pattern which has been used for interferometry originally. Using the proposal method, 3D shape of an object can be measured in real-time(60ms) with 5.5nm accuracy in height direction and 0.59μm resolution in XY plane. Finally, 3D shapes of human red blood cells are measured in measurement experiment. According to result of experiment, we conclude that the proposed 3D microscope can be applied to the field of precision medical analysis.

Sizing of off-grid renewable energy systems for drip irrigation in Mediterranean crops

In the Mediterranean region, there are many drip irrigation systems with pumps that are powered by diesel generator sets (gensets). Although they could be powered by renewable energy produced on-site, technical and economic factors make that difficult. Moreover, the seasonal nature of demand requires an oversizing of energy generation and/or storage, increasing system costs. In this paper, we sought renewable energy systems that were economically optimal. We focused on six farming facility case studies to find the optimal energy generation solution using a simulation and optimization tool based on genetic algorithms. Photovoltaic-diesel hybrids and diesel systems were found to be optimal, with energy costs from 0.13 to 1.08 €/kWh and from 0.32 to 0.52 €/kWh, respectively. The strong effect of demand management was an interesting finding, as it may indicate significant system size and cost reductions. In addition, the optimum photovoltaic fixed tilt angles depended not only on the seasonal profile of the demand, but also on the pumping schedule. Although the difference between market interest rates and the rise of fuel prices strongly influences the advantage of incorporating, or not, renewable generation, this study supports that hybrid photovoltaic-diesel systems can make profitable use of renewable energy in drip irrigation.

Development of High Efficiency Boost DC/DC Converter For EV

In this paper, reactorless high efficiency boost DC/DC converter for EV is proposed. In proposed converter, improves efficiency because decrease power loss when the switches are turned on/off using zero current switching (ZCS) at all switch of primary full bridge. By replacing reactance ingredients of L-C resonance circuit for ZCS with leakage inductance ingredients of high frequency transformer, it reduces system size and expense because of not add special reactor. For validity verification of proposed converter, in the paper implements simulation using PSIM and perform experiment by making 5KW DC/DC converter. In experimental results, efficiency of proposed converter conformed superiority. Today the use of electricity is increasing with the development of industries and vehicles with internal combustion engine are rapidly increasing for convenience of travel. To produce electricity and drive internal combustion engines, fossil fuels must be used, causing serious environmental problems. These days many people are making efforts to reduce CO2 which is the main culprit for the destruction of global environment. In particular, as vehicles account for over 50% of the CO2 emissions, active efforts to reduce them are being made all over the world. Typical examples of such efforts are the improvement of fuel economy and the introduction of electric vehicles. Recently, hybrid vehicles that use both internal combustion engine and electric motor have been developed with effective improvement of fuel economy. It is expected that in the future, the percentage of vehicles using internal combustion engine will gradually decrease and ultimately be replaced with pure electric vehicles and fuel-cell vehicles(1)(2). As the use of electric motors is increasing, traction motors mainly use 300 V or higher voltages considering losses and advantages in motor design. However, since such high- voltage power supply systems have such problems as electric shock, systems like NEV (Neighborhood Electric Vehicle) use low voltage batteries of maximum 70 V. Due to safety and efficiency issues, batteries are using low voltage while motors use high voltages. Thus, it is essential to develop a boost DC/DC converter with at least 4-fold boosting efficiency(3)(4). Furthermore, an insulation-type converter needs to be developed to address the electric safety issue. Accordingly, this paper proposes an insulated DC/DC converter that uses a voltage multiplier circuit composed of diodes and condensers at the output for high voltage multiplication, in particular, a new insulation-type DC/DC converter with a serial connection of two voltage multiplier circuits for 4-fold boosting. The proposed method maintained the ratio of the transformer as 1:1 for identical input and output characteristics of the converter considering the regenerative braking of vehicles in the future. Furthermore, the proposed converter reduced the switching loss of the power switch using a serial L-C resonance, and the size and cost of the total system can be reduced by replacing the reactance component required for the L-C resonance circuit with a transformer leakage reactance(5) . To verify the feasibility of the proposed insulated DC/DC converter using a voltage multiplier circuit, a simulation was conducted using PSIM, and the real converter was fabricated and tested. It was found that up to 4-fold boosting was possible with the voltage multiplier circuit and a serial circuit only with no separate control, and the maximum efficiency of the converter was very high at around 97%.

Capacitance‐sharing, dual‐output, compact, switched‐capacitor DC–DC converter for low‐power biomedical implants

A dual-output, compact, switched-capacitor DC–DC converter is presented for efficient voltage generation in low-power biomedical implants. By sharing the charge transfer capacitors between multiple independent switched-capacitor DC–DC converters, fewer capacitors are required, resulting in overall system size reduction. A proof-of-concept capacitance-sharing, dual-output DC–DC converter, converting 1.2 V – 0.4 V and 0.8 V, fabricated in a 0.13 μm CMOS technology, occupying 0.3 mm2 and achieving a peak efficiency of 97.6% is demonstrated.

A multi coding technique to reduce transition activity in VLSI circuits

Advances in VLSI technology have enabled the implementation of complex digital circuits in a single chip, reducing system size and power consumption. In deep submicron low power CMOS VLSI design, the main cause of energy dissipation is charging and discharging of internal node capacitances due to transition activity. Transition activity is one of the major factors that also affect the dynamic power dissipation. This paper proposes power reduction analyzed through algorithm and logic circuit levels. In algorithm level the key aspect of reducing power dissipation is by minimizing transition activity and is achieved by introducing a data coding technique. So a novel multi coding technique is introduced to improve the efficiency of transition activity up to 52.3% on the bus lines, which will automatically reduce the dynamic power dissipation. In addition, 1 bit full adders are introduced in the Hamming distance estimator block, which reduces the device count. This coding method is implemented using Verilog HDL. The overall performance is analyzed by using Modelsim and Xilinx Tools. In total 38.2% power saving capability is achieved compared to other existing methods.

Non-Darcy Natural Convection From a Vertical Cylinder Embedded in a Thermally Stratified and Nanofluid-Saturated Porous Media

In recent years, nanofluids have attracted attention as a new generation of heat transfer fluids in building heating, heat exchangers, plants, and automotive cooling applications because of their excellent thermal performance. Various benefits of the application of nanofluids include improved heat transfer, heat transfer system size reduction, minimal clogging, microchannel cooling, and miniaturization of systems. In this paper, a study of steady, laminar, natural convection boundary-layer flow adjacent to a vertical cylinder embedded in a thermally stratified nanofluid-saturated non-Darcy porous medium is investigated. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis, and a generalized porous media model, which includes inertia and boundary effects, is employed. The cylinder surface is maintained at a constant nanoparticles volume fraction, and the wall temperature is assumed to vary with the vertical distance according to the power law form. The resulting governing equations are nondimensionalized and transformed into a nonsimilar form and then solved by Keller box method. A comparison is made with the available results in the literature, and our results are in very good agreement with the known results. A parametric study of the physical parameters is made, and a representative set of numerical results for the velocity, temperature, and volume fraction, as well as local shear stress and local Nusselt and Sherwood numbers, are presented graphically. The salient features of the results are analyzed and discussed. The results indicate that, when the buoyancy ratio or modified Grashof number increases, all of the local shear stress, local Nusselt number, and the local Sherwood number enhance while the opposite behaviors are predicted when the thermophoresis parameter increases. Moreover, increasing the value of the surface curvature parameter leads to increases in all of the local shear stress and the local Nusselt and Sherwood numbers while the opposite behaviors are obtained when either of the thermal stratification parameter or the boundary effect parameter increases.

Solving Thermal Issues in a Three-Dimensional-Stacked-Quad-Core Processor by Microprocessor Floor Planning, Microchannel Cooling, and Insertion of Through-Silicon-Vias

The electronics industry is heading toward the three-dimensional (3D) microprocessor to cope with higher computing workloads. The 3D stacking of the processor and the memory components reduces the communication delay in multicore system-on-a-chip (SoCs), owing to reduced system size and shorter interconnects. The shorter interconnects in a multicore system lowers the memory access latencies and contributes to improvements in memory access bandwidth. The shorter interconnects in stacked architectures also enables small drivers for interconnections which further reduce interconnection-level-energy dissipations. On the down side, the 3D-stacked architectures have high thermal resistance, which in conjunction with poor thermal management techniques, poses a thermal threat to the reliability of the device. This paper establishes the significance of the microprocessor floor planning and single-phase microchannel cooling for solving the thermal issues arising in the 3D-stacked-quad-core processor. The 3D-stacked-quad-core processor considered in this study comprises of symmetric nonuniformly powered quad-core processor, liquid-cooled microchannel heat sink, dynamic random access memory (DRAM), thermal interface material (TIM), and heat spreader. The electrical through-silicon-vias (TSVs) between the processor and DRAM serve as interconnects, while the thermal TSVs reduce the internal thermal resistance. The effective cooling of the 3D-stacked-quad-core processor depends on the TSVs, quad-core layout and the optimized design of the microchannel heat sink for the desired coolant. The microchannel cooling of the 3D-stacked processor is done both by planar flow and impingement flow. The thermal efficiency of the cooling techniques is evaluated on the basis of hot spot temperature, hot spot spread, and number of hot spots.

Conceptual Design and Simulation Study of an ROI-Focused Panel-PET Scanner

Positron emission tomography (PET) is an important imaging modality for clincial use. Conventionally, the PET scanner is generally built to provide a roomy enough transverse field-of-view (FOV) for imaging most adults’ torsos. However, in many cases, the region-of-interest (ROI) for imaging is usually a small area inside the human body. Therefore, to fulfill a PET system which provides an FOV comparable in size to the target ROI seems appealing and more cost effective. Meanwhile, such a PET system has the potential for portable or bedside application with the reduced system size. In this work, we have investigated the feasibility of using dual-headed panel-detectors to build an ROI-focused PET scanner. A novel windowed list-mode ordered subset expectation maximization method was developed to perform the ROI image reconstruction. With this method, the ROI of the object can be reconstructed from the coincidences whose position determined by time-of-flight (TOF) measurements was inside the ROI. Monte Carlo simulation demonstrates the feasibility of detecting lesions not less than 1 cm in diameter, with a 300 ps full width at half maximum timing resolution. As a critical system performance, the impact of TOF information on image quality has been studied and the required TOF capability was assessed. With enhanced timing resolution, the distortions and artifacts were reduced effectively. The further improved TOF capability also shows a noticeable improvement of detection performance for low uptake lesions, as well as the recovery speed of lesion contrast, which is of practical significance in the lesion detection task.

New catalysts and reactor designs for the hydrogen economy

New catalyst and reactor designs are necessary to meet the expanding use of low temperature hydrogen based fuel cells. Residential and commercial power generation requires the reformer integrated to the fuel cell must be sufficiently small given that space is often a premium in many of these applications. Precious metal washcoated monolithic structures, similar to those successfully used since 1975 in automobile catalytic converters [1], provide high activity per unit reactor volume, low pressure drop and greater structural stability than traditional base metal catalysts in packed beds and thus are well suited for distributed hydrogen applications, New precious metal catalysts, with high activity densities, have been formulated for hydrogen generation since traditional base metal oxides have much lower activities per unit mass and thus are not sufficiently active when used in limited amounts as washcoats. The higher cost of precious metals is mitigated by savings due to reduced system size and existing metal recycling operations. Catalytic fuel processing, of infrastructure fuels (e.g. natural gas and LPG), are being reformed for the fuel cell to power homes, commercial and residential buildings, schools, hospitals. Such systems must operate safely and reliably in the user facilities while unattended. This brief review will illustrate the application of automotive washcoating technology to reformers for distributed hydrogen applications.

Nonlinear and adaptive control of NO/NO2 ratio for improving selective catalytic reduction system performance

Reducing the NOx emissions from Diesel engines remains as a challenging issue as the emission standards for Diesel engine powered vehicles have become more stringent than ever before. Urea-based selective catalytic reduction (SCR) systems have emerged as a promising technique in addressing this issue. However, the SCR performance in terms of NOx reduction and ammonia slip continues as an ongoing challenge due to the engine exhaust gas temperature variations, Diesel emission characteristics (especially high NO/NO2 ratio), and immature SCR controls. The purpose of this study is to improve the SCR performance by feeding the SCR system with exhaust gas having the desired NO/NO2 ratio. The proposed complete active NO/NO2 ratio control consists of a low-level adaptive NO/NO2 ratio controller and a high-level nonlinear soot mass controller. The low-level controller utilizes the pre-SCR catalysts such as Diesel oxidation catalyst (DOC) to convert part of NO into NO2, while the high-level controller was designed and coordinated with the low-level controller to avoid NO2 reduction through the Diesel particulate filter (DPF). Simulation and experimental results show that the proposed active NO/NO2 ratio control has the potentials of regulating the NO/NO2 ratio to the desired value and thus considerably improving the SCR performance. Simulation results also illustrate that the active NO/NO2 ratio control can enable the SCR system size reduction by a half without a significant sacrifice on the overall tailpipe emission control performance. Such an integrated aftertreatment system control can be instrumental in reducing the cost and improving the performance of SCR systems, especially in low-temperature operations.