Tuning Constants Research Articles

A comprehensive phenomenological model for unburned fuel emission simulation applied to natural gas engines

The development of lean-burn concepts for internal combustion engines, utilizing a homogeneous air/fuel charge, aims to improve multiple aspects simultaneously, including thermal efficiency, fuel consumption, nitric oxide, and carbon monoxide emissions. However, the adoption of this technology may result in a notable increase in the emission of unburned hydrocarbons (uHC) compared to stoichiometric engines. The sources of uHC are diverse and their relative significance depends on fuel characteristics, engine operating conditions, and geometric features of the combustion chamber. This concern becomes more pronounced when considering engines fueled with natural gas, as methane has a high global warming potential compared to other pollutant emissions. This research proposes an enhancement to an existing simulation model that describes the primary mechanisms involved in uHC formation, which are filling/emptying of the piston top-land crevice volume and the flame wall quenching, with subsequent uHC post-oxidation. The improvements include the calculation of flame penetration into crevice volumes, the description of uHC production from non-piston crevices, and the introduction of a novel scavenging model. The uHC model is integrated into commercial software (GT-Power) as a “user routine”. Validation of the model is conducted with reference to three large bore engines (W31DF, W31SG, and W46SG) with bore sizes of 31 cm and 46 cm, fueled with natural gas, and operated under lean mixtures (λ > 2), employing different ignition methods (dual fuel mode or pre-chamber device). The uHC model is validated against engine-out measurements, exhibiting an average error of 10.0 % for W31DF, 19.4 % for W31SG, and 14.0 % for W46SG engines, respectively. The reliability of the uHC model is demonstrated by the absence of case-specific adjustments to its tuning constants, even when there are significant variations in engine load and geometric design of the crevice volumes.

The Effectiveness of the Huber's Weight on Dispersion and Tuning Constant: A Simulation Study

Dispersion measurement and tuning constants are critical aspects of a model's robustness and efficiency. However, in the presence of outliers, the standard deviation is not a reliable measure of dispersion in Huber's weight. This research aimed to assess the efficacy of the Huber weight function in terms of dispersion measurement and tuning constant. The simulation study was conducted on a hybrid of the autoregressive (AR) model and the generalized autoregressive conditional heteroscedasticity (GARCH) model with 10% and 20% additive outlier contamination. In the simulation analysis, three dispersion measurements were compared: median absolute deviation (MAD), interquartile range (IQR), and IQR/3, with two tuning constant values (1.345 and 1.5). The numerical simulation results showed that during contamination with 10% and 20% additive outliers, the IQR/3 outperformed the MAD and IQR. Our findings also showed that IQR/3 is a potentially more robust dispersion measurement in Huber's weight. The tuning constant of 1.5 revealed a decrease in resistance to outliers and increased efficiency. The proposed IQR/3 model with a constant tuning value (h) of 1.5 outperformed the AR(1)-GARCH(1,2) model while minimising the effect of additive outliers.

A phenomenological model for the description of unburned hydrocarbons emission in ultra-lean engines

The adoption of lean-burn concepts for internal combustion engines working with a homogenous air/fuel charge is under development as a path to simultaneously improve thermal efficiency, fuel consumption, nitric oxides, and carbon monoxide emissions. This technology may lead to a relevant emission of unburned hydrocarbons (uHC) compared to a stoichiometric engine. The uHC sources are various and the relative importance varies according to fuel characteristics, engine operating point, and some geometrical details of the combustion chamber. This concern becomes even more relevant in the case of engines supplied with natural gas since the methane has a global warming potential much greater than the other major pollutant emissions. In this work, a simulation model describing the main mechanisms for uHC formation is proposed. The model describes uHC production from crevices and flame wall quenching, also considering the post-oxidation. The uHC model is implemented in commercial software (GT-Power) under the form of “user routine”. It is validated with reference to two large bore engines, whose bores are 31 and 46 cm (engines named accordingly W31 and W46). Both engines are fueled with natural gas and operated with lean mixtures (λ > 2), but with different ignition modalities (pre-chamber device or dual fuel mode). The engines under study are preliminarily schematized in the 1D simulation tool. The consistency of 1D engine schematizations is verified against the experimental data of BMEP, air flow rate, and turbocharger rotational speed over a load sweep. Then, the uHC model is validated against the engine-out measurements. The averaged uHC predictions highlight an average error of 7% and 10 % for W31 and W46 engines, respectively. The uHC model reliability is evidenced by the lack of need for a case-dependent adjustment of its tuning constants, also in presence of relevant variations of both engine load and ring pack design.

A Semi-Mechanistic Prediction of Residence Time Metrics in Twin Screw Granulation.

This work is concerned with the semi-mechanistic prediction of residence time metrics using historical data from mono-component twin screw wet granulation processes. From the data, several key parameters such as powder throughput rate, shafts rotation speed, liquid binder feed ratio, number of kneading elements in the shafts and the stagger angle between the kneading elements were identified and physical factors were developed to translate those varying parameters into expressions affecting the key intermediate phenomena in the equipment, holdup, flow and mixing. The developed relations were then tested across datasets to evaluate the performance of the model, applying a k-fold optimization technique. The semi-mechanistic predictions were evaluated both qualitatively through the main effects plots and quantitatively through the parity plots and correlations between the tuning constants across datasets. The root mean square error (RMSE) was used as a metric to compare the degree of goodness of fit for different datasets using the developed semi-mechanistic relations. In summary this paper presents a new approach at estimating both the residence time metrics in twin screw wet granulation, mean residence time (MRT) and variance through semi-mechanistic relations, the validity of which have been tested for different datasets.

Transient and troubleshoots management of aged small-scale steam power plants using Aspen Plus Dynamics

This study is motivated by the insufficient studies on the dynamic simulation, operation control optimization, and operation strategies for small-scale old plants. In such small power plants, there is a need for cautions and stability during various troubleshoots. This study aims at developing a simulation model that accurately predicts the behavior of small-scale real plants under various part loads and troubleshoots. The actual operation of a 110-MW steam power-plant was modeled using Aspen Plus Dynamics, which employs a single-input single-output proportional integral (PI) controller. The controller tuning constants, K and IT, were optimized, and operation strategies for handling five troubleshoots are proposed. The simulation results are in good agreement toward the measured values, with a maximum relative error of 2%. The recommended operation strategies could prevent plant trip and return to steady state in a maximum of 5 min when two different halts are mimicked. Full-load thermal efficiencies of 94%, 97.9%, 92.6% were achieved when four burners were shutdown, high-pressure feedwater heaters tripped, and all the heaters tripped, respectively. The simulation presents the possibility of stabilizing the old power plants operation with maximum possible efficiency under various conditions. An updated operation and troubleshoot manual can be provided for various circumstances.

Changepoint in Error-Prone Relations

Linear relations, containing measurement errors in input and output data, are considered. Parameters of these so-called errors-in-variables models can change at some unknown moment. The aim is to test whether such an unknown change has occurred or not. For instance, detecting a change in trend for a randomly spaced time series is a special case of the investigated framework. The designed changepoint tests are shown to be consistent and involve neither nuisance parameters nor tuning constants, which makes the testing procedures effortlessly applicable. A changepoint estimator is also introduced and its consistency is proved. A boundary issue is avoided, meaning that the changepoint can be detected when being close to the extremities of the observation regime. As a theoretical basis for the developed methods, a weak invariance principle for the smallest singular value of the data matrix is provided, assuming weakly dependent and non-stationary errors. The results are presented in a simulation study, which demonstrates computational efficiency of the techniques. The completely data-driven tests are illustrated through problems coming from calibration and insurance; however, the methodology can be applied to other areas such as clinical measurements, dietary assessment, computational psychometrics, or environmental toxicology as manifested in the paper.

Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations: Basic and explanatory data.

This data article contains basic and explanatory data of “Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations” [1], including thermodynamic models, vapor-liquid equilibrium diagrams, steady-state flowsheets, temperature profiles of columns, description and setpoint units of the abbreviation of inventory control loops, description of control loops of control flowsheet with DTC, control flowsheets of PCTC and DTC, temperature and composition tuning constants, faceplates and flowsheet equations, dynamic performances and integral absolute errors. It also contains other important information.

Assessment of varying primary/secondary breakup mechanism of diesel spray on performance characteristics of HSDI engine

Fuel spraying process and hydrodynamic interaction of fuel jet-air plays a crucial role in the mixture formation pattern. A baseline diesel engine is considered and based on the operational values ​​of the experimental engine, the geometric and spraying model is designed and meshed. The values ​​of the primary and secondary breakup coefficients are adjustable according to the tested engine. By fixing the geometrical features, different atomization models with related tuning constants are selected to determine the effect of these factors on the spray quality and engine output in terms of combustion and emissions, and to provide a general framework for model performance for the users. In the present study, both the primary breakup and atomization models, as well as the secondary breakup model are considered emphasizing the modification and identification of the functions of these parameters. In the second breakup of the WAVE model is adopted and the C2 coefficient or constant in the range of 10–60 in the 10 steps is launched by the software for each mode, then in the secondary breakup model, KH-RT with a coefficient of C2 = 12 is investigated. In the next step, the primary breakup model of “Core Injection” is evaluated with C1 coefficients between 10 and 50, and its C2 coefficient will be analyzed for the values 15, 25, and 35. It has been understood that there is a linear correlation between equivalence ratio and C2 of secondary breakup with the determination coefficient of R2 = 0.954. Increasing C2 of WAVE results in deceleration in spray droplet strip (dR/dt) such that C2 = 60 gives the biggest SMD, the lowest pressure, heat release rate, and soot amount.

Robust and automatic modeling of tunnel structures based on terrestrial laser scanning measurement

The terrestrial laser scanning technology is increasingly applied in the deformation monitoring of tunnel structures. However, outliers and data gaps in the terrestrial laser scanning point cloud data have a deteriorating effect on the model reconstruction. A traditional remedy is to delete the outliers in advance of the approximation, which could be time- and labor-consuming for large-scale structures. This research focuses on an outlier-resistant and intelligent method for B-spline approximation with a rank (R)-based estimator, and applies to tunnel measurements. The control points of the B-spline model are estimated specifically by means of the R-estimator based on Wilcoxon scores. A comparative study is carried out on rank-based and ordinary least squares methods, where the Hausdorff distance is adopted to analyze quantitatively for the different settings of control point number of B-spline approximation. It is concluded that the proposed method for tunnel profile modeling is robust against outliers and data gaps, computationally convenient, and it does not need to determine extra tuning constants.

Transient prediction capabilities of a novel physics-based ignition delay model in multi-pulsed direct injection diesel engines

This work is an extension of a novel physics-based ignition delay modeling methodology previously developed by the authors to predict physical and chemical ignition delays of multiple injections during steady operations in diesel engines. The modeling methodology is refined in this work to consider the influence of additional operating parameters such as volumetric efficiency, exhaust temperature and pressure on the ignition delay of multiple injections. Computational fluid dynamics predictions on two different engines indicated that the main spray encounters local temperatures about 60 K above average temperatures for about 1 mg of pilot. Hence, the modeling methodology was further refined to include this effect by considering the air mass trapped in pilot spray, computed based on the spray penetration and cone angle and tuned using results of the computational fluid dynamics studies. Comparisons of the ignition delay predictions with the stock boost temperature sensor and a specially incorporated, transient-capable fine wire thermocouple indicated that the measurements with stock sensor could be satisfactorily used for transients. Cycle-by-cycle changes in ignition delay could be predicted accurately when transients were imposed in boost pressure, rail pressure and main injection quantity in a turbocharged intercooled diesel engine controlled with an open engine control unit. Further validations were done even under a transient cycle when the engine was controlled by its stock engine control unit. The same tuning constants could be used for the prediction of the ignition delay under transients on another naturally aspirated engine. This indicates the suitability of the model for application in different engines. Finally, the model was incorporated within an open engine controller, and cycle-by-cycle prediction of ignition delays of the pilot and main injections were done in real time. It was possible to compute the ignition delays in less than 2 ms within engine control unit using the already available sensor inputs within an error band of ±60 µs.

Controller tuning constants for the Advanced Power Reactor 1400 Feedwater Control System based on Ms-Constrained Integral Gain Optimization Method

Failure to control the steam generator (SG) water levels causes unexpected shutdowns in the Advanced Power Reactor (APR) 1400 nuclear power plants. This impacts maintenance, operational life, and safety critically. Therefore, it is vital to stabilize the SG water level at different power levels, particularly at low powers, by improving the performance of the proportional integral (PI) controller in the Feedwater Control System (FWCS). The PI controller designed using Ms-Constrained Integral Gain Optimization (MIGO) mitigated this problem significantly. In order to design this PI controller for the FWCS, the SG model was developed as a process model with a system identification algorithm in MATLAB. The algorithm processed data sets obtained from the thermal-hydraulic model by the Safety and Performance Analysis Code (SPACE). The MIGO and the Ziegler-Nichols methods were each used to produce a design for the PI controller, and the controllers were compared. Simulations were run in MATLAB for resulting designs. The PI controller designed by the MIGO is more stable than the controller using the Ziegler-Nichols approach. Finally, the PI MIGO controller was applied to an overall schematic block diagram of the FWCS. The simulations of the diagram in MATLAB Simulink demonstrate the PI MIGO controller offers superior control and enhanced robustness in the FWCS.

Application of a distributed 2D overland flow model for rainfall/runoff and erosion simulation in a Mediterranean watershed

Soil erosion has reemerged as an environmental problem associated with climate change that requires the help of simulation tools for forecasting future consequences. This topic becomes even more relevant in Mediterranean catchments due to the highly variable and irregular rainfall regime. Hence, an approach that includes the rainfall/runoff and erosion phenomena is required for quantifying the amount of soil the catchments are transferring to the rivers. As the calibration process of the infiltration and erosion parameters can become cumbersome in terms of iterations to the optimal values to fit experimental data, a Simplified Catchment Model (SCM) is introduced as a first approach. The set of tuning constants that provides the best fit are used as input for re-calibrating the parameters by means of the simulation of the real catchment. The modeling effort here presented opens its application to the analysis of the hydro-sedimentary processes at larger temporal and spatial scales.

Reduced order modeling of two degree-of-freedom vortex induced vibrations of a circular cylinder

The effect of coupled transverse and in-line motion of an elastically mounted rigid circular cylinder, subjected to vortex induced vibrations (VIV), is predicted using a reduced-order model. The model comprises of coupled wake and structural oscillators, where the nonlinearities in the fluid damping and forcing terms of the structural oscillator are retained. The classical van der Pol equation is used to model the wake oscillator. The unknown model constants are tuned to fit to experimental data. The influence of these tuning constants on the model performance are identified. The nonlinear contributions are shown to be insignificant in predicting the VIV characteristics associated with the transverse (y-only) oscillations of the cylinder at low Re. Surprisingly, the nonlinear terms were found to play a key role in predicting the two degree-of-freedom (2 DoF) motion of the cylinder. The model results for the cylinder with mass ratios in the low and moderate ranges are in good agreement with the experiments.

RETRACTED ARTICLE: Cluster and cloud computing framework for scientific metrology in flow control

Scientific metrology is one evergreen and Omni present field that has been continuously experiencing a great deal of research in developing new measurement benchmarks to cope up with the real time advancement in the current market. This has been greatly aided in recent times with the advent of intelligent computing networks and communication protocols through which there has been a great deal of migration towards cloud based services on a demand basis. The essential feature of cloud is the provision of quality service to the clients. The proposed research paper has taken the metrology of monitoring the flow rate in an industrial piping system towards a boiler as the case study and real time implementation achieved with the help of Labview and MyDAQ environment. The data from this DAQ is interpreted into the cloud network with subset reduction and regrouping based on features using a fuzzy c means clustering approach. The experimentation has been done for varying values of tuning constants in order to maintain constant flow and compared with existing research contributions. The results clearly indicate a fast computation time with low complexity overhead which is achieved with the help of cloud distribution.

Statistical Approach on Visualizing Multi-Variable Interactions in a Hybrid Breakup Model under ECN Spray Conditions

The Direct Numerical Simulation (DNS) approach to solving the fundamental transport equations down to the smallest scales of motion is favorable should the requirement be a truly predictive solution of fluid dynamic problems, but the simulation run times are unacceptable for most practical industrial applications. Despite the steadily increasing computational capabilities, Reynolds Averaged Navier-Stokes (RANS) based frameworks remain the most commercially viable option for high volume sectors, like automotive. The sub models within RANS simplify the description of key physical phenomena and include several numerical constants. These so-called “tuning constants” introduce multivariable dependencies that are almost impossible to untangle with local sensitivity studies. This paper addresses the prevailing difficulties in setting up an adequate diesel spray simulation which arise from the mentioned multi-variable interactions of these “tuning constants”, by applying a statistical approach named Design of Experiments (DoE). Often combined with an optimizer, DoE is commonly used to find an optimum set of engine parameters for set criteria at reduced experimental effort. In this case, the methodology was applied to determine an optimal set of “tuning constants” for the simulations which best matched experimental data at five conditions taken from the Engine Combustion Network (ECN) database. Multi-variable DoE were run for each condition. Stochastic response models (SPM’s) highlighted crucial simulation sensitivities of the turbulent dissipation constant C2and liquid/gas-phase momentum transfer at injection pressure swings. Further, a comparison of the breakup models which produced matching simulations exhibited patterns which correspond with physical processes. Lastly, it was shown that while a single set of the constants can give reasonable results in the space explored, there is merit in adjusting key constants to suit the operating condition in the search for accuracy.

Documentation of atmospheric constants over Niamey, Niger: a theoretical aid for measuring instruments

ABSTRACTThe frequent failures of ground measuring devices, e.g. radiosondes, weather stations, in developing regions is worrisome. From the literature, established projects such as the Aerosol Robotic Network (AERONET) and the African Monsoon Multidisciplinary Analyses (AMMA) are burdened by the same challenge. At the moment, the AERONET and AMMA databases show a large volume of data loss. With only about 47% of data available to scientists, it is evident that accurate nowcasts or forecasts cannot be guaranteed. It is proposed that the challenge is not measuring device design error but systemic, i.e. the configuration of accurate calibration constants in the compact flash card of the devices. The calibration constants of most radiosonde or weather stations are not compatible with the atmospheric conditions of the West African climate. A dispersion model was developed to incorporate salient mathematical representations such as the unified number. The unified number was derived to describe the turbulence of aerosol transport in the frictional layer of the lower atmosphere. A 14 year dataset from the Multi‐angle Imaging SpectroRadiometer was tested using the dispersion model. A yearly estimation of the atmospheric constants over Niamey using the model was obtained with about 87.5% accuracy. This further revealed that the average atmospheric constants for Niamey, Niger, are a1 = 0.77975 and a2 = 0.693021 and the tuning constants are n1 = 0.140187 and n2 = 0.759236. Also, the yearly atmospheric constants confirmed that the lower atmosphere of Niamey is very dynamic. Hence, it is recommended that radiosonde and weather station manufacturers should constantly review the atmospheric constants over a geographical location to enable about 80% data retrieval.

Theoretical Study of Aerosols Loading and Retention Over Bolgatanga, Ghana

The aerosols loading and retention over West Africa have grave effect on life-forms through the impact on health, farming, rainfall pattern, cloud formation, and regional climate. Bolgatanga can be found on the latitude and longitude of 10.78°N and 0.85°W, respectively. This research is focused on an investigative consideration of the negative effect of atmospheric aerosols over Bolgatanga in Ghana through a conceptual model using analytical and descriptive statistical methods with MATLAB curve-fitting tool. The model was verified using aerosol optical depth data set from satellite imagery—multi-angle imaging specto-reflectometer (MISR)—obtained over a period of 13 years. The highest percentage increase of aerosol retention was 64.27% over the research site. The model was used to estimate the atmospheric constants as 0.67, tuning constants as 0.24, and phase difference as [Formula: see text]. The physical interpretation of the results was analyzed systematically.

Successive Difference Replication Variance Estimation in Two-Phase Sampling

Successive difference replication (SDR) is a method of variance estimation under systematic sampling. The method has been used at the U.S. Census Bureau for important studies, including the Current Population Survey and the American Community Survey. The statistical properties of SDR are evaluated in the context of other variance estimators applicable to single-phase systematic sampling. A simulation study is conducted to compare the behavior of SDR and balanced repeated replication (BRR) under various choices of their respective tuning constants. Further, SDR has been used to estimate variances in a two-phase setting, such as the National Survey of College Graduates (NSCG), a subsample of the American Community Survey (ACS). We study properties of a two-phase SDR variance estimator using a phase-one sample of ACS data and repeated phase-two samples from the ACS following the NSCG design. The estimator accounts for systematic sampling in phase one and stratified sampling in phase two. The estimator is conservative for some NSCG variables because the NSCG uses not only explicit stratification on some ACS variables but also systematic sampling within strata after sorting on additional ACS variables. The simulation results suggest that the two-phase SDR variance estimator, with an appropriate adjustment to account for the systematic sampling in phase two, performs well in this context of subsampling the NSCG from the ACS sample.

Statistical examination of the aerosols loading over Mubi-Nigeria: The satellite oobservation analysis

The problem of underestimating or overestimating the aerosols loading over Mubi is inevitable because of the absence of ground stations over the region. Aerosols pollution is a global challenge to life forms as it affects human health, agricultural produce, thermal comfort and weather. The modulation between high and low thermal comforts over Mubi is quite disturbing. The aim of the research is to seek a more reliable approach to estimate the aerosols loading and retention over Mubi. Thirteen years aerosol optical depth (AOD) data was obtained from the Multi-angle imaging spectroradiometer (MISR). Mubi is located on latitude 10.27oN and longitude 13.27oE. Statistical tools, as well as analytically derived model for aerosols loading were used to obtain the aerosols retention and loading over the area. It was discovered that the highest aerosols retention over Mubi is 12.7%. The atmospheric constants and tuning constants over Mubi were documented as 0.67 and 0.71 respectively. Due to the volume of aerosols over Mubi, it is necessary to change the International Telecommunication Union (ITU) model which relates to signal budgeting.

Research and Application of Thickness Control Strategies in Steel Plate Rolling

Thickness accuracy of plate production depends on Automatic Gauge Control (AGC) in the plate mill area. A typical modern thickness control system design and implementation of a steel plate mill is discussed together with the im- pact on the design of process models, available measurements, available control actuators and material properties. A high- level software design approach provides the ability to make quick and accurate modifications to both control loops and tuning constants. Control loop strategies and theoretical concepts of steel plate rolling are discussed. Performance results achieved during the startup of a steel plate mill are included.