8 research outputs found
Metamodel-based optimization of a PID controller parameters for a coupled-tank system
Get PDFLiquid flow and level control are essential requirements in various industries, such as paper manufacturing, petrochemical industries, waste management, and others. Controlling the liquids flow and levels in such industries is challenging due to the existence of nonlinearity and modeling uncertainties of the plants. This paper presents a method to control the liquid level in a second tank of a coupled-tank plant through variable manipulation of a water pump in the first tank. The optimum controller parameters of this plant are calculated using radial basis function neural network metamodel. A time-varying nonlinear dynamic model is developed and the corresponding linearized perturbation models are derived from the nonlinear model. The performance of the developed optimized controller using metamodeling is compared with the original large space design. In addition, linearized perturbation models are derived from the nonlinear dynamic model with time-varying parameters
Numerical evidence on deflagration fronts in a methane/n-dodecane dual-fuel shear layer under engine relevant conditions
No full textFunding Information: This study has been funded by the Academy of Finland (grant numbers 318024, 332784, and 297248). We acknowledge CSC, Finnish IT Center for Science for providing the computational resources. Funding Information: This study has been funded by the Academy of Finland (grant numbers 318024 , 332784 , and 297248 ). We acknowledge CSC, Finnish IT Center for Science for providing the computational resources. Publisher Copyright: © 2023 The Author(s)To date, high resolution spray-assisted dual-fuel (DF) studies have focused on capturing the ignition process while the subsequent post-ignition events have been largely neglected due to modeling requirements and high computational cost. Here, we use a simplified approach for studying ignition front evolution after ignition. Three-dimensional scale-resolved simulations of igniting shear layers (0≤Re≤1500) are studied to better understand reaction fronts in engine-relevant conditions. We carry out quasi-DNS in a DF combustion setup consisting of premixed n-dodecane/methane/air/EGR at 700K as a fuel stream and premixed methane/air as the oxidizer at a pressure of 60 atmospheres and an ambient temperature of 900 K. The flow solution resolution is δ/10, where δ=laminar flame thickness. The present study primarily focuses on the hypothesized flame formation and its characterization. Under these conditions, the simulations indicate two-stage ignition further leading to reaction front initiation and dual-fuel flame establishment. For Re<1500, a reaction front resembling DF deflagration is demonstrated close to the auto-ignition timescales. At Re=1500, mixing effects promote more rapid dilution and the DF deflagration front formation is slightly delayed although still observed. For the first time, at rather short timescales of 0.2−0.4 IDT (ignition delay time) after the ignition, we provide numerical evidence on DF deflagration front emergence in shear-driven DF combustion processes via 3D numerical simulations for 0<Re≤1500.Peer reviewe
Large-eddy simulation of diesel pilot spray ignition in lean methane-air and methanol-air mixtures at different ambient temperatures
No full textFunding Information: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is financially supported by the Academy of Finland (grant numbers 332784 and 318024). Publisher Copyright: © IMechE 2022.In dual-fuel compression-ignition engines, replacing common fuels such as methane with renewable and widely available fuels such as methanol is desirable. However, a fine-grained understanding of diesel/methanol ignition compared to diesel/methane is lacking. Here, large-eddy simulation (LES) coupled with finite rate chemistry is utilized to study diesel spray-assisted ignition of methane and methanol. A diesel surrogate fuel (n-dodecane) spray is injected into ambient methane-air or methanol-air mixtures at a fixed lean equivalence ratio phi(LRF) = 0.5 at various ambient temperatures (T-amb = 900, 950, 1000 K). The main objectives are to (I) compare the ignition characteristics of diesel/methanol with diesel/methane at different T-amb, (2) explore the relative importance of low-temperature chemistry (LTC) to high-temperature chemistry (HTC), and (3) identify the key differences between oxidation reactions of n-dodecane with methane or methanol. Results from homogeneous reactor calculations as well as 3 + 3 LES are reported. For both DF configurations, increasing T-amb leads to earlier first- and second-stage ignition. Methanol/n-dodecane mixture is observed to have a longer ignition delay time (IDT) compared to methane/n-dodecane, for example approximate to three times longer IDT at T-amb = 950 K. While the ignition response of methane to T-amb is systematic and robust, the T-amb window for n-dodecane/methanol ignition is very narrow and for the investigated conditions, only at 950 K robust ignition is observed. For methanol at T-amb = 1000 K, the lean ambient mixture autoignites before spray ignition while at T-amb = 900 K full ignition is not observed after 3 ms, although the first-stage ignition is reported. For methanol, LTC is considerably weaker than for methane and in fully igniting cases, heat release map analysis demonstrates the dominant contribution of HTC to total heat release rate for methanol. Reaction sensitivity analysis shows that stronger consumption of OH radicals by methanol compared to methane leads to the further delay in the spray ignition of n-dodecane/methanol. Finally, a simple and novel approach is developed to estimate IDT in reacting LES using zero-dimensional IDT calculations weighted by residence time from non-reacting LES data.Peer reviewe
Large eddy simulation of diesel spray–assisted dual-fuel ignition: A comparative study on two n-dodecane mechanisms at different ambient temperatures
No full textIn dual-fuel compression ignition engines, a high-reactivity fuel, such as diesel, is directly injected to the engine cylinder to ignite a mixture of low-reactivity fuel and air. This study targets improving the general understanding on the dual-fuel ignition phenomenon using zero-dimensional homogeneous reactor studies and three-dimensional large eddy simulation together with finite-rate chemistry. Using the large eddy simulation framework,n-dodecane liquid spray is injected into the lean ambient methane-air mixture at phi=0.5. The injection conditions have a close relevance to the Engine Combustion Network Spray A setup. Here, we assess the effect of two different chemical mechanisms on ignition characteristics: a skeletal mechanism with 54 species and 269 reaction steps (Yao mechanism) and a reduced mechanism with 96 species and 993 reaction steps (Polimi mechanism). Altogether three ambient temperatures are considered: 900, 950, and 1000 K. Longer ignition delay time is observed in three-dimensional large eddy simulation spray cases compared to zero-dimensional homogeneous reactors, due to the time needed for fuel mixing in three-dimensional large eddy simulation sprays. Although ignition is advanced with the higher ambient temperature using both chemical mechanisms, the ignition process is faster with the Polimi mechanism compared to the Yao mechanism. The reasons for differences in ignition timing with the two mechanisms are discussed using the zero-dimensional and three-dimensional large eddy simulation data. Finally, heat release modes are compared in three-dimensional large eddy simulation according to low- and high-temperature chemistry in dual-fuel combustion at different ambient temperatures. It is found that Yao mechanism overpredicts the first-stage ignition compared to Polimi mechanism, which leads to the delayed second-stage ignition in Yao cases compared to Polimi cases. However, the differences in dual-fuel ignition for Polimi and Yao mechanisms are relatively smaller at higher ambient temperatures.Peer reviewe
Large-eddy simulation of tri-fuel ignition: diesel spray-assisted ignition of lean hydrogen–methane–air mixtures
No full textWe present 3D numerical results on tri-fuel (TF) combustion using large-eddy simulation and finite rate chemistry. The TF concept was recently introduced by Karimkashi et al. (Int. J. Hydrogen Energy, 2020) in 0D. Here, the focus is on spray-assisted ignition of methane–hydrogen blends. The spray acts as a high-reactivity fuel (HRF) while the ambient premixed methane-hydrogen blend acts as a low-reactivity fuel (LRF) mixture. Better understanding on such a TF process could enable and motivate more extensive hydrogen usage in e.g. compression ignition marine engines where spray-assisted dual-fuel (DF) combustion is already utilised. The studied spray set-up is based on the modified ECN Spray A case, see Kahila et al. (Combustion and Flame, 2019) for DF combustion. The ambient pressure and temperature are (Formula presented.) 900 K and (Formula presented.) 60 bar. The hydrogen content of the LRF blend is varied systematically by changing the molar fraction (Formula presented.), (Formula presented.). The main added value of the study is that we extend the TF concept to 3D. The particular findings of the study are as follows: 1) Consistent with Karimkashi et al. 2020, hydrogen delays ignition also in 3D and the effect becomes significant for (Formula presented.). 2) The ratio between the first- and second-stage ignition delay times (Formula presented.) and (Formula presented.). Furthermore, the ratio between 3D and 0D ignition delay times is given as (Formula presented.) for all TF cases. 3) Finally, consistent with Karimkashi et al. 2020, also in 3D the high-temperature combustion heat release mode is shown to appear stronger in TF than the low-temperature combustion mode compared to DF methane–diesel combustion.Peer reviewe
Modeling and simulation of a wirelessly-powered thermopneumatic micropump for drug delivery applications
Get PDFThis paper presents modeling and finite element analysis of a thermopneumatic micropump with a novel design that does not affect the temperature of the working fluid. The micropump is operated by activating a passive wireless heater using wireless power transfer when the magnetic field is tuned to match the resonant frequency of the heater. The heater is responsible for heating an air-heating chamber that is connected to a loading reservoir through a microdiffuser element. The solution inside the reservoir is pumped through a microchannel that ends with an outlet hole. The thermal and pumping performances of the micropump are analyzed using finite element method over a low range of Reynold’s number ⩽ 10 that is suitable for various biomedical applications. The results demonstrate promising performance with a maximum flow rate of ∼2.86 μL/min at a chamber temperature of 42.5 ºC, and a maximum pumping pressure of 406.5 Pa. The results show that the developed device can be potentially implemented in various biomedical areas, such as implantable drug delivery applications
Large-eddy simulation of tri-fuel combustion: Diesel spray assisted ignition of methanol-hydrogen blends
No full textDevelopment of marine engines could largely benefit from the broader usage of methanol and hydrogen which are both potential energy carriers. Here, numerical results are presented on tri-fuel (TF) ignition using large-eddy simulation (LES) and finite-rate chemistry. Zero-dimensional (0D) and three-dimensional (3D) simulations for n-dodecane spray ignition of methanol/hydrogen blends are performed. 0D results reveal the beneficial role of hydrogen addition in facilitating methanol ignition. Based on LES, the following findings are reported: 1) Hydrogen promotes TF ignition, significantly for molar blending ratios β X = [H 2]/([H 2]+[CH 3OH]) ≥0.8. 2) For β X = 0, unfavorable heat generation in ambient methanol is noted. We provide evidence that excessive hydrogen enrichment (β X ≥ 0.94) potentially avoids this behavior, consistent with 0D results. 3) Ignition delay time is advanced by 23–26% with shorter spray vapor penetrations (10–15%) through hydrogen mass blending ratios 0.25/0.5/1.0. 4) Last, adding hydrogen increases shares of lower and higher temperature chemistry modes to total heat release.Peer reviewe
Metamodel-based Optimization of a PID Controller Parameters for a Coupled-tank System
Get PDFLiquid flow and level control are essential requirements in various industries, such as paper manufacturing, petrochemical industries, waste management, and others. Controlling the liquids flow and levels in such industries is challenging due to the existence of nonlinearity and modeling uncertainties of the plants. This paper presents a method to control the liquid level in a second tank of a coupled-tank plant through variable manipulation of a water pump in the first tank. The optimum controller parameters of this plant are calculated using radial basis function neural network metamodel. A time-varying nonlinear dynamic model is developed and the corresponding linearized perturbation models are derived from the nonlinear model. The performance of the developed optimized controller using metamodeling is compared with the original large space design. In addition, linearized perturbation models are derived from the nonlinear dynamic model with time-varying parameters
