scholarly journals A criterion based on computational singular perturbation for the construction of reduced mechanism for dimethyl ether oxidation

2013 ◽  
Vol 78 (8) ◽  
pp. 1177-1188
Author(s):  
Zuozhu Wu ◽  
Xinqi Qiao ◽  
Zhen Huang
Keyword(s):  
Steady State ◽  
Singular Perturbation ◽  
Dimethyl Ether ◽  
Reduction Process ◽  
Operating Conditions ◽  
Quasi Steady State ◽  
Reduced Mechanism ◽  
Wide Range ◽  
Computational Singular Perturbation ◽  
Premixed Laminar

A criterion based on the computational singular perturbation (CSP) method is proposed in order to determine the number of quasi-steady state (QSS) species. This criterion is employed for the reduction of a detailed chemical kinetics mechanism for the oxidation of dimethyl ether (DME), involving 55 species and 290 reactions, leading to a 20 steps reduced mechanism which involves 26 species. A software package, named I-CSP, was developed to make the reduction process algorithmic. Input to the I-CSP includes (i) the detailed mechanism, (ii) the numerical solution of the problem for a specific set of operating conditions, (iii) the number of quasi steady state (QSS) species. The resulting reduced mechanism was validated both in homogenous reactor, including auto-ignition and PSR, over a wide range of pressures and equivalence ratios, and in a one-dimensional, unstretched, premixed, laminar steady DME/Air flame. Comparison of the results calculated with the detailed and the reduced mechanisms shows excellent agreement in the case of homogenous reactor, but discrepancies can be observed in the case of the premixed laminar flame.

scholarly journals Development and validation of a reduced mechanism for methane using a new integral algorithm in a premixed flame

2014 ◽  
Vol 68 (5) ◽  
pp. 529-539
Author(s):  
Zuozhu Wu ◽  
Xinqi Qiao ◽  
Zhen Huang
Keyword(s):  
Reduction Process ◽  
Operating Conditions ◽  
Computational Domain ◽  
Fast Reaction ◽  
One Dimensional ◽  
Reduced Mechanism ◽  
Wide Range ◽  
Computational Singular Perturbation ◽  
Premixed Laminar ◽  
Development And Validation

A new algorithm based on Computational Singular Perturbation (CSP) is proposed to construct global reduced mechanism. The algorithm introduces species concentrations, species net production rates and heat release rates as integral weighting factors to integrate CSP-pointers, including radical pointers and fast reaction pointers, throughout the computational domain. A software package based on the algorithm was developed to make the reduction process more efficient. Input to the algorithm includes (i) the detailed mechanism, (ii) the numerical solution of the problem for a specific set of operating conditions, (iii) the number of quasi steady state (QSS) species. The proposed algorithm was applied to the reduction of GRI3.0 involving 53 species and 325 reactions leading to the development of a 15-species reduced mechanism with 10 lumped steps. Then the reduced mechanism was validated in a one-dimensional, unstretched, premixed, laminar steady flame over a wide range of equivalence ratio, and excellent agreements between results calculated with the detailed and the reduced mechanisms can be observed.

scholarly journals Ασυμπτωτική ανάλυση βιολογικών μηχανισμών Michaelis-Menten και ενεργειακού μεταβολισμού στον εγκέφαλο

2019 ◽  
Author(s):  
Δημήτριος Πατσατζής
Keyword(s):  
Perturbation Theory ◽  
Steady State ◽  
Singular Perturbation ◽  
Partial Equilibrium ◽  
Singular Perturbation Theory ◽  
Geometric Singular Perturbation Theory ◽  
Quasi Steady State ◽  
State Approximation ◽  
Steady State Approximation ◽  
Computational Singular Perturbation

Η Διδακτορική Διατριβή αυτή πραγματεύεται την ανάλυση δύο βιολογικών συστημάτων πολλαπλών χρονοκλιμάκων με την Υπολογιστική μέθοδο Ιδιόμορφων Διαταραχών (Computational Singular Perturbation, CSP). H CSP είναι μία αλγοριθμική μέθοδος της ασυμπτωτικής ανάλυσης, η οποία βρίσκει εφαρμογή στο ευρύτερο πλαίσιο της Γεωμετρικής Θεωρίας Ιδιόμορφων Διαταραχών (Geometric Singular Perturbation Theory). Η μέθοδος CSP έχει τη δυνατότητα να παρέχει τα κατάλληλα απλοποιημένα μοντέλα, τα κριτήρια για την εγκυρότητα τους και έναν αριθμό διαγνωστικών εργαλείων για την απόκτηση της φυσικής κατανόησης των υπό μελέτη μηχανισμών. Δεδομένου ενός δύσκαμπτου συστήματος (πολλαπλών χρονοκλιμάκων) οποιασδήποτε πολυπλοκότητας, η CSP μπορεί α) να κατασκευάσει έναν αριθμό απλοποιημένων μοντέλων, συμπεριλαμβανομένων και αυτών που παράγονται από τις παραδοσιακές τεχνικές της Προσέγγισης Μερικούς Ισορροπίας (Partial Equilibrium Approximation, PEA) και της Προσέγγισης Οιωνεί ΜόνιμηςΚατάστασης (Quasi Steady-State Approximation, QSSA), β) να καθορίσει τις συνθήκες υπό τις οποίες τα απλοποιημένα αυτά μοντέλα παρέχουν πρώτης τάξης ακρίβεια και ευστάθεια, γ) να αναγνωρίσει τις “γρήγορες” χημικές αντιδράσεις και μεταβλητές, δ) να εντοπίσει τις αντιδράσεις που παράγουν τις “γρήγορες”και “αργές” χρονοκλίμακες, ε) να διακρίνει τις αντιδράσεις που συνεισφέρουν στη δημιουργία του Slow Invariant Manifold που αναπτύσσεται στο χώρο των φάσεων, πάνω στο οποίο εξελίσσεται το σύστημα και στ) να αναγνωρίσει τις αντιδράσεις που επηρεάζουν την αργή εξέλιξη όλων των χημικών ενώσεων: δηλαδή,όλες τις πληροφορίες που απαιτούνται για τη ρύθμιση του μοντέλου. Τα δύο βιολογικά συστήματα πολλαπλών χρονοκλιμάκων που αναλύονται είναι (i) ο μηχανισμός Michaelis-Menten και (ii) ένας μηχανισμός μεταβολισμού γλυκόζης και γαλακτικού οξέος για την παραγωγή ενέργειας στα αστροκύτταρα και τους νευρώνες του ανθρώπινου εγκεφάλου. Ο μηχανισμός πολλαπλών χρονοκλιμάκων Michaelis-Menten (MM) προσομοιώνει τη δράση των ενζύμων σε ενδοκυτταρικό και εξωκυττταρικό επίπεδο και χρησιμοποιείται σε μεγάλη ποικιλία επιστημονικών πεδίων. Το βασικό αποτέλεσμα είναι η εισαγωγή μέσω της CSP μίας νέας έκφρασης για το ρυθμό του ΜΜ μηχανισμού, η οποία είναι έγκυρη σε όλο τον παραμετρικό χώρο που χαρακτηρίζεται από δυναμική πολλαπλών χρονοκλιμάκων. Η προσπάθεια κατασκευής μιας τέτοιας έκφρασης ξεκίνησε με την εισαγωγή του ΜΜ μοντέλου το 1913 και, συνεπώς, υπάρχει εκτενής βιβλιογραφία για τέτοιου είδους εκφράσεις και για τις συνθήκες εγκυρότητάς των. Η πιο διαδεδομένη από αυτές τις εκφράσεις εισήχθηκε το 1925, είναι γνωστή ως ΜΜ εξίσωση (MM equation) και είναι έγκυρη σε περιορισμένη περιοχή του παραμετρικού χώρου. Όλες οι υπάρχουσες εκφράσεις έχουν περιορισμένη εγκυρότητα στον παραμετρικό χώρο και έχουν παραχθεί μέσω των παραδοσιακών PEA/QSSA προσεγγίσεων. Η νέα έκφραση, απλοποιείται σε όλες τις υπάρχουσες εκ φράσεις, στις περιοχές στις οποίες η κάθε μία εξ’ αυτών είναι έγκυρη. Οι απλοποιήσεις αυτές εισάγουν έγκυρα κριτήρια για την ακρίβεια των PEA/QSSA προσεγγίσεων. Αποδείχθηκε ότι η έκφραση που παρείχε η CSP είναι πάντα ευσταθής και η πιο ακριβής από όλες τις γνωστές PEA/QSSA εκφράσεις, γεγονός που το καθιστά ιδανική επιλογή για την ανάλυση των πειραματικών αποτελεσμάτων. Ο μηχανισμός μεταβολισμού της γλυκόζης και του γαλακτικού οξέος στον ανθρώπινο εγκέφαλο, ο οποίος εμπεριέχει ΜΜ εκφράσεις, αναλύθηκε με σκοπό τη φυσική κατανόηση δύο αντικρουόμενων υποθέσεων στη νευροχημεία του εγκεφάλου. Οι αντετιθέμενες υποθέσεις αφορούν το κατά πόσον το γαλακτικό οξύ ρέει από τα αστροκύτταρα στους νευρώνες ή από τους νευρώνες στα αστροκύτταρα. Σημειωτέον ότι υπάρχουν πειραματικά αποτελέσματα, τα οποία ενισχύουν και τις δύο αυτές υποθέσεις. Στη παρούσα ανάλυση, τα αλγοριθμικά εργαλεία της CSP εφαρμόζονται για την ανάλυση της γρήγορης και αργής δυναμικής του συστήματος, με σκοπό την διερεύνηση εγκυρότητας των δύο αυτών υποθέσεων. Αρχικά,αναγνωρίζονται οι ισορροπίες που αναδύονται μέσω της γρήγορης δυναμικής και αποκαλύπτονται τα μονοπάτια μέσω των οποίων μεταφέρεται η γλυκόζη και το γαλακτικό οξύ, για κάθε υπόθεση. Δεδομένων αυτών των πληροφοριών, η αργή δυναμική του συστήματος αναλύεται περαιτέρω, αναδεικνύοντας τις αντιδράσεις και τις μεταβλητές που οδηγούν την αργή δυναμική του συστήματος. Αναδεικνύεται ότι και οι δύο υποθέσεις είναι έγκυρες σε διαφορετικές όμως περιοχές στον παραμετρικό χώρο και καθορίζονται οι βιολογικές διεργασίες που εξασφαλίζουν την εγκυρότητα της κάθε υπόθεσης. Τέλος, αποδεικνύεται ότι οι βιολογικές διεργασίες.

TRANSIENT OPERATION OF SENSIBLE FIXED-BED REGENERATORS

2022 ◽  
pp. 1-16
Author(s):  
Hadi Ramin ◽  
Easwaran N Krishnan ◽  
Gurubalan Annadurai ◽  
Carey J. Simonson
Keyword(s):  
Steady State ◽  
Fixed Bed ◽  
Operating Conditions ◽  
Design Parameters ◽  
Transient Temperature ◽  
Quasi Steady State ◽  
Transient Operation ◽  
Steady State Condition ◽  
Test Standards ◽  
Wide Range

Abstract Fixed-bed regenerator is a type of air-to-air energy exchanger and recently introduced for energy recovery application in HVAC systems because of their high heat transfer effectiveness. Testing of FBRs is essential for performance evaluation and product development. ASHRAE and CSA recently included guidelines for testing of FBRs in their respective test standards. The experiments on FBRs are challenging as they never attain a steady state condition, rather undergoes a quasi-steady state operation. Before reaching the quasi-steady state, FBRs undergo several transient cycles. Hence, the test standards recommend getting measurements after one hour of operation, assuming FBR attains the quasi-steady state regardless of test conditions. However, the exact duration of the initial transient cycles is unknown and not yet studied so far. Hence, in this paper, the duration of FBR's transient operation is investigated for a wide range of design and operating conditions. The test standards' recommendation for the transient duration is also verified. The major contributions of this paper are (i) quantifying the effect of design parameters (NTUo and Cr*) on the duration of transient operation and (ii) investigation of the effect of sensor time constant on the transient temperature measurements. The results will be useful to predict and understand the transient behavior of FBRs accurately.

Simulation of an Industrial Linear Low Density Polyethylene Plant

2011 ◽  
Vol 6 (1) ◽  
Author(s):  
Ali Farhangiyan Kashani ◽  
Hossein Abedini ◽  
Mohammad Reza Kalaee
Keyword(s):  
Steady State ◽  
Average Molecular Weight ◽  
Molar Fraction ◽  
Operating Conditions ◽  
Low Density Polyethylene ◽  
Process Equipment ◽  
Flow Index ◽  
Low Density ◽  
Linear Low Density Polyethylene ◽  
Wide Range

In this paper, an industrial linear low density polyethylene (LLDPE) production process including two serried fluidized bed reactors (FBR) and other process equipment was completely simulated in steady state mode. Both of FBRs were considered like two serried continuous stirred tank reactors (CSTR). In this simulation, a kinetic model that is based on a multiple active site heterogeneous Ziegler-Natta catalyst was used for simulation of reactions in two FBRs. Simulator by using this model is able to predict the important attributes of LLDPE like melt flow index (MFI), density (ρ), polydispersity (PDI), numerical and weight average molecular weight (Mn, Mw) and co-polymer molar fraction (SFRAC). On the other hand, this simulator can be applied in wide range of changing in inlet operating conditions. The results of the simulation are compared with industrial data of LLDPE plant. A good agreement is observed between the simulator predictions and actual plant data. Finally, by using of the simulator, the steady state operating conditions for producing different grades of polyethylene are obtained.

Ethanol Mechanism Reduction Based on DRGEPSA Method at Various Operating Ranges

2020 ◽  
Author(s):  
Shrabanti Roy ◽  
Omid Askari
Keyword(s):  
Sensitivity Analysis ◽  
Error Propagation ◽  
Cfd Simulation ◽  
Reduction Process ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Computational Time ◽  
Wide Range ◽  
Relation Graph ◽  
Future Work

Abstract Reducing the size of a detail chemical kinetic is necessary in the prospect of numerical computation. In this work a skeleton reduction is done on a detail mechanism of ethanol. The detailed ethanol mechanism used here is developed through reaction mechanism generator (RMG). The generated mechanism is validated at wide range of engine relevant operating conditions using laminar burning speed (LBS), ignition delay time (IDT) and species mole fraction calculation at different reactor conditions. This detail mechanism consists of 67 species and 1031 reactions. Though the mechanism is in a very good agreement at various operating ranges with experimental data, it is costly to use a detail mechanism for 3D computational fluid dynamics (CFD) analysis. To make the mechanism applicable for CFD simulation further reduction of species and reactions is essential. In this work a skeleton mechanism is generated using directed relation graph technique with error propagation and sensitivity analysis (DRGEPSA). The DRGEPSA method, works based on error calculation at user defined condition. This technique is a combination of two methods, directed relation graph with error propagation (DRGEP) and directed relation graph with sensitivity analysis (DRGASA). To ensure the wide range of applicability of the skeleton mechanism, IDT is calculated at temperature, pressure, and equivalence ratio ranges from 700–2000 K, 1–40 atm and 0.6–1.4 respectively. A 10% error estimation is considered during the process. Initially DRGEP is applied on the detail mechanism to eliminate unimportant species. Further, sensitivity analysis helps to identify and reduce more unimportant species from the mechanism. Reactions related to the deleted species are automatically removed from the mechanism in each step. The final skeleton mechanism has 42 species and 464 reactions. This skeleton mechanism is validated and compared with different IDT data for the conditions not used in reduction technique. Results of LBS and different species concentration from reactor conditions is considered for validation. The skeleton mechanism can reduce computational time by 35% for LBS and 25% for IDT calculation. For future work, this skeleton mechanism will be considered in optimum reduction process.

scholarly journals Simulation based study on improving the transient response quality of turbocharged diesel engines

2017 ◽  
Vol 23 (3) ◽  
pp. 297-309 ◽  
Author(s):  
Rakesh Mishra ◽  
Syed Mohammad Saad
Keyword(s):  
Steady State ◽  
Diesel Engine ◽  
Quality Indicators ◽  
Transient Response ◽  
Operating Conditions ◽  
Compressor Wheel ◽  
Turbocharged Diesel Engine ◽  
Content Type ◽  
Wide Range

Purpose Use of fossil fuels in automotive sector is one of the primary causes of greenhouse emissions. The automotive engines need to perform at their best efficiency point to limit these emissions. Most of the quality indicators in this regard are based on near steady state global operational characteristics for engines without considering local performance. In the present study, extensive numerical simulations have been carried out covering a wide range of steady state and transient operating conditions to quantify interaction of turbocharger with engines through turbo lag phenomena which may cause increased emissions during the load change conditions. Furthermore possible innovations have been explored to minimize turbo lag phenomena. The paper aims to discuss these issues. Design/methodology/approach In this paper quality indicators have been developed to quantify the performance of turbocharged diesel engine under the transient event of rapid change in fueling rate which has been rarely investigated. The rate of fueling is changed from 40 mm3/injection to 52 mm3/injection at 1,000 rpm engine speed which corresponds to normal operating condition. To improve quality of transient response, torque assistance method and reduction of inertia of compressor wheel have been used. Parametric study has been undertaken to analyze the quality indicators such as outlet pressure of the compressor and the compressor speed. The turbo lag is quantified to obtain the close to optimal transient response of turbocharged diesel engine. Findings It has been shown that, with torque assist the transient response of the internal combustion engine is significantly improved. On the other hand, marginal improvement in transient response is observed by the reduction in inertia of the compressor wheel. Research limitations/implications The findings indicate that turbo lag can be minimized by providing torque assistance by active and passive means. Practical implications The developed methods can be used in practice for efficient operation of vehicles. Social implications The work carried out in the paper provides a way to minimize harmful emissions. Originality/value The quality indicators developed provide a quantitative measure of turbo lag phenomena and address the above mentioned problems.

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