A novel active parameter selection strategy for the efficient optimization of combustion mechanismsMárton Kovács, Máté Papp, Tamás Turányi, Tibor Nagy
Proc. Combust. Inst., 39, available online (2023)

Optimization
of large combustion mechanisms means that a few dozen parameters
(called active parameters) are optimized within their uncertainty limits
to achieve a better reproduction of the experimental data, which is
usually measured by a mean square error function. In previous studies,
the active parameters were selected based either on their local
sensitivity coefficients (strategy S) or on the products of local
sensitivity coefficient and a corresponding uncertainty parameter
(strategy SU). This latter measure is known by various names:
optimization potential, sensitivity-uncertainty index or
uncertainty-weighted sensitivity coefficient. In this work, we proposed
three novel active parameter selection strategies of increasing
complexity (PCA-SU, PCA-SUE, PCALIN) and demonstrated their superior
performance in the optimization of pre-exponential factors (A) in a
methanol/NOx combustion mechanism (562 reaction steps of 70 species)
against 2360 data measured in shock tube, JSR and flow reactor
experiments. The novel methods are based on the principal component
analysis (PCA) of sensitivity matrices scaled by the uncertainties of
parameters (U) and the uncertainty of the experimental data (E). These
PCA-based methods take into account parameter correlations and designate
parameter groups and corresponding relevant subsets of experimental
data, thereby a factor of 4–7 savings in optimization time was achieved
over the S and SU methods. PCA-SUE method performed better than the
PCA-SU as it also considered the uncertainty of the experimental data.
The PCALIN strategy is similar to PCA-SUE, but it also considers the
linear change (LIN) of the error function, which depends on the
simulation error of experimental data, and thereby it could provide the
most accurate models as a function of the number of active parameters.
Based on the PCALIN strategy, fitting all three Arrhenius parameters
resulted in further improvements, however, it provided moderate
improvements over simple A-factor tuning and required significantly more
computer time.
Comparison and analysis of butanol combustion mechanisms
Martin Bolla, Máté Papp, Carsten Olm, Hannes Böttler, Tibor Nagy, István Gy. Zsély, Tamás Turányi
Energy&Fuels, 36, 11154–11176 (2022)

A
detailed review of the performances of 24 butanol combustion
mechanisms, published between 2008 and 2020, is given using a
comprehensive experimental data collection (89,388 data points in 266
datasets from 32 publications). The data cover wide ranges of
equivalence ratio (φ = 0.38–2.67), diluent ratio (0.15–0.98), initial
temperature (672–1886 K), and pressure (0.9–90 atm). The collection
includes ignition delay time measurements in shock tubes and rapid
compression machines, concentration determinations in shock tubes,
jet-stirred reactors, flow reactors, and laminar burning velocity
measurements. The experimental data were recorded in ReSpecTh Kinetics
Data Format (RKD format) v.2.3 XML data files, which are available in
the ReSpecTh site (http://respecth.hu). The standard deviations of the
measurements were estimated using both the published experimental
uncertainty and the scatter error of the datasets determined by code
Minimal Spline Fit. Mechanism CRECK 2020 was found to be the best
mechanism for n-butanol (biobutanol) combustion, while the mechanisms
Sarathy 2014, Vasu 2013, and Yasunaga 2012 (in this order) were the best
considering the experimental data for all isomers. A part of the
simulations failed, and to improve the ratio of successful simulations,
the code ThermCheck was created, which detects discontinuities and
nonsmoothness of thermodynamic functions defined by NASA polynomials
provided with the published mechanisms and corrects them by tuning their
coefficients. Local sensitivity analysis applied to the experimental
conditions was used to identify the most important reaction steps of the
mechanism Sarathy 2014. The sensitivity analysis was extended to the
adiabatic ignition of n-butanol–air mixtures by systematically changing
the initial temperature and pressure. All butanol combustion mechanisms
were also tested on a hydrogen combustion data collection, which
indicated that some of them were inaccurate due to their inadequate
hydrogen combustion reaction block. Suggestions were given for the
improvement of the Sarathy 2014 mechanism.
The importance of chemical mechanisms in sonochemical modelling
Cs. Kalmár, T. Turányi, I. Gy. Zsély, M. Papp, F. Hegedűs
Ultrasonics Sonochemistry, 83, 105925 (2022)

A
state-of-the-art chemical mechanism is introduced to properly describe
chemical processes inside a harmonically excited spherical bubble placed
in water and saturated with oxygen. The model uses up-to-date
Arrhenius-constants, collision efficiency factors and takes into account
the pressure-dependency of the reactions. Duplicated reactions are also
applied, and the backward reactions rates are calculated via suitable
thermodynamic equilibrium conditions. Our proposed reaction mechanism is
compared to three other chemical models that are widely applied in
sonochemistry and lack most of the aforementioned modelling issues. In
the governing equations, only the reaction mechanisms are compared, all
other parts of the models are identical. The chemical yields obtained by
the different modelling techniques are taken at the maximum expansion
of the bubble. A brief parameter study is made with different pressure
amplitudes and driving frequencies at two equilibrium bubble sizes. The
results show that due to the deficiencies of the former reaction
mechanisms employed in the sonochemical literature, several orders of
magnitude differences of the chemical yields can be observed. In
addition, the trends along a control parameter can also have dissimilar
characteristics that might lead to false optimal operating conditions.
Consequently, an up-to-date and accurate chemical model is crucial to
make qualitatively and quantitatively correct conclusions in
sonochemistry.
Comparison of methane combustion mechanisms using laminar burning velocity measurements
Peng Zhang, István Gy. Zsély, Máté Papp, Tibor Nagy,
Tamás Turányi
Combust Flame, 238, 111867 (2022)
Publication Date: December 22, 2021
Large
amount of experimental data for laminar burning velocity (LBV)
measurements of methane (+H2/CO) − oxygen − diluent mixtures (5500 data
points in 646 datasets) covering wide ranges of equivalence ratio,
diluent ratio, cold side temperature and pressure were collected from
111 publications. The diluents included N2 , H2O, CO2 , Ar and He. The
data files are available on the ReSpecTh site (http://respecth.hu).
Performances of 12 methane combustion mechanisms on reproducing these
LBV
measurements were analyzed according to experiment types and
conditions. Most mechanisms could predict well the LBVs for
stoichiometric and fuel-lean mixtures and for diluent ratios higher than
60%. The performances of several mechanisms were relatively poor at
other conditions. Focusing on the operating conditions of natural gas
engines, we recommend the application of mechanisms FFCM-I-2016,
SanDiego-2014, and NUIG1.1-2021 for engine simulations. Mechanisms
Aramco-II-2016, Konnov-2009, Caltech-2015 and Glarborg-2018 have the
lowest average errors for the reproduction of all available methane LBV
data.
Using local sensitivity analysis on the most accurate
mechanisms, we identified 29 important elementary reactions, which,
however, were not present in all the 12 mechanisms. We also collected
large amount of directly measured and theoretically calculated rate
coefficients for these reactions and compared them with the rate
coefficients used in the 12 mechanisms. Reactions found important in any
of the Aramco-II-2016, Konnov-2009 and Glarborg-2018 mechanisms, but
missing from the Aramco-II-2016, Konnov-2009, Glarborg-2018,
Caltech-2015, FFCM-I-2016 and NUIG1.1-2021 mechanisms were added to
these six mech-
anisms to investigate if the extended mechanism
performs better than the original one. Some of the extended mechanisms
became the best performing mechanisms.
Comparison of Methane Combustion Mechanisms Using Shock Tube and Rapid Compression Machine Ignition Delay Time MeasurementsP. Zhang, I. Gy. Zsély, V. Samu, T. Nagy, T. Turányi
Energy Fuels,
35, 12329–12351 (2021)
Publication Date: July 9, 2021
https://doi.org/10.1021/acs.energyfuels.0c04277-
We intended to collect all published experimental data on the ignition methane - oxygen mixtures, with possible added fuel: H2 and CO; possible diluents: N2, Ar, He). These included shock tube and RCM data (5521 data points in 643 datasets from 76 publications), covering wide ranges of temperature T, pressure p, equivalence ratio φ, and diluent concentration. Thirteen recent methane combustion mechanisms were tested against these experimental data.
Design of combustion experiments using differential entropyÉva Valkó, Máté Papp, Márton Kovács, Tamás Varga,
István Gy. Zsély, Tibor Nagy, Tamás Turányi
Combustion Theory and Modelling,
26, 67-90 (2022)
Publication Date: November 9, 2021
https://doi.org/10.1080/13647830.2021.1992506-

The
aim of several combustion experiments is the determination of the rate
coefficients of important elementary reactions. Sheen and Manion (J.
Phys. Chem. A, 118 (2014) 4929–4941) suggested a method for the design
of shock tube experiments based on differential entropy. Their method
was modified and extended in this work. In the extended method, both the
experimental and residual errors of the measurements are considered at
the calculation of the posterior uncertainty of the determined rate
parameters, the differential entropy matrix is calculated in an
analytical way and the net information flux value is calculated for each
suggested experimental point. In an iterative procedure, all
investigated experimental points with negative net information flux
values are discarded and the remaining experimental conditions are
recommended for the measurements. The most valuable candidate
experimental points can be determined based on the net information flux
values.