Comment on “Comparison of Methods for Estimating Critical Properties of Alkyl Esters and Its Mixtures”

Comment on “Comparison of Methods for Estimating Critical Properties of Alkyl Esters and Its Mixtures

Understanding the Relationship between Cetane Number and the Ignition Delay in Shock Tubes for Different Fuels Based on a Skeletal Primary Reference Fuel (<i>n</i>‑Hexadecane/Iso-cetane) Mechanism

A new skeletal oxidation mechanism for the primary reference fuel (PRF) was established with a decoupling methodology. The mechanism is composed of <i>n</i>-hexadecane and iso-cetane submechanisms, containing 44 species and 139 reactions. Using the present mechanism, the relationship between cetane number and the ignition delay in shock tubes was investigated. First, based on the ignition delay data in shock tubes, the cetane number of various fuels was estimated using the present PRF mechanism and a weighted least-squares method. The prediction of cetane number investigated in this study primarily focused on the operating conditions of practical diesel engines (i.e., the equivalence ratio of 1.0 and pressures from 19–80 atm), which encompass the cetane number from 15 to 100. Under the test operating conditions, the mean absolute deviation of the predicted cetane number is within 3.327. Furthermore, according the cetane number of different fuels, the ignition delays in shock tubes were reproduced by the present mechanism focusing on a wide range of equivalence ratios (0.5–3.0) and pressures (20–50 atm). The results indicated that the predicted IDs of alkanes were more accurate than those of other types of fuels and blended fuels because of the consistent molecular structure of the <i>n</i>-hexadecane/iso-cetane used in the present mechanism. Because of the compact size of the skeletal mechanism, its application can considerably reduce the computational time for 3D combustion simulations, especially for practical fuels with complicated compositions

Understanding the Relationship between Cetane Number and the Ignition Delay in Shock Tubes for Different Fuels Based on a Skeletal Primary Reference Fuel (<i>n</i>‑Hexadecane/Iso-cetane) Mechanism

A new skeletal oxidation mechanism for the primary reference fuel (PRF) was established with a decoupling methodology. The mechanism is composed of <i>n</i>-hexadecane and iso-cetane submechanisms, containing 44 species and 139 reactions. Using the present mechanism, the relationship between cetane number and the ignition delay in shock tubes was investigated. First, based on the ignition delay data in shock tubes, the cetane number of various fuels was estimated using the present PRF mechanism and a weighted least-squares method. The prediction of cetane number investigated in this study primarily focused on the operating conditions of practical diesel engines (i.e., the equivalence ratio of 1.0 and pressures from 19–80 atm), which encompass the cetane number from 15 to 100. Under the test operating conditions, the mean absolute deviation of the predicted cetane number is within 3.327. Furthermore, according the cetane number of different fuels, the ignition delays in shock tubes were reproduced by the present mechanism focusing on a wide range of equivalence ratios (0.5–3.0) and pressures (20–50 atm). The results indicated that the predicted IDs of alkanes were more accurate than those of other types of fuels and blended fuels because of the consistent molecular structure of the <i>n</i>-hexadecane/iso-cetane used in the present mechanism. Because of the compact size of the skeletal mechanism, its application can considerably reduce the computational time for 3D combustion simulations, especially for practical fuels with complicated compositions

Comprehensive influence of uncertainty propagation of chemical kinetic parameters on laminar flame speed prediction: a case study of dimethyl ether

The uncertainties existing in the parameters of chemical kinetic models have a non-negligible influence on the model predictions. It is necessary to conduct a quantitative uncertainty analysis to explore the influence of each parameter on chemical mechanism predictions. To comprehensively consider the effect of the uncertainties of reaction rate parameters, thermodynamic parameters, and transport parameters on model predictions, local sensitivity analysis, local-sensitivity-based uncertainty analysis (LSUA), and random-sampling high dimensional model representation (RS-HDMR) method were coupled to investigate the uncertainty propagation of the chemical kinetic parameters to the calculated laminar flame speed of dimethyl ether under a wide range of conditions using a detailed mechanism. First, the uncertainty analysis was conducted using the local sensitivity analysis and the LSUA method under a wide range of operating conditions to identify the important operating conditions and chemical kinetic parameters. It is found that the prediction uncertainty of laminar flame speed is more obvious under the conditions of high dilution ratio, high pressure, and large equivalence ratio than that under other conditions. According to the results of LSUA, the prediction uncertainty is mainly from the reaction rate coefficients and thermodynamic data. Then, the uncertainty propagation from the significant parameters to the calculated laminar flame speed under important conditions was analysed using the RS-HDMR method. To reduce the huge computational cost of the RS-HDMR method, the backpropagation artificial neural network was employed. The RS-HDMR results indicate that the reaction H + O2 = O + OH has the highest sensitivity coefficient under the whole investigated conditions, which is different from the results using the LSUA method. The non-linear relationship between the rate coefficient and the predicted laminar flame speed is responsible for the discrepancy. Furthermore, it is found that the sensitivity coefficient of the input parameters strongly depends on the operating conditions.</p

Development of a New Skeletal Chemical Kinetic Model of Toluene Reference Fuel with Application to Gasoline Surrogate Fuels for Computational Fluid Dynamics Engine Simulation

On the basis of our recent experience in developing a skeletal chemical kinetic model of primary reference fuel (PRF) with a semi-decoupling methodology, a new general and compact skeletal model of toluene reference fuels (TRF) consisting of 56 species and 168 reactions is presented for the oxidation of gasoline surrogate fuels. The skeletal submodel of toluene is added to the PRF model using reaction paths and sensitivity analysis. An improvement has been made in comparison to the existing skeletal models of TRF on laminar flame speed and important species evolution, while predictions of precise ignition delay are maintained. The skeletal model in this work is validated by comparison to the experimental data in a shock tube, jet-stirred reactor, flow reactor, and premixed laminar flame speed, as well as an internal combustion engine over extensive ranges of equivalence ratio, temperature, and pressure for each single fuel component and their blends. The new skeletal model is also tested using two ternary surrogates with different compositions on shock tube, laminar flame speed, and internal combustion engine. The results indicate that the overall satisfactory agreements between the predictions and experimental data are achieved

Development of a Phenomenological Soot Model Coupled with a Skeletal PAH Mechanism for Practical Engine Simulation

A new chemical mechanism with 12 species and 26 reactions for formation of polycyclic aromatic hydrocarbons (PAHs) was developed and integrated into a skeletal mechanism for oxidation of primary reference fuel (PRF). Coupled with the new skeletal PRF-PAH mechanism, an improved phenomenological soot model was further constructed based on our previous work. By validating against the experimental data on the related PAHs in four premixed laminar flames of <i>n</i>-heptane/iso-octane and three counterflow diffusion flames of <i>n</i>-heptane, it is indicated that the major species concentrations were well reproduced by the model. Moreover, validations of the new soot model show that the soot yield, particle diameter, and number density were predicted with reasonable agreement with the experimental data in a rich <i>n</i>-heptane shock tube over wide temperature and pressure ranges. Compared with the soot model with acetylene as precursor species, the new model agrees better with the measurement, which proves the necessity of including PAHs chemistry for soot modeling. Finally, the model was applied to simulate the soot distributions in <i>n</i>-heptane sprays in the Sandia constant-volume combustion chamber under high EGR conditions, as well as the evolutions of PAH and soot concentrations in an engine fueled with <i>n</i>-heptane. It is also found that the experimental data was reasonably well reproduced by the model

Development of a New Skeletal Chemical Kinetic Model of Toluene Reference Fuel with Application to Gasoline Surrogate Fuels for Computational Fluid Dynamics Engine Simulation

On the basis of our recent experience in developing a skeletal chemical kinetic model of primary reference fuel (PRF) with a semi-decoupling methodology, a new general and compact skeletal model of toluene reference fuels (TRF) consisting of 56 species and 168 reactions is presented for the oxidation of gasoline surrogate fuels. The skeletal submodel of toluene is added to the PRF model using reaction paths and sensitivity analysis. An improvement has been made in comparison to the existing skeletal models of TRF on laminar flame speed and important species evolution, while predictions of precise ignition delay are maintained. The skeletal model in this work is validated by comparison to the experimental data in a shock tube, jet-stirred reactor, flow reactor, and premixed laminar flame speed, as well as an internal combustion engine over extensive ranges of equivalence ratio, temperature, and pressure for each single fuel component and their blends. The new skeletal model is also tested using two ternary surrogates with different compositions on shock tube, laminar flame speed, and internal combustion engine. The results indicate that the overall satisfactory agreements between the predictions and experimental data are achieved

Kinetic and Numerical Study on the Effects of Di-<i>tert</i>-butyl Peroxide Additive on the Reactivity of Methanol and Ethanol

A numerical investigation was conducted to study the effects of di-<i>tert</i>-butyl peroxide (DTBP) additive on the reactivity of methanol and ethanol fuels. First, a reduced primary reference fuel (PRF)–​​methanol–​​ethanol–​​DTBP mechanism was proposed to simulate the homogeneous charge compression ignition (HCCI) combustion processes of PRF and alcohol–​​DTBP fuel mixtures. By linking through the combustion phasing of HCCI operation with the PRF fuels, effective PRF number maps were generated for the alcohol–​DTBP fuels. The agreement between experimental and simulation results was reasonably good. Both the experiments and simulations showed that DTBP enhances the fuel reactivity of the alcohols and that the rate of reactivity enhancement decreases with increasing DTBP percentage. The reasons for the enhancement of reactivity by DTBP addition to both methanol and ethanol fuels were then explored kinetically. It was found that both thermal and chemical effects contribute to the reactivity enhancement, and this can be attributed to the heat released in the DTBP decomposition process, the reactive radicals generated through the CH₃ → CH₃O₂ → CH₃O₂H → OH pathway, and the reaction pathway of fuel + CH₃O₂ → CH₃O₂H → OH. The major reason for the different response of DTBP between methanol and ethanol was found to be the higher DTBP content in methanol–​DTBP mixtures for the same operating conditions, and this was further confirmed by the fact that the effects of DTBP addition on methanol and ethanol reactivity were quite similar if the same absolute DTBP mass was added to these two alcohols

Kinetic and Numerical Study on the Effects of Di-<i>tert</i>-butyl Peroxide Additive on the Reactivity of Methanol and Ethanol

A numerical investigation was conducted to study the effects of di-<i>tert</i>-butyl peroxide (DTBP) additive on the reactivity of methanol and ethanol fuels. First, a reduced primary reference fuel (PRF)–​​methanol–​​ethanol–​​DTBP mechanism was proposed to simulate the homogeneous charge compression ignition (HCCI) combustion processes of PRF and alcohol–​​DTBP fuel mixtures. By linking through the combustion phasing of HCCI operation with the PRF fuels, effective PRF number maps were generated for the alcohol–​DTBP fuels. The agreement between experimental and simulation results was reasonably good. Both the experiments and simulations showed that DTBP enhances the fuel reactivity of the alcohols and that the rate of reactivity enhancement decreases with increasing DTBP percentage. The reasons for the enhancement of reactivity by DTBP addition to both methanol and ethanol fuels were then explored kinetically. It was found that both thermal and chemical effects contribute to the reactivity enhancement, and this can be attributed to the heat released in the DTBP decomposition process, the reactive radicals generated through the CH₃ → CH₃O₂ → CH₃O₂H → OH pathway, and the reaction pathway of fuel + CH₃O₂ → CH₃O₂H → OH. The major reason for the different response of DTBP between methanol and ethanol was found to be the higher DTBP content in methanol–​DTBP mixtures for the same operating conditions, and this was further confirmed by the fact that the effects of DTBP addition on methanol and ethanol reactivity were quite similar if the same absolute DTBP mass was added to these two alcohols

Clinical features and prognostic implications of ecotropic viral integration site 1 (<i>EVI1</i>) in childhood acute lymphoblastic leukemia

In contrast to the extensive knowledge on EVI1 in myeloid malignancies, few data are available on the EVI1 transcript in pediatric ALL. The purpose of this study was to examine the clinical and biological significance of EVI1 and validate its prognostic significance in pediatric patients with ALL. Here, we examined the clinical and biological significance of EVI1 expression, as measured by real-time polymerase chain reaction (PCR) in 837 children with newly diagnosed ALL treated on the National Protocol of Childhood Leukemia in China (NPCLC)-ALL-2008 protocol, and aimed to explore their prognostic significance in pediatric ALL patients. The EVI1 expression was detected in 27 of 837 (3.2%) patients. No statistically significant differences in prednisone response, complete remission (CR) rates and relapse rates were found between EVI1 overexpression (EVI1+) group and EVI1− group. Moreover, we found no significant difference in event-free survival (EFS) and overall survival (OS) between these two groups, also multivariate analysis did not identify EVI1+ as an independent prognostic factor. In the subgroup analysis, there was no difference in clinical outcome between EVI1+ and EVI1− patients in standard‑risk (SR), intermediate-risk (IR) and high-risk (HR) groups. In the minimal residual disease (MRD)−4 group, EVI1+ patients have significantly lower EFS and OS rates compared to EVI1− patients. Further large‑scale and well‑designed prospective studies are required to confirm the results in the future.</p