Predicting the Sauter Mean Diameter of Swirl Cup Airblast Fuel Injector Based on Backpropagation (BP) Neural Network Model.

This study was dedicated to introducing a new method for predicting the Sauter mean diameter (SMD) buildup in the swirl cup airblast fuel injector. There have been considerable difficulties with predicting SMD mainly because of complicated flow characteristics in a spray. Therefore, the backpropagation (BP) neural network-based machine learning was applied for the prediction of SMD as a function of geometry, condition parameters, and axial distance such as primary swirl number, secondary swirl number, venturi angle, mass flow rate of fuel, and relative air pressure. SMD was measured by a phase Doppler particle analyzer (PDPA). The results show that the prediction accuracy of the trained BP neural network was excellent with a coefficient of determination (R2) score of 0.9599, root mean square error (RMSE) score of 1.4613, and overall relative error within 20%. Through sensitivity analysis, the relative air pressure drop and primary swirl number were the largest and smallest factors affecting the value of SMD, respectively. Finally, the prediction accuracy of the BP neural network model is far greater than the current prediction correlations. Moreover, for the predicting target in the present study, the BP neural network shows the advantages of a simple structure and short running time compared with PSO-BP and GRNN. All these prove that the BP neural network is a novel and effective way to predict the SMD of droplets generated by a swirl cup airblast fuel injector.

Central recirculation zone induced by the DBD plasma actuation.

Central recirculation zone (CRZ) is commonly formed in the near field of the injector exit by the vane swirler and used to stabilize the flame. In our experiment, a CRZ induced by the DBD plasma actuation was observed in the low swirl burner configuration for the first time, which clearly demonstrated that the mechanism of the combustion control by the plasma swirler is mainly through the aerodynamic effect. Three dielectric barrier discharge (DBD) actuators are placed in a circular array around the axis to generate ionic wind in the circumferential direction of the injector. Characteristics of the flow field have been measured using Laser Doppler Anemometry. It is found that a central recirculation zone with the shape of an ellipsoid is formed in the non-reacting flow field with the plasma actuation. The position of the upstream stagnation point was determined by the strength of the actuation. Although the CRZ disappears in the reacting flow field as the result of combustion heat release, the influence of the discharge on the flame lift-off height is noticeable. The results demonstrate that swirl enhancement by the plasma swirler is feasible, flexible and effective as a non-intrusive measure for flow control.

Accurate prediction of enthalpies of formation for a large set of organic compounds.

This article describes a multiparameter calibration model, which improves the accuracy of density functional theory (DFT) for the prediction of standard enthalpies of formation for a large set of organic compounds. The model applies atom based, bond based, electronic, and radical environmental correction terms to calibrate the calculated enthalpies of formation at B3LYP/6-31G(d,p) level by a least-square method. A diverse data set of 771 closed-shell compounds and radicals is used to train the model. The leave-one-out cross validation squared correlation coefficient q(2) of 0.84 and squared correlation coefficient r(2) of 0.86 for the final model are obtained. The mean absolute error in enthalpies of formation for the dataset is reduced from 4.9 kcal/mol before calibration to 2.1 kcal/mol after calibration. Five-fold cross validation is also used to estimate the performance of the calibration model and similar results are obtained.

Accurate prediction of thermodynamic properties of alkyl peroxides by combining density functional theory calculation with least-square calibration.

Owing to the significance in kinetic modeling of the oxidation and combustion mechanisms of hydrocarbons, a fast and relatively accurate method was developed for the prediction of Delta(f)H(298)(o) of alkyl peroxides. By this method, a raw Delta(f)H(298)(o) value was calculated from the optimized geometry and vibration frequencies at B3LYP/6-31G(d,p) level and then an accurate Delta(f)H(298)(o) value was obtained by a least-square procedure. The least-square procedure is a six-parameter linear equation and is validated by a leave-one out technique, giving a cross-validation squared correlation coefficient q(2) of 0.97 and a squared correlation coefficient of 0.98 for the final model. Calculated results demonstrated that the least-square calibration leads to a remarkable reduction of error and to the accurate Delta(f)H(298)(o) values within the chemical accuracy of 8 kJ mol(-1) except (CH(3))(2)CHCH(2)CH(2)CH(2)OOH which has an error of 8.69 kJ mol(-1). Comparison of the results by CBS-Q, CBS-QB3, G2, and G3 revealed that B3LYP/6-31G(d,p) in combination with a least-square calibration is reliable in the accurate prediction of the standard enthalpies of formation for alkyl peroxides. Standard entropies at 298 K and heat capacities in the temperature range of 300-1500 K for alkyl peroxides were also calculated using the rigid rotor-harmonic oscillator approximation.

An ab initio/Rice-Ramsperger-Kassel-Marcus prediction of rate constant and product branching ratios for unimolecular decomposition of propen-2-ol and related H + CH2COHCH2 reaction.

Enols have been found to be important intermediates in the combustion flames of hydrocarbon [C. A. Taatjes et al., Science 308, 1887 (2005)]. The removal mechanism of enols in combustion flame has not been established yet. In this work, the potential energy surface for the unimolecular decomposition of syn-propen-2-ol and H + CH(2)COHCH(2) recombination reactions have been first investigated by CCSD(T) method. The barrier heights, reaction energies, and geometrical parameters of the reactants, products, intermediates, and transition states have been investigated theoretically. The results show that the formation of CH(3)CO + CH(3) via the CH(3)COCH(3) intermediate is dominant for the unimolecular decomposition of syn-propen-2-ol and its branching ratio is over 99% in the whole temperature range from 700 to 3000 K, and its rate constant can be expressed as an analytical form in the range of T=700-3000 K at atmospheric pressure. This can be attributed to the lower energy barrier of this channel compared to the other channels. The association reaction of H with CH(2)COHCH(2) is shown to be a little more complicated than the unimolecular decomposition of syn-propen-2-ol. The channel leading to CH(3)CO + CH(3) takes a key role in the whole temperature range at atmospheric pressure. However at the higher pressure of 100 atm, the recombination by direct formation of syn-propen-2-ol through H addition is important at T<1000 K. In the range of T>1400 K, the recombination channel leading to CH(3)CO + CH(3) turns out to be significant.

[Impact of chronic schistosomiasis japonica on the protective immunity induced by vaccine against hepatitis B virus].

OBJECTIVE: To study the impact of chronic schistosomiasis on the protective immunity induced by vaccine against hepatitis B virus. METHODS: 24 patients with chronic or advanced schistosomiasis (experimental group) and 26 healthy volunteers (control group) all without hepatitis B virus infection were selected for the study. Sera of the subjects in the two groups were collected before inoculation and on the 35th day after inoculation with yeast-derived recombinant hepatitis B vaccine. The level of anti-Hbs, IL-2 and TNF-alpha in sera was examined by ELISA respectively. RESULTS: Anti-Hbs in both groups were negative before inoculation, with an average absorbance (A value) of 0.134 and 0.150 respectively. After inoculation, positive rate of anti-Hbs was 17% (4/24, average A value 0.145 ) in experimental group and 92% (24/26, average A value was 1.210) in control group. The vaccine against hepatitis B induced significantly higher level of anti-Hbs in healthy volunteers compared with that in schistosomiasis patients (P < 0.01). The level of IL-2 and TNF-alpha increased in both groups after inoculation without significant difference compared with the level before inoculation. CONCLUSION: The results suggest that the protective immunity of patients with chronic schistosomiasis is deficient to the stimulation of hepatitis B virus and it may involve in a higher incidence of hepatitis B among schistosomiasis patients.