Papers by Keyword: Chemical Kinetics

Abstract: The pozzolanic additions are widely used as concrete component for numerous technical, economic and environmental reasons. Obviously the hydration process in a pozzolana containing system differs from hydration of Ordinary Portland Cement (OPC) what is indicated macroscopically by slower increase of strength and lower hydration heat. This paper aims to study pozzolanic reaction from perspective of chemical kinetics. From this point of view pozzolanic reaction and carbonation are two parallel reactions which are competing for portlandite (Ca (OH)₂). The rate of each of these two reactions is characterized by rate constant and order of reaction. The system under study was 1:1 mixture lime – ceramic powder. The course of reaction was primarily studied by thermogravimetry which results were further subjected to kinetic analysis. MAS NMR spectroscopy was used for study of structural changes taking place in material in the course of pozzolanic reaction.

Abstract: In this paper the work deals with the computational analysis of early direct injected HCCI engine with turbocharger using the CHEMKIN-PRO software. The computational analysis was carried out in the base of auto ignition chemistry by means of reduced chemical kinetics. For this study the neat diesel and Bio ethanol diesel blend (E20) were used as fuel. The inlet pressure was increased to 1.2 bar to simulate the turbocharged engine operation. The injection time was advanced to 18° before top dead centre (BTDC) i.e., 5° BTDC than normal injection time of 23° BTDC. The equivalence ratio was kept at 0.6 (ɸ=0.6) and the combustion, emission characteristics and chemical kinetics of the combustion reaction were studied. Since pressure and temperature profiles plays a very important role in reaction path at certain operating conditions, an attempt had been made here to present a complete reaction path investigation on the formation/destruction of chemical species at peak temperature and pressure conditions. The result showed that main draw backs of HCCI combustion like higher levels of unburned hydrocarbon emissions and carbon monoxide emissions are reduced in the turbocharged operation of the HCCI engine when compared to normal HCCI engine operation without turbocharger.

Abstract: A numerical study was conducted to understand the flame characteristics of ethylene under O₂/CO₂ atmosphere by detailed chemical kinetic models. Special interest is focused on the effects of CO₂ on flame propagation velocity and ignition delay. A modified reaction mechanism was established, and the ability of the reaction scheme was evaluated through comparison with well-defined laboratory data in the literature. A key result of the study is that the flame temperature and flame speed are significantly reduced because of the chemical and thermal effects of CO₂. The most important reactions as well as the dominant reaction steps under both O₂/CO₂ atmosphere and air atmospheres were also studied. It can be concluded that although the main reaction paths of fuel oxidation under both atmospheres are quite similar, the most important elementary reactions are different from each other. Besides, the same reactions assume great importance for ignition under air atmosphere become less qualified under O₂/CO₂ atmosphere.

Abstract: The high-performance solid propellants play very important role in defense industry, which required highly energetic binders with good mechanical properties. In order to get the activation parameters for energetic binders, In-Situ FT-IR spectroscopic technique is used to study the chemical kinetics of glycidyl azide polymer (GAP) and hydroxyl terminated poly butadiene (HTPB) with isophorone diisocyanate (IPDI) at various temperatures. The reaction was followed by monitoring the change in intensity of the absorption band of NCO stretching at 2257cm^-1 and CO stretching at 1731cm^-1. The polyurethane reaction has been found to be second order and the rate constant seems to be different between GAP/IPDI and HTPB/IPDI due to reactivity difference of OH groups. Dibutyl tin dilurate (DBTDL) was used as curing catalyst. By using Arrhenius and Eyring equations, the activation parameters were obtained at different temperatures (60, 70, 80 and 90°C). The apparent activation energy for the two systems GAP/IPDI and HTPB/IPDI were found to be 63.51 kJ mol^-1 and 41.06 kJ mol^-1 while the enthalpy and entropy of activation were found to be 62.35 kJ mol^-1 and-36.24 kJ.mol^-1K^-1, 39.08 J mol^-1 and-98.84 J mol^-1K^-1 respectively.Key words: In-Situ FT-IR; glycidyl azide polymer (GAP); hydroxyl terminated poly butadiene (HTPB); chemical kinetics; polyurethane; dibutyl tin dilurate (DBTDL).

Abstract: To determine the hydrocarbon - generating characteristics of Shuangyang Formation in Well Chang 27.We selected dark mudstone in Shuangyang Formation to launch Rock-Eval (open system) thermal simulation. Through thermal simulation data to demarcate a kinetic model,the Shuangyang Stratum mudstone samples reveal the gas intensity is mainly distributed in (210~230) kJ/mol),the average activation energy is 223kJ/mol. The hydrocarbon - generating characteristics of Shuangyang Formation in Well Chang 27 whose hydrocarbon generation stage mainly in the period (37~24) Ma, corresponding the late period of the Yongji Formation deposition to the late period of the Qijia Formation deposition. In Chang 27 Well area,the average generating strength of gas in Shuangyang Formation is (21~37×10⁸) m³·km². The hydrocarbon generation stage of Shuangyang Formation in Chang 27 Well area is mainly in (37~24) Ma, corresponding to the late deposition period of the Yongji Formation and Qijia Formation. Both the shorter periods of hydrocarbon generation and late hydrocarbon generation period made great contributions to accumulation, in which Shuang_1 formation played a bigger role.

Abstract: A model for Premixed Ammonium Perchlorate (AP)/Hydroxyl-terminated Polybutadiene (HTPB) combustion based on detailed chemical kinetics was established on two-dimensional cylindrical coordinates using the Vorticity-Velocity formulation, finite difference methods and several essential mathematical algorithms. This model includes both solid and condensed phase combustion mechanisms and the detailed chemical kinetics of the gas phase with 37 species and 127 reactions. Results obtained from the model, such as temperature and burning rate, match data from experiments. It is found that the model established in the current study is reliable and accurate, and the Vorticity-Velocity approach combined with finite difference methods is capable of and efficient in dealing with premixed AP/HTPB combustion.

Abstract: The chemical kinetics dissolution of rock salts from Sakon Nakhon Basin is characterized by drill cores and compared to geochemical compositions of natural brines obtained within the study areas in Udon Thani and Sakon Nakhon Province, Thailand. A criterion for rock salt core analysis depends upon the maximum amount of halite, based on X-ray diffractometry. Mass balance relation between brines and rock salt dissolution is conducted by the difference of initial and final weights of the core sample in each experimental batch. To monitor salinity related to its dissolution, the concentrations of total dissolved solids (TDS) are determined for each time period. The dissolution rate of rock salts can be evaluated from chemical compositions of the reactants; sodium-chloride (Na-Cl, halite) and calcium-sulphate (Ca-SO₄, anhydrite), corresponding to the TDS content, against the experimental variables of time and temperature. The most important aspect of brine and rock salt interfaces concerns the chemical kinetics developed for the rate of reaction (R) and rate constant (k) as R = k [NaC^0.7[CaSO₄]^0.8. The overall order of the reaction is experimentally 1.5 with respect to concentration of sodium chloride and calcium sulphate. Phase transitions based on the behavior of the thermodynamic free energy as a function of thermodynamic variables are accompanied by the release of heat. The activation energy needs for the dissolution reaction of rock salt is-18.08 kJ/mol. The experimental result indicates the exothermic reaction, similar to the calculation by theoretical thermodynamics. Saturation indexes of brines as a function of anhydrite reveal the supersaturating condition while rock salt dissolution reaches the equilibrium condition.

Abstract: Several influence for the soot and NOx emission of methanol and n-heptane dual fuel combustion is advised, using homogeneous charge compression ignition model in CHEMKIN-PRO. The calculating results indicate that methanol plays an important role in the course of soot formation, but the effect of methanol is smaller for NOx. With the increase of methanol quantities, the soot formation is reduced and the soot particle diameter is smaller; if the fuel equivalence ratio is small, the influence of methanol is obvious to NOx emission. If the fuel equivalence ratio ≥ 1.0 , the trend of NOx emission changed. With the increase of methanol, NOx emission early increased, and decreased late.

Abstract: The modellings of the respiration rate of papaya by using enzyme kinetics, chemical kinetics and artificial neural network (ANN) were developed respectively, and all the models were parameterized with experimental data obtained at temperatures of 8, 18 and 28 °C by the closed system method for comparison. The ANN model was thought to be the best after being evaluated by the mean absolute percentage error (MAPE) and the two-tailed Pearson correlation coefficient r. The study demonstrated that the ANN model and the chemical kinetic model can be applied to the prediction of papaya’s respiration rate.

Abstract: The splitting-operator method has been widely used in the numerical simulation of complex combustion system with its high computation efficiency. The main difficult encountered in the method is how to integrate the stiff chemical kinetics ordinary differential equation (ODE) efficiently and accurately in each grid node of flow field. Although several ODE software packages such as LSODE and VODE have very predominant performance in integrating stiff and non-stiff case, it couldn’t ensure the positivity of mass fraction in integrating stiff chemical kinetic ODE. A detail liquid rocket hypergolic bipropellant combination of Monomethylhydrazine (MMH)/Red Fuming Nitric Acid (RFNA) chemical mechanism consisting of 550 elementary reactions among 83 species was constituted basing on several relevant literatures firstly. And then a modified implicit iterative difference algorithm with variable time steps was developed to tackle the problem of mass fraction non-positive. The results from the integration of MMH /nitrogen tetroxide (NTO) chemical kinetic ODE indicate that the algorithm is always retain stability and positive value of mass fraction. The time step length would also be automatically adjusted at different chemical reaction time in the algorithm to keep its computational efficiency.