What Are Strategy Dynamics?

Combustion kinetics is a part of chemical kinetics, and research follows the general laws of chemical kinetics. Combustion kinetics mainly studies the combustion reaction mechanism, combustion reaction speed and its influencing factors. Due to the complexity of combustion reactions, the diversity of combustion measurement methods and the engineering application background of combustion dynamics in national defense and national economy, combustion research has become an important multidisciplinary field.

In order to improve combustion efficiency and control emissions of combustion pollutants, it is critical to study combustion phenomena in depth and explore the nature of combustion. However, combustion is a complex physical and chemical process in which chemical reactions, flows, coexistence of mass and heat, and interactions coexist. Chemical reactions play an important role in the combustion process, and it has a profound effect on controlling combustion phenomena such as ignition, flame propagation, flameout, flammability limit, combustion stability, and pollutant emissions. In order to better study the complex chemical reactions in the combustion process, combustion kinetics came into being. Combustion kinetics mainly studies the combustion reaction mechanism, combustion reaction speed and its influence factors.

The combustion reaction kinetic model (referred to as the model) developed based on elementary reaction research and combustion diagnosis can be used to predict combustion parameters such as heat release rate, flame propagation, flameout, and ignition, and to understand the combustion process in power plants and the pollutants. The emission mechanism provides accurate chemical mechanism for the actual combustion process (diesel, gasoline, gas turbine, etc.), and is also the basis for the simplified mechanism required for CFD calculations. Therefore, the development of combustion reaction kinetics can provide important theoretical guidance for engineering combustion research. ^[1]

Mankind's theory of fuel from the phenomenon of combustion has opened the door to modern chemistry. However, today, more than 300 years later, human understanding of the nature of combustion is still far behind the use of combustion. Combustion dynamics bridges the combustion micro-mechanism and macro-phenomenon. At the end of the 1970s, research on the complex mechanism of combustion started internationally. So far, a series of combustion of single-component fuels and petroleum-based mixed fuels have been published Reaction mechanism. However, due to the high complexity of combustion reactions, people still have a superficial understanding of complex combustion reactions.

The mechanism of the combustion reaction, that is, the path experienced by the combustion reaction:

In fact, the mechanism of the combustion reaction is very complicated, including almost all combustion reactions, not simply obeying the law of mass action and Arrhenius' law. Many characteristics of combustion cannot be explained by simple reaction mechanisms. , Not exactly in one step as shown in the reaction equation, but to complete through many intermediate steps, these intermediate reactions are composed of free atoms or free radicals: free atoms: such as H, 0, free radicals: such as OH , CH3, etc. These free atoms and free radicals are highly reactive. When encountering gas molecules, only a small amount of activation energy is required to react. Therefore, the free atoms and free radicals that easily cause reactions are called activation. center. Experiments show that it is much easier to carry out the reaction by activating the center than the original reactants.

In combustion applications, the combination of the combustion reaction and the directional flow of the gas forms the power base of the vehicle. The combustion numerical simulation method based on the combustion reaction mechanism to calculate the rate of chemical species generation and the turbulence model to solve the governing equations is the most effective way to describe the flow field structure of the flow path in the engine. Therefore, the construction of the combustion reaction mechanism is the combustion value Prerequisites for simulation. However, the diversity of fuel molecular structure and the complexity of combustion reactions determine the long-term nature of the study of reaction mechanisms. According to different research needs, the reaction mechanism can be either a detailed mechanism containing tens of thousands of elementary reactions, a smaller simplified mechanism, or a turnkey mechanism constructed based on some goals. The study of combustion reaction kinetics is not only a scientific need, but also an urgent need for the development of the national economy.

(1) Effect of concentration: As the concentration increases, the number of molecular collisions increases, and the reaction rate increases. At a certain temperature, the gas-phase chemical reaction rate is proportional to the product of the concentration of the reactants at that time. If the reaction is completed in one step according to the relationship of a chemical reaction equation, the order of the concentration of each reactant is equal to the Reaction stoichiometry. This relationship is called the law of mass action.

Elementary Reaction Kinetics of Combustion Kinetics

First of all, the research on elementary reaction kinetics is the premise of the development of combustion reaction kinetics models, which largely determines the accuracy of the models. Combustion models are composed of hundreds or thousands of chemical reactions, in which the determination of elementary reaction paths (qualitative) and the acquisition of rate constants (quantitative) are the focus and difficulty of combustion reaction kinetics research. At present, the information on elementary reaction paths and rate constants obtained through experimental methods has high reliability, and is usually used as an evaluation benchmark for other data sources. However, the experimental detection is often limited by the actual conditions such as temperature and pressure. It can only obtain rate constants in a limited temperature and pressure range, which is not suitable for direct application in the model. ^[4]

Combustion kinetics to obtain basic combustion experimental data under a wide range of conditions

Secondly, obtaining basic combustion experimental data under a wide range of conditions (different temperature zones, pressures, reaction atmospheres, physical models, etc.) is the basis for the validation of the combustion reaction kinetic model, and also provides a guarantee for the development of a universal combustion reaction kinetic model. Obtaining basic combustion experimental data under a wide range of conditions depends on the development of different combustion platforms. Each combustion platform is sensitive to certain reaction rate constants in the combustion model under its combustion conditions, so as to constrain the rate constants of these reactions and improve the model. Accuracy. Extensive verification of the experimental data provided by various experimental platforms can greatly increase the accuracy and applicability of the model. In addition, in order to provide more comprehensive micro-information for model validation under specific combustion conditions, such as the measurement of active free radicals, peroxides, and PAHs concentrations, various combustion platforms need to fully develop the advantages of multiple diagnostic methods, so The continuous innovation of diagnostic technology is undoubtedly the cornerstone of the rapid development of basic combustion research. ^[4]

Combustion dynamics development strategy for establishing a reasonable combustion dynamics model

Based on the above two aspects of research, the development strategy of a reasonable combustion dynamics model is established. In recent years, the development of the model has basically formed a trend from a fuel with a simple structure to a fuel with a complicated structure, and from a single-component fuel to an alternative fuel, so as to finally reveal the combustion nature of practical fuels. At the same time, model simplification based on detailed fuel dynamics models is also an important aspect of dynamics research, providing theoretical support for practical engineering research. ^[4]