MODELING OF HEAT EXCHANGE PROCESSES EXPECTING IN CYLINDERS OF THE INTERNAL COMBUSTION ENGINES
Authors: Hashchuk P. , Nikipchuk S. 
Published: October 2019

The general principles of model reflection of working processes in the internal combustion engine are investigated. Like that intramolecular (chemically effective), molecular (thermodynamically active) or macroscopic (ordered by external manifestation) motion in substances causes mass transfer - diffusion, impulse transfer - viscosity, as well as they form the transfer of energy of disordered motion - heat-exchanging. By tying the phenomena of mass, momentum and energy transfer with molecular, intraocular and ordered motions, respectively, the leading, radial and convection components of each of these phenomena can be distinguished. Due to the common condition, diffusion, viscosity, heat transfer are interconnected phenomena and play a decisive role in processes passing through cylinders of the internal combustion engine. Therefore, they together should have been subject to some general harmonious theory of motion and energy exchange, which is based on the uniform physical and mathematical principles of environmental reflection. However, today such a theory does not exist. Because of this, in the study of heat exchange processes in the internal combustion engines we have to move, relying heavily on the principles of empiricism.

In spite of the extremely complex phenomenon of  heat transfer, the internal combustion engine in the working space of the engine is such that it allows us to rely on relatively simple model descriptions based on the principles of empiricism.

The purpose of the work — based on the principles of the theory of similarity, to justify the possibility of adequate reflection and formalized generalization of experimentally identified information about the laws of the flow of heat transfer processes in the engines of Otto (the engine of rapid internal combustion).

The main object of empirical research is the coefficient of heat transfer. Only meaningful transparency and ease of use can be explained by the fact that so far this concept is widely used, although it is completely motivated can be replaced by a more general dimensionless characteristic. A great deal of empirical dependencies are proposed for calculating this coefficient. Each of them has own level of universality and it is applicability limits for adequacy. Generally, universality and adequacy are not mutually conductive characteristics of the quality of empirical relationships. That is why studying a certain set of engine operating modes, it is desirable to involve in the mathematical and experimental apparatus of research, such analytically displayed empirical relationships, which within this set remained unchanged by the structure and values of its main parameters.

Heat transfer in the cylinder of the engine of rapid internal combustion between the gas and the wall of the combustion space occurs mainly due to forced convection. Actually in the engine operating on the Otto cycle, the heat transfer as a result of radiation in the course of fueling is generally negligible because (unlike a diesel engine), in the projectile of combustion, there is not a significant amount of fired particles of soot, and by themselves, gases as emitters, as compared to forced turbulent convection, can tolerate a relatively small amount of heat, which is unlikely to be taken into consideration in general.

Equation of forced convection is traditionally based on a similarity relationship between criteria Nusselt (Nu), Reynolds (Re), Prandtl (Pr); C, n, m, — constant. G.Woschni found out that the values of the degrees of power are acceptable  and .But in general it turned out that good simulation results can be obtained on the basis of experimental information on the flow of pressure and average temperature in the engine cylinder, taking  and for each mode of operation of the engine its meaning  from the range .Examples of model reproduction of the change in the coefficient of heat output from the angle of rotation of the motor shaft for different loads are given.