Mathematical Modeling of the Working Process of a Two-Stroke Engine with Countermoving Pistons

Simulation of the working process of an internal combustion engine is the basis for all further calculations and studies of the engine. Of particular relevance is the availability of an adequate mathematical model of the engine process due to the fact that due to the trend of continuous improvement of engine performance, it is necessary to take into account many influencing factors to obtain a satisfactory result. The most complex and dependent on many physicochemical parameters is the process of combustion of fuel in the engine. Models of combustion in diesel engines can be divided into three groups: detailed models; empirical and semipemirical models. The analysis of world experience in research and mathematical modeling of combustion process in internal combustion engines is performed in the work. The advantages and disadvantages of different mathematical models are indicated. It is proposed to use a semi-empirical mathematical model of combustion which describes the differential characteristic of the combustion rate by two curves corresponding to the periods of the first flash and diffusion combustion. Use of such model simplifies performance of calculations and at the same time allows to receive qualitative results considering many factors of influence.

Turbulent Superstructures in Inert Jets and Diffusion Jet Flames

An experimental study of spatially localized very large-scale motion superstructures, propagating in a jet of carbon dioxide at low Reynolds numbers, was carried out. A hot-wire anemometer and a high-speed 2D PIV with a frequency of 7 kHz were used as measuring instruments. Such a puff-type superstructure in a jet with a longitudinal dimension of up to 20–30 nozzle diameters are initially formed in the jet source—a long tube in a laminar-turbulent transition mode (without artificial disturbances). It is shown that this regime with intermittency in time, when part of the time flow is laminar and the other part of time is turbulent, exists both at the exit from the nozzle and in the near field of the jet. Thus, the structural stability of such turbulent superstructures in the near field of the jet was found. Despite the large longitudinal scale, these formations have a transverse dimension of the order of several nozzle diameters. These structures have a complex internal topology, that is, superstructures are a conglomeration of vortices of different sizes from macroscale to microscale. Using the example of diffusion combustion of methane in air, it is demonstrated that in reacting jets, the existence of such large localized perturbations is a powerful physical mechanism for a global change in the flame topology. At the same time, the presence of a cascade of vortices of different sizes in the puff composition can lead to fractal deformation of the flame front.

A study and comparison of the modes of diffusion combustion of hydrogen and methane at their outflow from the annular nozzle together with the flow of supplied air from the coaxially located circular nozzle

The article presents qualitative data on the study of the process of diffusion combustion during the outflow of a gas jet from a nozzle apparatus with a certain arrangement of nozzles. The nozzle apparatus is a round nozzle with a straight channel and a coaxially located annular slot. In the experiments, hydrogen or methane was supplied through an annular slot, and the air was supplied through a central circular micro nozzle. The main features of the diffusion combustion of hydrogen and methane during the outflow from the nozzle apparatus are revealed and a qualitative comparison of the processes is carried out. In both cases, at the initial stage, laminar combustion is observed near the nozzle exit and a breakthrough of the flame front occurs with the release of an incombustible mixture of combustible gas and air. At a high flow rate, the flame separates from the nozzle exit. The fundamental difference is that hydrogen exhibits significantly better combustion stabilization characteristics at the nozzle exit.

Analytical Model of the Process of Thermal Barrier Coating by the MO CVD Method

Integral regularities in the growth of 7YSZ thermal barrier coatings during MO CVD (Metal–Organic Chemical Vapor Deposition) are proposed. Within the framework of the model of the reacting boundary layer, the coating deposition process is considered as a process of independent global reactions of diffusion combustion of Zr(dpm)4 and Y(dpm)3 under convection conditions on a permeable surface. The rate of coating growth and the efficiency of using a precursor are analytically evaluated. The correctness of the proposed approach is confirmed by comparison with known experimental data. The considered model can be used to analyze the deposition of coatings from various mixtures of precursors, such as Nd(dpm)3, Hf(dpm)4, and Sm(dpm)3.

Study of synthesis and combustion of composite fuels based on n-decane and Al nanoparticles

The article is devoted to the analysis of a diffusion combustion of a composite fuel (formed by an addition of non-oxidized aluminum (Al) nanoparticles (NP’s) to n-decane) with oxygen. The process of obtaining Al NP’s consisted of a laser fragmentation of initially large commercially produced NP’s (so called “Alex” with mean diameter is about 450 nm) in the solution of isopropanol. A final size distribution of NP’s was determined by a CPS DC2400 measuring disk centrifuge. The morphology of NP’s was characterized with the Transmission Electron Microscope (TEM) JEM-100C. The measured average diameter of NP’s was about 40 nm. In the final step of a preparation of a composite fuel an isopropanol was exchanged on n-decane. To characterize the composite fuel, diffusion combustion was used in combination with the laser diagnostic technique CARS. Temperature distributions along the x direction were measured at two values of distances from the nozzle. It has been shown that, for the fuel consistent of 0.1% mass concentration of Al NP’s in n-decane, the temperature at the distance equaled 14 mm downstream from the nozzle exit of a burner in the vicinity of the flame front was significantly higher (by 200–300 K) than that upon burning of pure n-decane.

Numerical and Experimental Study of Inverse Diffusion LPG-Air Flames Pulsation

This study uses Ansys 16 commercial package to investigate an accurate numerical model that can trace the flame shape from inverse diffusion combustion of LPG with a focus on the effect of air pulsation on the combustion characteristics. The simulation is based on solving the energy, mass and momentum equations. The large eddy simulation turbulence model and the non-premixed combustion model are used to simulate the pulsating combustion reaction flows in a cylindrical chamber with an air frequency of 10,20,50,100 and 200 rad/sec. The numerical results are in great agreement with the experimental results in the flame shape and the temperature distribution along the combustion chamber in both pulsating and non-pulsating combustion. Diffusion combustion responds positively to pulsating combustion and increases mixing in the reaction zone. Increasing the air frequency increases the temperature fluctuations, the peak turbulent kinetic energy and maximum velocity magnitude, respectively, by 27.3%, 300%, and 200%. Increasing the Strouhal number to 0.23 shortens the flame by 40% and reduces nitric oxide and carbon monoxide by 12% and 40%, respectively, including an environmentally friendly combustion product. The maximum average temperature dropped from 1800 K to 1582 K with a very homogeneous temperature distribution along the combustion chamber which is very important for furnaces.