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Calculation models used in the DIESEL-RK

 

      Selection of engine models used in the DIESEL-RK is stipulated by the requirements of a high accuracy of results, high rate of calculation and generality. The last condition is a reason of refusal from empirical equations, which are correct only in narrow boundaries. Authors have preferred frequently laborious methods which consider the physical nature of phenomena in engines. A number of calculation methods was developed by authors of this project.
Mathematical models of main phenomena in engine are described in Dr. Sc. (Tech) Dissertation of Prof. A. Kuleshov: Simulation and Optimization of ICE Working Processes

  • The parameters of gas in cylinders and manifolds of an engine are defined by step-by-step solution of the system of difference equations of conservation of energy, mass, and also equation of state written for open thermodynamic systems. The dependence of properties of gas on a composition and temperature is taken into account. The method of difference equations exceeds conventional ones in an accuracy and rate one-fifth as large.

  • To calculate combustion in petrol and gas engines including prechamber engines a multizone model is used. The rate of heat release is calculated by Wiebe method.

  • Mixture formation and combustion in diesel engines are simulated with RK-model. Simulation method of RK-model was developed by Prof. Razleytsev in 1990-1994. After this method was modified and complemented by Dr. Kuleshov. RK-model takes into account:    
    -  shape of the injection profile including multiple injection;
    - drop sizes;
    - direction of sprays in the combustion chamber;
    - dynamic of evolution of fuel sprays;
    - dynamic and profile of swirl;
    - interaction of sprays with an air swirl and walls.

    The method takes into account conditions of evolution of each fuel spray and near wall flows generated by sprays, and also interaction between near wall flows. RK-model allows determination the emission of soot and emission of NO depending on mixture formation and combustion conditions. The software makes it possible to find the optimum of piston bowl shape, fuel sprays directions, diameters and numbers of nozzles, intensity of air swirl and the injection profile shape.

  • Calculation of NO emission is carried out by two ways. 
    • Technique developed by Prof. Zvonov with using  Zeldovich mechanism on the base of chemical equilibrium estimated by 18 species for conventional diesels.
    • Detail Kinetic Mechanism (DKM) (199 reactions, 33 species) for correct prediction of NO emission in engine with large EGR, multiple injection and HCCI. DKM is supported by the local release of DIESEL-RK.
       
  • Soot emission model was developed by Prof. Razleytsev.

  • Design of EGR system is taken into account.

  • A model of gas exchange takes into account a non-steady gas flow in ports, design of engine ports, influence of the neighboring cylinders and the pulse converter design. Two-stroke engine scavenging model including perfect mixing, perfect displacement and short closing being used. It permit a computational optimizing of valve timing, and also determining the best configuration of intake and exhaust ports of two-stroke engines.

  • A heat transfer is simulated separately for different surfaces . The surfaces temperatures are determined by the decision of a heat transfer equation. Coefficient of gas-walls heat transfer in cylimder is determined by the Woschni's formula.
    Heat transfer in valve and piston controlled ports as well as in manifolds is taken into account. 

  • Parameters of turbines and compressors are determined by different ways:
       a) set explicitly or calculate on pressure ratios and efficiency including power balance of turbocharger at each operating mode;
       b) matching of turbine and compressor maps with a piston engine.
    The technique of joint calculation of an internal combustion engine and units of turbocharging on various operating modes allows predicting the performances of turbo and supercharged engines:
    - at variation of speed,
    - at variation of torque,
    - at variation of height of flight,
    - at variation of diving depth in the sea and others.
    Selection of turbocharging units for maintenance of the required characteristics of the supercharged engine is also possible.
    DIESEL-RK supports modeling and research of engines with two-stage turbocharging, Hiperbar systems, etc.

      The program DIESEL-RK makes it possible to simulate a working process of any type of internal combustion engines. Applied calculation models provide high accuracy of results.
      The experience of usage of the program in modeling and researches of engines with different size and application has shown that the program needs no preliminary set-up of empirical coefficients for a concrete engine. It is enough to use Wizard of New Project Creation. This wizard on the basis of the most common data on researched engine will generate files of input data, using the most known technical decisions accepted in area of propulsion engineering. Thus essentially becomes simpler not only process of input data entering but also the most difficult stage of computational research: calibration of engine model. The last is especially important for the students who are not having enough experience, time and experimental data for customizing of the program on object of research, and also for researchers who makes express estimation of an ICE design.
      To obtain authentic calculation results, if you search for the ways of improvement of the engine performances or the ways of decrease of harmful materials emission, etc., it is necessary to carry out the comparison between calculated and measured data for a base engine configuration at several regimes and calibrate models if mismatch occur.
     The amount of empirical coefficients is not great, and they are strictly constant for any operating regimes of engine and for any its configuration.

     Calibrated calculation model provides accuracy simulation of engine over whole operating range with identical values of empirical coefficients. It makes it possible to use DIESEL-RK for development of controlling algorithm of fuel injection system over whole operating range including part load and idling.

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