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An improved version of the ECFM-3Z combustion model coupled with advanced models for NO and soot formation has been implemented in the CFD code FIRE and validated with respect to its applicability to conventional and alternative Diesel combustion. For this purpose the set of models was applied to the calculation of combustion and pollutant formation in a high-speed DI Diesel engine for selected operating points adopting a large number of DoE based combustion system parameter variations. Assessment of the models' performance was enabled via comparison of the calculation results with the corresponding experimental data. Good agreement of calculated and measured in-cylinder pressure traces as well as pollutant formation trends could be observed for both the conventional and alternative Diesel combustion modes for the investigated parameter variations.

The present contribution gives an overview of the use of different simulation tools for the optimisation of injection parameters of a Diesel engine. With a one-dimensional tool, the behaviour of the mechanics and fluid dynamics of the entire injection system is calculated. This simulation provides information on the dynamic needle lift, injection rates, pressures etc. The flow within the injector is simulated using a three-dimensional CFD tool. By use of a two-phase model it is possible to analyse the cavitating flow inside the injector and to calculate the effective nozzle hole area as well as the exit flow characteristics. Mixture formation, combustion and pollutant formation simulation is performed adopting three-dimensional CFD. In order to provide the initial and boundary conditions for the engine CFD simulation and to optimize the engine cycle performance a one dimensional tool is adopted.

The present contribution gives an overview of the use of different simulation tools for the optimization of injection parameters of a diesel engine. With a one-dimensional tool, the behavior of the mechanics and fluid dynamics of the entire injection system is calculated. This simulation provides information on the dynamic needle lift, injection rates, pressures, etc. The flow within the injector is simulated using a three-dimensional CFD tool. By use of a two-phase model, it is possible to analyze the cavitating flow inside the injector and to calculate the effective nozzle hole area as well as the exit flow characteristics. Mixture formation, combustion and pollutant formation simulation is performed adopting three-dimensional CFD. In order to provide the initial and boundary conditions for the engine CFD simulation and to optimize the engine cycle performance a one-dimensional tool is adopted.

The paper describes a 1D-3D modeling technique for the simulation of the fuel injection systems. The technique is based on the one-dimensional modeling of the fuel flow and the mechanical motion of the injection system with the AVL software HYDSIM (from e.g. the fuel rail up to the nozzle chamber) and three-dimensional modeling of the nozzle flow with AVL-FIRE (from the needle seat through the spray holes up to the combustion chamber). The nozzle mesh, including the nozzle sac region with spray holes and (optionally) the lower part of the nozzle chamber, is created with the FIRE Preprocessor. The interface between the 1D and the 3D simulation regions can be freely chosen within the nozzle chamber at any position between the needle seat and guide.

Computational Fluid Dynamics is applied to the analysis and optimization of combustion and pollutant formation in a high-speed DI diesel engine. The work focuses on the analysis of the impact of in-cylinder swirl, start-of-injection, injection pressure and residual gas content on the engine performance and emissions characteristics for a part load operating point. The 3D-CFD calculations are carried out with the commercial CFD code AVL FIRE. The methodology adopted in the present study follows a Design of Experiment (DoE) approach in order to minimize the number of calculation runs for analysis of the impact of the relevant combustion system parameters on the engine combustion and emission performance. Validation of the adopted methodology with respect to both the accuracy of the adopted combustion and pollutant formation models and the DoE-based calculation approach is achieved by comparison of the computational results with engine measurement data.

A 0.5 liter optical HCCI engine firing a mixture of n-heptane (50%) and iso-octane (50%) with air/fuel ratio of 3 is studied using large eddy simulation (LES) and laser diagnostics. Formaldehyde and OH LIF and in-cylinder pressure were measured in the experiments to characterize the ignition process. The LES made use of a detailed chemical kinetic mechanism that consists of 233 species and 2019 reactions. The auto-ignition simulation is coupled with LES by the use of a renormalized reaction progress variable. Systematic LES study on the effect of initial temperature inhomogeneity and turbulence intensity has been carried out to delineate their effect on the ignition process. It was shown that the charge under the present experimental condition would not be ignited without initial temperature inhomogeneity. Increasing temperature inhomogeneity leads to earlier ignition whereas increasing turbulence intensity would retard the ignition.

For the simultaneous evaluation of the influence on engine knock of both chemical conditions and global operating parameters, a combined tool was developed. Thus, a two-zone kinetic model for SI engine combustion calculation (Ignition) was implemented into an engine cycle simulation commercial code. The combined model predictions are compared with experimental data from a single-cylinder test engine. This shows that the model can accurately predict the knock onset and in-cylinder pressure and temperature for different lambda conditions, with and without EGR. The influence of nitric oxide amount from residual gas in relation with knock is further investigated. The created numerical tool represents a useful support for experimental measurements, reducing the number of tests required to assess the proper engine control strategies.

In this work, constant volume combustion is studied using a zero-dimensional FORTRAN code, which is a wide-ranging chemical kinetic simulation that allows a closed system of gases to be described on the basis of a set of initial conditions. The model provides an engine- or reactor-like environment in which the engine simulations allow for a variable system volume and heat transfer both to and from the system. The combustion chamber is divided into two zones as burned and unburned ones, which are separated by an assumed thin flame front in the combustion model used for this work. Equilibrium assumptions have been adopted for the modeling of the thermal ionization, where Saha's equation was derived for singly ionized molecules. The investigation is focused on the thermal ionization of NO as well as for other species. The outputs generated by the model are temperature profiles, species concentration profiles, ionization degree and an electron density for each zone.

Numerical simulations of diesel engine combustion and emission formation have been performed using a detailed soot model. Operating conditions typical for modern truck-size engines have been investigated, and calculated results show encouraging agreement with experimental data for soot in engine exhaust gas. Predictions of details in the soot formation process compare well with detailed experimental data from the literature. The modelling of the soot/flow-field interaction is based on a flamelet approach. Source terms of the soot volume fraction are taken from a flamelet library using a presumed probability density function and integrating over mixture fraction space. In order to save computer storage and CPU time, the flamelet library of sources was constructed using a multi-parameter fitting procedure resulting in simple algebraic equations and a proper set of parameters.

The intention of the presented work was to develop a new simulation tool that fits into a CFD (computational fluid dynamics) workflow and provides information about the soot particle size distribution. Additionally it was necessary to improve and use state-of-the-art measurement techniques in order to be able to gain more knowledge about the behavior of the soot particles and to validate the achieved simulation results. The work has been done as a joint research financed by the European Community under FP5.

A stochastic model based on a probability density function (PDF) was developed for the investigation of different conditions that determine knock in spark ignition (SI) engine, with focus on the turbulent mixing. The model used is based on a two-zone approach, where the burned and unburned gases are described as stochastic reactors. By using a stochastic ensemble to represent the PDF of the scalar variables associated with the burned and the unburned gases it is possible to investigate phenomena that are neglected by the regular existing models (as gas non-uniformity, turbulence mixing, or the variable gas-wall interaction). Two mixing models are implemented for describing the turbulent mixing: the deterministic interaction by exchange with the mean (IEM) model and the stochastic coalescence/ dispersal (C/D) model. Also, a stochastic jump process is employed for modeling the irregularities in the heat transfer.