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The scavenging and injection processes on a 50 cc. crankcase-scavenged compressed air-assisted direct fuel injection 2-stroke engine are analyzed by means of multidimensional CFD modeling. A moving mesh including the intake ports, cylinder and exhaust port has been built, solving the interface at ports. The information at boundaries is obtained from a one-dimensional wave action model. A detailed analysis of the scavenging process is presented. A motored engine with suitable optical access has been used to measure in-cylinder velocities by Laser Doppler Velocimetry LDV. Due to the small engine size some technical problems had to be solved to carry out the measurements. The comparison between the modeled and measured velocities shows good agreement. Finally, the validated multidimensional modeling has been used for the optimization of the injection process in terms of fuel short-circuit to the exhaust and also of mixture quality.

The objective of this paper is to analyse the flow characteristics inside the cylinder of a DI Diesel engine at variable swirl number. Initially, the cylinder head is characterised by means of three-dimensional calculations of the steady flow through the intake ports. These calculations have been made for several positions of the throttles, from wide open, to closed, using the STAR-CD commercial CFD code. They have been validated with steady flow experimental data measured with torque-meter. Next, 3D calculations of the compression stroke are presented and compared with experimental measurements. The initial conditions inside the cylinder in the TDC have been estimated using the head characterisation tests and a zero-dimensional model. The results obtained are in good agreement with the experiments.

Accurate simulation tools are needed for rapid and cost effective engine development in order to meet ever tighter pollutant regulations for future internal combustion engines. The formation of pollutants such as soot and NOx in Diesel engines is strongly influenced by local concentration of the reactants and local temperature in the combustion chamber. Therefore it is of great importance to model accurately the physics of the injection process, combustion and emission formation. It is common practice to approximate Diesel fuel as a single compound fuel for the simulation of the injection and combustion process. This is in many cases sufficient to predict the evolution of the in-cylinder pressure and heat release in the combustion chamber. The prediction of soot and NOx formation depends however on locally component resolved quantities related to the fuel liquid and gas phase as well as local temperature.

The aim of this paper is to analyse the swirling flow in the cylinder of DI Diesel engines. Both steady state flow rig and CFD calculation techniques on three Diesel engines at different configurations have been used to carry out this study. On one hand, results obtained by means of steady state flow rig measurements with torque-meter are presented. On the other hand, the intake and compression strokes are calculated using a CFD commercial code on real geometries of three engines at different working conditions. The experimental and the CFD methods are compared in terms of Swirl Number and Flow Coefficient, so some correlations are achieved at BDC and TDC and a general equation -valid for different geometries- has been obtained to estimate the Swirl Number in the cylinder of DI Diesel engines at TDC directly from the data -Mean Swirl Number- provided by the experimental tests.

It is known that in-cylinder airflow structures during intake and compression strokes deeply affects the combustion process in compression ignition (CI) engines. This work presents a methodology for the analysis of the swirling structures by means of the CFD proprietary code Converge 2.3. The methodology is based on the CFD modelling and the comparison of results with in-cylinder velocity fields measured by particle image velocimetry (PIV). Furthermore, the analysis is extended to the accuracy evaluation of other methods available to define the flow in the cylinder of internal combustion engines, such as experiments in steady flow rigs. These methods, in junction with simple phenomenological models, have been traditionally used to determine some of the fundamental variables that define the in-cylinder flow in ICE engines. The CFD analysis is focused in the flow structures around top dead centre (TDC) at the end of the compression stroke.

The Engine Combustion Network (ECN) is a coordinate effort from research partners from all over the world which aims at creating a large experimental database to validate CFD calculations. Two injectors from ECN, namely Spray C and D, have been compared in a constant pressure flow vessel, which enables a field of view of more than 100 mm. Both nozzles have been designed with similar flow metrics, with Spray D having a convergent hole shape and Spray C a cylindrical one, the latter being therefore more prone to cavitation. Although the focus of the study is on reacting conditions, some inert cases have also been measured. High speed schlieren imaging, OH* chemiluminescence visualization and head-on broadband luminosity have been used as combustion diagnostics to evaluate ignition delay, lift off length and reacting tip penetration. Parametric variations include ambient temperature, oxygen content and injection pressure variations.

Major accuracy for prediction tools like CFD codes require precise experimental validation. The ultraviolet and visible light absorption and scattering (UV-VIS LAS) is proposed for characterizing air-fuel mixture formation. UV-VIS LAS technique is employed to quantitatively determine spatial concentration distribution of vapor fuel, in combination with simultaneous liquid length and spray penetration measurements by means of Mie-scattering and Schlieren. Decane, Hexadecane and a 50/50 of both fuels have been chosen for this study, to evaluate mixing formation under Diesel conditions. Work has been performed at an optical engine under non-reacting atmosphere, with ambient pressures and temperatures up to 7.3 MPa and 900 K. Fuel optical properties for the two paraffines under engine conditions have been analyzed, and fuel concentration distribution has been obtained for pure fuels.