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This paper presents a study of the turbulence field in an optical diesel engine operated under motored conditions using both large eddy simulation (LES) and Particle Image Velocimetry (PIV). The study was performed in a laboratory optical diesel engine based on a recent production engine from VOLVO Car. PIV is used to study the flow field in the cylinder, particularly inside the piston bowl that is also optical accessible. LES is used to investigate in detail the structure of the turbulence, the vortex cores, and the temperature field in the entire engine, all within a single engine cycle. The LES results are compared with the PIV measurements in a 40 × 28 mm domain ranging from the nozzle tip to the cylinder wall. The LES grid consists of 1283 cells. The grid dynamically adjusts itself as the piston moves in the cylinder so that the engine cylinder, including the piston bowl, is described by the grid.

Engine thermal behavior has been solved previously in steady and transient conditions thanks to a lumped capacity model, also called nodal model. But serious shortcomings appear in the heat flux formulation introduced in the model. In this paper, we show that using steady-state maps of heat transfer coefficients to simulate transient thermal response of diesel engines is not sufficient. The heat transfer is strongly influenced by the injection pattern, the intake air conditions and the walls temperatures, which are not taken into account in the previous model. Introducing a single cylinder multi-zone combustion model, a better description of the combustion process and so of the heat release can be obtained. The coupled models are used to describe a 1,9l, 4-cylinder direct injection diesel engine during a warm-up. The results (oil and coolant temperatures) show a good agreement between measures and simulations. This approach offers a great potential for further applications.

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.

With the increasing efficiency of D.I. Diesel engines, the heat power needed to warm the passengers compartment becomes too low during the warm-up period. So the temperature increase of oil and water may be accelerate. This paper is devoted to the understanding of the phenomena involved in this process and their modeling. A diesel engine enclosed in a calorimeter is mounted on a test bench and largely instrumented. From the recorded data, the instantaneous energy balance is set up for different running conditions. Some general trends may be pointed out. During the first minute, 50% of the fuel energy is absorbed by the heat capacity of the heavy metallic components. This part progressively decreases to the benefit of heat transferred to the coolant. Furthermore, for increasing distance from the combustion chamber in the block, the rate of temperature rise decreases. Concerning the oil temperature evolution, it lags behind the water one.