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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.

It has been known from multi-zone simulations that HCCI combustion can be significantly affected by temperature stratification of the in-cylinder gas. With the same combustion timing (i.e. crank angles at 50% heat release, denoted as CA50), large temperature stratification tends to prolong the combustion duration and lower down the in-cylinder pressure-rise-rate. With low pressure-rise-rate HCCI engines can be operated at high load, therefore it is of practical importance to look into more details about how temperature stratification affects the auto-ignition process. It has been realized that multi-zone simulations can not account for the effects of spatial structures of the stratified temperature field, i.e. how the size of the hot and cold spots in the temperature field could affect the auto-ignition process. This question is investigated in the present work by large eddy simulation (LES) method which is capable of resolving the in-cylinder turbulence field in space and time.

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.

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.

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.

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.