Search Results

In order to simulate the working process, an accurate description of heat transfer occurring between in-cylinder gases and combustion chamber walls is required, especially regarding thermal efficiency, combustion and emissions, or cooling strategies. Combustion chamber wall heat transfer models are dominated by zero-dimensional semi-empirical models due to their good compromise between accuracy, complexity and computational efficiency. Classic models such as those from Woschni, Annand or Hohenberg are still widely used, despite having been developed on rather ancient engines. While numerous authors have worked on this topic in the past decades, little information can be found concerning the systematic calibration process of heat transfer models. In this paper, a systematic calibration method based on experimental data processing is tested on the complete operating map of a turbocharged GDI engine.

Diesel engines are being more commonly used for light automotive applications, due to their higher efficiency. However, pollutant emissions can be higher than their gasoline counterparts, being difficult to reduce and control because reducing one pollutant increases another. One way to reduce emissions is by using multiple injection strategies. However, understanding multiple injections is no easy task, so far done by trial and error and experience. Therefore, a numerical 1D model is to be adapted to simulate multiple injection situations in a diesel engine. In a previous paper by the authors, an existing model was adapted with a thermal dilatation model to consider both radial and axial dilatations in the diesel spray. The base model used is that of Ma et al (based on the Eulerian model of Musculus and Kattke for inert diesel jets).

Diesel engines are being more commonly used for light automotive applications, due to their higher efficiency, despite the difficulty of depollution and extra associated costs. They require more accessories to function properly, such as turbocharging and post-treatment systems. The most important pollutants emitted from diesel engines are NOx and particles (in conventional engines), being difficult to reduce and control because reducing one increases the other. Low temperature combustion (LTC) diesel engines are able to reduce both pollutants, but increase emissions of CO and HC. Besides HCCI and EGR systems, one method that could achieve LTC conditions is by using multiple injections (pilot/main, split injection, etc.). However, understanding multiple diesel injection is no easy task, so far done by trial and error and complex 3D CFD models, or too simplified by 0D models. Therefore, a numerical 1D model is to be adapted to simulate multiple injection situations in a diesel engine.

In this paper, a new 1D combustion model is presented. It is expected to combine good predictive capacities with a contained CPU time, and could be used for engine design. It relies on a eulerian approach, based on Musculus 1D transient spray model. The latter has been extended to model vaporizing, reacting sprays. The general features of the model are first presented. Then various sub models (spray angle and dilatation, vaporization, thermodynamic properties) are detailed. Chemical kinetics are described with a global scheme to keep computational time low. The spray discretization (mesh) and angle model are first discussed through a sensitivity analysis. The model results are then compared to experiments from ECN data base (SANDIA) realized in constant volume bombs, for both inert and reacting cases. Some detailed analysis of model results are performed, including comparisons of vaporizing and non-vaporizing cases, as well as inert and reacting cases.

Reducing NOx tailpipe emissions is one of the major challenges when developing automotive Diesel engines which must simultaneously face stricter emission norms and reduce their fuel consumption/CO2 emission. In fact, the engine control system has to manage at the same time the multiple advanced combustion technologies such as high EGR rates, new injection strategies, complex after-treatment devices and sophisticated turbocharging systems implemented in recent diesel engines. In order to limit both the cost and duration of engine control system development, a virtual engine simulator has been developed in the last few years. The platform of this simulator is based on a 0D/1D approach, chosen for its low computational time. The existing simulation tools lead to satisfactory results concerning the combustion phase as well as the air supply system. In this context, the current paper describes the development of a new NOx emission model which is coupled with the combustion model.

Stoichiometric Diesel combustion (SDC, also called stoichiometric compression ignition) is a concept which tries to combine high efficiency of Diesel engine with the use of a relatively inexpensive three-way catalyst (TWC) for NOx post-treatment. A preliminary literature survey shows that relatively few studies have been performed in this regard. They show the major role of the injection system and the piston shape and confirm that a TWC effectively removes NOx, CO and HC on such an engine. The aim of this paper is to present an experimental study carried out on a modern turbocharged, common-rail automotive Diesel engine running under stoichiometric conditions. Most engine parameters are modified: EGR rate, inlet air temperature and pressure, injection strategy (single injection and split injection, start(s) of injection(s), rail pressure). A particular emphasis is put on intake strategies: the influence of boost pressure and EGR rate is studied; and two levels of swirl are tested.

Pollutant emissions standards (such like EURO 6 in Europe) are increasingly severe and force a search of new in-cylinder strategies and/or aftertreatment devices / schemes at a reasonable cost. On a conventional Diesel engine an excess of air is usually used to allow very high combustion efficiencies and reasonable levels of soot which can then be after-treated in a diesel particulates filter (DPF). As a consequence, NOx emissions cannot be easily after-treated (lean NOx trap (LNT) and selective catalytic reduction (SCR) are quite expensive even if effective, solutions), as a result they are generally controlled by means of internal measures such as High Pressure (HP) or Low Pressure (LP) exhaust gas recirculation (EGR). In light of ever more stringent NOx emissions regulations, NOx aftertreatment devices seem to be becoming unavoidable.

Unsteady flow in the inlet and exhaust systems of Internal Combustion Engines can be simulated with multi-dimensional simulation codes. Due to their computational time, other methods are widely used and give the opportunity of coupling it with a model of the complete engine. This paper reports on an investigation undertaken to compare the accuracy of the method of inertia, the acoustic method and the one-dimensional method for modeling the gas flow in pipe systems. Results of this study give the advantage and disadvantage of each approach. The comparison shows good agreement between one-dimensional and experimental results while the calculation time is kept acceptable.