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Increasingly restrictive emission standards and CO2 targets drive the need for innovative engine architectures that satisfy the design constraints in terms of performance, emissions and drivability. Downsizing is one major trend for Spark-Ignition (SI) engines. For downsized SI engines, the increased boost levels and compression ratios may lead to a higher propensity of abnormal combustions. Thus increased levels of Exhaust Gas Recirculation (EGR) are used in order to limit the appearance of knock and super-knock. The drawback of high EGR rates is the increased tendency for Cycle-to-Cycle Variations (CCV) it engenders. A possible way to reduce CCV could be the generation of an increased in-cylinder turbulence to accelerate the combustion process. To manage all these aspects, 1D simulators are increasingly used. Accordingly, adapted modeling approaches must be developed to deal with all the relevant physics impacting combustion and pollutant emissions formation.

More and more stringent restrictions concerning the pollutant emissions of ICE (Internal Combustion Engines) constitute a major challenge for the automotive industry. New combustion strategies such as LTC (Low Temperature Combustion), PCCI (Premixed Controlled Compression Ignition) or HCCI (Homogeneous Charge Compression Ignition) are promising solutions to achieve the imposed emission standards. They permit low NOx and soot emissions via a lean and highly diluted combustion regime, thus assuring low combustion temperatures. In next generation of ICE, new technologies allow the implementation of complex injection strategies in order to optimize the combustion process. This requires the creation of numerical tools adapted to these new challenges. This paper presents a 0D Diesel HCCI combustion model based on a physical 3D CFD (Computational Fluid Dynamics) approach.

Combustion in SI engines strongly depends on in-cylinder turbulence characteristics. Turbulence by definition presents three-dimensional (3D) features; accordingly, 3D approaches are mainly used to investigate the in-cylinder flow and assist the engine design. However, SI engine architectures are becoming more and more complex and the generalization of technologies such as Variable Valve Timing (VVT) and Direct Injection (DI) considerably increases the number of degrees of freedom to deal with. In this context, the computing resources demanded by 3D CFD codes hugely increase and car manufacturers privilege system simulation approaches in the first phases of the design process. Accordingly, it is essential that the employed 0D/1D models well capture the main physics of the system and reproduce the impact that engine control parameters have on it.

Diesel engine pollutant emissions legislation is becoming more and more stringent. New driving cycles, including increasingly severe transient engine operating conditions and low ambient-temperature conditions, extend considerably the engine operating domain to be optimized to attain the expected engine performance. Technological innovations, such as high pressure injection systems, Exhaust Gas Recirculation (EGR) loops and intake pressure boosting systems allow significant improvement of engine performance. Nevertheless, because of the high number of calibration parameters, combustion optimization becomes expensive in terms of resources. System simulation is a promising tool to perform virtual experiments and consequently to reduce costs, however models must account for relevant in-cylinder physics to be sensitive to the impact of technology on combustion and pollutant formation.

IFP Energies nouvelles (IFPEN) has a large experience in the development of engine simulation platforms. During the last decade, the Dual Flame Model (DFM), a physical 0-dimensional (0D) combustion model designed for Diesel applications, was developed and continuously improved. The DFM formalism allows to represent quite precisely the in-cylinder combustion process scenario, by accounting for the first order relevant physics impacting fuel oxidation. First of all, this allows to account for the impact of engine actuators on combustion (e.g. injection systems performing complex injection strategies, Low Pressure and High Pressure EGR loops,…) and then to describe the pollutant emissions formation processes, being chemical kinetics strongly dependent on the in-cylinder thermochemical conditions. The aim of this communication is to present the potential of using the DFM model in the different stages of a Diesel engine development process for pollutant emissions optimization.

This paper presents a phenomenological quasi-dimensional model of the processes that lead to charge preparation in a Direct-Injection Spark-Ignition (DI-SI) engine, focusing on the physics of atomization and drop evaporation, spray development and the mutual interaction between these phenomena. Atomization and drop evaporation are addressed by means of constant-diameter drop parcels, which provide a discrete drop-size distribution. A discrete Probability Density Function (PDF) approach to fuel/air mixing is proposed, based on constant-mixture-fraction classes that interact with each other and with the drop parcels. The model has been developed in the LMS Imagine.Lab Amesim™ system simulation platform for multi-physical modeling and integrated in a generic SI combustion chamber submodel, CFM1D [15], of the IFP-Engine library.

The present social context imposes effective reductions of transport greenhouse gases and pollutant emissions. To answer to this demand, car manufacturers adopted technologies such as downsizing, turbocharging, intense in-cylinder aerodynamics and diluted combustion process. In this context, to master mixture ignition is crucial to ensure an efficient heat release. To get to a clearer knowledge about the physics holding early stages of premixed mixture combustion, the PRISME institute in the framework of the French government research project ANR MACDOC generated a consistent experimental database to study ignition and spherical flame propagation processes in a constant volume vessel in laminar and turbulent environment.

Recently, the car manufacturers are moving towards innovative Spark Ignition (SI) engine architectures with unconventional combustion concepts, aiming to comply with the stringent regulation imposed by EU and other legislators. The introduction of burdensome cycles for vehicle homologation, indeed, requires an engine characterized by a high efficiency in the most of its operating conditions, for which a conventional SI engine results to be ineffective. Combustion systems which work with very lean air/fuel mixture have demonstrated to be a promising solution to this concern. Higher specific heat ratio, minor heat losses and increased knock resistance indeed allow improving fuel consumption. Additionally, the lower combustion temperatures enable to reduce NOX production. Since conventional SI engines can work with a limited amount of excess air, alternative solutions are being developed to overcome this constraint and reach the above benefit.