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A workflow for the assessment and validation of internal aerodynamics and mixture preparation in a representative high-tumble optical engine using Large Eddy Simulation with the commercial code CONVERGETM is proposed. First, the prediction of the aerodynamic movement in the engine is compared to Particle Image Velocimetry (PIV) measurements. The global velocity fields and position of the center of the tumble for the average experimental and simulation cycles are compared, showing a very good match of the global behavior. The cycle to cycle aerodynamic variability is investigated thanks to velocity profiles, showing that the simulated cycles feature comparable velocity fluctuations to the experiments. In a second part, to account for Direct Injection (DI), a Lagrangian spray modeling approach is used to take into account the injection process. Experimental spray penetration data are used for the calibration of the spray models, leading to a faithful representation of the spray.

Meeting Euro 6d NOx emission regulations lower than 80 mg/km for light duty diesel (60 mg/km gasoline) vehicles remains a challenge, especially during cold-start tests at which the selective catalyst reduction (SCR) system does not work because of low exhaust gas temperatures (light-off temperature around 200 °C). While several exhaust aftertreatment system (EATS) designs are suggested in literature, solutions with gaseous ammonia injections seem to be an efficient and cost-effective way to enhance the NOx abatement at low temperature. Compared to standard SCR systems using urea water solution (UWS) injection, gaseous NH3 systems allow an earlier injection, prevent deposit formation and increase the NH3 content density. However non-uniform ammonia mixture distribution upstream of the SCR catalyst remains an issue. These exhaust gas/ NH3 inhomogeneities lead to a non-optimal NOx reduction performance, resulting in higher than expected NOx emissions and/or ammonia slip.

Ever growing traffic has a detrimental effect on health and environment. In response to climate warming and health concerns, governments worldwide enforce more stringent emission standards. NOx emissions limits are some of the most challenging to meet using fuel-efficient lean-burn engines. The Selective Catalytic Reduction (SCR) is one consolidated NOx after-treatment technique using urea water solution (UWS) injection upstream of the catalytic converter. A recent development of SCR, using gaseous ammonia injection, reduces wall deposit formation and improves the cold-start efficiency. The mixing of gaseous ammonia with the exhaust gases is one of the key challenges that need to be overcome, as the effectiveness of the system is strongly dependent on the mixture uniformity at the inlet of the SCR catalyst.

In spite of the increasingly stringent emission standards, the constant growth of road traffic contributes to climate change and induces detrimental effects on the environment. The European REWARD project (REal World Advanced Technologies foR Diesel Engines) aims to develop a new generation of Diesel engines complying with stricter post Euro 6 legislation and with lower CO2 emissions. Among the different technologies developed, a fuel-efficient two-stroke Diesel engine suited for C-segment passenger cars will be designed and experimentally evaluated. One major challenge for two-stroke engines is the achievement of an efficient scavenging. As the emptying of the in-cylinder burnt gases and the filling by fresh gases is performed at the same time, the challenge consists in removing as much burnt gases as possible while avoiding the by-pass of fresh air toward the exhaust line.

Reduction of CO2 emissions is becoming one of the great challenges for future gasoline engines. The aim of the current research program (OOD: Octane On Demand) is to use the octane number as a tuning parameter to simultaneously make the engine more efficient and reduce CO2 emissions. The idea is to prevent knock occurrence by adapting the fuel RON injected in the combustion chamber. Thus, the engine cycle efficiency is increased by keeping combustion phasing at its optimum. This is achieved by a dual fuel injection strategy, involving a low-RON base fuel (Naphtha or Low RON cost effective fuel) and a high-RON octane booster (ethanol). The ratio of fuel quantity on each injector is adapted at each engine cycle to fit the RON requirement as a function of engine operating conditions. A first part of the project, described in [18], was dedicated to the understanding of mixture preparation resulting from different dual-fuel injection strategies.

The accumulation of particulate matter in lubricant oil can become an important issue in Diesel engines where large amounts of Exhaust Gas Recirculation (EGR) are used at medium to high load operating conditions. Indeed, the transport and subsequent accumulation of particulate matter in the engine oil can negatively impact the oil lubricant properties which is critical to ensure mechanical durability and limit the vehicle Total Cost of Ownership (TCO) by reducing the servicing intervals. The objective of this investigation was to gain an improved understanding of the underlying mechanisms that are responsible for the accumulation of particulate matter in the lubricating oil, and ultimately provide design guidelines to help limit this phenomenon. The present study presents the development and validation of experimental and numerical tools used to investigate this phenomenon.

Reduction of CO2 emissions is becoming one of the great challenges for future gasoline engines. Downsizing is one of the most promising strategies to achieve this reduction, though it facilitates occurrence of knocking. Therefore, downsizing has to be associated with knock limiting technologies. The aim of the current research program is to adapt the fuel Research-Octane-Number (RON) injected in the combustion chamber to prevent knock occurrence and keep combustion phasing at optimum. This is achieved by a dual fuel injection strategy, involving a low-RON naphtha-based fuel (Naphtha, RON 71) and a high-RON octane booster (Ethanol, RON107). The ratio of fuel quantity on each injector is adapted to fit the RON requirement as a function of engine operating conditions. Hence, it becomes crucial to understand and predict the mixture preparation, to quantify its spatial and cycle-to-cycle variations and to apprehend the consequences on combustion behavior - knock especially.

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.

Increasing global efficiency of direct injection spark ignition (DISI) engine is nowadays one of the main concerns in automotive research. A conventional way to reduce DISI engine fuel consumption is through downsizing. This approach is well suited to the current homologation cycle as NEDC, but has the drawback to induce over-consumptions in customer real driving usage. Moreover, the driving cycles dedicated to EURO 6d and future regulations will evolve towards higher load operating conditions with higher particulate emissions. Therefore, efficiency of current DISI has to be strongly increased, for homologation cycle and real driving conditions. This implies to deeply understand and improve injection, mixing and flame propagation processes.

Recent work has demonstrated the potential of gasoline-like fuels to reduce NOx and particulate emissions when used in Diesel engines. In this context, straight-run naphtha, a refinery stream directly derived from the atmospheric crude oil distillation process, has been identified as a highly valuable fuel. The current study is one step further toward naphtha-based fuel to power compression ignition engines. The potential of a cetane number 25 fuel (CN25), resulting from a blend of hydro-treated straight-run naphtha CN35 with unleaded non-oxygenated gasoline RON91 was assessed. For this purpose, investigations were conducted on multiple fronts, including experimental activities on an injection test bed, in an optically accessible vessel and in a single cylinder engine. CFD simulations were also developed to provide relevant explanations.

An automatic mesh generation process for a body fitted 3D CFD code is presented in this paper along with the methodology to guarantee the mesh quality. This tool named OMEGA (Optimized MEsh Generation Automation) uses a direct coupling procedure between the IFP-C3D solver and a hybrid mesher Centaur. Thanks to this automatic procedure, the engineering time needed for body fitted 3D CFD simulation in internal combustion engines is drastically reduced from a few weeks to a few hours. Valve and piston motion laws are just given as input files and geometries and meshes are automatically moved and generated. Unlike other procedures, this automatic mesh generation does not use an intermediate geometry discretization (STL file, tetrahedral surface mesh) but directly the original CAD that has been modified thanks to the geometry motion functionalities integrated into the mesher.

The target of substantial CO₂ reductions in the spirit of the Kyoto Protocol as well as higher engine efficiency requirements has increased research efforts into hybridization of passenger cars. In the frame of this hybridization, there is a real need to develop small Internal Combustion Engines (ICE) with high power density. The two-stroke cycle can be a solution to reach these goals, allowing reductions of engine displacement, size and weight while maintaining good NVH, power and consumption levels. Reducing the number of cylinders, could also help reduce engine cost. Taking advantage of a strong interaction between the design office, 0D system simulations and 3D CFD computations, a specific methodology was set up in order to define a first optimized version of a two-stroke uniflow diesel engine. The main geometrical specifications (displacement, architecture) were chosen at the beginning of the study based on a bibliographic pre-study and the power target in terms.

Dedicated experiments were performed in an optically-accessible, constant volume combustion vessel whose geometry and aerodynamic flow was representative of a pentroof SI engine combustion chamber. A detailed characterization of the flowfield was conducted in several near-wall regions where flame-wall interaction occurs using high-speed Particle Image Velocimetry (PIV). Simultaneous heat flux measurements were also performed at these same spatial locations. From a numerical point of view, current Reynolds Averaged Navier Stokes (RANS) or Large Eddy Simulation (LES) models take into account the effects of the wall on the flame however the effects of the turbulent flame-wall interaction on wall heat flux are not accounted for. Direct Numerical Simulations (DNS) of a 2D, premixed, steady-state V-flame were performed in order to aid the development and validation of a new model based on the flame surface density concept in order to take into account flame-wall interaction effects [1].

A full 3D Large Eddy Simulation (LES) of a four-stroke, four-cylinder engine, performed with the AVBP-LES code, is presented in this paper. The drive for substantial CO₂ reductions in gasoline engines in the light of the global energy crisis and environmental awareness has increased research into gasoline engines and increased fuel efficiencies. Precise prediction of aerodynamics, mixing, combustion and pollutant formation are required so that CFD may actively contribute to the improvement/optimization of combustion chamber, intake/exhaust ducts and manifold shapes and volumes which all contribute to the global performance and efficiency of an engine. One way to improve engine efficiency is to reduce the cycle-to-cycle variability, through an improved understanding of their sources and effects. The conventional RANS approach does not allow addressing non-cyclic phenomena as it aims to compute the average cycle.

The introduction of alternative fuels is crucial to limit greenhouse gases. CNG is regarded as one of the most promising clean fuels given its worldwide availability, its low price and its intrinsic properties (high knocking resistance, low carbon content...). One way to optimize dedicated natural gas engines is to improve the CNG slow burning velocity compared to gasoline fuel and allow lean burn combustion mode. Besides optimization of the combustion chamber design, hydrogen addition to CNG is a promising solution to boost the combustion thanks to its fast burning rate, its wide flammability limits and its low quenching gap. This paper presents an investigation of different methane/hydrogen blends between 0% and 40 vol. % hydrogen ratio for three different combustion modes: stoichiometric, lean-burn and stoichiometric with EGR.

This paper presents an innovative methodology and the corresponding results of a study whose goal is to identify the main links between in-cylinder charge motion and the development of combustion without taking into consideration how to create this charge motion (shape of the intake ducts, valve timing, etc …). During this study a specific methodology was developed and used. It is based on the calculation of a “3D numerical test bench” matrix planned following the Design Of Experiments method. Many aerodynamic configurations obtained by combining the three main aerodynamic motions with several different intensities (tumble, cross-tumble or swirl) at the intake valve closing were calculated.

Future emissions standards for passenger cars require a reduction of NOx (nitrogen oxide) and CO₂ (carbon dioxide) emissions of diesel engines. One of the ways to reach this challenge while keeping other emissions under control (CO: carbon monoxide, HC: unburned hydrocarbons and particulates) is to reduce the volumetric compression ratio (CR). Nevertheless complications appear with this CR reduction, notably during very cold operation: start and idle. These complications justify intensifying the work in this area. Investigations were led on a real 4-cylinder diesel 13.7:1 CR engine, using complementary tools: experimental tests, in-cylinder visualizations and CFD (Computational Fluid Dynamics) calculations. In previous papers, the way the Main combustion takes place according to Pilot combustion behavior was highlighted. This paper, presents an in-depth study of mixture preparation and the subsequent combustion process.

With a high thermal efficiency and low CO2 (carbon dioxide) emissions, Diesel engines become leader of transport market. However, the exhaust-gas legislation evolution leads to a drastic reduction of NOx (nitrogen oxide) standards with very low particulate, HC (unburned hydrocarbons) and CO (carbon monoxide) emissions, while combustion noise and fuel consumption must be kept under control. The reduction of the volumetric compression ratio (CR) is a key factor to reach this challenge, but it is today limited by the capabilities to provide acceptable performances during very cold operation: start and idle below −10°C. This paper focuses on the understanding of the main parameter’s impacts on cold operation. Effects of parameters like hardware configuration and calibration optimization are investigated on a real 4 cylinder Diesel 14:1 CR engine, with a combination of specific advanced tools.

Future emission standards for Diesel engine will require a drastic reduction of engine-out NOx emissions with very low level of particulate matter (PM), HC and CO, and keeping under control fuel consumption and combustion noise. One of the most promising way to reach this challenge is to reduce compression ratio (CR). A stringent limitation of reducing Diesel CR is currently cold start requirements. Indeed, reduction of ambient temperature leads to penalties in fuel vaporization and auto ignition capabilities, even more at very low temperature (-20°C and below). In this paper, we present the work operated on an HSDI Common rail Diesel 4-cyl engine in three area: engine tests till very low temperature (down to -25°C); in cylinder imaging (videoscope) and CFD code development for cold start operation. First, combustion chamber is adapted in order to reach low compression ratio (CR 13.7:1).

The drive for substantial CO2 reductions in gasoline engines in the light of the Kyoto Protocol and higher fuel efficiencies has increased research on downsized, turbocharged engines. Via a higher intake air pressure, an increase in specific power output can be reached on a comparatively smaller sized engine, in order to ensure high torque capabilities, while allowing a fuel saving of about 20%. This fuel efficiency benefit includes the advantages of direct injection (DI) technology which avoids crossflow of fuel. This paper presents the capabilities of Computational Fluid Dynamics to aid in the development of such engines. Particularly, the IFP-C3D code offers several recently developed models which permit to estimate, with good accuracy, the evolution of the combustion under given working conditions. Moreover, the capability of the model to predict knock occurrence is very helpful for engine designers within the framework of development of new downsized turbocharged engines.