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In the last two decades, piston engine specifications have deeply evolved. Indeed, new challenges nowadays concern the reduction of pollutant emissions (EURO regulations) and CO2 emissions. To satisfy these new requirements, powertrains have become very complex systems including a large number of high technology components (high pressure injectors, turbocharger, Exhaust Gas Recirculation (EGR) loop, after-treatment devices...). In this context, the engine control plays a major role in the development and the optimization of powertrains. Few years ago, engine control strategies were mainly defined by experiments on engine test benches. This approach is not adapted to the complexity of future engines: on the one hand, tests are too expensive and on the other hand, they do not give much information to understand interactions between components. Today, a promising alternative to tests may be the use of 0D/1D simulation tools.

Regulations in terms of pollutant emissions are becoming more and more constraining. The car manufacturers need to adopt a global optimisation approach of engine and exhaust after-treatment systems. An engine architecture definition coupled to an adapted control strategy seem to be an ideal way to address this issue. The problem is particularly complex, considering the trade off between the drivability which must be maintained, the reduction of the in-cylinder pollutant emissions, the reduction of the fuel consumption and the optimisation of the operating conditions to reach high conversion efficiencies via exhaust gas after-treatment systems. Sophisticated control strategies and models can only be developed with a complete understanding of the physical phenomena occurring in the combustion chamber, thanks to experimental measurements and engine system simulations.

Meeting the upcoming NOx emissions standards is a major challenge for the lean-burn engines, thus requiring a highly efficient exhaust gas aftertreatment. Currently, the Selective Catalytic Reduction (SCR) appears to be the most promising technology, especially when operated with two kinds of reductants: ammonia (generally derived from urea) and ethanol. In order to reach high conversion levels while avoiding the overinjection of the reductant, a very accurate model-based control assisted with at least one NOx sensor is required. This study focuses on the sensitivity of NOx sensors to the main nitrogenous species encountered: ammonia, isocyanic acid (HNCO) and hydrogen cyanide (HCN). The cross-sensitivity to ammonia is the only one to be already described in literature and already used in the urea-SCR control systems to limit the risks of ammonia-slip. However, HNCO can also be found downstream of a catalyst during urea-SCR if the urea delivery or the catalyst are deficient.

The numerical simulation of internal aerodynamic of automotive combustion chamber is characterised by complex displacements of moving elements (piston, intake/exhaust valves…) and by a strong variation of volume that cause some problems with classical numerical based mesh methods. With those methods (FEM, FVM) which use geometric polyhedral elements (hexaedron, tetrahedron, prismes…), it is necessary to change periodically the mesh to adapt the grid to the new geometry. This step of remeshing is very fastidious and costly in term of engineer time and may reduce the precision of calculation by numerical dissipation during the interpolation process of the variables from one mesh to another. Recently, the researcher community has renewed his interest for the development of a generation of numerical to circumvent the drawbacks of the classical methods.

In spark-ignition engines, cyclic variability limits the optimisation of operating conditions (choice of spark advance and/or injection timing) since it induces load variations and the occurrence of misfire and/or knock. This, in turn, restricts the operation range of new concepts such as downsizing or stratified combustion. To understand the basic physical phenomena behind cyclic variations, careful experimental studies are necessary to simultaneously characterise the combustion and the unsteady flow in the complete engine set-up. With a well-characterised experimental engine set-up, Large Eddy Simulation (LES) modelling can be easily combined with experiment in order to tackle intricate physical phenomena couplings. This paper describes an experimental database acquired on an optical research engine. The single-cylinder spark-ignition engine is equipped with four valves, a pentroof combustion chamber and a flat piston. The database is dedicated to the validation of LES models.

Oxygenated fuels are studied in spark combustion engines because of their potentially positive impact on greenhouse emissions, and as part of alternative renewable fuels. Furthermore, engine test results position them as a promising lever to reduce engine-out emissions, and most notably, particles. This study focuses on oxygenated fuel Butanol, which is a potential output of recent developments on Algae and Cyanobacteria harvest process. Its blending into gasoline and application into spark ignition engines is investigated. Blending levels of n-Butanol and iso-Butanol have been proposed based on standard gasoline’s octane number, RON, at two ethanol concentration levels, 10 and 25%. Fuel blend impact on combustion, and on regulated and non-regulated emissions is analysed. Fuel knock resistance properties, RON and MON, determine the knocking tendencies for ethanol and butanol at 2000 rpm. However, test results highlight different knocking sensibility behaviour at higher engine speed.

A 300 cc gasoline engine has been experimentally and numerically studied to compare PFI and DI operation on naturally-aspirated and turbocharged full load operating points. Experiment outlines the benefits from DI operation in terms of volumetric efficiency, fuel economy and knock propensity but also clearly indicates worse raw engine-out CO emissions. The latter is an indication of the survival of a large scale mixture heterogeneity in this downsized GDI engine even when early injection and intense induced fluid motion are combined. For such a full load operation, the application of optical diagnostics to study mixture heterogeneity cannot be considered because pressure and temperature exceed sustainable levels for transparent materials. Therefore, 3D CFD RANS computations of the intake, injection, combustion and pollutant formation processes including detailed chemistry information are performed to complement the experimental data.

The aim of this work is to study the effect of ethanol/gasoline blends on stratified operation in a single-cylinder GDI engine and to build up a large database that will be used to improve engine simulation codes. The effects of three different fuel blends are compared: a reference RON 95 fuel without oxygenates, E20 with 20% in volume of ethanol added to the RON 95 fuel, and E85 corresponding to 85% of ethanol added to the RON 95 fuel. The engine was equipped with a centrally-mounted piezoelectric injector. A wide range of engine speed and load operating conditions were studied: from 1000 to 4000 rpm and from 1.5 to 9 bar IMEP. Injection strategies were optimized using up to three injections per working cycle. It was shown that multi-injection is necessary to improve stratified combustion stability and to limit particulate emissions.

In this paper three turbulent combustion models with different underlying hypothesis are compared with measurements from an extensive experimental database. The reference model is ECFM3Z, with the Tabulated Kinetics of Ignition (TKI) model for auto-ignition modeling, together with the CO reduced kinetics (CORK) model and the extended Zeldovich model for the nitrogen oxides. The VVTHC (Variable Volume Tabulated Homogeneous Chemistry) model predicts both the heat release and species evolutions (including CO). The most evolved model proposed is the ADF-PCM (Approximated Diffusion Flame-Presumed Conditional Moment) approach, based on the laminar flamelet equation of the progress variable. ADF-PCM and VVTHC are tabulated models based on a progress variable approach and are then coupled to the tabulated NO model NORA based on relaxation (NO Relaxation Approach). All the present combustion models are coupled to a phenomenological soot kinetics PSK approach.

Hydrogen may be used to feed a fuel cell or directly an internal combustion engine as an alternative to current fossil fuels. The latter option offers the advantages of already existing hydrocarbon fuel engines - autonomy, pre-existing and proven technology, lifetime, controlled cost, existing industrial tools and short time to market - with a very low carbon footprint and high tolerance to low purity hydrogen. Hydrogen is expected to be relevant for light and heavy duty applications as well as for off road applications, but currently most of research focus on small engine and especially spark ignition engine which is easily adaptable. This guided us to select modern high-efficient gasoline-based engines to start the investigation of hydrogen internal combustion engine development. This study aims to access the properties and limitations of hydrogen combustion on a high-efficiency spark ignited single cylinder engine with the support of the 3D-CFD computation.

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].

In spark-ignition engines, Cycle-to-Cycle Variations (CCV) limit the optimization of engine operation since they induce torque variations and the occurrence of misfire and/or knock. A mean for limiting the related negative impact of CCV on fuel consumption and emissions would be control strategies able to address them. At present, engine simulation codes used for control purposes can only describe CCV linked to variations of gas exchanges in the air loop. CCV of the in-cylinder flow motion cannot be naturally captured by classical quasi-dimensional combustion chamber models. A convenient way to mimic CCV is to impose stochastic distributions of the combustion model parameters. Nevertheless, it is not always clear if these perturbations have physical bases as well as realistic ranges of variation.

Compared to Spark Ignition (SI) engines, Compression Ignition (CI) engines are more efficient because of the higher compression ratios and leaner operation. However, thanks to stoichiometric air fuel ratio, SI engines allow efficient pollutants after treatment, particularly for NOx emissions. In this context, IFP Energies nouvelles (IFPEN) has developed the concept of diesel-gasoline combustion in order to combine the advantages of both fuels and both combustion processes. Focusing on a passenger car application, experiments have been performed using a modified DI turbocharged small diesel engine (the combustion chamber has been redesigned and port fuel injectors have been added). In-Cylinder Fuel Blending (ICFB) using port-fuel-injection of gasoline and optimized direct injection of diesel was used to control combustion phasing and duration. This modified engine can still run on diesel alone.

In a context of a fossil reserve depletion and reduction of greenhouse gases (GHG) emissions, the search for new energy for transport is fundamental. Among those new energies, alternative fuels and especially synthetic fuel from Fischer-Tropsch process (so-called XtL, "X-to-Liquid" fuels) seem to have an interesting potential in terms of availability and GHG emission reduction, according to the feedstock used. Due to the special properties of such products, especially high cetane number, several strategies of incorporation can be envisaged: as a blend in specific basestocks in order to obtain a conventional fuel or a premium fuel or as a pure component. In order to assess these strategies; a standard diesel fuel (B0), a blend with 40%vol of Fischer-Tropsch and a neat Fischer-Tropsch have been tested on a modern downsized high pressure direct injection single-cylinder diesel engine. The used Fischer-Tropsch fuel is a commercial GtL - Gas to Liquid, with a cetane number higher than 80.

Nowadays Spark Ignition (SI) engine efficiency is mainly limited by abnormal combustion (knock) and stability issues at high dilution rate (both EGR and air). Increasing the combustion velocity is a relevant way to overcome these limitations. Main strategy to increase the combustion velocity is to enhance the flow motion in the cylinder (tumble motion) in order to increase the turbulence during the combustion. Such approach is mainly performed by working on intake port design which lead to engine volumetric efficiency penalties. Another approach to increase the combustion velocities is to have multiple ignition kernels in the chamber. This can be obtained thanks to Turbulent Jet Ignition (TJI) which uses a pre-chamber to spread the initial flame kernel throughout the combustion chamber. To achieve pre-chamber optimization a deep understanding of the complex phenomena involved in TJI as well as validated numerical tools is required.

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.

Large Eddy Simulation (LES) appears today as a prospective tool for engine study. Even if recent works have demonstrated the feasibility of multi-cycle LES, they have also pointed out a lack of detailed experimental data for validation as well as for boundary condition definition. The acquisition of such experimental data would require dedicated experimental set-ups. Nevertheless, in future industrial applications, unconditional dedicated experimental set-ups will not be the main stream. To overcome this difficulty, a methodology is proposed using system simulation to define fluid boundary conditions (crank-resolved intake/exhaust pressures and temperatures) and wall temperatures. The methodology combines system simulation for the whole experimental set-up and LES for the flow in the combustion chamber as well as a part of the intake and exhaust ducts. System simulation provides the crank-resolved temperature and pressure traces at the LES mesh inlet and outlet.

In this paper, an integrated simulation-based methodology demonstrating feasibility and performance of several electric-hybrid concepts is developed. Several advanced tools are coupled to define the specifications of each component of the hybrid powertrain, to select the most promising hybrid architecture and finally to assess the proposed powertrain with regard to CO2 and pollutants emissions. Concurrent minimization of NOx and CO2 emissions enables to find the best compromise to fulfil Euro 6 standards while lowering fuel consumption. This stage consists in an iterative co-optimization of the power split strategies between the electric drive and the Diesel engine and of the engine settings (injection pressure, EGR rate, etc.). The methodology combines optimal control laws and optimization methodology based on global statistical models using single-cylinder design of experiments. After several iterations, this method allows to find the optimal NOx/CO2 trade-off curve.

With the emergence of stringent emissions standards and needs for fuel diversification, many countries are considering a massive use of natural gas for transportation. In this context, dual fuel diesel-CNG combustion is considered as a promising solution for highly efficient internal combustion engines. This concept offers the possibility to combine a diesel pilot injection as a high energy combustion initiation event, with an indirect injection of methane as main energy source. Low CO2 emissions can be reached thanks to the use of a conventional compression ignition engine with high compression ratio, and thanks to methane's high knocking resistance and low carbon content. Another benefit of dual fuel operation with high diesel substitution rates is the drastic reduction of PM emissions since methane is a very stable molecule containing no soot precursor.

Current progress in the development of diesel engines substantially contributes to the reduction of NOx and Particulate Matter (PM) emissions but will not succeed to eliminate the application of Diesel Particulate Filters (DPFs) in the future. In the past we have introduced a Multi-Functional Reactor (MFR) prototype, suitable for the abatement of the gaseous and PM emissions of the Low Temperature Combustion (LTC) engine operation. In this work the performance of MFR prototypes under both conventional and advanced combustion engine operating conditions is presented. The effect of the MFR on the fuel penalty associated to the filter regeneration is assessed via simulation. Special focus is placed on presenting the performance assessment in combination with the existing differences in the morphology and reactivity of the soot particles between the different modes of diesel engine operation (conventional and advanced). The effect of aging on the MFR performance is also presented.