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The role of numerical simulations in the development of innovative and sustainable powertrains is constantly growing thanks to their capabilities to significantly reduce the calibration efforts and to point out potential synergies among different technologies. In such a framework, this paper describes the development of a fully physical 1D-CFD engine model to support the calibration of the highly efficient spark ignition engine of the PHOENICE (PHev towards zerO EmissioNs & ultimate ICE efficiency) EU H2020 project. The availability of a reliable simulation platform is essential to effectively exploit the combination of the several features introduced to achieve the project target of 47% peak gross indicated efficiency, such as SwumbleTM in-cylinder charge motion, Miller cycle combined with high Compression Ratio (CR), lean mixture exploiting cooled low pressure Exhaust Gas Recirculation (EGR) and electrified turbocharging.

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.

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.

Non-conventional operating conditions and fuels in diesel engines can produce longer ignition delays compared to conventional diesel combustion. If those extended delays are longer than the injection duration, the ignition and combustion progress can be significantly influenced by the transient following the end of injection (EOI), and especially by the modification of the mixture field. The objective of this paper is to assess how those long ignition delays, obtained by injecting at low in-cylinder temperatures (e.g., 760-800K), are affected by EOI. Two multi-hole diesel fuel injectors with either six 0.20mm orifices or seven 0.14mm orifices have been used in a 2.34L single-cylinder optical diesel engine. We consider a range of ambient top dead center (TDC) temperatures at the start of injection from 760-1000K as well as a range of injection durations from 0.5ms to 3.1ms. Ignition delays are computed through the analysis of both cylinder pressure and chemiluminescence imaging.

Within the Engine Combustion Network (ECN) research frame, the mixing process and the fuel mass concentration fields were investigated at spray G conditions and variants with optical diagnostics. Experiments were conducted in a high-temperature high-pressure constant-volume pre-combustion vessel. The target condition, called “Spray G”, which is representative of gasoline direct-injection engine conditions, uses well-defined ambient (573 K, 6 bar, 3.5 kg/m3, O2-free) and injector conditions (200 bar, eight-hole injector, 0.165 mm orifice diameter). Measurements were also conducted at 6 and 9 kg/m3 for temperatures of 700 and 800 K respectively. Two techniques were used to visualize the jet formation: p-difluorobenzene laser induced fluorescence (LIF) imaging and high-repetition-rate schlieren visualization. Images from both methods were compared in terms of jet penetration and size.

Emission regulations have become increasingly stringent in recent years. Current regulations need the development of a new worldwide driving cycle which gives greater weight to the pollutants emitted during transient phases or cold starts. Powertrains contain a large number of components such as multistage turbocharger systems; exhaust gas recirculation, after-treatment devices and sometimes an electric motor. In this context, 0D predictive models of heat transfer in the exhaust line, calibrated with experimental data, are particularly interesting. Many investigations are related to the development of precise control laws in order to optimize the light-off of after-treatment elements during the engine starting phase. A better understanding of the thermal phenomena occurring in the exhaust line is necessary. To study the heat transfer in the exhaust line of a Diesel engine during transient conditions, the temperature in the exhaust line must be known precisely.

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.

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.

Burned gas recirculation is emerging as a promising technology to reduce fuel consumption without compromising performance in turbocharged spark ignited engines. This recirculation can be done internally through Internal Gas Residual (IGR) using Variable Valve Timing (VVT) or externally through classical Exhaust Gas Recirculation circuit (EGR). Both have a large impact on combustion. The purpose of the paper is to give clues to get the best compromise at moderate load between these two technologies in terms of fuel consumption. This experimental work was performed on a Gasoline Direct Injection (GDI) engine, 2.0L displacement, dual independent VVT, equipped with a Low Pressure, cooled and catalyzed EGR loop (LP EGR). The load region covers 6 to 10 bar Indicated Mean Effective Pressure (IMEP). EGR rates obtained vary between 0 and 15%. IGR variation is obtained by using the VVT in order to vary the valve overlap. IGR rates vary from 4 to 8%.

Within the Engine Combustion Network (ECN) spray combustion research frame, simultaneous line-of-sight laser extinction measurements and laser-induced incandescence (LII) imaging were performed to derive the soot volume fraction (fv). Experiments are conducted at engine-relevant high-temperature and high-pressure conditions in a constant-volume pre-combustion type vessel. The target condition, called "Spray A," uses well-defined ambient (900 K, 60 bar, 22.8 kg/m₃, 15% oxygen) and injector conditions (common rail, 1500 bar, KS1.5/86 nozzle, 0.090 mm orifice diameter, n-dodecane, 363 K). Extinction measurements are used to calibrate LII images for quantitative soot distribution measurements at cross sections intersecting the spray axis. LII images are taken after the start of injection where quasi-stationary combustion is already established.

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.

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].

Both, the continuous strengthening of the exhaust emission legislation and the striving for a substantial reduction of carbon dioxide output in the traffic sector depict substantial requirements for the development of future diesel engines. These engines will comprise not only the mandatory diesel oxidation catalyst (DOC) and particulate filter DPF but a NOx aftertreatment system as well - at least for heavier vehicles. The oxidation catalysts as well as currently available NOx aftertreatment technologies, i.e., LNT and SCR, rely on sufficient exhaust gas temperatures to achieve a proper conversion. This is getting more and more critical due to the fact that today's and future measures for CO₂ reduction will result in further decrease of engine-out temperatures. Additionally this development has to be considered in the light of further engine electrification and hybridization scenarios.

Both, the continuous strengthening of the exhaust emission legislation and the striving for a substantial reduction of the carbon dioxide output in the traffic sector depict substantial requirements for the global automotive industry and especially for the engine manufacturers. From the multiplicity of possible approaches and strategies for clear compliance with these demands, engine internal measures offer a large and, eventually more important, very economical potential. For example, the achievements in fuel injection technology are a measure which in the last years has contributed significantly to a notable reduction of the emissions of the modern DI Diesel engines at favorable fuel efficiency. Besides the application of modern fuel injection technology, the linked combustion control (Closed Loop Combustion Control) opens possibilities for a further optimization of the combustion process.

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.

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.

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 this study the fuel influence of several bio-fuel candidates on homogeneous engine combustion systems with direct injection is investigated. The results reveal Ethanol and 2-Butanol as the two most knock-resistant fuels. Hence these two fuels enable the highest efficiency improvements versus RON95 fuel ranging from 3.6% - 12.7% for Ethanol as a result of a compression ratio increase of 5 units. Tetrahydro-2-methylfuran has a worse knock resistance and a decreased thermal efficiency due to the required reduction in compression ratio by 1.5 units. The enleanment capability is similar among all fuels thus they pose no improvements for homogeneous lean burn combustion systems despite a significant reduction in NOX emissions for the alcohol fuels as a consequence of lower combustion temperatures.

From current point of view future emission legislations for heavy-duty engines as well as industrial engines will require complex engine internal measures in combination with sophisticated aftertreatment systems as well as according control strategies to reach the emission targets. With EU VI, JP 09/NLT and US10 for heavy-duty engines as well as future Tier4 final or stage IV emission legislation for industrial applications, EGR + DPF + SCR probably will be combined for most applications and therefore quite similar technological approaches will be followed up in Europe as well as in the US and in Japan. Most “emerging markets” all over the world follow up the European, US or Japanese emission legislation with a certain time delay. Therefore similar technologies need to be introduced in these markets in the future. On the other hand specific market boundary conditions and requirements have to be considered for the development of tailored system concepts in these markets.