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Conventional spark-ignition engines are currently incapable of meeting rising customer performance demands while complying with even stringent pollutant-emissions regulations. As a result, innovative ignition systems are being developed to accomplish these targets. Radio-Frequency corona igniters stand out for their ability to accelerate early flame growth speed by exploiting the combined action of kinetic, thermal and transport effects. Furthermore, a volumetric discharge enables the promotion of combustion over a wide area, as opposed to the local ignition of traditional spark. The present work wants to evaluate the advantages of a Streamer-type Radio Frequency corona discharge at about 100 kHz with respect to those of traditional spark igniter.

Emission legislation for light and heavy duty vehicles is requiring a drastic reduction of exhaust pollutants from internal combustion engines (ICE). Achieving a quick heating-up of the catalyst is of paramount importance to cut down cold start emissions and meet current and new regulation requirements. This paper describes the development and the basic characteristics of a novel burner for diesel engines exhaust systems designed for being activated immediately at engine cold start or during vehicle cruise. The burner is comprised of a swirled fuel dosing system, an air system, and an ignition device. The main design characteristics are presented, with a detailed description of the atomization, air-fuel interaction and mixture formation processes. An atomizer prototype has been extensively analyzed and tested in various conditions, to characterize the resulting fuel spray under cold-start and ambient operating conditions.

The goal of mitigating climate change has driven research to the use of carbon-free energy sources. In this regards, green hydrogen appears as one of the best options, however, its storage remains difficult and expensive. Indeed, there is room to consider the use of ammonia (an efficient hydrogen carrier) directly as a fuel for internal combustion engines or gas turbines. Currently, there are very few works in the literature describing liquid ammonia sprays, both from experimental and modeling point of view, and especially dealing with flash-boiling conditions. In this research work, the direct injection ammonia spray is modeled with the Lagrangian particle approach, building up a numerical model within the OpenFOAM framework, for transient analyses using the U-RANS approach.

Computational fluid dynamics is used with the aim to gain further insights of the hydrogen injection process in internal combustion engines. To this end, three-dimensional RANS simulations of hydrogen under-expanded jets under a variety of injection pressures and temperatures and chamber backpressure are performed. A numerical framework that accounts for real-fluid effects is used which includes accurate non-linear mixing rules for thermodynamic and transport properties with multiple species. Jet formation process, transition to turbulent regime, and mixing process are investigated which are key aspects for the design of efficient injection and combustion. Different simulations are discussed to investigate the structures in the near field, such as Mach disk, barrel, and reflected shocks. It is found that for direct injection applications, especially in high back-pressure cases, accounting for real fluid behavior of hydrogen-air mixtures is important for accurate predictions.

Engine research community is developing innovative strategies capable of reducing fuel consumption and pollutant emissions while ensuring, at the same time, satisfactory performances. Spark ignition engines operation with highly diluted or lean mixture is demonstrated to be beneficial for engine efficiency and emissions while arduous for combustion initiation and stability. Traditional igniters are unsuitable for such working conditions, therefore, advanced ignition systems have been developed to improve combustion robustness. To overcome the inherent efficiency limit of combustion engines, the usage of renewable fuels is largely studied and employed to offer a carbon neutral transition to a cleaner future. For such a reason, both innovative ignition systems and bio or E-fuels are currently being investigated as alternatives to the previous approaches. Within this context, the present work proposes a synergetic approach which combines the benefits of a biofuel blend, i.e.

Emission legislation for passenger cars is requiring a drastic reduction of exhaust pollutants from internal combustion engines (ICE). In this framework, achieving a quick heating-up of the catalyst is of paramount importance to cut down the cold start emissions and meet future regulation requirements. This paper describes the development and the basic characteristics of a novel burner for gasoline engines exhaust systems designed for being activated immediately at engine cold start. The burner is comprised of a fuel injector, an air system, and an ignition device. The design of the combustion chamber is first presented, with a description of the air-fuel interactions and mixture formation processes. Swirl is used along with a flame-holder concept to anchor the flame at the mixer exit. Spray-swirl and spray-walls interaction are also discussed. Computational Fluid Dynamics (CFD) analyses have been used to investigate these aspects.

Lean operation of spark ignition engines is a promising strategy for increasing thermal efficiency and minimize emissions. Variability on the other hand is one of the main shortcomings in these conditions. In this context, the present study looks at the interaction between the spark produced by a J-type plug and the surrounding fluid flow. A combined experimental and numerical approach was implemented so as to provide insight into the phenomena related to the ignition process. A sweep of cross-flow velocity of air was performed on a dedicated test rig that allowed accurate control of the volumetric flow and pressure. This last parameter was varied from ambient to 10 bar, so as to investigate conditions closer to real-world engine applications. Optical diagnostics were applied for better characterization of the arc in different operating conditions. The spatial and temporal evolution of the arc was visualized with high-speed camera to estimate the length, width and stretching.

Ducted Fuel Injection (DFI) is a new technology recently developed with the aim of reducing soot emission formation in diesel compression ignition engines. DFI concept consists of the injection of fuel spray through a small duct located downstream of the injector nozzle leaving a certain gap, the so-called Stand-off distance. Currently, CFD modelers have investigated its performance using classical spray modeling techniques such as the Discrete Drops Method (DDM). However, as discussed in the literature, this type of technique is inappropriate when applied to dense jets as those occurring in diesel sprays, especially in the near-nozzle region (where the duct is placed). Therefore, considering a more appropriate modeling technique for such a problem is mandatory. In this research work, an Eulerian single-fluid diffuse-interface model called Σ-Y and implemented in the OpenFOAM framework is utilized for the simulation of non-reacting conditions.

Currently, conventional spark-ignition engines are unfit to satisfy the growing customer requirements on efficiency while complying with the legislations on pollutant emissions. New ignition systems are being developed to extend the engine stable operating range towards increasing lean conditions. Among these, the Radio-Frequency corona igniters represent an interesting solution for the capability to promote the combustion in a much wider region than the one involved by the traditional spark channel. Moreover, the flame kernel development is enhanced by means of the production of non-thermal plasma, where low-temperature active radicals are ignition promoters. However, at low pressure and at high voltage the low temperature plasma benefits can be lost due to occurrences of spark-like events. Recently, RF barrier discharge igniters (BDI) have been investigated for the ability to prevent the arc formation thanks to a strong-breakdown resistance.

Nowadays internal combustion engines can operate under lean combustion conditions to maximize efficiency, as long as combustion stability is guaranteed. The robustness of combustion initiation is one of the main issues of actual spark-ignition engines, especially at high level of excess-air or dilution. The enhancement of the in-cylinder global motion and local turbulence is an effective way to increase the flame velocity. During the ignition process, the excessive charge motion can hinder the spark discharge and eventually cause a misfire. In this perspective, the interaction between the igniter and the flow field is a fundamental aspect which still needs to be explored in more detail to understand how the combustion originates and develops. In this work, a combined experimental and numerical study is carried out to investigate the flow field around the spark gap, and its effect on the spark discharge evolution.

Low-temperature heat release (LTHR) in spark-ignited internal combustion engines is a critical step toward the occurrence of auto-ignition, which can lead to an undesirable phenomenon known as engine knock. Hence, correct predictions of LTHR are of utmost importance to improve the understanding of knock and enable techniques aimed at controlling it. While LTHR is typically obscured by the deflagration following the spark ignition, extremely late ignition timings can lead to LTHR occurrence prior to the spark, i.e., pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection SI engine was numerically investigated using three-dimensional computational fluid dynamics (CFD). A hybrid approach was used, based on the G-equation model for representing the turbulent flame front and the multi-zone well-stirred reactor model for tracking the chemical reactions within the unburnt region.

The new real driving emission cycles and the growing adoption of turbocharged GDI engines are directing the automotive technology towards the use of innovative solutions aimed at reducing environmental impact and increasing engine efficiency. Water injection is a solution that has received particular attention in recent years, because it allows to achieve fuel savings while meeting the most stringent emissions regulations. Water is able to reduce the temperature of the gases inside the cylinder, coupled with the beneficial effect of preventing knock occurrences. Moreover, water dilutes combustion, and varies the specific heat ratio of the working fluid; this allows the use of higher compression ratios, with more advanced and optimal spark timing, as well as eliminating the need of fuel enrichment at high load. Computational fluid dynamics simulations are a powerful tool to provide more in-depth details on the thermo-fluid dynamics involved in engine operations with water injection.

In this last decade, non-destructive X-ray measurement techniques have provided unique insights into the internal surface and flow characteristics of automotive injectors. This has in turn contributed to enhancing the accuracy of Computational Fluid Dynamics (CFD) models of these critical injection system components. By employing realistic injector geometries in CFD simulations, designers and modelers have identified ways to modify the injectors’ design to improve their performance. In recent work, the authors investigated the occurrence of cavitation in a heavy-duty multi-hole diesel injector operating with a high-volatility gasoline-like fuel for gasoline compression ignition applications. They proposed a comprehensive numerical study in which the original diesel injector design would be modified with the goal of suppressing the in-nozzle cavitation that occurs when gasoline fuels are used.

In order to understand supercritical jet flows further, well resolved large eddy simulations (LES) of a n-dodecane jet mixing with surrounding nitrogen are conducted. A real fluid thermodynamic model is used to account for the fuel compressibility and variable thermophysical properties due to the solubility of ambient gas and liquid jet using the cubic Peng-Robinson equation of state (PR-EOS). A molar averaged homogeneous mixing rule is used to calculate the mixing properties. The thermodynamic model is coupled with a pressure-based solver to simulate multispecies reacting flows. The numerical model is based on a second order accurate method implemented in the open source OpenFOAM-6 software. First, to evaluate the present numerical model for sprays, 1D advection and shock tube benchmark problems at supercritical conditions are shown.

In this study, the combustion system of a light-duty compression ignition engine running on a market gasoline fuel with Research Octane Number (RON) of 91 was optimized using computational fluid dynamics (CFD) and Machine Learning (ML). This work was focused on optimizing the piston bowl geometry at two compression ratios (CR) (17 and 18:1) and this exercise was carried out at full-load conditions (20 bar indicated mean effective pressure, IMEP). First, a limited manual piston design optimization was performed for CR 17:1, where a couple of pistons were designed and tested. Thereafter, a CFD design of experiments (DoE) optimization was performed where CAESES, a commercial software tool, was used to automatically perturb key bowl design parameters and CONVERGE software was utilized to perform the CFD simulations. At each compression ratio, 128 piston bowl designs were evaluated.

The modeling of fuel jet atomization is key in the characterization of Internal Combustion (IC) engines, and 3D Computational Fluid Dynamics (CFD) is a recognized tool to provide insights for design and control purposes. Multi-hole injectors with counter-bored nozzle are the standard for Gasoline Direct Injection (GDI) applications and the Spray-G injector from the Engine Combustion Network (ECN) is considered the reference for numerical studies, thanks to the availability of extensive experimental data. In this work, the behavior of the Spray-G injector is simulated in a constant volume chamber, ranging from sub-cooled (nominal G) to flashing conditions (G2), validating the models on Diffused Back Illumination and Phase Doppler Anemometry data collected in vaporizing inert conditions.

This paper presents a computational fluid dynamics (CFD) study of the Engine Combustion Network (ECN) Spray G under non-vaporizing condition, focusing on the impacts of fuel properties as well as realistic geometry on the atomization process. The large-eddy-simulation method, coupled with the volume-of-fluid method, is used to model the high-speed turbulent two-phase flow. A moving-needle boundary condition is applied to capture the internal flow boundary condition accurately. The injector geometry was measured with micron-level resolution using x-ray tomographic imaging at the Advanced Photon Source at Argonne National Laboratory, providing detailed machining tolerance and defects from manufacturing and a realistic rough surface. A 2.5-μm fine mesh is used to sufficiently resolve the details of liquid-gas interface and the breakup process.

Spray modeling techniques have evolved from the classic DDM (Discrete Drops Method) approach, where the continuous liquid jet is discretized into “drops” or “parcels” till advanced spray models often based on Eulerian approaches. The former technique, although computationally efficient, is essentially inadequate in highly dense jets, as in the near nozzle region of compression ignition engines, while the latter could lead to extreme levels of computational effort when resolved interface capturing methods, such as VoF (Volume of Fluids) and LS (Level-Set) types, are used. However, in a typical engineering calculation, the mesh resolution is considerably coarser than in these high fidelity computations. If one presumes that these interfacial details are far smaller than the mesh size, smoothing features over at least one cell ultimately results in a diffuse-interface treatment in a Eulerian framework.

In this study, three-dimensional large eddy simulations were performed to study the internal nozzle flow of the ECN Spray C diesel injector. Realistic nozzle geometry, full needle motion, and internal flow imaging data obtained from X-ray measurements were employed to initialize and validate the CFD model. The influence of injection pressure and fuel properties were investigated, and the effect of mesh size was discussed. The results agreed well with the experimental data of mass flow rate and correctly captured the flow structures inside the orifice. Simulations showed that the pressure drop near the sharp orifice inlet triggered flow separation, resulting in the ingestion of ambient gas into the orifice via a phenomenon known as hydraulic flip. At higher injection pressure, the pressure drop was more significant as the liquid momentum increased and the stream inertia was less prone to change its direction.

In order to reduce engine emissions and fuel consumption, extensive research efforts are being devoted to develop innovative ignition devices, able to extend the stable engine operating range towards increasing lean conditions. Among these, radio frequency corona ignition systems, which produce a strong electric field at a frequency of about 1 MHz, can create discharges characterized by simultaneous thermal and kinetic effects. These devices can considerably increase the early flame growth speed, initiating the combustion process in a wide region, as opposed to the local ignition generated by traditional sparks. To explore the corona ignition behavior, experimental campaigns were carried out to investigate different operating conditions, in a constant volume calorimeter designed to measure the deposited thermal energy. The present work compares the combustion development generated by a traditional spark and the corona igniter through computational fluid dynamics simulations.