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Fuel film deposits on combustion chamber walls are understood to be the main source of particle emissions in GDI engines under homogenous charge operation. More precisely, the liquid film that remains on the injector tip after the end of injection is a fuel rich zone that undergoes pyrolysis reactions leading to the formation of poly-aromatic hydrocarbons (PAH) known to be the precursors of soot. The physical phenomena accompanying the fuel film deposit, evaporation, and the chemical reactions associated to the injector film are not yet fully understood and require high fidelity CFD simulations and controlled experimental campaigns in optically accessible engines. To this end, a simplified model based on physical principles is developed in this work, which couples an analytical model for liquid film formation and evaporation on the injector tip with a stochastic particle dynamics model for particle formation.

The temperature of fuel injectors can affect the flow inside nozzles and the subsequent spray and liquid films on the injector tips. These processes are known to impact fuel mixing, combustion and the formation of deposits that can cause engines to go off calibration. However, there is a lack of experimental data for the transient evolution of nozzle temperature throughout engine cycles and the effect of operating conditions on injector tip temperature. Although some measurements of engine surface temperature exist, they have relatively low temporal resolutions and cannot be applied to production injectors due to the requirement for a specialist coating which can interfere with the orifice geometry. To address this knowledge gap, we have developed a high-speed infrared imaging approach to measure the temperature of the nozzle surface inside an optical diesel engine.

Selective Catalytic Reduction stands for an effective methodology for the reduction of NOx emissions from Diesel engines and meeting current and future EURO standards. For it, the injection of Urea Water Solution (UWS) plays a major role in the process of reducing the NOx emissions. A LES approach for turbulence modelling allows to have a description of the physics which is a very useful tool in situations where experiments cannot be performed. The main objective of this study is to predict characteristics of the flow of interest inside the injector as well as spray morphology in the near field of the spray. For it, the nozzle geometry has been reconstructed from X-Ray tomography data, and an Eulerian-Eulerian approach commonly known as Mixture Model has been applied to study the liquid phase of the UWS with a LES approach for turbulence modeling. The injector unit is subjected to typical low-pressure working conditions.

A comparison of the flame structure for two different fuels, dodecane and oxymethylene dimethyl ether (OMEX), has been performed under condition of Spray A of the Engine Combustion Network (ECN). The experiments were carried out in a constant pressure vessel with wide optical access, at high pressure and temperature and controlled oxygen concentration. The flame structure analysis has been performed by measuring the formaldehyde and OH radical distributions using planar Laser-Induced Fluorescence (PLIF) techniques. To complement the analysis, this information was combined with that obtained with high-speed imaging of OH* chemiluminescence radiation in the UV. Formaldehyde molecules are excited with the 355-nm radiation from the third harmonic of a Nd:YAG laser, whilst OH is excited with a wavelength of 281.00-nm from a dye laser.

Experimental visualization of current gasoline direct injection (GDi) systems are even more complicated especially due to the proximity of spray plumes and the interaction between them. Computational simulations may provide additional information to understand the complex phenomena taking place during the injection process. Nozzle flow simulations with a Volume-of-Fluid (VOF) approach can be used not only to analyze the flow inside the nozzle, but also the first 2-5 mm of the spray. A methodology to obtain plume direction and spray angle from the simulations is presented. Results are compared to experimental data available in the literature. It is shown that plume direction is well captured by the model, whilst the uncertainty of the spray angle measurements does not allow to clearly validate the developed methodology.

It is known that in-cylinder airflow structures during intake and compression strokes deeply affects the combustion process in compression ignition (CI) engines. This work presents a methodology for the analysis of the swirling structures by means of the CFD proprietary code Converge 2.3. The methodology is based on the CFD modelling and the comparison of results with in-cylinder velocity fields measured by particle image velocimetry (PIV). Furthermore, the analysis is extended to the accuracy evaluation of other methods available to define the flow in the cylinder of internal combustion engines, such as experiments in steady flow rigs. These methods, in junction with simple phenomenological models, have been traditionally used to determine some of the fundamental variables that define the in-cylinder flow in ICE engines. The CFD analysis is focused in the flow structures around top dead centre (TDC) at the end of the compression stroke.

The Engine Combustion Network (ECN) is a coordinate effort from research partners from all over the world which aims at creating a large experimental database to validate CFD calculations. Two injectors from ECN, namely Spray C and D, have been compared in a constant pressure flow vessel, which enables a field of view of more than 100 mm. Both nozzles have been designed with similar flow metrics, with Spray D having a convergent hole shape and Spray C a cylindrical one, the latter being therefore more prone to cavitation. Although the focus of the study is on reacting conditions, some inert cases have also been measured. High speed schlieren imaging, OH* chemiluminescence visualization and head-on broadband luminosity have been used as combustion diagnostics to evaluate ignition delay, lift off length and reacting tip penetration. Parametric variations include ambient temperature, oxygen content and injection pressure variations.

Ever decreasing permitted emission levels and the necessity of more efficient engines demand a better understanding of in-cylinder phenomena. In swirl-supported compression ignition (CI) engines, mean in-cylinder flow structures formed during the intake stroke deeply influence mixture preparation prior to combustion, heat transfer and pollutant oxidation all of which could potentially improve engine performance. Therefore, the ability to characterize these mean flow structures is relevant for achieving performance improvements. CI mean flow structure is mainly described by a precessing vortex. The location of the vortex center is key for the characterization of the flow structure. Consequently, this work aims at evaluating algorithms that allow for the location of the vortex center both, in ensemble-averaged velocity fields and in instantaneous velocity fields.

A prototype multi-hole diesel injector operating with n-heptane fuel from a high-pressure common rail system is used in a high-pressure and high-temperature test rig capable of reaching 1100 Kelvin and 150 bar under different oxygen concentrations. A novel optical set-up capable of visualizing the soot cloud evolution in the fuel jet from 30 to 85 millimeters from the nozzle exit with the high-speed color diffused back illumination technique is used as a result of the insertion of a high-pressure window in the injector holder opposite to the frontal window of the vessel. The experiments performed in this work used one wavelength provide information about physical of the soot properties, experimental results variating the operational conditions show the reduction of soot formation with an increase in injection pressure, a reduction in ambient temperature, a reduction in oxygen concentration or a reduction in ambient density.

In the past few years’ various studies have shown how the application of a highly premixed dual fuel combustion for CI engines leads a strong reduction for both pollutant emissions and fuel consumption. In particular a drastic soot and NOx reduction were achieved. In spite of the most common strategy for dual fueling has been represented by using two different injection systems, various authors are considering the advantages of using a single injection system to directly inject blends in the chamber. In this scenario, a characterization of the behavior of such dual-fuel blend spray became necessary, both in terms of inert and reactive ambient conditions. In this work, a light extinction imaging (LEI) has been performed in order to obtain two-dimensional soot distribution information within a spray flame of different diesel/gasoline commercial fuel blends. All the measurements were conducted in an optically accessible two-stroke engine equipped with a single-hole injector.

A radiation-based 2-color method (2C) and light extinction imaging (LEI) have been performed simultaneously to obtain two-dimensional soot distribution information within a diesel spray flame. All the measurements were conducted in an optically accessible two-stroke engine equipped with a single-hole injector. The fuel used here is a blend of 30% Decane and 70% Hexadecane (in mass). According to previous research, operating conditions with three different flame soot amounts were investigated. The main purpose of this work is to evaluate the two soot diagnostics techniques, after proper conversion of soot-related values from both methods. All the KL extinction values are lower than the saturation limit. As expected, both techniques show sensitivity with the parametric variation. The soot amount increases with higher ambient gas temperature and lower injection pressure. However, the LEI technique presents more sensitivity to the soot quantity.

Major accuracy for prediction tools like CFD codes require precise experimental validation. The ultraviolet and visible light absorption and scattering (UV-VIS LAS) is proposed for characterizing air-fuel mixture formation. UV-VIS LAS technique is employed to quantitatively determine spatial concentration distribution of vapor fuel, in combination with simultaneous liquid length and spray penetration measurements by means of Mie-scattering and Schlieren. Decane, Hexadecane and a 50/50 of both fuels have been chosen for this study, to evaluate mixing formation under Diesel conditions. Work has been performed at an optical engine under non-reacting atmosphere, with ambient pressures and temperatures up to 7.3 MPa and 900 K. Fuel optical properties for the two paraffines under engine conditions have been analyzed, and fuel concentration distribution has been obtained for pure fuels.

Schlieren/shadowgraphy has been adopted in the combustion research as a standard technique for tip penetration analysis of sprays under diesel-like engine conditions. When dealing with schlieren images of reacting sprays, the combustion process and the subsequent light emission from the soot within the flame have revealed both limitations as well as considerations that deserve further investigation. Seeking for answers to such concerns, the current work reports an experimental study with this imaging technique where, besides spatial filtering at the Fourier plane, both short exposure time and chromatic filtering were performed to improve the resulting schlieren image, as well as the reliability of the subsequent tip penetration measurement. The proposed methodology has reduced uncertainties caused by artificial pixel saturation (blooming).

This publication is the result of a multidisciplinary collaboration between the academia and the industry. An attempt to pre-ionize and influence the trajectory and the fluid mechanics of the injected fuel into an experimental injection system by means of electromagnetic fields was made. This collaboration project started from research proposal, which aims at exploring the effects of a highly ionized environment on the fuel injection event and how the momentum of the injected fuel droplets may be affected by the electromagnetic fields in form of quantified variables, such as spray penetration, spreading angle and the spray axis angle. An influence of the applied electromagnetic field on the fuel spray depending on the electrode configuration was observed and is presented and discussed in this publication.

The Flamelet Generated Manifold (FGM) method is a promising technique in engine combustion modeling to include tabulated chemistry. Different methodologies can be used for the generation of the manifold. Two approaches, based on igniting counterflow diffusion flamelets (ICDF) and homogeneous reactors (HR) are implemented and compared with Engine Combustion Network (ECN) experimental database for the baseline n-heptane case. Before analyzing the combustion results, the spray model is optimized after performing a sensitivity study with respect to turbulence models, cell sizes and time steps. The standard High Reynolds (Re) k-ε model leads to the best match of all turbulence models with the experimental data. For the convergence of the mixture fraction field an appropriate cell size is found to be smaller than that for an adequate spray penetration length which appears to be less influenced by the cell size.

In the wake of the Turbulent Nonpremixed Flames group (TNF) for atmospheric pressure flames, an open group of laboratories belonging to the Engine Combustion Network (ECN) agreed on a list of boundary conditions -called “Spray A”- to study the free diesel spray under steady-state conditions. Such conditions are relevant of a diesel engine operating at low temperature combustion conditions with moderate EGR, small nozzle and high injection pressure. The objective of this program is to accelerate the understanding of diesel flames, by applying each laboratory's knowledge and skills to a specific set of boundary conditions, in order to give an extensive and reliable experimental database to help spray modeling. In the present work, “Spray A” operating condition has been achieved in a constant pressure, continuous flow vessel. Schlieren high-speed imaging has been conducted to measure the spray penetration under evaporative conditions.

Evaporating diesel sprays from multi-hole nozzles have been visualized by means of a double-pass Shadowgraphy/Schlieren technique using a metal mirror attached on the injector-mount plane. Injection has been carried out in an inert environment of nitrogen gas in order to study the mixture process, avoiding mirror and glass window fouling by soot deposition from combustion. Studies have been carried out for four different gas densities during spray injection, changing pressure and temperature. The effect of optical system alignment on image characteristics has been analysed for different beam angles relative to the optical axis. This parameter was varied in a range of 2 degrees to define the optimal optical configuration. If the angle equals 0, the Shadowgraphy/Schlieren system using a light reception back from the metallic mirror captures the spatial gradients of ambient gas density, and turbulent flow structures are clearly registered.

The goal of this paper is to obtain a simple fast model that provides information about the spray tip penetration (for free and wall jet), droplets velocity distribution and fuel concentration distribution. This model would be an important first step in the construction of a simple model capable to provide online information about the spray behaviour in engine conditions, although for the moment, the model only concerns cold sprays. As this model is based in momentum and mass flux conservation, and the patterns observed in gaseous turbulent jets, its agreement with experimental Diesel results will help to improve understanding of the spray structure in terms of the similarities and differences with a gas jet, as well as of the importance of the spray front structure in its penetration.

This paper has the objective of characterising the macro and microscopic behaviour of Diesel sprays generated by a common-rail system and quantifying the influence of injection parameters and boundary conditions through a broad experimental study. The main purpose of this research is to validate and extend the different correlations available in the literature to the case of sprays generated by common-rail systems, i.e. at high injection pressures with small nozzle holes. The sprays are characterised in an environment which simulates the in-cylinder air density existing in the real engine when the injection starts. However, it should be pointed out that isothermal conditions at room temperature are considered and very little evaporation occurs.

This paper deals with the influence of the fuel characteristics, mainly fuel density and viscosity on the injection system and spray behaviour. Experiments have been performed with seven different blends representative of automotive Diesel engine fuels, with a conventional engine injection system, spraying in a high density environment at room temperature. Injection rate measurements allow for the analysis of the influence of the fuel properties on the injection system, and high speed imaging and PDA measurements were used to get insight into the spray behaviour and atomisation process. The experimental results obtained have been fitted to simple equations to get predictive capabilities.