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Diesel low-temperature combustion strategies often rely on early injection timing to allow sufficient fuel-ambient mixing to avoid NOx and soot-forming combustion. However, these early injection timings permit the spray to penetrate into a low ambient temperature and density environment where vaporization is poor and liquid impingement upon the cylinder liner and piston bowl are more likely to occur. The objective of this study is to measure the transient liquid and vapor penetration at early-injection conditions. High-speed Mie-scatter and shadowgraph imaging are employed in an optically accessible chamber with a free path of 100 mm prior to wall impingement and using a single-spray injector. The ambient temperature and density within the chamber are well-controlled (uniform) and selected to simulate in-cylinder conditions when injection occurs at -40 crank-angle degrees (CAD) or fewer before top-dead center (TDC).

An accurate prediction of internal nozzle flow in fuel injector offers the potential to improve predictions of spray computational fluid dynamics (CFD) in an engine, providing a coupled internal-external calculation or by defining better rate of injection (ROI) profile and spray angle information for Lagrangian parcel computations. Previous research has addressed experiments and computations in transparent nozzles, but less is known about realistic multi-hole diesel injectors compared to single axial-hole fuel injectors. In this study, the transient injector opening and closing is characterized using a transparent multi-hole diesel injector, and compared to that of a single axial hole nozzle (ECN Spray D shape). A real-size five-hole acrylic transparent nozzle was mounted in a high-pressure, constant-flow chamber. Internal nozzle phenomena such as cavitation and gas exchange were visualized by high-speed long-distance microscopy.

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.

Split injection processes have been analyzed by means of a Quasi-1D spray model that has been recently coupled to a laminar tabulated unsteady-flamelet progress-variable (UFPV) combustion model. The modelling approach can predict ignition delay and lift-off for long injection profiles, and it is now extended to a two-pulse injection scheme. In spite of the simplicity of the approach, relevant phenomena are adequately reproduced. In particular, the faster penetration of the second injection pulse compared to the first one is captured by the model both under inert and reacting conditions. The second pulse ignites much faster than the first one due to the injection into the remnants of the first one, where high temperature oxygen-depleted regions can be found. Ignition of the second pulse happens as soon as the first pulse reaches this region, with a faster low- to high-temperature transition.

This work investigates the effects of cavitation on spray characteristics by comparing measurements of liquid and vapor penetration as well as ignition delay and lift-off length. A smoothed-inlet, converging nozzle (nominal KS1.5) was compared to a sharp-edged nozzle (nominal K0) in a constant-volume combustion vessel under thermodynamic conditions consistent with modern compression ignition engines. Within the near-nozzle region, the K0 nozzle displayed larger radial dispersion of the liquid as compared to the KS1.5 nozzle, and shorter axial liquid penetration. Moving downstream, the KS1.5 jet growth rate increased, eventually reaching a growth rate similar to the K0 nozzle while maintaining a smaller radial width. The increasing spreading angle in the far field creates a virtual origin, or mixing offset, several millimeters downstream for the KS1.5 nozzle.

Actual combustion strategies in internal combustion engines rely on fast and accurate injection systems to be successful. One of the injector designs that has shown good performance over the past years is the direct-acting piezoelectric. This system allows precise control of the injector needle position and hence the injected mass flow rate. Therefore, understanding how nozzle flow characteristics change as function of needle dynamics helps to choose the best lift law in terms of delivered fuel for a determined combustion strategy. Computational fluid dynamics is a useful tool for this task. In this work, nozzle flow of a prototype direct-acting piezoelectric has been simulated by using CONVERGE. Unsteady Reynolds-Averaged Navier-Stokes approach is used to take into account the turbulence. Results are compared with experiments in terms of mass flow rate. The nozzle geometry and needle lift profiles were obtained by means of X-rays in previous works.

Understanding and prediction of flash-boiling spray behavior in gasoline direct-injection (GDI) engines remains a challenge. In this study, computational fluid dynamics (CFD) simulations using the homogeneous relaxation model (HRM) for not only internal nozzle flow but also external spray were evaluated using CONVERGE software and compared to experimental data. High-speed extinction imaging experiments were carried out in a real-size axial-hole transparent nozzle installed at the tip of machined GDI injector fueled with n-pentane under various ambient pressure conditions (Pa/Ps = 0.07 - 1.39). The width of the spray during injection was assessed by means of projected liquid volume, but the structure and timing for boil-off of liquid within the sac of the injector were also assessed after the end of injection, including cases with different designed sac volumes.

In the present work a constant-pressure flow facility able to reach 15 MPa ambient pressure and 1000 K ambient temperature has been employed to carry out experimental studies of the combustion process at Diesel engine like conditions. The objective is to study the effect of orifice diameter on combustion parameters as lift-off length, ignition delay and flame penetration, assessing if the processing methodologies used for a reference nozzle are suitable in heavy duty applications. Accordingly, three orifice diameter were studied: a spray B nozzle, with a nominal diameter of 90 μm, and two heavy duty application nozzles (diameter of 194 μm and 228 μm respectively). Results showed that nozzle size has a substantial impact on the ignition event, affecting the premixed phase of the combustion and the ignition location. On the lift-off length, increasing the nozzle size affected the combustion morphology, thus the processing methodology had to be modified from the ECN standard methodology.

The use of predictive models in the study of Internal Combustion Engines (ICE) allows reducing developing cost and times. However, those models are challenging due to the complex and multi-phase phenomena occurring in the combustion chamber, but also because of the different spatial and temporal scales in different components of the injection systems. This work presents a methodology to accurately simulate the spray by Discrete Droplet Models (DDM) without experimentally measuring the injector mass flow rate and/or momentum flux. Transient nozzle flow simulations are used instead to define the injection conditions of the spray model. The methodology is applied to a multi-hole Gasoline Direct injection (GDi) injector. Firstly, the DDM constant values are calibrated comparing simulation results to Diffused Back-light Illumination (DBI) experimental technique results. Secondly, transient nozzle flow simulations are carried out.

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.

Studies of transient diesel spray characteristics at high injection pressures were conducted in a constant volume chamber by utilizing a high speed photography and light extinction optical diagnostic technique. Two different types of nozzle hole entrances were investigated: a sharp-edged and a round-edged nozzle. The experimental results show that for the same injection delivery, the sharp-edged inlet injector needed a higher injection pressure to overcome the higher friction loss, but it produced longer spray tip penetration length, larger spray angle, smaller droplet sizes, and also lower particulate emission from a parallel engine test. For the round-edged and smooth edged tips at the same injection pressure, the sharp-edged inlet tip took a longer injection duration to deliver a fixed mass of fuel and produced larger overall average Sauter Mean Diameter (SMD) droplets.

This paper describes the validation of a CFD code for mixture preparation in a direct injection hydrogen-fueled engine. The cylinder geometry is typical of passenger-car sized spark-ignited engines, with a centrally located injector. A single-hole and a 13-hole nozzle are used at about 100 bar and 25 bar injection pressure. Numerical results from the commercial code Fluent (v6.3.35) are compared to measurements in an optically accessible engine. Quantitative planar laser-induced fluorescence provides phase-locked images of the fuel mole-fraction, while single-cycle visualization of the early jet penetration is achieved by a high-speed schlieren technique. The characteristics of the computational grids are discussed, especially for the near-nozzle region, where the jets are under-expanded. Simulation of injection from the single-hole nozzle yields good agreement between numerical and optical results in terms of jet penetration and overall evolution.

This paper details results of a numerical and experimental investigation into the relative performance of vaned and vaneless mixed flow turbines for application to medium and heavy-duty diesel engines utilizing pulse exhaust systems. Previous investigations into the impact of nozzle vanes on turbine performance considered only open turbine housings, whereas a majority of medium and heavy-duty diesel engine applications are six-cylinder engines using pulse exhaust systems with divided turbines. The two turbine stages for this investigation were carefully designed to meet the constraints of engines with pulse exhaust systems and to control confounding factors that would undermine the vaned vs vaneless performance comparison. Detailed CFD analysis and turbine dynamometer test results confirm a significant efficiency advantage for the vaned turbine stage under both full and partial admission conditions.

The in-cylinder charge motion during the compression stroke of an optically accessible engine equipped with direct injection of hydrogen fuel is measured via particle image velocimetry (PIV). The evolution of the mean flow field and the tumble ratio are examined with and without injection, each with the unmodified 4-valve pent-roof engine head and with the intake ports modified to yield higher tumble. The measurements in the vertical symmetry plane of the cylinder show that intake modification produces the desired drastic increase in tumble flow, changing the tumble ratio at BDC from 0.22 to 0.70. Either intake-induced flow is completely disrupted by the high-pressure hydrogen injection from an angled, centrally located single-hole nozzle. The injection event leads to sudden reversal of the tumble. Hence the tumble ratio is negative after injection. However, the two intake configurations still differ in tumble ratio by about the same magnitude as before injection.

Past experiments have shown that numerous micro-hole sprays in close proximity produce drop sizes that are sensitive to the nozzle arrangement. Numerical studies have been performed to identify the interaction mechanisms between closely spaced sprays. It is shown that nozzle configurations can lower the drop-gas relative velocity and droplet Weber number, leading to reduced atomization intensity. However, the collisions involving droplets from neighboring sprays have a much greater effect on droplet size. Thus, neighboring sprays primarily interfere with each other through droplet collision.

This paper examines the interaction of bulk flow and jet-induced fuel convection in an optically accessible hydrogen-fueled engine with direct injection. Planar laser-induced fluorescence (PLIF) of gaseous acetone as a fuel tracer was performed to obtain quantitative images of the hydrogen mole-fraction in the operating engine. With the engine motored, fuel was injected into inert bulk gas from a centrally located injector during the compression stroke. The injector had a single-hole nozzle with the jet angled at 50 degrees with respect to the vertical injector axis. Two parameters were varied in the experiments, injector orientation and tumble intensity, and for each of these, the injection timing was varied. Image series of the mean fuel mole-fraction between injection and near-TDC crank angles capture the mixture-formation process for each configuration and injection timing.

Diesel injection parameters effect on liquid-phase diesel spray penetration after the end-of-injection (EOI) is investigated in a constant-volume chamber over a range of ambient and injector conditions typical of a diesel engine. Our past work showed that the maximum liquid penetration length of a diesel spray may recede towards the injector after EOI at some conditions. Analysis employing a transient jet entrainment model showed that increased fuel-ambient mixing occurs during the fuel-injection-rate ramp-down as increased ambient-entrainment rates progress downstream (i.e. the entrainment wave), permitting complete fuel vaporization at distances closer to the injector than the quasi-steady liquid length. To clarify the liquid-length recession process, in this study we report Mie-scatter imaging results near EOI over a range of injection pressure, nozzle size, fuel type, and rate-of-injection shape. We then use a transient jet entrainment model for detailed analysis.

Reduced-order models typically assume that the flow through the injector orifice is quasi-steady. The current study investigates to what extent this assumption is true and what factors may induce large-scale variations. Experimental data were collected from a single-hole metal injector with a smoothly converging hole and from a transparent facsimile. Gas, likely indicating cavitation, was observed in the nozzles. Surface roughness was a potential cause for the cavitation. Computations were employed using two engineering-level Computational Fluid Dynamics (CFD) codes that considered the possibility of cavitation. Neither computational model included these small surface features, and so did not predict internal cavitation. At steady state, it was found that initial conditions were of little consequence, even if they included bubbles within the sac. They however did modify the initial rate of injection by a few microseconds.

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.

In order to improve understanding of the primary atomization process for diesel-like sprays, a collaborative experimental and computational study was focused on the near-nozzle spray structure for the Engine Combustion Network (ECN) Spray D single-hole injector. These results were presented at the 5th Workshop of the ECN in Detroit, Michigan. Application of x-ray diagnostics to the Spray D standard cold condition enabled quantification of distributions of mass, phase interfacial area, and droplet size in the near-nozzle region from 0.1 to 14 mm from the nozzle exit. Using these data, several modeling frameworks, from Lagrangian-Eulerian to Eulerian-Eulerian and from Reynolds-Averaged Navier-Stokes (RANS) to Direct Numerical Simulation (DNS), were assessed in their ability to capture and explain experimentally observed spray details. Due to its computational efficiency, the Lagrangian-Eulerian approach was able to provide spray predictions across a broad range of conditions.