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The influence of spray-to-spray interaction after wall impingement of spray flames on the combustion characteristics in high pressure and high temperature ambient gas like in combustion chambers of diesel engines was examined with a constant volume vessel. Fuel was injected onto a flat wall from two nozzles to form two parallel, adjacent sprays in the vessel, causing the spray-to-spray interaction after the wall impingement. The combustion was analyzed with the rate of heat release calculated from the pressure transition in the vessel and the spray flame was visualized by high-speed video. The 310 nm UV light images of the chemiluminescence from OH radicals are recorded to demonstrate the reaction activity in the spray flame. The images of transmitted light throughout the constant volume vessel were recorded to visualize the soot formation and oxidation processes as well as to quantify the soot concentrations as the KL factors. The results showed that the rate of heat release from the main combustion decreases and the afterburning increases with the spray-to-spray interaction after the wall impingement of the spray flame. Combustion suppression with the spray-to-spray interaction occurred in all the conditions of the experiments here when changing the distance from the nozzle to the impinging wall between 25 and 40 mm and the fuel injection pressures between 100 and 200 MPa. Inside the spray-to-spray interaction zone, the chemiluminescence from OH radicals is weaker, supporting the inactive combustion due to difficulties of the air entrainment, and the lower transmitted light intensities with larger KL factors, indicating higher soot concentrations. The spray-to-spray interaction zone on the impingement wall advances toward the inside of the vessel between the sprays and it moves away from the wall, entraining the unutilized air and causing a relatively active combustion as well as rapid soot oxidation during the late afterburning stage. [ABSTRACT FROM AUTHOR]

The purpose of this study is to understand evaporation and ignition phenomena and the mixture formation process of the diesel spray near the ignition position at the ignition timing. In this study, we measured the ignition region and ignition delay of diesel spray from OH radical emission and analyzed the quantitative distribution of mixture concentration by the laser induced exciplex fluorescence (LIEF) method. It seems that ignition occurs near the tip of the spray, where there is no liquid phase and the air-fuel mixture becomes homogeneous due to entrainment of the ambient air. [ABSTRACT FROM AUTHOR]

This study presents the effects of piston bowl size on the characteristics of a four-stroke single-cylinder diesel engine, which is considered in relation to changes in factors such as fuel injection pressure and turbocharger pressure. The study was carried out by 3D modeling using AVL Fire with an omega combustion chamber size and dimensions determined by the ratio between the diameter and depth of the piston bowl, which varies from 3.4 to 10.0. Additionally, the turbocharger pressure varies from 0.15 to 0.45 MPa at an engine speed of 1400 rpm and fuel injection pressure up to 300 MPa. The results show that the engine reaches the best values of indicated power, fuel efficiency, and a substantial decrease in emissions of nitrogen oxides at a turbocharger pressure from 0.25 to 0.35 MPa and with a ratio of the diameter to the depth from 7.8 to 10. However, the injection angle changes slightly, and the penetration depth and the tip velocity decrease with increasing boost pressure. While the piston bowl parameters only impact significantly on the tip velocity, the penetration and the spray angle are almost unchanged. In addition, the variation in the diameter of the combustion chamber has an influence on the fluctuation of the spray tip velocity and penetration. [ABSTRACT FROM AUTHOR]

The unburned components that do not contribute to combustion emitted from internal combustion engines should be significantly reduced. In this study, enhancement of a post oxidation under cold conditions was investigated by controlling the in-cylinder gas properties of a directinjection gasoline engine equipped with a variable valve system. The combination of "Late Intake Valve Opening" and "Late Exhaust Valve Opening" functions was verified. The results showed that THC and PN were further improved due to the increased superheat, intake air flow enhancement, and re-burn effect of the exhaust process. [ABSTRACT FROM AUTHOR]

Highly oxygenated fuels can effectively reduce afterburning in diesel diffusion combustion and improve the degree of constant volume heat release in spite of increases in injection duration due to smaller heating values. The mechanism of afterburning reduction and the structural differences in the diesel fuel spray with changing the oxygen content in the fuel were investigated in a constant volume vessel and analyzed with 3D CFD simulation. The result showed that the equibalance ratio inside the spray decreased with increases in the oxygen content due to lower theoretical air-fuel ratios, promoting the spray combustion after the end of injection. Further, the combustion characteristics and the exhaust gas emissions of the oxygenated fuels were investigated in an experimental single cylinder diesel engine with modern specifications. With increasing oxygen contents, the degree of constant volume heat release increased with reductions in the afterburning, resulting in higher indicated thermal efficiencies. However, the indicated thermal efficiency showed a maximum at around 27 mass% of the oxygen in fuel and further increases in the oxygen contents resulted in lower indicated thermal efficiencies due to larger cooling losses. [ABSTRACT FROM AUTHOR]

This study presents the effects of piston bowl size on the characteristics of a four-stroke single-cylinder diesel engine, which is considered in relation to changes in factors such as fuel injection pressure and turbocharger pressure. The study was carried out by 3D modeling using AVL Fire with an omega combustion chamber size and dimensions determined by the ratio between the diameter and depth of the piston bowl, which varies from 3.4 to 10.0. Additionally, the turbocharger pressure varies from 0.15 to 0.45 MPa at an engine speed of 1400 rpm and fuel injection pressure up to 300 MPa. The results show that the engine reaches the best values of indicated power, fuel efficiency, and a substantial decrease in emissions of nitrogen oxides at a turbocharger pressure from 0.25 to 0.35 MPa and with a ratio of the diameter to the depth from 7.8 to 10. However, the injection angle changes slightly, and the penetration depth and the tip velocity decrease with increasing boost pressure. While the piston bowl parameters only impact significantly on the tip velocity, the penetration and the spray angle are almost unchanged. In addition, the variation in the diameter of the combustion chamber has an influence on the fluctuation of the spray tip velocity and penetration.

The atomization process of fuel spray injection in internal combustion engines affects the spray mixture formation process, the combustion characteristics, and the formation of toxic substances. Therefore, several optical measurement procedures have been developed and applied to capture spray features, including imaging methods and laser diagnostics. It has been concluded that the spatial resolution of fine spray droplets detection in imaging with silver halide film is much better than with a CCD imaging device. Therefore, the authors previously developed a novel imaging technique called Super High Spatial Resolution Photography (SHSRP), which allows for whole spray imaging while maintaining the spatial resolution of tiny droplets. This is a wide-field, high-resolution imaging method that can measure the entire spray area at the droplet scale. However, the image analysis method analyzes the intensity gradient of the outer edge of the droplet, and the accuracy of droplet analysis deteriorates as the droplet diameter is small. In this study, a new image analysis method with wide-field and high-resolution images acquired by SHSRP was developed to improve the analysis accuracy of spray droplets. The analysis method of depth of object field, which depends on droplet size, was changed from one-dimensional analysis of the intensity gradient of the outer edge of the droplet to two-dimensional analysis using the intensity deviation of the entire droplet area. For the developed analysis method, analysis of error based on scattering theory was conducted and the droplet capture ratio in diesel spray was analyzed to verify the accuracy. As a result, it was found that the particle size distribution obtained has no peaks due to noise effects, and that the presented analysis method is accurate enough to characterize the particle size distribution of diesel spray.

A better understanding of why and how pollutant emissions from compression ignition engines are produced is one of the strategies to reduce them, and to achieve this it is important to understand what happens in the fuel injection inside the combustion chamber and in the combustion process. Experimentally, it is difficult to analyse the fuel spray right at the initial moments when it enters the combustion chamber due to its high velocity. These initial moments of the fuel spray affect its complete development and, consequently, the combustion process inside the chamber. This fact has motivated the approach of this work, in which a parametric study of the spray penetration as a function of variables that can be measured has been proposed. The purpose of this model is to understand which variables of the injection system significantly affect the spray penetration in the initial instants and how they affect it. This study was carried out using diesel and serves as a reference framework for similar studies using pure or blended sustainable advanced fuels. A computational fluid dynamics (CFD) model that determines the spray penetration at initial instants under different injection pressures and nozzle hole diameters is presented in this work. To tune the model, experiments were carried out on an optical engine. The modelled and experimental results exceed 94.8% agreement in all cases studied. [ABSTRACT FROM AUTHOR]

To prevent extreme climate events, it is urgent to reduce greenhouse gas emissions, and research on alternative fuels for internal combustion engines is necessary. In this study, diesel spray and combustion characteristics were investigated when Fatty Acid Methyl Ester (FAME) was blended with Hydrotreated Vegetable Oil (HVO) in any ratio. As a result, blending HVO with FAME promoted atomization and improved evaporation, resulting in a lean mixture. Also, the shorter ignition delay suppressed premixing combustion, resulting in lower cylinder temperatures and lower NOx emissions, but increased THC and Smoke emissions. [ABSTRACT FROM AUTHOR]

A combination of a fuel injector with staggered nozzle hole arrangement with a combustion chamber divided into upper and lower layers by placing a lip at the middle of the side wall is proposed to improve diesel combustion with suppression of interactions among fuel spray flames. The fuel injector has twelve alternately arranged spray holes (ϕ 0.09 mm), staggered at two injection angles, 79° and 55° from the central axis of the injector. Two ordinary injectors with eight (ϕ 0.113 mm) and twelve (ϕ 0.092 mm) holes with an injection angle of 78° from the central axis with a conventional re-entrant combustion chamber were also examined as references. The experimental results showed that the improvements in thermal efficiencies and the reduction in smoke emissions can be established over a wide IMEP range with the proposed combination of the staggered nozzle hole injector and the divided combustion chamber. The exhaust loss is reduced with the combination of the injector and the combustion chamber while the cooling loss increases slightly. The rate of heat release from the combination of the injector and the combustion chamber has a more active main combustion and smaller afterburning than conventional systems. The three-dimensional CFD simulations showed that the combination of the injector and the combustion chamber can efficiently suppress the interactions among fuel spray flames at the combustion chamber wall after the impingement of fuel spray flames and also suitably distribute the fuel mixture, resulting in reductions in the afterburning and the smoke emissions. The slight increase in cooling loss with the proposed combination may be due to the increase in contact area of hot burned gas on the cylinder head; further improvements in thermal efficiency can be expected with optimization of the design factors related to the fuel injection and the combustion chamber configuration. [ABSTRACT FROM AUTHOR]

The highly dynamic response of a continuously injected liquid fuel jet to rotating detonation waves is a critical parameter in the design, performance optimization, and modeling of a rotating detonation engine (RDE). In this work, this response is spatio-temporally resolved from the fuel injection point to the detonation channel using planar laser-induced fluorescence (PLIF) at imaging rates up to 1 MHz. A rotating detonation combustor (RDC) is operated on hydrogen and air to sustain stable detonation waves that interact in a one-way coupled manner with a single liquid fuel jet that propagates into the combustion chamber with cycle periods of ∼ 250 µs. Diesel is utilized as a realistic fuel surrogate with higher aromatic compounds to enable fluorescence excitation using the 355 nm third-harmonic output of a burst-mode Nd:YAG laser. By optimizing the technique to accommodate orders of magnitude variations in the fuel density throughout the injection process, the PLIF data enable measurements of (i) the overall refill dynamics after the arrival of the detonation wave, (ii) changes in the liquid spray trajectory with microsecond temporal resolution, and (iii) the time required to reestablish the quasi-steady axial refilling process as a function of peak chamber pressure relative to the air- and liquid-injector pressure drops. As the passage of the detonation wave imparts significant changes in the momentum flux ratio, the qualitative liquid break-up process and spatial distribution of the spray also vary significantly in time. Only as the injection system recovers late in the cycle does the fuel spray eventually return to a quasi-steady position and allow comparisons with theoretical jet trajectories. These data, enabled by ultra-high-speed PLIF imaging, represent some of the first detailed measurements for quantifying the dynamic response and recovery of liquid jets exposed to periodic detonations in an operating RDC. [ABSTRACT FROM AUTHOR]

In order to comply with increasingly stringent emission regulations, including EURO7, it is necessary to enhancement of fuel evaporation under cold start, when fuel vaporization and atomization are insufficient, and to significantly reduce unburned components that do not contribute to combustion. It has been shown that controlling the in-cylinder gas properties to be equivalent to that at high temperature, fuel vaporization can be accelerated and emission at cold start can be reduced. In this study, the mechanism of cold emission reduction was clarified through high-speed exhaust gas measurements on an actual engine, PN particle size distribution measurements, and combustion observations on a visualized engine. [ABSTRACT FROM AUTHOR]

The unburned components that do not contribute to combustion exhausted from internal combustion engines should be significantly reduced. In this study, enhancement of fuel evaporation under cold conditions was investigated by controlling the in-cylinder gas properties of a directinjection gasoline engine equipped with a variable valve system. It was confirmed by controlling the degree of superheat for liquid fuels allows the reduction of unburned hydrocarbons and particulate numbers in cold conditions. Late intake valve opening (LIVO) has achieved lower emissions and superior combustion stability under extremely cold conditions by effectively utilizing the energy of the intake air flow. [ABSTRACT FROM AUTHOR]

The Conventional Laser Absorption Scattering (C-LAS) technique is used to measure the mixture concentration and visualize the vapor phase. The former is determined by the attenuation of visible and ultraviolet light whereas the latter is achieved via light absorption and scattering theory. The C-LAS uses the Nd: YAG pulsed laser and CCD cameras to provide one spray shot at a particular instance which requires time and effort. However, the temporal measurement of a single spray shot is not possible. To record the distribution of the whole vapor phase in an injection event and measure liquid and vapor concentrations inside the spray, a High-Speed Laser Absorption Scattering (HS-LAS) technique was developed. The HS-LAS consists of continuous diode light sources, high-speed video cameras, and an image intensifier for UV light, which can provide the temporal variation of a single-shot spray. In the experiment, a commercial seven-hole injector with a hole diameter of 0.123 mm allowing high injection pressure of up to 100 MPa was used to avoid the potential inconsistencies with a single-hole test injector. The diesel surrogate fuel which consists of 97.5% n-tridecane and 2.5% of volume-based 1-methylnaphthalene was used. The injection amount of 5.0 mg/hole was selected to investigate the structure and mixture formation process of the spray. The findings of the experiments show that this imaging approach is a promising diagnostic technique for concurrently obtaining quantitative information on the quantity of vapor and droplets in a fuel spray. Furthermore, the turbulent/vortex fluid dynamics’ temporal development/variation can be investigated.

Lean burning as one of the low-temperature combustion strategies has the potential to reduce pollution emissions and improve fuel efficiency. However, highly diluted mixtures cause internal combustion engines to suffer from severe combustion instabilities. Turbulent jet ignition (TJI) technology is considered an effective way to solve these issues, but most previous work mainly considers the passive TJI systems fueled by gaseous fuel. In this work, an active TJI system with gasoline as an auxiliary fuel was investigated using three-dimensional computational fluid dynamics (CFD) simulations in rapid compression machines (RCM). High-pressure low-temperature operating conditions were established to mimic the combustion situation of supercharged spark-ignition engines. Different injection parameters for pre-chamber were considered, including injection timing, injection angle, and injection pulse width, and the influence of injection parameters on the evolution of turbulent jet flame in the main chamber with lean mixtures was investigated. The results show that the hedging effect between reverse squeezed flow and high-speed fuel spray during piston compression promotes gasoline spray atomization, evaporation, and mixing in the pre-chamber. The initial lambda of the pre-chamber plays a significant role in the jet exit velocity, while the initial lambda of the main chamber exhibits a greater impact on the jet propagation distance. Meanwhile, there are generally three stages for the entire combustion in the main chamber, including jet penetration, jet ignition, and spontaneous combustion. The present work can provide useful insights into the optimization and design of active TJI systems in realistic engines. [ABSTRACT FROM AUTHOR]

The Conventional Laser Absorption Scattering (C-LAS) technique is used to measure the mixture concentration and visualize the vapor phase. The former is determined by the attenuation of visible and ultraviolet light whereas the latter is achieved via light absorption and scattering theory. The C-LAS uses the Nd: YAG pulsed laser and CCD cameras to provide one spray shot at a particular instance which requires time and effort. However, the temporal measurement of a single spray shot is not possible. To record the distribution of the whole vapor phase in an injection event and measure liquid and vapor concentrations inside the spray, a High-Speed Laser Absorption Scattering (HS-LAS) technique was developed. The HS-LAS consists of continuous diode light sources, high-speed video cameras, and an image intensifier for UV light, which can provide the temporal variation of a single-shot spray. In the experiment, a commercial seven-hole injector with a hole diameter of 0.123 mm allowing high injection pressure of up to 100 MPa was used to avoid the potential inconsistencies with a single-hole test injector. The diesel surrogate fuel which consists of 97.5% n-tridecane and 2.5% of volume-based 1-methylnaphthalene was used. The injection amount of 5.0 mg/hole was selected to investigate the structure and mixture formation process of the spray. The findings of the experiments show that this imaging approach is a promising diagnostic technique for concurrently obtaining quantitative information on the quantity of vapor and droplets in a fuel spray. Furthermore, the turbulent/vortex fluid dynamics' temporal development/variation can be investigated. [ABSTRACT FROM AUTHOR]

Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion. Interactions between fuel droplets (discrete phase) and fluid flow (continuous phase) have a considerable effect on liquid fuel evaporation. In this paper, both the single- and two-phase modeling of liquid fuel injection into a model evaporating chamber are presented. The influences of important issues such as turbulence models, coupling between gas phase and droplets, secondary break-up and air swirling on the current spray simulation are investigated. Accordingly, the shear stress transport turbulence model, Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase flow. Atomization and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian approach. The current results show an acceptable agreement with the experiments. Adjacent the fuel atomizer, bigger droplets are detected near the spray edge and minor droplets are situated in the middle. With increasing the droplets axial position, the droplets diameter decreases with a finite slope. The smaller droplets have a deeper penetration, but their lifetime is smaller and they evaporate sooner. A linear relation between penetration and lifetime of smaller droplets is detected. Maximum droplet penetration and mean axial velocity of gas phase are observed for no air swirling case. The effect of variation of swirl number on the lifetime of droplets is almost negligible. By enhancing the swirl number, the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain. [ABSTRACT FROM AUTHOR]

CFD (Computational Fluid Dynamics) simulations are widely used for the research and development in the field of thermal fluidics, including internal combustion engines􀀑 Spray breakup models significantly affect the liquid film formation on the intake port wall impingement and mixture formation. However, there is no model for the atomization process under port fuel injection conditions with the plate-type multi-hole nozzles which have great atomization characteristics. The purpose of this study is to investigate the spray atomization process and predict the breakup process in multi-hole nozzle spray for port fuel injection. In previous studies, the authors have experimentally investigated the liquid sheet breakup process and droplet behavior of fuel sprays under port fuel injection conditions, and have modeled the droplet generation process based on the liquid sheet breakup theory. In this report, liquid sheet breakup model was modified and simulated the spray atomization process. [ABSTRACT FROM AUTHOR]

In order to be able to use the full potential of regenerative fuels, a comprehensive characterization is necessary to identify the differences between conventional fuels and regenerative fuels. In the current work, we compare OME3−5 and 1-Octanol with diesel-like Dodecane in terms of mixture formation under ECN Spray A conditions for single and multi-injection. To determine the mixtures, i.e., the mass distribution and the resulting air-fuel equivalence ratio, Naber and Siebers’ model as well as Musculus and Kattke’s model are used, which are based on experimental data. For this work, the mass flow rates and also the liquid and gaseous penetration depths of the fuel spray are measured. Results show that the mass ratios for the quasi-steady state of a single main injection for all three fuels are nearly the same, whereas the air-fuel equivalence ratios are very different. In addition, multiple injections are used to show that the fuel influences the opening and closing behavior of the injector. In the transient case of multiple injections, completely different mixtures result. In summary, it can be stated that OME3−5 and also 1-Octanol show a clearly different physio-chemical behavior from Dodecane and cannot simply be used as a drop-in fuel. Therefore, a simple exchange is not possible without major adaptations.

A better understanding of why and how pollutant emissions from compression ignition engines are produced is one of the strategies to reduce them, and to achieve this it is important to understand what happens in the fuel injection inside the combustion chamber and in the combustion process. Experimentally, it is difficult to analyse the fuel spray right at the initial moments when it enters the combustion chamber due to its high velocity. These initial moments of the fuel spray affect its complete development and, consequently, the combustion process inside the chamber. This fact has motivated the approach of this work, in which a parametric study of the spray penetration as a function of variables that can be measured has been proposed. The purpose of this model is to understand which variables of the injection system significantly affect the spray penetration in the initial instants and how they affect it. This study was carried out using diesel and serves as a reference framework for similar studies using pure or blended sustainable advanced fuels. A computational fluid dynamics (CFD) model that determines the spray penetration at initial instants under different injection pressures and nozzle hole diameters is presented in this work. To tune the model, experiments were carried out on an optical engine. The modelled and experimental results exceed 94.8% agreement in all cases studied.

The presented test results contain an analysis of the variable control of fuel flow from high-pressure gasoline injectors. To control such a system, the cRIO 9063 system and NI-driven module were used. This system allows controlling a piezoelectric injector with a time-varying needle height, which affects the time-varying fuel flow during a single-time opening of the injector needle. The tests were carried out in a constant volume chamber with a constant fuel dose (Pinj = 15 MPa and qo = 17.4 mg), with two values of medium back pressure: Pb = 1.0 and 1.5 MPa as well as different injector opening times (resulting from equal doses of fuel). Analyzes of changes in linear and radial fuel spray range as well as the fuel spray volume were made. It has been found that injection rate-shaping allows to control the fuel flow from the injector at a variable needle height. A reduction of the linear range of the spray by 50% and a radial range by 40% compared to conventional settings within a specified time from the start of the injection was achieved. The surface area of the spray is limited by a maximum of 60% compared to the settings at the maximum control voltage. The use of injection rate-shaping may be an effective method of controlling the variable fuel flow from the injector and may allow the replacement of multi-stage fuel injection. [ABSTRACT FROM AUTHOR]

• ML models are trained to predict high-pressure gasoline fuel spray characteristics. • Tree-based models outperform neural networks in predicting spray parameters. • ML is a powerful tool for decoupling non-linear behaviors from physical processes. • ML spray modeling offers greater prediction accuracy and reduced computational cost. Compression ignition engines when operated on gasoline fuels cause significant reduction in NO x and particulate emissions. In such advanced combustion strategy, the fuel-oxidiser mixing process, intensified by the prolonged ignition delays of gasoline fuels, directly affects the stability and efficiency of combustion. Thus, optimising fuel spray characteristics leads to optimisation of injector design, engine performance and subsequent decrease in emissions. Since spray development is a complex process that involves wide range of length and time scales, computationally expensive modelling techniques can be replaced with machine learning (ML) models. These ML models are employed to predict spray characteristics utilizing datasets generated from comprehensive spray studies. In this work, a dataset of about 5400 instances taken from non-evaporating gasoline fuel spray imaging experiments under Gasoline Compression Injection (GCI) engine conditions is used to train various ML models with data split of 70 % and 30 % for training and testing, respectively, with five-folds cross-validation performed within the training. The fuel injection pressure (60 – 150 MPa), chamber pressure (0.1 – 2 MPa), nozzle diameter, nozzle hole conicity and injection duration are used as input features to the models for predicting the spray tip penetration and spray angle. The performance of four ML models was evaluated and compared under default and tuned hyperparameters against experimental data and available physics-based correlations in the literature. The models include random forest, extreme gradient boosting, multilayer perceptron, and elastic-net. The results show that the hyperparameter-tuned extreme gradient boosting model performs best in predicting the spray parameters. The overall model performance was evaluated using the coefficient of determination (R2), mean absolute error (MAE), and root mean squared error (RMSE), resulting in values of 0.884, 0.651, and 1.571, respectively. This study presents compelling evidence demonstrating the effectiveness of ML as a powerful tool for isolating non-linear behaviors from physical processes. By effectively decoupling these behaviors, ML enhances the accuracy of predicting spray characteristics while significantly reducing computational costs. The application of ML in fuel injector design has the potential to revolutionize engine performance and contribute to substantial reductions in emissions. [ABSTRACT FROM AUTHOR]

High injection pressure in diesel engines can lead to cavitation-induced erosion in injector nozzles. One important factor affecting the severity of erosion is the fuel and its properties. Traditionally, modeling and simulation studies have used single-component representations of fuels, but realistic fuels feature a multitude of components and can even include volatile additives such as water and alcohol. To provide realistic benchmarks and comparisons, experimental measurements quantifying erosion characteristics were made using ultra-low sulfur diesel (ULSD) and two alternative diesel fuels (ADF). X-ray imaging and computed tomography were used to investigate cavitation-induced erosion onset and progression. Hard X-ray tomography revealed injector internal geometry, including details such as surface marks from the manufacturing process and erosion patterns from repeated injections. Erosion progression was measured using X-ray tomography and imaging performed between injections. The critical erosion site was found to be similar across different fuel blends, while the erosion rate and incubation time were sensitive to the fuel blend. The injector geometry and the erosion characteristics were also prepared for numerical model development and validation.

The effect of split injection on the fuel spray and combustion processes in a rapid compression and expansion machine was investigated using the visualization process. A two-dimensional piston cavity, designed with the cross section of a reentrant piston, was installed in the combustion chamber to observe the combustion process from the lateral side. Combustion experiments were conducted with injection pressures of 80 MPa, 120 MPa, and 180 MPa and an O2 concentration of 15%. The spray/wall interaction, mixture distribution, and ignition location were investigated using the shadow method. Along with natural flame luminescence, different spray impinging behaviors on combustion process were studied. Furthermore, the combustion characteristics of in-cylinder pressure, apparent heat release rate, and combustion phase were recorded and analyzed simultaneously. The results showed that both high injection pressure and split injection with a longer interval effectively improved the combustion performance. In addition, when the pilot injection was advanced further, the injection interval had a larger influence in reducing soot generation, while the effect of high injection pressure on heat release decreased. Flame separation was found to occur at high injection pressures. It was observed that the flame separation caused by the strong spray momentum was beneficial for reducing soot generation owing to the greater fuel-air interaction area. The spray and combustion processes were investigated in detail, and the significant effects of different injection pressures and injection intervals on combustion performance with the split injection method were highlighted. [ABSTRACT FROM AUTHOR]

In this paper, air entrainment into diesel spray was investigated. To visualization of the ambient air flow and measurement of entrainment characteristics, the Laser Induced Fluorescence-Particle Image Velocimetry (LIF-PIV) method was applied to the surrounding air of the spray upstream in a non-evaporative conditions. Also, we investigated the effects of injection pressure on the entrainment characteristics. The results show that the entrainment velocity increases and the tangential velocity decreases as the downstream of the spray. In addition, in the set-off region of the quasi-steady diesel spray, the entrainment velocity and entrainment mass flow rate increase with increasing injection pressure, although the ratio of entrainment mass flow rate to fuel injection rate changes slightly with injection pressure. [ABSTRACT FROM AUTHOR]

A deep learning-based method for denoising and detecting the gas turbine engine spray droplets in the light-scattered image (Mie scattering) is proposed for the first time. A modified U-Net architecture is employed in the proposed method to denoise and regenerate the droplets. We have compared and validated the performance of the modified U-Net architecture with standard conventional neural networks (CNN) and modified ResNet architectures for denoising spray images from the Mie scattering experiment. The modified U-Net architecture performed better than the other two networks with significantly lower Mean Squared Error (MSE) on the validation dataset. The modified U-Net architecture also produced images with the highest Power Signal to Noise Ratio (PSNR) compared to the other two networks. This superior performance of the modified U-Net architecture is attributed to the encoder-decoder structure. During downsampling, as part of the encoder, only the most prominent features of the image are selectively retained by excluding any noise. This reconstruction of the noise-free features has produced a more accurate and better denoised image. The denoised images are then passed through a center predictor CNN to determine the location of the droplets with an average error of 1.4 pixels. The trained deep learning method for denoising and droplet center detection takes about 2.13 s on a single graphics processing unit (GPU). This study shows the promise for real-time processing of the experimental data using the well-optimized network.

To comply with latest standards regarding emission regulations, diesel technology focuses on how to obtain a very good spray quality, by identifying the appropriate geometry for injector nozzles, the optimum size of injection holes and the best hydraulic parameters for efficient fuel spray evolution and dispersion. In practice, injectors are often subject to operating problems, mainly because inside the diesel fuel injector nozzle, accumulation of deposits might occur. To control the phenomenon, the scientific literature proposes anti-corrosion treatment. The present paper studies the effect of applying anti-corrosion treatment to a new diesel injector. The investigation method consists in using a Scanning Electron Microscope next to EDX Spectrometry. The results indicate that chemical treatment can lead to new deposits that also contaminate the nozzles. Concluding, the anticorrosion treatment must include monitoring and control of the process and as a final step, a method to remove detergent deposits. [ABSTRACT FROM AUTHOR]

The effects of the split ratio on the mixture formation and combustion process of a diesel spray in a constant-volume chamber were experimentally investigated. A commercial seven-hole injector was used in this experiment. The effects of the mass-dependent split ratio and dwell time were observed when the total fuel injection was 5.0 mg/hole. Three split ratios were considered: 3:7, 5:5 and 7:3, while the dwell time of 120 µs was fixed for every condition. A laser absorption-scattering technique was adopted to examine the formation of mixtures with regarding to the equivalence ratio. A high-speed video camera was used to observe natural flame luminosity, and a two-colour pyrometer system was employed to evaluate the temperature and soot concentrations in the flame. Among the distribution ratios tested in this study, the 7:3 split ratio exhibited the best performance for the lean mixture formation considering the overall equivalence ratio distribution. The air entrainment wave at the end of injection timing of the first injection caused the fuel near the nozzle to lean at a rapid rate. The soot formation process for the 3:7 and 5:5 split ratios was observed because the second injection fuel caught the flame of the previous injections; this deteriorated the combustion region and influenced soot formation. The result also revealed that for the 7:3 split ratio, accelerated the soot deduction rate to the cycle of soot oxidation during the combustion period. [ABSTRACT FROM AUTHOR]

• A novel high-speed laser absorption scattering method is used to characterize diesel sprays. • The mixture concentration of liquid and vapor phases are measured simultaneously. • Temporal behavior and shot-to-shot variations are recorded. In Diesel Engines, the injection process plays a decisive role in the combustion efficiency. Hence, the characterization of diesel sprays is very important. Several methods are developed, however, none of them records the temporal fuel distribution throughout the individual injection event and measures the liquid/vapor concentration of an evaporating diesel spray. In this work, two light sources i.e., an ultraviolet LED and a continuous wave laser, were used with two high-speed video cameras. A fuel mixture with the compositions of 97.5 % n-tridecane and 2.5 % of volume-based 1-methylnaphthalene was selected as the test fuel. The fuel was intermittently injected into an inert environment at 4.8 MPa and 800 K by applying a seven-hole injector with a hole diameter of 0.123 mm. The injection pressure was set at 100 MPa and the injection amounts were set as 2.5 and 5.0 mg/hole to observe the effect of the injected mass on the spray characteristics and mixture formation process. Calibration, based on the scattering by non-evaporating sprays and molar absorption coefficients for fully evaporated sprays, indicates a measurement error of 15 %. The findings of the experiments show that, under large injection mass conditions, the liquid phase equivalence ratio is quite low and close to zero just after the end of injection which points out that as the air-fuel mixing quality improves, the majority of the liquid fuel is rapidly converted to vapor. The air-fuel mixture is overall richer at large injected mass compared to the small mass condition. Furthermore, after the end of injection, the high fuel vapor concentration area near the nozzle soon mixes with ambient gas, decreasing the equivalence ratio to low levels, whereas a high-vapor-concentration region is still present at the spray head. This study provides a valuable insights into the behavior of the fuel spray, which could be used to improve the efficiency and performance of diesel engines. [ABSTRACT FROM AUTHOR]

The compression-ignition engine has been widely applied in various fields due to its high efficiency, fuel economy, and adaptability. With the increasing awareness of environmental issues, emission regulations have become more stringent, leading to a growing demand for high-pressure and small-sized engines. Since developing new engines is often both costly and time-consuming, leveraging the similarity between spray and combustion processes for new engine development can significantly reduce the required resources and time. However, to date, systematic research on the similarity and normalization of sprays and combustion processes, especially under ultra-high injection pressure and micro-hole diameter conditions, remains lacking. In this study, conversion models and normalization models for spray characteristics were developed based on both time scale and multi-dimensional space scale. The spray transformation and normalization were verified for different aperture sizes, injection pressures, ambient temperatures, densities, and pressures. The results show that the models exhibit good interchangeability and normalization effects. This research outcome will provide valuable references for optimizing and designing more efficient and environmentally friendly internal combustion engines. • A novel similarity and normalization model for spray characteristics is proposed. • The model's validity is successfully demonstrated through extensive validation with varying parameters. • Near-field spray characteristics under ultra-high pressure and micro-hole conditions are unveiled. ▪ [ABSTRACT FROM AUTHOR]

This research investigates GDI (Gasoline Direct Injection) fuel spray characteristics, and spray impingement on cylinder-wall oil film were carried out in a constant volume chamber. For studying free spray and spatial distribution characteristics of oil film under spray impinging conditions, the backlight method and LIF (Laser Induced Fluorescence) technology were used, respectively. The influence of injection pressure, ambient pressure, and ambient temperature on the distribution characteristics of oil film with spray impingement were examined. Detailed results on coalescence/splash thresholds criteria of oil film were obtained by considering the incident spray Weber number and the injected fuel mass. In addition, the formation mechanism of oil dilution and splash following the collision were analyzed. It has been found that the incident Weber number is not the only discriminant parameter that can be used to determine the splash criticality of a fuel droplet or spray hitting an oil film. Meanwhile, spray impingement at a higher injection pressure results in a wider spread of oil film, whereas a higher ambient pressure inhibits the spread of oil film. • The impingement behavior of fuel spray on oil film was investigated. • The method LIF is used to distinguish the oil film from the fuel spray. • Experimental results allow to propose empirical correlations. [ABSTRACT FROM AUTHOR]

• Inhomogeneity and separability of supercritical state were verified experimentally. • The liquid-like and gas-like phases were visualized by optical diagnostic techniques. • The widom line is the crossover line in the supercritical state. Sufficient understanding of the supercritical state is important for exploring supercritical jet spray in thermodynamic cycle power machinery. However, in conventional studies, the phase division of supercritical state and supercritical jet spray is simple and rough, and whether the pseudo-boiling (or widom) line exists widely in various fluids, especially fossil fuels, is still not proved by experiments. In this paper, the phase inhomogeneity and separability in the supercritical state of fossil fuels are studied by using high-speed Mie scattering and UV-LAS (ultraviolet–visible laser absorption/scattering) optical diagnostic techniques. Acetone is selected as the single representative component of fossil fuels. The results show that acetone is inhomogeneous in the supercritical state at fuel temperature T f < 1.13 T c and fuel pressure P f < 1.74 P c , where T c and P c are the critical temperature and pressure, and can be further divided into liquid-like phase and gas-like phase, which is similar to the properties of inert fluids and simple fluids reported in previous literatures. The transition region (measured at interval of pressure 0.2 MPa) between the liquid-like phase and gas-like phase contains thermodynamic extremum lines such as constant pressure specific heat, volume expansion coefficient, and isothermal compression rate, which supports the view that the widom (or pseudo-boiling) line is used as the crossover in the supercritical state. When the state of acetone spray passes through the transition region, the liquid-like and gas-like phases will have dramatic changes in the optical and macroscopic properties of spray (For example, when the injection temperature is equal to the critical temperature of 235 °C, the stable liquid-like areas crossing the pseudo-boiling line decreases by 9 times as much as that without crossing the pseudo-boiling line). The results of this paper have important reference values for the study of the supercritical spray atomization regime and the establishment of the simulation model. [ABSTRACT FROM AUTHOR]

The impact of injection pressure on the startability of compression ignition (CI) diesel engines has not been thoroughly studied yet, especially for the startup at low-temperature conditions. This research investigates the effects of injection pressure on diesel spray and flame characteristics under low ambient temperatures (close to the critical ignition temperature of diesel spray) in a constant volume combustion chamber (CVCC) using Schlieren, Mie scattering, and direct photography. Different from past engine startability research, the ignition delay time under quasi-critical ignition temperature is measured to be first shortened then prolonged with increasing injection pressure. The primary cause of such phenomenon is analyzed to be the trade-off effects between spray atomization and heat convection from the fuel to the ambience, which is quantitatively validated by the analytical calculation based on the Arrhenius-type correlation. • Injection pressure with short IDT and stable flame is decided under cold-start. • Trade-off between spray atomization and heat convection results in the IDT change. • Analytical calculation is performed to explain the trend of IDT under cold-start. [ABSTRACT FROM AUTHOR]

• " Ins number" is proposed to evaluate the effect of cross-flow on spray CCV. • Surface waves are observed on windward side, where optical thickness variation is larger. • COV of vertical penetration is largest in the initial stage of injection. • Variation of horizontal penetration is enhanced by cross-flow/ injection pressure. Owing to cavitation inside the nozzle, spray breakup, and complex flow fields in the cylinder of a spark ignition engine, a certain degree of cycle-to-cycle variation (CCV) remains in different spray cycles under the same operating conditions, thereby affecting the spark ignition engine significantly. Therefore, the effect of cross-flow on the cyclic variation of the spray characteristics is investigated in this work. The CCV of fuel spray characteristics is evaluated via the statistical analysis of 30 repeated experiments under atmospheric pressure. First, the coefficient of variation (COV) is used to assess variations in the spray penetration, area, and optical thickness. Moreover, the effects of injection pressure and cross-flow velocity on the statistical characteristics of the spray are analyzed at the end of injection (EOI). Finally, a dimensionless " Ins number", which is defined as the parameter of any spray characteristic at a certain time divided by the average experimental value, is proposed to evaluate the spray variation characteristics under cross-flow conditions. Therefore, when the absolute value of the Ins number approaches 1, the CCV of the spray characteristic parameters is low. Results show that the COV of the spray penetration is the largest in the initial stage of injection and then decreases gradually. Meanwhile, the COV of the vertical penetration can be categorized into two stages. Furthermore, it is discovered that the variation in the horizontal penetration is enhanced by the cross-flow and injection pressure at the EOI. In addition, in terms of the COV of the optical thickness, the variation on the windward side is greater, and the cross-flow enhanced the variation in the spray tip region. Most of the Ins numbers of the spray characteristics range from 0.9 to 1.1 (±10%) in this study, and they can provide data support for improving the accuracy of empirical prediction equations and models. [ABSTRACT FROM AUTHOR]