Search

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]

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.

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]

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 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.

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. [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]

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]

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.

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]

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.

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]

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]

Effect of spray/wall interaction in a rapid compression and expansion machine on mixture formation, ignition location, and soot generation was investigated. A two-dimensional piston cavity designed as the cross section of a reentrant piston was utilized to observe the spray and combustion process from the lateral side. The experiment was conducted at 120 MPa injection pressure under single and split injection strategies with an ambient gas of 15% O2 concentration. A shadow methodology was applied to investigate the interaction between the fuel spray and the piston cavity. Combined with the natural flame luminosity captured by a high-speed color video camera, the behaviors of the impinging spray and the combustion process were studied. The combustion characteristics of the in-cylinder pressure, heat release and combustion phase were recorded and analyzed simultaneously. The results showed that the split injection strategies effectively softened the heat release trace and promoted the onset of the main combustion. The cool-flame phenomenon was captured by using the high-speed color video camera, and the intense ignition was observed when the pilot spray was controlled to impinge on the lower lip of the piston rim. Moreover, results also showed that further extending the mixing process of the pilot spray is inclined to form a homogeneous mixture which was beneficial for the promotion of low-temperature combustion and the reduction of soot generation. This research provides a detailed investigation on the spray and combustion process and it highlights the significant effect of spray/wall interaction on the subsequent combustion process. [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]

Diesel particulate filters are used to capture the particulate matter in engine exhaust, and the post fuel is injected for a regular regeneration of the diesel particulate filter to avoid plugging of the diesel particulate filter with the particulate matter. The concept of the post fuel injection is as follows: the post fuel is injected in the expansion stroke, the vaporized fuel gas is oxidized by the diesel oxidation catalyst, here the high temperature gas oxidizes the particulate matter on the diesel particulate filter, and the diesel particulate filter is regenerated. However, the post fuel impinges and adheres on the cylinder wall due to the low temperature and pressure conditions in the expansion stroke in actual engine operation and this causes diesel engine lubricant oil dilution, the deterioration of fuel consumption characteristics in diesel engines, as well as ash plugging of the diesel particulate filter. In this article, the post fuel spray behavior and adhesion on oil-wet cylinder liners were investigated with a high pressure--temperature optical constant volume chamber instead of engine tests. The in-cylinder temperature and pressure at the 30, 60, and 90 °CA after top dead center, commonly employed in post fuel injection timings, were measured in engine operation. To create the post fuel injection conditions of diesel engines in the constant volume chamber, pre-mixed gas containing ethylene, oxygen, and nitrogen is introduced into the chamber and ignited by the spark plug. Then, fuel masses of 0.5, 1.0, and 1.5 mg per injection hole at the after top dead center settings were injected to a wall adhesion plate with a 5-mm thick oil film that simulates the surface of the cylinder liner and the post fuel impinges on and splashes oil away from the oil film on the cylinder wall. The quantities of splashed oil and adhering fuel on the wall adhesion plate were measured by a precision balance and a thermostatic chamber. With the early post injection, most of the injected fuel vaporizes without penetrating to the cylinder liner and gaseous diesel fuel is condensed on the cylinder wall; however, with the late post fuel injections, the strong penetration of liquid fuel reaches the cylinder wall, and much engine oil becomes splashed away. The droplet size of the fuel spray was measured by telescope ultra-high resolution image analysis with a digital single-lens reflex camera, and the fuel impingement phenomena on the cylinder wall are explained by theWeber number, calculated from velocity and diameter values, droplet density, and surface tension. [ABSTRACT FROM AUTHOR]

In modern gasoline direct injection engines, the fuel is (partially) superheated for a significant proportion of the time during operation. This means that the vapour pressure of the fuel, or at least of many of its components, is higher than the ambient pressure inside the engine during injection. If the excess fuel enthalpy cannot be removed by evaporation at the free surface of the spray, the liquid phase boiling creates new surfaces. This phenomenon is known as flash boiling. Flashboiling atomization produces smaller droplets and can therefore be beneficial as an additional atomization mechanism. Furthermore, it can reduce the penetration depth of a spray, although it also decreases the stability of fuel sprays. This is manifested in undesired targeting changes, that is, spray contraction due to jet-to-jet interaction. In extreme cases, a complete spray collapse can occur, where a multi-hole or hollow-cone spray contracts towards the spray axis and forms a jet-like structure that increases penetration depth. To understand the relationship between flash-boiling atomization and targeting changes, flash boiling was investigated with a single-hole generic injector without jet-to-jet interaction. In addition to macroscopic spray parameters, this study also focused on the flow field of the spray itself measured using laser Doppler anemometry, as well as the spray-induced flow field of the surrounding gas phase measured using fluorescent particle image velocimetry. The results show a strong radial expansion of the jet directly after nozzle exit, caused by internal flash boiling. It is shown that this expansion is caused by a zone of expanding fuel vapour in the centre of the spray. As a result, the displacement of air after injector opening as well as at the front of the spray is significantly increased, causing a decrease in spray front velocity and penetration depth. The stationary air entrainment, however, is only moderately increased as is the total amount of captured air, since the fuel vapour displaces air in the spray. [ABSTRACT FROM AUTHOR]

Fuel spray and mixing in linear engines is coupled by dynamics, combustion, and gas exchange, which differs from that in conventional engines. This work presents a system simulation to reveal the multi-process coupling effect of injection position on the fuel spray and mixing of a free piston linear diesel engine (FPLE). A full-cycle fuel spray model which couples with dynamic, combustion, and gas exchange is established to predict the coupled effect on mixture formation. The results indicate that the variable injection position changes the FPLE motion through multi-process coupling effect, resulting in different boundary conditions for fuel spray and mixing. Relatively large injection advance position leads to more residual gas, fast speed, intense turbulence, low gas pressure, and temperature at the moment of injection for mixture formation. The earlier fuel injection generally makes the longer spray penetration, smaller Sauter mean diameter of droplets, less fuel impingement, faster fuel evaporation rate, and more evaporated fuel mass. However, too early injection does not support the above results. Suggesting that in order to achieve homogeneous combustion mode, the large injection advance position injection schedule operation is a good choice for the FPLE due to its long ignition delay duration for fuel atomization, evaporation, and mixing. [ABSTRACT FROM AUTHOR]

The free-piston engine generator becomes a new-type potential substitute for the conventional crankshaft combustion engine. This article presents a simulation to study the fuel spray and mixing characteristics of a diesel free-piston engine generator by comparing a corresponding crankshaft combustion engine. A full-cycle model which couples with piston dynamics, combustion, and gas exchange is developed to simulate the fuel spray, atomization, and mixing in the free-piston engine generator. The result indicates that compared with the crankshaft combustion engine, the free-piston engine generator provides a higher temperature and pressure for fuel spray and mixing during the ignition delay, but its ignition delay lasts shorter. The free-piston engine generator shows a shorter spray penetration and more fuel impingement due to its smaller combustion chamber volume during the injection process. The free-piston engine generator exhibits a lower level of air utilization and worse uniformity of fuel--air mixture in combustion chamber. In addition, the shorter ignition delay of free-piston engine generator makes the time of atomization, evaporation, and mixing of fuel shorter, and the mixing effect of free-piston engine generator is worse, resulting in less combustible mixture formed during the ignition delay. In addition, some guiding suggestions have been proposed to improve the fuel spray and fuel--air mixing characteristics of free-piston engine generator. [ABSTRACT FROM AUTHOR]

Many applications use hydrogen addition and high-pressure fuel injection technology to improve combustion performance. In this study, spray atomization and combustion characteristics of a diesel fuel jet, under the injection pressure of 350 MPa, injecting into a constant volume combustion vessel filled with air-hydrogen mixture at the diesel engine relevant condition are investigated by simulation method. A simplified mechanism of the n-heptane (C 7 H 16) oxidation chemistry mechanism consisting of 26 reactions and 25 species integrated with the Kéromnès-2013 hydrogen combustion mechanism and EDC combustion model are utilized to predict the diesel fuel spray auto-ignition and combustion. The ambient gas is the mixture of air and hydrogen range in volume fraction from 0% to 10%. The ambient temperature and pressure is set to 1000 K and 3.5 MPa, respectively. The results indicate that as the hydrogen volume fraction is 2%, the minimum overall droplet SMD (Sauter Mean Diameter) is approximately 0.95 μm, which is obviously smaller than that of the case with the conventional high injection pressure. In cases that H 2 v/v% larger than 4%, the maximum gaseous temperature increased significantly up to 2700 K. There are two peaks in the temperature growth rate curves as the hydrogen fraction of 8% and 10%. The high temperature at the outer edge of the spray is clearly seen due to its high value when the hydrogen fraction is larger than 4%. The hot reaction layer is the main location of CO formation. The H, OH radicals are formed at the edge of the spray where the temperature is high. The hydrogen species obviously promotes the oxidation and combustion of diesel fuel. • Numerical study of the diesel-hydrogen dual fuel combustion with an injection pressure of 350 MPa. • The minimum overall droplet SMD reaches about 0.95 μm in this study. • Finding a relationship between H 2 fraction and the characteristics of diesel-spray combustion. • The hydrogen addition obviously promotes the oxidation and combustion of diesel fuel. [ABSTRACT FROM AUTHOR]

Spray-wall interactions directly affect fuel-air mixture preparation and emissions formation. They are therefore among the most critical physical processes in engines today. This special issue of International Journal of Engine Research presents 11 papers that investigate spray-wall interactions and their effects at both fundamental and practical levels. This brief article offers background and context for the special issue and summarizes each research paper in the collection. [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]

The fuel oil atomization is closely related to the combustion performance of the fuel in the internal combustion engine. However, during the oil atomization, the fast evaporating and moving oil droplets interact strongly with the surrounding gas, posing challenges towards the precise simulation of the combustion process. To precisely capture the interactions between fuel droplets and the surrounding gas, a new multi-droplets motion and evaporation model is deduced by introducing the local parameters surrounding the fuel droplets. The proposed model is validated comparing the simulation results against the experimental data of the containment spray process. Subsequently, the present model is adopted to simulate the fuel spray process in the typical constant volume bomb. The parameters evolution is presented during the course of the spray such as the gas temperature, droplet temperature, evaporating rate, velocity, radii variation, vapor concentration and air-fuel ratio. The analysis of the spray performance is conducted and the superiority of the new model is also discussed. The simulation analysis reveals that the spray droplets interact strongly with the surrounding gas; the developed droplet motion and evaporation model is advantageous in the simulation of the dense multi-droplets spray process.

• Under non-evaporation condition, high ambient increases the fuel adhesion mass, area and average thickness by decelerating the droplets. • Under evaporation condition, the high ambient pressure inhibits the evaporation of the fuel to a certain degree is another reason for the increased fuel adhesion on the wall. • High ambient pressure improves the uniformity of the adhesion on the wall. The formation of the fuel adhesion on the wall is demonstrated as the major cause for the efficiency loss and particle number (PN) emission increase in direct-injection spark-ignition (DISI) engines, making it difficult to meet the regulation of the future standards. In this study, experiments were performed in a constant high-pressure chamber to clarify the characteristics of impinging spray injected by a mini-sac gasoline injector with a single hole. The fuel spray and adhesion were measured by Mie scattering and Refractive Index Matching (RIM) methods, respectively. The effects of ambient pressure on the spray-wall interaction under room and high temperature conditions were checked. The results showed that the increased ambient pressure decreases the spray tip penetration but increases the impinging spray height by strong air-fuel entrainment under both room and high temperature conditions. However, for fuel adhesion, under room temperature, the ambient pressure promotes better atomization by stronger air drag force, resulting in more fuel adhesion on the wall. Moreover, the increased ambient pressure decelerates the droplets, leading to the transition of droplets behavior from "splashing" to "spread" or even "stick", thus increasing the fuel adhesion on the wall. While, when evaporation occurs, apart from these reasons above, higher ambient pressure suppresses the fuel evaporation, leading to more fuel adhesion on the wall. [ABSTRACT FROM AUTHOR]

Combustion simulation helps us to predict the pollutant formation and allows us to understand various coupling phenomena of physical and chemical processes. Diesel engine combustion simulation requires models of the spray dynamics, chemistry and heat transfer. The interaction between the chemistry and turbulence is one of the major parameters which had been modelled. Combustion simulation has been carried out by using Computational Fluid Dynamics (CFD). CFD model solves three-dimensional Naiver-Stokes equations with k-e turbulence model. Combustion simulation has been carried out for one cycle by considering the two strokes compression and expansion with no load conditions. Fuel injection begins at 725°CA ends at 748°CA. Charge motion within the cylinder, turbulent kinetic energy, peak pressure rise, penetration length, and apparent heat release rate were analysed with respect to crank angle. [ABSTRACT FROM AUTHOR]

Abstract The free-piston engine generator (FPEG) is regarded as a substitute of conventional combustion engine (CCE) because of special operation mechanism and potential advantages. This article presents an investigation to analyze the fuel spray and mixture formation characteristics of a direct injection gasoline FPEG by comparing a corresponding CCE. A full-cycle multi-dimensional fuel spray model is established by coupling with dynamic, and then it is validated experimentally to predict fuel diffusion and mixture formation in the FPEG. Results indicate that compared with the CCE, the FPEG operates with lower in-cylinder gas turbulence, pressure and temperature during injection stage, so the fuel spray in FPEG receives a smaller gas resistance and behaves more impingement, longer penetration, slower evaporation, larger sauter mean diameter (SMD), and lower mixture uniformity in this stage than the CCE. However, the slower compression process of FPEG not only makes that the fuel droplets evaporates earlier, but also provides a longer duration for fuel-air mixing and diffusion. Therefore, at the moment of spark ignition, a more homogeneous mixture is formed in the FPEG, and it shows smaller SMD and higher concentration around spark plug than the CCE. This phenomenon may facilitate the spark ignition and high efficiency combustion. Highlights • The fuel spray and mixing of a gasoline FPEG was evaluated by comparing a CCE. • The effect of motion on fuel-air mixing of the FPEG was revealed. • Finding that the FPEG shows higher uniformity of mixture than the CCE. • The spray of FPEG has more impingement, longer penetration, and slower evaporation. [ABSTRACT FROM AUTHOR]