Spray Behavior Research Articles

Tribological Behavior and Microstructural Analysis of Atmospheric Plasma Spray Deposited Thin Coatings on Cardan Cross Spindles.

Cardan joints are used in transmissions between misaligned shafts, as in all-wheel-drive (AWD) cars and railway applications. Their functioning is accompanied by heavy cyclical loads, with the cardan cross spindles subjected to intensive abrasive wear and pitting. In this paper, a solution to the mentioned issue is proposed, thin anti-wear coatings of Metco 32 and Metco 72 metallic powders deposited by atmospheric plasma spray (APS) on cylindrical samples cut from spindles of two cardan crosses made of 40Cr10 and RUL2 steel. The morphological analysis of the coated surfaces was realized by scanning electron microscopy (SEM), and the elemental composition of the tested samples was elaborated by energy-dispersive X-ray spectroscopy (EDS). To investigate the wear resistance of the coated samples in dry and grease-lubricated conditions, tests at constant load and constant speed were carried out using an AMSLER tribometer. The results of greased tests proved that the expulsion of the lubricant from the tribological contact occurred no matter the combination of coated or uncoated samples. During grease-lubricated tests of ten minutes, the least coefficient of friction was measured for uncoated specimens with better surface finishing; but in dry friction tests, the lowest values of the mean friction coefficients were obtained for the Metco 72 coatings. The porous coatings may act as lubricant reservoirs in long-lasting tests, providing a solution to the expulsion phenomenon of the lubricant to the boundary outside the area of the larger-diameter roller.

Development of diesel surrogates for reproducing the effect of fuel properties on engine combustion and emissions using an optimized decoupling physical–chemical surrogate (DPCS) model

An optimized decoupling physical–chemical surrogate (DPCS) model was carried out to formulate different diesel surrogates effectively. In the optimized DPCS model, the physical candidates of ten components and the chemical candidates of four components are coupled by the rule of hydrocarbon type to match the physical–chemical properties of diesel fuel. The composition of the physical components is determined using genetic algorithm (GA), and then the coupling rule is applied to derive the composition of the chemical components. To validate the robustness of the optimized DPCS model, the prediction results are compared with the experimental results containing vapor penetration distance in a constant volume bomb (CVB) and the combustion and emission characteristics in a convention diesel combustion (CDC) engine utilizing different diesel fuels. The results show that the predictions of the diesel surrogates formulated by the optimized DPCS model accurately fit the experimental results, and the impacts of diesel fuel properties on the spray and combustion behaviors can be well reproduced. Besides, the factors that dominate the spray and combustion features of different diesel fuels are identified.

COMPARISON OF SPRAYABILITY AND SOLUBILITY OF BIO-BASED LUBRICANTS WITH LIQUID CARBON DIOXIDE

In recent years, cryogenic minimum quantity lubrication (CMQL) has been established in comparison to pure cryogenic cooling. The used oil has a crucial influence on the success of the technology. The aim of this study is to investigate the influence of oils from renewable resources with regard to their miscibility with carbon dioxide (CO2) and their spraying behavior. Ten different bio-based oils (synthetic ester, natural ester and fatty alcohol) have been examined regarding their suitability for CMQL compared to a conventional mineral hydrocrack oil. A validation based on sprayability and solubility properties with liquid CO2 has been performed. The sprayability and the resulting oil droplet size have an impact on the amount of oil entering the process zone and thus on the lubrication performance of the coolant concept. For this reason, a high-speed camera has been used to capture shadow images of the jet from an external cooling nozzle. In addition the width, intensity and uniformity of the oil application were evaluated. The solubility of the bio-based oils in CO2 is investigated in a static mixing chamber with varied mixing ratio. The miscibility of the bio-based oils in a single channel supply system was investigated with high-speed recordings of a dynamic mixing chamber. The results of the various experimental setups have been compared.

Evaporating characteristics of diesel sprays under split-injection condition with a negative dwell time

This paper investigates the effects of the split-injection strategy with a negative dwell time using a multi-hole diesel injector under evaporating conditions. To compare with negative dwell conditions, the single-injection and positive and zero dwell conditions were adopted. The Laser Absorption Scattering (LAS) technique was employed to measure the temporal and spatial evolution of fuel evaporation and mixture concentration in the experiments. The split injection of 7:3 was selected according to the results of the previous study that proposed a homogeneous mixture after the end of injection. The dwell times of −50 us, 0 us, and 120 us were selected based on the measurement of the injection rate. The blended fuel consisting of 97.5% of n-tridecane and 2.5% of 1-methylnaphthalene in volume was used. The results show that a shorter spray tip penetration was present in the split injection with a negative dwell time. This phenomenon is expected to reduce the possibility of wall impingement and result in fewer nitrogen oxides (NOx) and unburned hydrocarbons (UHCs) under the injection conditions with a negative dwell time, especially for the conditions of a large injection amount and small-bore engines. Moreover, different spray shapes and behavior occurred in the case of different injection strategies. The spray of split-injection strategy with a negative dwell time has large radial dispersion, and it can improve the air utilization inside a cylinder.

Impact of Temperature on the Spray Characteristics of Jatropha Curcas Biodiesel and Diesel Fuel Blends

Abstract There is an increasing demand of energy because of an increase in the number of vehicles with internal combustion engines, because of which industrial and automotive fields are concerned about fossil fuel depletion, environmental issues, and energy conservation. These challenges force the world to explore other alternative sources of energy. The extensive use of biodiesel as compression ignition engine fuel has further compelled the researchers to regulate the emission and improve the engine performance. Fuel spray behavior affects mixture formation, and this affects engine combustion and performance. This research work involves the evaluation of the relationship between spray parameters of used Jatropha curcas biodiesel fuel, including spray penetration, cone angle, and preheating temperature, compared with diesel fuel, conducted at ambient condition. In addition to this, the high-speed spray pattern photography is undertaken by using single-hole and multi-hole injectors. The spray behavior is analyzed through spray parameters such as spray cone angle and spray penetration for all test fuels. The fuel temperature has a strong relationship with spray behavior at high temperatures; as the fuel temperature increases, the spray tip penetration decreases due to the evaporation of the fuel having a low boiling point and good fuel atomization, which leads to smaller droplets and an increase in spray cone angle with the increase in temperature.

A morphological study of supercritical fuel flash-boiling spray

The optimization of fuel injection is one of the key technologies to achieve cleaner and more efficient engines. Extensive studies have demonstrated that the flash-boiling of superheated fuel would dramatically improve the atomization, mixing and combustion process. Further increasing the fuel temperature can make the fuel at a supercritical state, the flash-boiling spray of which has rarely been noticed in existing studies. The relevant data and analysis of the behavior and characteristics of supercritical fuel flash-boiling spray are still lacking. In this study, the supercritical flash-boiling injection was achieved by heating the fuel inside the injector, and its spray behavior was examined by high-speed backlit imaging. This study found that the supercritical fuel flash-boiling spray has a transient formation process different from common sprays due to the supersonic effect during the initial injection. The spray structure was carefully analyzed based on its thermodynamic state and hydrodynamic state. The spray penetration, radial expansion, location of Mach disk was also systematically investigated. The characteristics of the supercritical fuel flash-boiling spray are very similar to that of the highly under-expanded jet.

Liquid Propane Injection in Flash-Boiling Conditions

This study aimed to investigate the influence of flash-boiling conditions on liquid propane sprays formed by a multi-hole injector at various injection pressures. The focus was on spray structures, which were analysed qualitatively and quantitatively by means of spray-tip penetration and global spray angle. The effect of flash boiling was evaluated in terms of trends observed for subcooled conditions. Propane was injected by a commercial gasoline direct injector into a constant volume vessel filled with nitrogen at pressures from 0.1 MPa up to 6 MPa. The temperature of the injected liquid was kept constant. The evolution of the spray penetration was observed by a high-speed camera with a Schlieren set-up. The obtained results provided information on the spray evolution in both regimes, above and below the saturation pressure of the propane. Based on the experimental results, an attempt to calibrate a simulation model has been made. The main advantage of the study is that the effects of injection pressure on the formation of propane sprays were investigated for both subcooled and flash-boiling conditions. Moreover, the impact of the changing viscosity and surface tension was limited, as the temperature of the injected liquid was kept at the same level. The results showed that despite very different spray behaviours in the subcooled and flash-boiling regimes, leading to different spray structures and a spray collapse for strong flash boiling, the influence of injection pressure on propane sprays in terms of spray-tip penetration and spray angle is very similar for both conditions, subcooled and flash boiling. As for the numerical model, there were no single model settings to simulate the flashing sprays properly. Moreover, the spray collapse was not represented very well, making the simulation set-up more suitable for less superheated sprays.

Research on the internal flow and macroscopic characteristics of a diesel fuel injection process.

The internal flow and macroscopic spray behaviors of a fuel injection process were studied with schlieren spray techniques and simulations. The injection pressures(Pin)and ambient pressures(Pout)were applied in a wide range. The results showed that increasing the Pin is likely to decrease the flow performance of the nozzle. Furthermore, increasing the Pin can increase the spray tip penetration. However, the effect of Pin on the spray cone angle was not evident. The spray cone angle at an injection pressure of 160MPa was 21.7% greater than at a pressure of 100MPa during the initial spraying stage. Additionally, the discharge coefficient increased under high Pout, and the decrease in Pout can promote the formation of cavitation. Finally, increasing the Pout can decrease the penetration, while the spray angle becomes wider, especially at the initial spray stage, and high Pout will enhance the interaction of the spray and the air, which can enhance the spray quality.

Thermodynamic modeling of trans/supercritical fuel sprays in internal combustion engines based on a generalized cubic equation of state

Redlich-Kwong-Peng-Robinson (RK-PR) was developed in recent years as a promising generalized cubic equation of state (EoS) to allow for a good representation of fluids with different critical compressibility factors (Zc), but it cannot be mathematically applied to high Zc fluid such as H2 and CO, thus limiting its application on engine problems. In this work, the Zc ratio was modeled as a function of Zc to extend the calculable range of RK-PR and to achieve higher accuracy for various n-alkanes, liquid oxygen and nitrogen. The thermodynamic and transport properties framework based on RK-PR show superiority over those of SRK and PR for typical IC engine fuels and spray mixtures. In addition, the high-fidelity simulations of n-dodecane spray were performed to investigate qualitatively and quantitatively the effects of EoS and thermodynamic conditions on trans/supercritical spray behavior and characteristics, emphasizing the necessity of applying an accurate EoS for high fidelity spray simulations.

ECN Spray D visualization of the spray interaction with a transparent wall under engine-like conditions. Part I: Non-reactive impinging spray

The possibility for a jet of fuel to collide against the surfaces of the combustion chamber or the piston bowl into a thermal engine, has a direct effect on the droplets breakup and the spray atomization. In order to study the spray/wall interaction phenomenon and its influence on the macroscopic spray behavior, a diesel spray was visualized when impinging on a flat wall made of quartz at various ambient, injection and wall position conditions. Two high-speed cameras were employed simultaneously to perform Schlieren imaging and diffuse back illumination diagnostics, in order to observe both spray vapor and liquid phases during their contact with the wall. The experiments were performed in a constant pressure-flow test rig, able to reproduce diesel-like thermodynamic conditions. Two different fuels (n-dodecane and diesel #2) were injected within the chamber by employing a single-hole injector referred to as Spray D into the framework of ECN research group. To place the wall in the spray path, a wall positioning structure capable of being fitted into the chamber and of support the wall at various inclination angles and distances from the injector tip, was designed. The test rig was filled with N2 to keep an inert atmosphere and isolate the spray development from possible alterations produced by combustion. Results provide the influence of the injected fuel, operating and wall conditions on the macroscopic features of the transient spray in terms of spreading onto the wall and spray thickness characterized both temporally and spatially. Spray spreading was evaluated by a novel penetration-based parameter. It showed to be proportional to the square root of time similarly as free-penetration and is largely affected by the wall inclination respect to the spray axis. Spray angle showed to be influenced by the morphology of the spray that affects its air entrainment capacity and that changes with a wall respect to a free-jet configuration. This variation in the morphology also has a remarkable effect on spray evaporation, characterized in terms of liquid length and liquid spreading onto the wall. Finally, the large amount of data was used to obtain correlations for all the studied parameters.

Atomization of misaligned impinging liquid jets

This study numerically investigated the atomization characteristics of misaligned impinging jets, with the misalignment ratio ê ranging between 0 and 0.2, by employing the volume of fluid method with an adaptive mesh refinement algorithm. The results show that the droplet Sauter mean diameter varies non-monotonically with ê and reaches the minimum value, which implies the best atomization performance, at ê=0.1 under operating conditions concerned in the present work. Meanwhile, the moderately misaligned impingement also leads to a more uniform spatial dispersion of the atomized fragments and droplets. These unique spray behaviors can be attributed to the instability and disintegration of the liquid sheet formed upon jet impingement, as evident from the non-monotonic dependence of the breakup length of the liquid sheet on the misalignment ratio ê. Analyses on the velocity fluctuation and vorticity distribution further suggest that the misalignment alters the intrinsic instability mode of the liquid sheet by introducing a lateral stretch effect, which diverts the peak streamwise momentum away from the centerline. The current finding indicates that misalignment tuning could be a promising optimization and control technique in propellant mixing and atomization.

Experimental Investigation on Behavior of an Impingement Diesel Spray on a Wall with Adhering Liquid Fuel

Experimental Investigation on Behavior of an Impingement Diesel Spray on a Wall with Adhering Liquid Fuel

Nozzle configuration and in-cylinder pressure effects on fuel spray behaviour: studies using a rapid cycling machine

Efforts to improve the efficiency of internal combustion engines in applications such as heavy-duty vehicles where electric propulsion is currently unfeasible or need complementing are essential. However, studying the conditions of actual internal combustion engines whilst accessing their combustion chambers whilst they are in operation remains difficult. To allow for the characterization of practical operating conditions of diesel engine designs, detailed studies examining the influence of the injector nozzle configuration, peak in-cylinder pressure conditions, and fuel injection pressure values up to 25% greater than those hitherto typically reported using rapid cycling machines for diesel spray diagnosis were carried out. A rapid cycling machine using a production diesel engine piston design, equipped with optical windows and fitted with a high-pressure common rail fuel injection equipment was used with temporal spray liquid and vapour penetration values obtained using Schlieren and Mie scattering imaging techniques for injector nozzles of various k-factor values. Even though the effects of the different injector nozzle conicity values on the fuel spray liquid and vapour penetration values observed were not significant, the studies supported the use of such methods to evaluate the piston and cylinder wall wetting which can have significant effects on the emissions and fuel consumption from internal combustion engines. These are also useful for internal combustion engine design and numerical spray code development.

Dynamic behavior of jet-swirl spray under resonance condition with external excitation

Gas-centered swirl coaxial (GCSC) injectors are used in many liquid propellant rocket engines to improve combustion efficiency. In this study, fluctuation of the mass flow rate is analyzed to investigate influence of external excitation in gas feed line on the mass flow rate distribution of sprays. Water and air are used as simulants for the liquid kerosene and gas oxygen, respectively. With external excitation (354 and 1062 Hz), atomization processes changes and periodic breakup phenomenon of a spray occurs. Liquid film thickness at the exit of the injector shows that the width of liquid mass flow rate wave is reserved when the instability mode changes. However, behavior of the liquid droplets captured with a structured laser illumination planar imaging (SLIPI) system for laser diagnostics indicates that time domain concentration of liquid mass becomes more severe with the second instability mode outside the injector. This study can provide a reference for liquid mass distribution with external excitation on gas and imply that resonance in injector feeding systems is one of the important factors in combustion instability.

The effect of heat treatment and impact angle on the erosion behavior of nickel-tungsten carbide cold spray coating using response surface methodology

This study elucidates the performance of cold-sprayed tungsten carbide-nickel coating against solid particle impingement erosion using alumina (corundum) particles. After the coating fabrication, part of the specimens followed two different annealing heat treatment cycles with peak temperatures of 600 °C and 800 °C. The coatings were examined in terms of microstructure in the as-sprayed (AS) and the two heat-treated conditions (HT1, HT2). Subsequently, the erosion tests were carried out using design of experiments with two control factors and two replicate measurements in each case. The effect of the heat treatment on the mass loss of the coatings was investigated at the three levels (AS, HT1, HT2), as well as the impact angle of the erodents (30°, 60°, 90°). Finally, the response surface methodology (RSM) was applied to analyze and optimize the results, building the mathematical models that relate the significant variables and their interactions to the output response (mass loss) for each coating condition. The obtained results demonstrated that erosion minimization was achieved when the coating was heat treated at 600 °C and the angle was 90°.

Spray Behaviors and Gasoline Direct Injection Engine Performance Using Ultrahigh Injection Pressures up to 1500 Bar

High fuel injection pressure systems for Gasoline Direct Injection (GDI) engines have become widely used in passenger car engines to reduce emissions of particulates and pollutant gases. Current commercial systems operate at pressures of up to 450 bar, but several studies have examined the use of injection pressures above 600 bar, and some have even used pressures around 1500 bar. These works revealed that high injection pressures have numerous benefits including reduced particulate emissions, but there is still a need for more data on the possible benefits of injection pressures above 1000 bar. This article presents spray and engine data from a comprehensive study using several measurement techniques in a spray chamber and optical and metal engines. Shadowgraph imaging and Phase Doppler Interferometry (PDI) were used in a constant volume chamber to interpret spray behavior. Particle Image Velocimetry (PIV) was used to capture near-nozzle air entrainment. Optical engine experiments were performed to visualize the spray's position relative to the piston at different start of injection (SOI) timings. A single-cylinder GDI engine was used to investigate the effects of injection pressure on emissions and combustion characteristics. The spray tests showed that high-pressure sprays tend to exhibit better atomization and create more air entrainment, accelerating evaporation and mixing. However, high pressures also cause high spray tip penetration due to the high spray velocity, potentially causing wall film formation. At commonly used SOI timings, the benefits of high-pressure injection are relatively insignificant. The improvements in combustion stability and emissions of hydrocarbon (HC) and particulates are greater when the SOI timing is advanced (≈340°bTDC) or retarded (later than 180°bTDC). Wall film occurs at advanced SOI timing for all injection pressures, but high injection pressures significantly reduce particle number (PN) emissions by affecting wall film formation. At late SOI timings, high injection pressures yield acceptable combustion stability and emissions because they shorten the injection and promote mixing. These results suggest that high-pressure sprays allow HC and PN emissions to be greatly reduced and increase flexibility with respect to injection timing without sacrificing engine performance or increasing other emissions. Fuel consumption is also improved, but the effect is more significant when the injection pressure is 1000 bar.

Effect of diesel/gasoline/HCB blends and temperature on string cavitating flow in common-rail injector nozzle

Renewable clean fuel such as biodiesel, alcohol-based fuel blended with fossil fuel has been widely studied for applications in engines aiming at partial solution of fuel consumption and environment emission issues. These blending fuels have also shown advantages in new combustion modes like GCI and LTC. However, the fuel injector nozzle internal flow and spray behaviors of these blending fuels are still not well understood, which may largely influence the subsequent fuel–air mixture, combustion, and emission characteristics. The investigation of cavitation flow in the high-pressure common-rail injector nozzle and spray characteristics with blending fuels of gasoline, diesel, and hydrogenated catalytic biodiesel (HCB) was conducted in the present work. The real-size optical nozzle was used to visualize the nozzle internal cavitating flow and spray. It was found that, by adding gasoline into diesel and HCB, the string cavitation increased significantly, and the spray cone angle expanded, especially under low needle lift. This behavior can be interpreted as the lower viscosity and higher saturation vapor pressure of gasoline enhanced vortex and cavitation. It can be concluded that increasing fuel temperature significantly impacted the cavitation and affected the vortex lightly, suggesting that with higher temperatures, blended fuels show better performance. As the fraction of HCB of gasoline/HCB blends increased, the cavitation inside nozzles was restrained due to its high viscosity. String cavitation can be interrupted by the needle tip, and the spray cone angle fluctuated enormously under this situation, which may cause uneven mixing of fuels and air.

Modeling of the entire processes of diesel spray tip penetration including the start- and end-of-injection transients

The start-of-injection (SOI) and end-of-injection (EOI) transients are important for sprays with multiple-injection strategy. Owing to the change of needle position and sac pressure, the spray behaviors in the transient processes are significantly different from those in the quasi-steady stage. In this study, considering the sac pressurization processes during the SOI transients and effects of ''entrainment wave'' after the EOI, a theoretical zero-dimensional model for the entire development processes of the spray tip penetration (Stip) is summarized. Then, a high-speed CMOS camera and constant-volume chamber are employed to study the spray characteristics and verify the model. The model and experimental results clarify four key time points in the entire development processes of Stip: the sac pressurization time (tp), breakup time (tb), injection duration (ti) and two injection durations (2ti). Five stages can be divided according to these four time points: the acceleration stage (Stip proportion to t1.5), transition stage 1 (t1 or t0.75), quasi-steady stage (t0.5), transition stage 2 (t0.5) and decelerating stage ((t-ti) 0.25). Moreover, the newly developed model is compared with the Wakuri model, the Hiroyasu & Arai model, and the Naber & Siebers model. The results show that all the models can well predict Stip during the quasi-steady stage and transition stage 2 with the optimized model constants. While the other models overpredict Stip in the acceleration and decelerating stages, the newly developed model still works very well.

Turbulent spray flames of kerosene issuing from a hybrid electrohydrodynamic-air-blast atomiser

This paper presents an experimental study of turbulent spray flames of kerosene atomised using a new hybrid air-blast/electrohydrodynamic atomiser. Electrohydrodynamic (EHD), or charge injection atomization applies to electrically insulating fuels where the liquid is a dielectric and does not require conductive additives. The study focuses on the influence of electric charge on the global stability and downstream flow-field and reaction zone structure of turbulent spray flames. Stability characteristics for the burner are examined with and without electric charge, and cover sprays over a broad range of aerodynamic Weber numbers, We. The velocity and droplet fields are measured using laser/phase Doppler anemometry, and results indicate a notable increase in particle concentration with the application of charge for both reacting and non-reacting sprays. With the addition of electric charge, it is found that the mean and rms velocity fields are not significantly influenced but a significant rise in particle concentration is noted and this is more pronounced for the lower We number cases. Planar laser induced fluorescence of OH shows clear influence of charge on the reaction zone structures pushing them to outer radial locations, whilst also reducing the intermittency in the area of OH fields over time. The burner provides a new experimental platform that enables the study of hybrid atomization as a means to modify spray and flame behaviour.

Behavior and body size modulate the defense of toxin-containing sawfly larvae against ants

The sawfly larvae of most Argidae and Pergidae (Hymenoptera: Symphyta) species contain toxic peptides, and these along with other traits contribute to their defense. However, the effectiveness of their defense strategy, especially against ants, remains poorly quantified. Here, five Arge species, A. berberidis, A. nigripes, A. ochropus, A. pagana, A. pullata, plus three Pergidae species, Lophyrotoma analis, Lophyrotoma zonalis, Philomastix macleaii, were tested in laboratory bioassays on ant workers mainly of Myrmica rubra. The experiments focused on short-term predator–prey interactions, sawfly survival rate after long-term interactions, and feeding deterrence of the sawfly hemolymph. The larvae of Arge species were generally surrounded by few ants, which rarely bit them, whereas larvae of Pergidae, especially P. macleaii, had more ants around with more biting. A detailed behavioral analysis of Arge-ant interactions revealed that larval body size and abdomen raising behavior were two determinants of ant responses. Another determinant may be the emission of a volatile secretion by non-eversible ventro-abdominal glands. The crude hemolymph of all tested species, the five Arge species and L. zonalis, was a strong feeding deterrent and remained active at a ten-fold dilution. Furthermore, the study revealed that the taxon-specific behavior of ants, sting or spray, impacted the survival of A. pagana but not the large body-sized A. pullata. The overall results suggest that the ability of Arge and Pergidae larvae to defend against ants is influenced by the body size and behavior of the larvae, as well as by chemicals.