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The thermal load in the piston head is becoming heavy with the application of supercharging technology. This makes the piston cooling become more challenging to ensure the reliability of the piston. In this study, an oil-injection cooling process in a medium-speed V-type diesel engine is numerically investigated. The simulations are performed for the direct coupling of the piston head structure and the two-phase flow in the cooling gallery. The effect of the flow pattern on heat transfer characteristics during the whole process is discussed. The results reveal a series of the flow characteristics including thrown flow, interrupted flow, wall impingement, oil oscillating and sedimentation during the reciprocating movement of the piston and the flow characteristics become more obvious with the increase of the engine speed, but the cooling oil is more widely distributed in the oil gallery due to more intense oscillation. After multi-cycle calculations, the flow characteristics of the cooling oil and the heat transfer characteristics of the piston both have a certain periodicity. [ABSTRACT FROM AUTHOR]

The wall-impingement phenomenon significantly impacts mixture formation, combustible performance, and pollutant release in DISI engines. However, there is insufficient knowledge regarding the behavior of fuel adhesion. Thus, here, we examine adhesive fuel features at various injection pressure levels (5 and 10 MPa) in a cross-flow field (0 to 50 m/s). The RIM optical method was employed to track the expansion and distribution of fuel adhesion. As a result, adhesive fuel features such as area, mass, thickness, and lifetime were assessed. Postprocessing image analysis reveals that fuel adhesion was consistently thinner at the edge region. With increased injection pressure, the cross flow led to a rise in the fuel-adhesion area and mass; however, small changes in pressure did not affect adhesive thickness. Adhesive thickness significantly decreased in the cross flow, indicating enhanced evaporation potential. Furthermore, lifetime prediction was conducted to quantitatively evaluate the impact of cross flow and injection pressure upon fuel adhesion, which could be calculated by examining the decreasing trend in adhesive area. Results show that the lifetime was dramatically reduced with higher cross-flow velocity, and slightly decreased with lower injection pressure. Under injection pressure of 10 MPa, the adhesive lifetime in the cross-flow field of 50 m/s was reduced by 77.5% compared with the static flow field (0 m/s). The experimental results provide corresponding guidance for low-carbon fuel utilization and emission reduction in DISI engines. [ABSTRACT FROM AUTHOR]

We present a novel device for generating suspension droplets and studying droplet impact against solid substrates. The proposed droplet generator extends beyond previous designs by introducing hydraulic machinery that includes separate hydraulic and test containers. This eliminates mixing between the test liquid and the hydraulic liquid above the latch that connects the two containers, thus ensuring reliable clogless operation. The device can produce droplets of controllable sizes between 0.75 and 4.4 mm, and droplets can contain suspension particles of 45 μm to 300 μm size. Repeatability tests show that, at constant control parameters, the median relative droplet size deviation from the target value is ±0.9% and the maximum relative deviation is ±9.1%. We also explore different collision scenarios, which we change from spreading to bouncing by varying the substrate wettability. In addition, the shape of the stain and the resulting spatial distribution of particles are found to be sensitive to particle size. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wall impingement can shorten ignition delay by stagnation when H / D is larger than 7. • Ignition initiates from near wall region or the jet root among different H / D. • Secondary jet induced by swirl-shape wall is favorable for ignition. Pre-chamber turbulent jet ignition is a promising high-efficiency combustion technique to achieve stable lean-burn operation for spark-ignition engines. Wall impingement by a high momentum turbulent jet could exert a critical influence on jet ignition behavior. In this work, the passive jet ignition characteristics of premixed methane/air mixture under wall impinging condition was investigated based on optical experiments in a constant volume chamber and numerical simulations. Two ignition modes were found for flat wall impinging cases across a range of non-dimensional impinging distances (H / D) from 5.7 to 20. In mode 1, ignition initiates from near wall region. Under lean conditions of λ = 1.3, compared with that in the free jet case, the ignition delay time characterized by a 5 % mass fraction burned (MFB-05), decreases by 3.3 ms at H = 30 mm and increases by up to 6.6 ms at H = 20 mm. In mode 2, ignition initiates from the jet root. The ignition delay times are shorter for all impinging distances (H = 20, 30, 40 mm), with MFB-05 decreasing by up to 3.4 ms. Simulations reveal that when the wall is located in the jet developing zone with H / D below 7, wall impinging deteriorates the ignition, which is attributed by higher turbulent kinetic energy (TKE) and lower Damköhler (Da) number near the stagnation zone, resulting in extended ignition delay. Conversely, as H / D increases, ignition is promoted by the stagnation effect with a shorter ignition delay. Additionally, the effect of wall shapes was analyzed. Using sharp-tip V-shaped wall, the stagnation region with high TKE is minimized. A blunt-tip V-shaped wall shows enhanced impinging but no obvious increase of Da number at stagnation point. Using M-shaped wall, the ignition mode with a "lift-off" flame was found. Besides, ignition is more favorable in the secondary jet zone with active radicals and higher Da number. [ABSTRACT FROM AUTHOR]

The objective of the investigation is to explore the spray evaporation and dispersion characteristics of impinged biodiesel-butanol blends at various n-butanol ratios (0, 10%, 30%, 50%) and ambient conditions. A total of 180 experimental cases were performed in a constant-volume combustion chamber. The liquid- and vapor-phase sprays were captured by backlight imaging technique and Schlieren imaging technique, respectively. Several macroscopic parameters were measured and discussed, including impinged spray structure, width, height, and area. Some novel parameters are derived to analyze spray evaporation and dispersion. Results show that biodiesel blended with 30% n-butanol transits better from liquid-phase to vapor-phase compared with other blends, displaying rapid liquid-phase evaporation an steady vapor-phase dispersion. After wall impingement, an increase in the ambient pressure or temperature hinders the liquid-phase dispersion in the vertical direction significantly, leading to a rapid decrease in the height of the impinged spray. The vapor-phase diffusion rate in the horizontal direction is about four times the rate in the vertical direction, and the rate ratio is slightly affected by ambient conditions and injection pressure. Compared with the free jet, the impinged spray is not beneficial for liquid-phase evaporation and vapor-phase dispersion, presenting larger liquid-phase area and smaller vapor-phase area. However, impinged biodiesel blended with 30% n-butanol displays better spray evaporation and dispersion. [ABSTRACT FROM AUTHOR]

Diesel engines are commonly used for public transportation on-road and off-road applications. Growth production of the diesel engine is very significant from year to year. Nitride Oxide (NOx) from diesel engine was one of the major sources of air pollution. Selective Catalytic Reduction (SCR) has been successfully used to reduce NOx from a diesel engine with a chemical reaction from ammonia (NH3). The mixing reaction between NOx and NH3 reaction can produce steam (H2O) and Nitrogen (N2). However, ammonia uniformity pattern usually not homogenization and the ammonia was difficult to mix with NOx. The constant air flows incomplete to assist the spray injector to spread NH3 to all corners of SCR. The impact study of turbulent phenomena and standard k-epsilon Low-Reynolds Number model to the mixing process in the SCR system using STARCCM+. The simulation studies are conducted under different pressure (4 to 6 bars), the injection rate (0.04 g/s) and temperature (338 K – 553 K) and the high pressure and high velocity magnitude creating turbulent swirl flow. The ammonia decomposition process and mixing process with NOx were investigated using a box with optical access. The simulation and numerical study results validated using back pressure value and the distribution of NOx concentration value from the catalyst outlet. The wall temperature will increase the urea evaporation to generate ammonia and gas pressure will increase the mixing process and chemical process in the SCR system. These reactions enable to optimize the SCR system technology which eventually able to reduce the NOx quantity from a diesel engine.

The most undesired diesel engine pollutants are nitride oxide (NOX), particulate matter (PM), carbon monoxide (CO), and unburned hydrocarbon (HC). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully employed to remove NOX from diesel emissions via chemical reactions to yield steam (H2O) and nitrogen (N2). However, the ammonia homogenization process is usually incomplete and difficult to mix with NOX. This reaction affected from the urea injection process in the system when the condition is not suitable for urea decomposition process. Therefore, a study on the effects of urea injection timing to predict the NOX reduction efficiency was needed in order to identification the suitable condition based on temperature, flow mass, pressure, etc. In this study, the experiments and simulations were conducted to obtain constant and stable conditions in the SCR system, as constant conditions can optimize the uniformity of ammonia distribution in the system. The engine conditions in the experiment were computed from turning an engine on to determine the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. The temperatures used for processing ammonia uniformity in diesel SCR systems were investigated with operation at ambient temperature (298 K) and inlet gas temperature (686 K). Numerical results were validated using the experimental results of ammonia concentration distribution. [ABSTRACT FROM AUTHOR]

• 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]

Numerical calculations were carried out to investigate the formation of a fuel–air mixture as well as ignition and combustion processes associated with a diesel spray impinging on a wall. This was performed by modeling the spray formed by injecting n -heptane into a constant-volume vessel under high temperature and pressure, with the fuel droplets described by a discrete droplet model. The flow and turbulent diffusion processes were calculated based on the large eddy simulation method to simulate the formation of a local non-homogeneous mixture and the accompanying heat release. The flame structure and heat transfer to the wall during impingement were also assessed. The results show that heat transfer to the wall is increased in the peripheral region around the stagnation point, as a result of the high temperature and thin boundary layer. Conversely, in the outer region, the heat transfer decreases as the boundary layer becomes more developed. [ABSTRACT FROM AUTHOR]

Reducing heat loss is one of the most important development concerns for improving the thermal efficiency of the diesel engine. In order to know heat transfer through the combustion chamber wall more clearly, the effects of flame impingement on transient heat flux to the wall were investigated. Using a high-pressure and high-temperature chamber under diesel engine–like conditions, fuel was injected from a single-hole injector against an impingement wall. Surface heat flux of the impingement wall was measured by temperature with three thin film thermocouple heat flux sensors. Simultaneously, luminous flame, flame temperature, and soot distribution were also investigated. The results showed that temperature near the wall and flame contact area have great influence on the local heat flux. Furthermore, local heat flux, combustion, and soot formation reached maximum levels at some spray impingement distance to the wall. [ABSTRACT FROM AUTHOR]

The automotive industry has been restricted by several regulations to reduce nitrogen oxide emissions from diesel engines. To adhere to the emission regulation, advanced engine technology aims to control oxygen access, compression, and ignition engine, while achieving both reduced fuel consumption and lowering unburnt HC, CO2, and CO levels. However, it is difficult to meet the NOx limits of the European standard (EURO VI) and American standard (US TIER 2 BIN 5). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully employed to remove NOx from diesel engines. However, uniform ammonia distribution is usually difficult to achieve. Therefore, a study on ammonia uniformity to predict NOx reduction efficiency in SCR systems is needed. The engine utilized in the experiment was turned on for a few minutes to obtain the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. This study was performed at engine operating conditions of 1500 rpm, 2000 rpm, and 3000 rpm; simulation was performed with a fixed pressure and velocity, as in the experiment, thus creating a similar turbulent swirl flow in the SCR system. Numerical results were validated using experimental results of ammonia concentration distribution. [ABSTRACT FROM AUTHOR]

Abstract Spray-wall impingement has been proved unavoidable in direct-injection spark-ignition (DISI) engines, which affects the fuel-air formation as well as combustion and exhaust emissions, making it difficult to meet the regulation of particle number (PN) in the future standards. In this study, the characteristics of fuel adhesion injected by a mini-sac gasoline injector with a single hole were investigated in a constant high-pressure chamber. The fuel spray and adhesion were measured via Mie scattering and refractive index matching (RIM) methods, respectively. The effect of injection pressure on the spray-wall interaction under room and high temperature condition were tested. The results showed that under room temperature, the injection pressure promotes better atomization, resulting in longer spray tip penetration, larger impinging spray height, and more fuel adhesion on the wall. However, when evaporation occurs, higher injection pressure favors the fuel evaporation due to the small droplets size, leading to shorter spray tip penetration, smaller impinging spray height, and less fuel adhesion on the wall. Moreover, under non-evaporation condition, high injection pressure has less effect on the uniformity of the fuel adhesion on the wall, while under evaporation condition, it improves the uniformity of the fuel adhesion. Owing to the different mechanisms of the fuel adhesion formation in the primary impingement (Region I) and secondary impingement (Region II) regions, injection pressure has more influence on the fuel adhesion in Region I, especially under evaporation condition. [ABSTRACT FROM AUTHOR]

Abstract The automotive industry has been restricted by several regulations to reduce pollutant from diesel engines. To fulfill the emission regulation, advanced engine technology purposes to control pollutant reduction and lowering the unburnt HC, CO2 and CO level. However, it is difficult to meet the NOx limits of the world standard like a European standard (EURO VI) and American standard (US TIER 2 BIN 5). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully to remove NOx from diesel engines. However, uniform ammonia distribution is usually difficult to achieve. Therefore, a study on the effects of urea injection timing to predict NOx reduction efficiency is needed. In this study, the simulations and experimental work to obtain constant and stable conditions in the SCR system were conducted. Because the constant condition can optimize the ammonia uniformity. The engine in experiment was compute from engine turned on to find the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. The numerical results were validated using experimental results of ammonia concentration distribution. [ABSTRACT FROM AUTHOR]

This study was performed to analyze the wall impingement and fuel film formation in a DISI engine with injection strategies using image-based analysis and CFD. The direct injection engine uses a high-pressure injection strategy to improve the homogeneity of the air-fuel mixture, so the spray behavior was analyzed by spray visualization for various injection pressures, and the wall impingement was predicted for various engine operating conditions based on the acquired images. The mass distribution of the injected fuel was calculated using the injection profiles and the spray image, and the amount of fuel that impinges on the piston and wall (i.e., the geometric boundaries of the cylinder) was calculated using data from the spray behavior for various engine operation conditions such as load and engine speed. The image-based analysis was limited to understanding the influence of the injection strategy on the droplet behavior after wall impingement of the fuel spray. Therefore, CFD using KIVA 3 V code was additionally conducted to analyze the effects of the injection strategies on wall film formation and droplet rebounding reflecting in-cylinder conditions. In the early- and late-injection conditions, the initial piston position is high, and most of the injected fuel impinges on the piston. As the injection pressure increases, the injection timing at which wall impingement occurs is advanced because of the rapid spray development. The results of the 3D analysis for the temperature and the intake flow in the engine cylinder showed that both the wall impingement and the fuel film were reduced as the injection pressure increased because the fuel evaporation increased due to improved atomization. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction is the most promising technique for NOx reduction from diesel engine exhaust emissions. The greatest challenge to implementing the system is solid deposit formation. Spray wall impingement of UWS was investigated in a constant volume chamber by numerical simulation using STAR CCM+ CFD code. The realizable k-ε two-layer approach together with standard wall functions and all y+ treatment was implemented for the modeling of turbulence flow. The two-phase flow was modeled by using Eulerian- Lagrangian approach. The heated wall temperature was maintained from 338 K to 573 K during the UWS spray wall impingement. The development of the spray after impinging on the heated wall was visualized and measured. UWS droplet size distribution, wall film formation and droplet evaporation rates were estimated, which are vital parameters for the system performance but not well researched. User-defined functions (UDF) were developed to input the Leidenfrost temperature limit in the calculation and to estimate the desired parameters. The investigation reveals that wall temperature is the most important parameter that significantly affects spray development after impingement, droplet size distribution, wall film formation and droplet evaporation. Increasing the wall temperature leads to longer spray front projection length, smaller droplet size, faster droplet evaporation and smaller film thickness, which are preconditions for urea crystallization reduction. The numerical model and parameters were validated by comparing with experimental data. [ABSTRACT FROM AUTHOR]

Using cardiac MRI as a gold standard, the presence of a flail mitral leaflet or a wall-impinging mitral regurgitant jet on transthoracic echocardiography were associated with severe mitral regurgitation, but not diagnostic of it. [ABSTRACT FROM AUTHOR]

The combustion of wall-impinging diesel spray of heavy-duty diesel engines deteriorates combustion quality under cold-start conditions, making it difficult to control soot emissions. To investigate the causes of soot increase in the combustion of wall-impinging spray at low temperature and low speed starting conditions, the effect of the starting fuel mass on the soot formation and oxidation process was analyzed using a multidimensional computational fluid dynamics (CFD) model. The results show that the diesel spray is guided by the piston wall and the limited space, the spray impinged on the wall and the vapor-phase fuel flowed in the spray interaction zone. Thus, the soot mainly accumulates in the spray interaction zone, the region near the cylinder head and the bowl wall in the combustion chamber bowl. The soot from the vapor of deposited fuel film in the piston bowl wall and near wall region accumulates continuously in the after combustion stage, becoming the main source of soot emissions at the time of exhaust valve opening (EVO). Increasing the mass of starting fuel raises the mass of the rich mixture and wall-impinging fuel, which enhances the mismatch between fuel and air, resulting in higher soot generation, while soot is more difficult to be completely oxidized by OH radicals, and ultimately soot emissions increase significantly. It can be deduced that the engine-optimized injection strategy may mitigate the increase in soot emissions at high start-up fuel injection conditions. [Display omitted] • Soot generation mechanism for wall-impinging spray is revealed at low temperature. • Soot in the spray interaction zone is first generated and oxidized during combustion. • Soot formed by the fuel film vapor is the main source of soot emission. • Higher fuel injection mass increases the mass of rich mixture and deposited fuel film. • High starting fuel mass hinders the oxidation process of soot by OH radicals. [ABSTRACT FROM AUTHOR]

The DI (Direct Injection) in SI (Spark Ignition) engines is rapidly developing and seems very attractive offering the possibility of multi-mode operation, homogeneous and stratified charge, with valuable benefits respect to conventional PFI (Port Fuel Injection). One of the major drawbacks of the GDI-fueled engine is the impingement of liquid fuel on the combustion chamber walls that generally produces an increasing of HC emissions and detrimental effects on the combustion process, like soot formation in the wall guided engines due to the diffusive combustion of fuel film deposits on the piston head. This paper investigates the structure of gasoline spray-wall interaction generated by a single-hole injector for GDI engines in an optically-accessible quiescent vessel. The axially-disposed hole diameter is 0.200 mm with a L/d ratio of 1.0 while the injection pressure and the wall temperature varied in the range of 10.0–20.0 MPa and ambient to 300 °C, respectively. Injection duration of 1.0 ms was investigated and the nozzle tip-wall distance was 22.5 mm. Optical investigations were carried out at atmospheric backpressure by an in-line schlieren optical setup using a LED source while the cycle-resolved images of the evolving impact were captured by a C-Mos high-speed camera with a time resolution of 80 μs and a window size of 640 × 464 pixels. The optic-geometrical setup realized a spatial resolution of 0.039 mm/pixel. The images were treated by a digital processing software for background subtraction and both liquid and vapor contour extractions. The spatial and temporal evolution of the liquid and vapor phases as a function of the wall temperature is described for the different operative conditions. [ABSTRACT FROM AUTHOR]

This study presents a joint experimental and numerical investigation of a spray used in selective catalytic NOx reduction (SCR) after-treatment systems for Diesel engine exhaust gases. The focus lies on the impingement conditions and distribution and mixing mechanisms of the spray in cross-flowing exhaust gases. These aspects are vital to system performance but still not well described. A pressure-driven SCR injector is characterized in an optically accessible flow test rig at different temperatures and mass flow rates representative of Diesel engine exhaust gas conditions by means of Mie scattering and Phase Doppler Anemometry (PDA). The effects of cross-flow velocity and temperature on spray structure, droplet size and velocity distributions are assessed resulting in a comprehensive characterization of the spray. Results show that the dense spray core, with droplets up to 200 μm, only moderately reduces in density as smaller droplets are entrained at high exhaust flows. Wall impingement conditions however vary substantially as impingement angles are shallower at higher cross-flow velocities. A detailed assessment of the numerical model is presented and validation is carried out at different measurement locations of interest. The predicted droplet size distributions and velocities follow the observed trends and impingement angles as well as spray film areas on the channel floor are also in agreement with the experimental data. The validated model is subsequently used to numerically study the mixing dynamics. The findings suggest that at low cross-flow conditions two counter-rotating kidney vortices are formed which entrain reflected droplets of the spray impinging on the channel floor, which leads to improved mixing. Vapor concentrations increase close to the side walls and reflected droplets lead to film-formation on the side walls. At higher cross-flow velocities, vortex formation is not evident and spray-wall interaction is less pronounced – impairing mixing and leading to a reduction in concentration uniformity at down-stream locations. Film formation and high vapor concentrations are restricted to the bottom channel centerline. [ABSTRACT FROM AUTHOR]

The main objective of this study is to get insight into the dynamic behavior of viscoplastic drop in impingement process in which the Capillary number is greater than one. In numerical analysis, Volume Of Fluid (VOF) approach was used for capturing the liquid-gas interface. Two different drop shapes (spherical and tear shapes) were used to investigate the drop morphology in an impingement process. According to the results, the numerical results concerning the tear shape drop showed proper agreement with experimental reports (mean deviation of 16 %) in different impact velocities. The flow field was discussed during the impact process in terms of its effect on apparent viscosity and spreading length. Influence of contact angle, consistency, power law index, and surface tension variations on spreading parameter (ratio of contact diameter on the substrate to equivalent initial drop diameter) were investigated. Furthermore, three different rheological models (consisting of Herschel-Bulkley, Casson, and Robertson-Stiff) were employed to study the effects of rheological models on simulation outcomes.

A comparative study of effect of different biodiesel–diesel blends (B5, B10, B15, B20, B25, B50 and B100) on injection, spray, combustion, performance, and emissions of a direct injection diesel engine at constant speed (1500 rpm) was carried out. The penetration distance increased with increase in percentage of biodiesel in diesel due to enhanced in-line fuel pressure. The simulation results indicate the spray penetration with biodiesel–diesel blend up to B15 does not lead to wall impingement but B20 is to be a critical limit of wall impingement (within uncertainty ±1.3%). However, it is observed clearly from the simulation results that probability of wall impingement is more with higher blends (B25, B50 and B100). The ignition delay period decreased with all biodiesel blends due to higher cetane number resulting in less rate of pressure rise and the smooth engine running operation. The engine torque does not change significantly with biodiesel–diesel blends up to 20% (B20). However, the torque reduction is about 2.7% with B100 at the rated load. Carbon monoxide (CO), hydrocarbon (HC) and smoke emissions decreased with all biodiesel–diesel blends. However, oxides of nitrogen (NOx) emission increased in the range of 1.4–22.8% with all biodiesel–diesel blends at rated load due to oxygenated fuel, automatic advance in dynamic injection timing (DIT), higher penetration and higher in-cylinder temperature. A notable conclusion emerged from this study is the optimum biodiesel–diesel blend based on no wall impingement (B15: 0% and B20 ±1.3% uncertainty limit) and increase in NOx emission (B15: 4.1% and B20: 15.6%) in a conventional (unmodified) diesel engine is up to B15. [ABSTRACT FROM AUTHOR]

Background: Anatomic placement of the bone tunnel reportedly reduces impingement of the graft with the intercondylar roof, but as a trade-off, the risk of impingement with the lateral wall of the intercondylar notch would increase instead in anatomic doublebundle anterior cruciate ligament (ACL) reconstruction. Purpose: The 2 grafts for the anteromedial bundle (AMB) and posterolateral bundle (PLB) were separately analyzed for the frequency of and risk factors for graft impingement on the wall of the intercondylar notch. Study Design: Case control study; Level of evidence, 3. Methods: A total of 51 patients (53 knees) who underwent primary anatomic double-bundle ACL reconstruction were enrolled. Based on the graft orientation plane reconstructed with 3-dimensional imaging software, graft-wall impingement was defined as overlap between the lateral wall of the notch and the line connecting each center of the intra-articular apertures of the femoral and tibial bone tunnels. The rate of wall impingement was assessed for each bundle. Parameters for bone tunnel positioning in the femur and tibia, notch width index, and knee joint rotation angle were compared between patients with and without wall impingement. The most important risk factors for wall impingement were assessed by logistic regression analysis. Results: Wall impingement for the AMB was observed in 22 knees (42%), whereas no patients exhibited wall impingement for the PLB. Regarding femoral bone tunnel positioning according to the quadrant method, the AMB bone tunnel was placed significantly higher in impingement-positive patients than in impingement-negative patients (P = .03). Regarding tibial tunnel positioning, the tunnel was placed significantly more anteriorly (P = .02) and laterally (P = .02) in the impingement-positive group than in the impingement-negative group. Bone tunnels positioned 48% to 50% from the medial border of the tibia demonstrated a 100% incidence of wall impingement. Based on logistic regression analysis, lateral deviation of the AMB tibial bone tunnel was significantly associated with wall impingement (odds ratio, 1.403; P = .048). Conclusion: The tibial bone tunnel position in the coronal orientation was most likely associated with wall impingement. Considering that tibial bone tunnels are generally created with the knee in 90° of flexion and move laterally as the knee extends because of screw-home movement, the AMB bone tunnel for the tibia should be positioned as medially as possible within its footprint to minimize the risk of wall impingement after anatomic double-bundle ACL reconstruction. [ABSTRACT FROM AUTHOR]

Under certain conditions diesel jet wall impingement results in triangular (polygonal) splashing shapes. This process has been found to be almost independent of injection pressure, injection frequency or of the injection duration. The triangular splashing shapes are observed at a given transition time after diesel jet wall contact. This time depends on the distance from the wall and on the injection pressure (jet velocity). This triangular splashing process is dependent on the distance from the wall, and does not correspond to a typical hydraulic jump process. The wall jet created after jet impingement along the solid wall is not responsible for triangular splashing. The process investigated depends on the degree of the diesel jet development and is characterized by impingement of the jet core on the wall only. A hypothesis of a non-homogeneous jet core has been formulated and verified to explain triangular splashing regions. For very small distances between nozzle and wall, the resulting splashing may be observed as a star-like three-jet structure. These jets, rebounding in three pre-dominating directions, will spread the preliminary circular splashing (just after wall contact of the primary jet), rendering the splashing geometry more and more triangular in shape until the transition time occurs. [ABSTRACT FROM AUTHOR]

This study investigates the spray characteristics before and after wall impingingment of gasoline spray in suction air flow. For this study, a rectangular model intake port was made of acrylic glass, and suction air was generated by using the forced air blower contrariwise. The injector for this study was a pintle-type port gasoline injector in which an air-assist adaptor is installed to supply assisted air. A PDPA system was employed to simultaneously measure the size and velocity of droplets near the wall. Measured droplets are divided into 'pre-impinging droplets' with positive normal velocity and 'post-impinging droplets' were negative normal velocity for the suction flow. The velocities, size distributions and Sauter mean diameter (SMD) of pre- and post-impinging droplets for varions injection angles and air-assists are comparatively analyzed. [ABSTRACT FROM AUTHOR]

• Droplet diameter and velocity along different splashing directions were analyzed. • The velocity after impingement determines the secondary-breakup droplets location. • After impingement, the ligaments at tip tend to breakup into large droplets. Microscopic characteristics of the impinging spray have a significant effect on atomization and pollutant emissions. Therefore, understanding the droplet behavior of the impinging spray comprehensively is essential to evaluate the spray atomization characteristics. However, in experiments, the size and distribution of droplets are hardly investigated in direct-injection spark-ignition (DISI) engines because of the high droplet density during the fuel injection period. In this paper, a spray slicer was adopted to cut the dense spray into thin flake with the objective of observing discrete droplets. And the particle image analysis (PIA) technique was used to detect droplet behaviors at different locations under various injection pressures of 10, 20, and 30 MPa. The results showed that the number density and velocity of droplets at the spray tip gradually decreased along the direction of spray development. The droplet away from the wall has a larger Y component of velocity (V y). Furthermore, with an increase in injection pressure, the droplet velocity at the spray tip increased dramatically, and the atomization was greatly improved. Besides, sauter mean diameter (SMD) significantly declined at the upstream. However, Weber number (We) was almost the same at the fixed downstream locations under all injection pressures. Finally, We distribution of droplets concentrated at significantly smaller values under the fixed pressure. With an increase in injection pressure, We of droplets distributed near a large value range at all fixed locations. [ABSTRACT FROM AUTHOR]

• SMD and mean velocity decrease with spray development owing to the better atomization and kinetic energy loss. • Md increases with spray development owing to better dispersion. • The periphery location is a special one with best atomization and lowest velocity but moderate dispersion. • High injection pressure increases velocity and Md but decreases SMD at a certain degree. Wall-impingement is a serious problem for engine research owing to the possible source of hydrocarbons and soot emission. Therefore, impinging spray becomes the hotpot for investigation, especially for the microscopic characteristics. Droplet behaviors are significantly important to evaluate the atomization for predicting the impingement phenomena, such as stick, spread or splash. Many studies on it for both gasoline and diesel engines were published. However, these researches failed to capture the droplet behaviors clearly in the dense region owing to the overlap of the droplets. Only periphery or far field of the spray was tested. Therefore, a special cone structure named "spray slicer" was designed to cut the spray before observation with the consideration of good observation and less effect on droplet velocity. The experiment was conducted in a constant volume chamber under increased injection pressures between 10 and 30 MPa. Heptane was used as the surrogate fuel injected by a mini-sac injector with a single hole. Microscopic behaviors were recorded by particle image analysis (PIA) method to obtain the droplets size, velocity and minimum distance (Md). Results showed that microscopic behaviors can be observed clearly at different locations. Sauter mean diameter (SMD) and mean velocity decrease with spray development, and the smallest values occur at the periphery. Md increases with spray development owing to better dispersion. Moreover, high injection pressure decreases the droplet size but increases the velocity and Md at a certain degree. [ABSTRACT FROM AUTHOR]

• Mie scattering fails to capture the small size droplets. • The droplets impacting on the wall is the main reason for adhesion increase AEOI. • Most droplets impinging to the wall locate in the first quadrant AEOI. • With spray development, Md firstly decreases then increases with better dispersion. Many investigations on droplet behaviors during the injection were published. However, studies after the end of injection (AEOI) were seldom reported. Owing to the fuel adhesion on the wall still increases even AEOI, it is significantly important to observe the droplet behaviors for understanding the mechanisms. In this study, bottom view of fuel adhesion and side view of impinging spray were recorded through refractive index matching (RIM) method and Mie scattering observation, respectively. Morphologies of the fuel adhesion with impinging spray were shown, suggesting that even AEOI, fuel adhesion still increases on the wall. The incoming droplets in the air is supposed to be the main reason for it, although the fuel droplets were difficult to be detected through Mie scattering images. Therefore, quantitative measurement for fuel droplet was conducted by particle image analysis (PIA) technique. The microscopic behaviors of fuel droplets were obtained at 3, 5, 10 and 20 ms ASOI. Results showed that due to the small size of the droplets, Mie scattering fails to capture small droplets moving in the air AEOI. However, these small-size droplets really exit and still move towards the wall until impacting on it, which proves that after injection, droplets in the air could adhere on the wall is the main reason for adhesion increase. Furthermore, the droplets size, velocity and minimum distance distributions at different locations with different timings ASOI were analyzed in detail. [ABSTRACT FROM AUTHOR]

• Fuel adhesion firstly evaporates from periphery, then the "hollow" occurs and develops. • "Hollow" facilitates the fuel evaporation and deteriorates the uniformity of the fuel adhesion. • The fuel adhesion mass and area decrease with enhanced injecting pressure but increases with enhanced ambient pressure. • The fuel adhesion lifetime is shortened by increasing injection pressure and it extends with an increase in ambient pressure. In direct-injection spark-ignition (DISI) engines, spray-wall impingement affects the mixture formation as well as combustion and exhaust emissions, making it difficult to satisfy the regulation of particle number (PN) in the future standards. In order to understand the mechanisms deeply, not only the formation but the evaporation characteristics of fuel adhesion should be investigated in detail. In this study, the fuel adhesion thickness was measured using the refractive index matching (RIM) method, then mass, area and thickness of the fuel adhesion were calculated. The evaporation evolution of fuel adhesion on the wall was discussed. Moreover, the lifetime of fuel adhesion was compared at the fixed conditions. The results showed fuel adhesion firstly evaporates from periphery, then the "hollow" occurs and develops, which facilitates the fuel evaporation. The increased injection pressure favors the droplets evaporation owing to the better atomization, leading to the decreased fuel adhesion mass and area on the wall. However, due to the strong momentum exchange between fuel droplets and air, the increased ambient pressure increases the fuel adhesion mass and area on the wall. Moreover, high injection pressure shortens the fuel adhesion lifetime by increasing evaporation rate, but high ambient pressure prolongs it due to the liquid/vapor phase changing. [ABSTRACT FROM AUTHOR]