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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]

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]

Direct injection is an attractive technology for improving fuel economy and engine performance in gasoline engines. However, the adhered fuel formed on the piston surface has significant influence on the combustion efficiency and emissions. To obtain a better understanding of fuel adhesion, this work involved investigation of the spray and impingement on a flat wall through a mini-sac injector with a single hole. Different impingement distances and injection pressures were investigated. The evolution of the impinging spray was obtained by the Mie scattering method. The refractive index matching method was applied to measure fuel adhesion. The mass, area, and thickness of adhesion under different conditions were compared. The experimental results show that the fuel adhesion on the wall increases significantly with a large impingement distance. Moreover, the maximum thickness increases and the thickness uniformity of the fuel adhesion declines under a large impingement distance condition. [ABSTRACT FROM AUTHOR]

• Cross-flow/ wall-impingement effects on fuel adhesion studied with split injection. • Fuel adhesion area decline rate rises with cross-flow velocity, stabilizing after 20 m/s. • Increased cross-flow velocity leads to a reduction in fuel adhesion thickness. • Fuel adhesion thickness also decreases with increasing wall-impingement distance. • Higher cross-flow velocity increases fuel adhesion mass reduction rate in later stages. In direct-injection spark ignition (DISI) engines, high-pressure fuel injectors introduce fuel into the cylinder, causing the spray to come into contact with and adhere to the cylinder wall; this is known as fuel adhesion. Over time, fuel adhesion contributes to carbon deposition on the cylinder wall, which affects its thermal conductivity and consequently diminishes engine combustion efficiency. This study investigates the influence of different impingement distances and cross-flow velocities on fuel adhesion under the triple injection strategy. The fuel adhesion propagation and side-view spray are measured using refractive index matching (RIM) and Mie scattering, respectively. The findings demonstrate that high cross-flow velocity promotes the fuel adhesion shape to be elongated strips. In the early stage, the growth rate of the fuel adhesion area increases with an increase in cross-flow velocity. In the later stage, the decrease rate in the fuel adhesion area initially increases with an increase in the cross-flow velocity; however, when the critical velocity threshold (20 m/s) is exceeded, the decrease rate in the fuel adhesion area tends to stabilize. The average fuel adhesion thickness then accordingly decreases with the increase in the cross-flow velocity and impingement distance in the later stage. In addition, the cross-flow promotes the volatilization of spray and fuel adhesion, thereby decreasing the fuel adhesion mass over time. In the context of carbon neutrality, this study underscores the importance of optimizing fuel injection conditions to reduce emissions and fuel consumption. [ABSTRACT FROM AUTHOR]

Post fuel injection in the expansion stroke is used for diesel particulate filter regeneration; however, fuel spray impinges on the cylinder liner due to the low temperature and pressure conditions. Fuel adhesion and fuel flowing down across the cylinder liner, the so-called "wall-flow," was observed by high-speed video images, and this adhesion is a cause of diesel engine lubricant oil dilution and the deterioration of fuel consumption in diesel engines. In this article, the fuel adhesion and the wall-flow of post diesel fuel injections were investigated with a high pressure-temperature constant volume optical chamber. The in-cylinder temperatures and pressures at 30, 60, and 90 °CA ATDCs, conditions commonly employed in post fuel injection timings, were measured by an actual engine, and similar conditions were created in the constant volume chamber by the combustion of a pre-mixed gas of ethylene, oxygen, and nitrogen. Fuel masses of 0.6, 1.1, and 1.7mg per hole were injected at each ATDC setting. The weight of the adhered fuel on the wall and the fuel in the piston-cylinder crevice were measured by precision balance, and the liquid--vapor phases in the spray were observed by Mie scattering and shadowgraph methods. To measure the thickness of the adhered fuel on the cylinder wall, the laser-induced fluorescence method was employed. The results show that the fuel spray penetration and adhesion on the cylinder wall were different in the test conditions investigated here. 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. A thin and widely spread out fuel film is formed on the cylinder wall; however, no wall-flow could be confirmed by the high-speed video images. With late post fuel injections, the strong penetration of liquid fuel reaches the cylinder wall, and a thick and widely spread out fuel film was formed on the cylinder wall and the wall-flow phenomenon was observed here. However, the quantity of fuel involved in the wall-flow was smaller than that of the fuel adhering to the cylinder wall. The effects of in-cylinder pressure and temperature on the fuel adhesion on the cylinder wall were investigated. With the increase in pressure and temperature, the quantity of adhering fuel was reduced, suggesting that the boost pressure increase by turbo charging and a higher engine load is effective to reduce fuel adhesion. Furthermore, the effects of multiple post fuel injections on fuel adhesion to the cylinder wall were investigated, maintaining the total fuel injection amounts. With increases in the number of fuel injections, the total percentage of adhering post fuel on the cylinder wall was reduced. In the multiple fuel injections, it was observed that fuel motion takes place during the spray pass after the first and second fuel injections and that the penetration length of the second and third fuel sprays increases [ABSTRACT FROM AUTHOR]

• Effect of injection strategies on fuel adhesion are investigated with cross-flow. • The cross-flow can promote the diffusion and evaporation of fuel adhesion. • Triple injection decreases the fuel adhesion characteristics in cross-flow field. • Deformation coefficient I d is proposed to evaluate the distortion of fuel adhesion. The flat-wall wetting phenomenon is inevitable because of the smaller cylinder volume and higher injection pressure inside direct-injection spark ignition (DISI) engines. The fuel adhesion phenomenon after wall impingement negatively affects the fuel spray mixture formation, the fuel consumption, and the pollutant emissions. In this study, the effects of different fuel injection strategies on the wall-impingement behavior were compared under static flow and cross-flow field conditions. The refractive index matching (RIM) method and high-speed video (HSV) camera were adopted to measure the propagation of fuel adhesion and the spray structure of the vertical plane, respectively. Meanwhile, a dimensionless parameter named "deformation coefficient I d ," which is defined as the fuel adhesion length divided by the width, is proposed to evaluate the degree of distortion of the fuel adhesion. Therefore, when I d approaches 1, the fuel adhesion shape approaches a circle. The results show that the cross-flow promotes the diffusion of the fuel spray, which leads to an increase in the fuel adhesion area. The fuel adhesion shape is similar to that of a slender strip under cross-flow field conditions, but almost maintains a circle under static flow field conditions. The cross-flow decreased the average fuel adhesion thickness. Meanwhile, the cross-flow also promotes the evaporation of the adhered fuel on a flat-wall, which leads to a reduction in the fuel adhesion area and mass with time. Additionally, it was found that triple injection can decrease the fuel adhesion thickness, area, and mass ratio under cross-flow field conditions. To achieve carbon neutrality, optimizing fuel injection strategies to reduce emissions is one of the primary purposes of this study. [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]