Fuel Film Research Articles

Experimental Study on Macroscopic Spray and Fuel Film Characteristics of E40 in a Constant Volume Chamber

In the modern industrial field, there is a strong emphasis on energy-saving and emission reduction. Increasing the amount of ethanol in ethanol–gasoline blends has the potential to replace fossil fuel gasoline more effectively, improving energy efficiency and lowering emissions. The interaction between liquid fuel film generation on the piston crown and spray impingement in the combustion chamber in the setting of GDI engines has a substantial impact on particle emissions and engine combustion. In this study, 92# gasoline and ethanol by volume are combined to create the ethanol–gasoline blend E40. The spray characteristics and film properties of both gasoline and the intermediate proportion ethanol–gasoline blend E40 were researched utilizing a constant volume combustion platform and the schlieren method and refractive index matching (RIM) approach. The results show that, for 0.1–25 operating conditions, gasoline consistently displays greater macroscopic spray characteristic parameters than E40. This shows that gasoline fuel spray evaporation is superior to E40. Similar results are seen in the analysis of wall-attached fuel films, where the volume and thickness of the gasoline film are less than those of the E40 film under the given operating conditions. In contrast, E40 consistently exhibits stronger macroscopic spray characteristic values than gasoline under the 0.1–150 and 0.4–150 operating conditions, along with lower film thickness and volume. As a result, under these two operating conditions, E40 fuel performs better during spray evaporation.

Experimental study and theoretical analysis on the criterion of boiling of wall film for different fuels

In direct-injection engines, the formation and vaporization of wall-attached fuel film after the spray impingement is the main factor affecting the emissions of hydrocarbon (HC), soot, and other pollutants. In response to this situation, the formation and evolution characteristics of the fuel film formed by a high-pressure spray impingement onto a heated wall were investigated. The change in the fuel film thickness during the evolution process was measured with the refractive index matching (RIM) method for three different fuels. This paper also quantitatively studied the boiling criterion of the micrometer-scale wall film at various film temperatures. The results indicate that there exists a critical film thickness to trigger the boiling phenomenon, which is closely related to the film temperature. According to the theoretical analysis, it is concluded that the critical thickness is essential for the fuel film boiling at the corresponding fuel film temperature. At the same fuel superheat degree, the critical thickness of different fuels highly relies on their physical properties, among which surface tension is the dominant factor, while the effect of saturation temperature and enthalpy of vaporization is relatively weak.

Flame Spread over a Liquid Fuel Film in an Oxygen-Enriched Environment

Flame Spread over a Liquid Fuel Film in an Oxygen-Enriched Environment

Flame Propagation Over a Liquid Fuel Film in Oxygen-Enriched Environment

Flame Propagation Over a Liquid Fuel Film in Oxygen-Enriched Environment

Relationship between wall surface roughness and fuel film evaporation for spray impingement

In this study, formation and evaporation of fuel films on various surface roughness walls were investigated. Iso-octane was injected from multi-hole DISI injector. Injected spray was impinged on an aluminum wall having low or high roughness (Ra = 0.63 μm to 8.30 μm) and fuel film was formed on the wall. Wall surface temperature before fuel spray impingement was controlled by an electric heater (25°C to 130°C). Fuel film behavior with elapsed time under various wall conditions was captured by a high-speed camera. Fuel film spreading area change and evaporation lifetime of the fuel film were obtained from the captured top view image. As a result, it was found that the fuel film spreading area became narrower with an increase of the surface roughness. The evaporation lifetime of fuel film became shorter with an increase of the surface roughness. Therefore, it was considered that heat transfer from the wall to the fuel film increased owing to an increase of a substantial contact area between the wall surface and the fuel film.

Observation of Behavior of Post-injected Fuel Film Using Photochromism Visualization Technique

Observation of Behavior of Post-injected Fuel Film Using Photochromism Visualization Technique

Evaporation of Fuel Film formed by an Impinging GDI Spray on a Hot Wall with High Surface Roughness

Evaporation of Fuel Film formed by an Impinging GDI Spray on a Hot Wall with High Surface Roughness

The Effects of Fuel Film on Soot Formation of GDI Injector using Optical Diagnostics

The Effects of Fuel Film on Soot Formation of GDI Injector using Optical Diagnostics

Deflagration-to-detonation Transition in Stratified Oxygen – Liquid Fuel Film Systems

ABSTRACT Deflagration-to-detonation transition (DDT) in gas (oxygen)–liquid n-heptane film and gas (oxygen)–liquid n-decane film systems is registered experimentally using a fused or exploding wire as a weak ignition source that generates a primary shock wave with a Mach number ranging from 1.02 to 1.6. In a straight smooth-walled channel of rectangular cross section 54 × 24 mm, 3 and 6 m long with one open end, the DDT is obtained at distances 900 to 4000 mm from the ignition source 3 to 1700 ms after ignition. The DDT is obtained for n-heptane and n-decane films 0.2 to 0.7 mm thick, which corresponds to the overall fuel-to-oxygen equivalence ratios of 15 to 40. The registered detonation velocities range from 1400 to 2000 m/s. In several experiments, a high-velocity quasi-stationary deflagration front propagating at an average velocity of 700–1100 m/s is recorded. The structure of this front includes the leading shock wave followed by the reaction zone separated from each other by a time delay of 90 to 190 μs. The results obtained are important for explosion safety and for better understanding of the operation process in the continuous-detonation and pulse-detonation combustors of advanced rocket and air-breathing engines with the supply of liquid fuel in the form of a wall film.

Experimental and numerical investigation of evaporating fuel films in combustion

Fuel films evaporating throughout combustion can cause soot formation in spark-ignited direct-injection (DI) engines. In this work, laser-induced fluorescence (LIF), combustion imaging, 3D computational fluid dynamics (CFD), and a low-dimensional model (LDM) were used to investigate fuel-film evaporation, combustion, and soot formation in an atmospheric-pressure constant-flow facility that serves as a DI model experiment. A six-hole injector laterally injects isooctane doped with toluene as a fluorescent tracer. Most of the fuel evaporates into the preheated air crossflow, but some impinges on a quartz window on the opposite side, forming fuel films. The fuel/air-mixture can be ignited by spark electrodes protruding into the chamber. LIF was used to image the fuel-film thickness at different times after start of injection (aSOI). From that, the film mass and evaporation rate are calculated. The large eddy simulation (LES) CFD employs a Lagrangian treatment for the dispersed phase in combination with models for spray/wall interaction and the wall film. CFD and LIF consistently find that evaporation rates are highest for early times aSOI and remain constant from about 10 ms aSOI. At ambient temperature the evaporation rates from LIF and CFD are almost the same while at elevated temperatures the CFD predicts about a two times higher evaporation rate than measured. LIF, CFD, and LDM reveal a strong dependence of the evaporation rate on the wall temperature, while there is very little influence of combustion and thus convective heat transfer. The simulations show that the fuel-film temperature rapidly reaches the wall temperature that remains approximately constant throughout evaporation. High-speed combustion imaging and CFD show the inception of soot pockets at similar times, close to the evaporating fuel films, and consistent in spatial extent.

Simulation of Liquid Film Spreading on Tip of Spray Injector

The behaviors of fuel films adhering to the tip of a fuel injector for automotive gasoline direct-injection engines was simulated by the computational fluid dynamics. Liquid film adhering to the tip of the fuel injector is a source of carbon deposits; the film spreads on the surfaces of the tip and remains there under certain wetting conditions. The deposit build-up can clog the injector nozzles, which can alter the spray pattern, furthermore, deposits on the tips of injectors are a source of particulate matter (PM) discharged from the engine. In order to prevent air pollution, it is essential to develop a technology to reduce PM. The spread of fuel adhering to the tip of a fuel injector was simulated using the moving particle semi-implicit method, and a previously developed particle/grid hybrid method was used to study the effects of spray plumes. The simulated distribution of the film qualitatively agreed with the measured distribution of carbon deposits. Fuel film formed on the concave and convex wall surfaces. The fuel film and carbon deposits were unevenly distributed in the air flow direction. Investigation of the behaviors of floating droplets around the tip between fuel injections revealed that the droplets were pulled toward the tip wall due to a reverse air flow generated by the fuel plumes ejected by the injector nozzles. These droplets then merged as a part of the fuel film, which spread toward the injection nozzles due to the air flow directed at the nozzles. Some of the film was sucked into the spray plumes and then re-injected into the air region again. The simulated fuel film behaviors on the tip qualitatively agreed with the measured ones. Furthermore, the simulation showed that optimizing the surface shape of the fuel injector tip, particularly the concave portion, is important for reducing particulate matter.

Study on Impinging Ignition and Wall-Attached Fuel Film Combustion Characteristics of Light- to Heavy-Duty Diesel Engines at Low Temperatures

Study on Impinging Ignition and Wall-Attached Fuel Film Combustion Characteristics of Light- to Heavy-Duty Diesel Engines at Low Temperatures

Flame Propagation over a Liquid Fuel Film on a Substrate with Low Thermal Conductivity

Flame Propagation over a Liquid Fuel Film on a Substrate with Low Thermal Conductivity

Measurements of fuel thickness for prefilming atomisers at elevated pressure

This work describes an experimental study of the fuel flows on the prefilmer of an aerospace gas turbine airblast atomiser at elevated pressure. The work identifies the physics leading to contradictory findings within the literature. This concerns an important atomisation boundary condition, whether the thickness of the fuel film on the prefilming surface influences the downstream drop size distribution. Analysis of the experimental data shows that fuel film thickness becomes uncorrelated with the downstream drop size if surface tension forces dominate inertia at the prefilmer tip. Fuel film thickness however provides the initial length scale for primary atomization if fuel inertia exceeds surface tension forces. It is the high inertial conditions that are associated with gas turbine operation, but the low inertial conditions that are readily achievable at laboratory scale through momentum flux scaling. Additionally, a detailed statistical description of the fuel flow has been provided for the atomiser tested. This reveals the importance of upstream hydrodynamic and aerodynamic boundary conditions on the probability of a ligament forming. Surprisingly, operating pressure is shown to have limited effect on the probability of ligament formation, a significant advantage for future modelling of the primary atomization processes.

Wall Temperature Change and Behavior of Fuel Film after Fuel Spray Impingement on Aluminum and Quarts Glass Wall

Wall Temperature Change and Behavior of Fuel Film after Fuel Spray Impingement on Aluminum and Quarts Glass Wall

Behavior of Fuel Film formed by Wall Impingement Spray

Behavior of Fuel Film formed by Wall Impingement Spray

Nozzle tip wetting in gasoline direct injection injector and its link with nozzle internal flow

Fuel film in the gasoline direct injection injector tip, or so-called nozzle tip wetting, has been found to be an important contributor of particle emissions. Attempts have been made to reduce the nozzle tip wetting by optimizing nozzle geometry designs. However, the inherent mechanism of the nozzle tip wetting formation and its link with nozzle internal flow is still unclear yet due to the lack of direct observations. To overcome this insufficiency, the nozzle internal flow and the formation process of the nozzle tip wetting were visualized in the real-scale aluminum nozzles using the X-ray phase-contrast technique. Results showed that the needle bouncing, injection pressure, and hole configuration affect the formation of the nozzle tip wetting, while the influence of needle bouncing is the most critical. A further study was conducted to examine the effect of nozzle counterbore diameter on the nozzle tip wetting. It was found that with an increase in counterbore diameter, the nozzle tip wetting slightly increased first and then decreased sharply after the counterbore diameter exceeded 0.40 mm. The mechanisms of the aforementioned phenomena were discussed in detail, which can contribute to the better understandings and control strategies of nozzle tip wetting.

Dynamics of spray impingement wall film under cold start conditions

Fuel film that adhered on engine walls from spray impingement is considered a primary source of harmful combustion emissions. However, the physics of the wall film formation, propagation, and breakup is not fully understood yet because of its multiphase nature. Existing literature has revealed that the mass transportation within the fuel film takes a wave propagation form. This article aims to identify the dynamics of the wall film during spray impingement via high-speed laser diagnostics. In this work, a single-hole injector was used and the spray impinged onto a stage made of sapphire glass for diagnostics purposes. Iso-octane was used as the fuel and 10% ethanol was blended to dope rhodamine 6G as the fluorescent species for laser excitation. Simultaneous optical measurements, such as laser-induced fluorescence and Mie scattering, are performed to obtain the characteristics of the wall film quantitatively. Various aspects of the wall film, including the frequency of the wave, wave speed, and wave height, are inspected. The impact of fuel temperature and wall temperature under typical cold-start conditions are also studied to investigate the temperature dependence of the wall film dynamics. The research is also intended to provide quantitative experimental data for numerical models for impingement prediction and thus help the process of emission reduction and combustion optimization of internal combustion engines.

Film breakup of tilted impinging spray under various pressure conditions

Fuel film on engine walls caused by spray impingement would dramatically cause engine friction deterioration, incomplete combustion, and significant cycle-to-cycle variations. In a previous work, it has been demonstrated that fuel film would break up via wave entrainment induced by the high-speed coflow. Meanwhile, the film breakup dynamics depend on various boundary conditions, such as injection pressure, ambient pressure, and so on. However, such impact on the wall film formation was not investigated thoroughly in existing literature. This work aims to perform a parameter study to investigate possible means to enhance wave entrainment effect as to reduce the amount of impingement fuel mass. In this study, simultaneous measurements of macroscopic structure and its corresponding footprint of impinging spray are conducted using a single-hole, prototype injector in a constant volume chamber. The macroscopic spray structure was captured by high-speed backlit imaging, and the film was obtained using laser-induced fluorescence under different conditions. The laser-induced fluorescence signal is converted to film thickness following a calibration procedure where laser-induced fluorescence signals from a series of known-thickness film are captured. A mathematical processing method is used to analyze both the dynamic behavior of film thickness and amount of droplet detachment caused by high-speed coflow. It is found that at the leading edge of film waves, a remarkable amount of liquid droplets detaches from the liquid film and the quantity of film mass on the wall decreases during this process. Quantitative analysis is conducted and the mass ratio of detached droplets over residual liquid film is estimated. We hold that the film breakup percentage increases with both ambient and injection pressure due to the enhanced high-speed coflow. Then, variation laws for various boundary conditions are obtained based on the observations.

Experimental Investigation on Effect of Wall Roughness and Lubricant Film on the Adhered Fuel Film of N-Butanol-Diesel Blends after Spray Impingement

The effect of wall roughness with different lubricant film thicknesses on the characteristics of adhered fuel films of diesel-n-butanol blending fuels after spray impingement has been investigated. Four steel plates with different types of roughness (root mean square height-Sq) that were coated with different lubricant film thicknesses (hl) were used as impinged walls. The experimental conditions included dry walls (hl = 0), semi-wetted walls (SWW) with different thin oil films (0 < hl/Sq < 1), and fully wetted walls (FWW) with a thick lubricant film (hl > Sq). The results indicate that the adhered fuel mass ratio (ε) of blended fuel with 25% n-butanol (B25) was higher than that of blended fuel with 15% n-butanol (B15) under the same conditions. ε increased with an increase in Sq on the dry walls, but, under SWW conditions, it decreased with an increase in oil film thickness. The fuel film morphology was almost unaffected by the change in Sq, but the results implied that the roughness parameter-Skewness (Ssk) exerted a greater impact. The mean thickness ha and accumulated diameter Dl of the adhered fuel film increased with an increase in hl, but, under FWW conditions, the effect of the roughness on the adhered film’s features was insignificant.