Vapor Phase Penetration Research Articles

Effect of sintering and infiltration conditions on nanoscale dual network SiO2/polymethyl metacrylate composites mimicking human enamel

ObjectiveThe aim of this study was to achieve facile sintering conditions and rapid penetration of organic substances into the structure of sintered silica network on the nano-scale in order to prepare polymer infiltrated ceramic network mimicking human enamel. MethodsStepwise temperature programming (stepwise isothermal firing) was used to create a cohesive ceramic network containing interconnected pores, which is essential to provide polymer/ceramic dual networks. Liquid phase self-penetration, ultrasonic irradiation assisted liquid phase penetration and vapor phase penetration routes were used to infiltrate methyl methacrylate monomers and benzoyl peroxide reagent into the porous silica blocks. ResultsThe use of stepwise isothermal firing route, in comparison with high temperature sintering methods, significantly reduces the time and temperature required for the preliminary preparation of the SiO2 samples and reaching the appropriate interconnected porous structure. The most appropriate method for monomer and oxidant reagents infiltration is to use liquid phase infiltration assisted by ultrasound irradiation of pre-sintered nano-silica blocks. It was found that the amount of infiltrated monomer and oxidizing agent, degree of conversion of the monomer to the polymer and surface hardness of the samples strongly depend on the infiltration route. Clinical significanceThe use of inexpensive silica nanoparticles and low temperature sintering and the use of ultrasound waves to quickly and effectively penetrate methyl methacrylate monomers and increase the polymerization efficiency lead to the preparation of composites with a transparent appearance and mechanical properties similar to human tooth enamel.

Numerical and Experimental Investigations on the Ignition Behavior of OME

On the path towards climate-neutral future mobility, the usage of synthetic fuels derived from renewable power sources, so-called e-fuels, will be necessary. Oxygenated e-fuels, which contain oxygen in their chemical structure, not only have the potential to realize a climate-neutral powertrain, but also to burn more cleanly in terms of soot formation. Polyoxymethylene dimethyl ethers (PODE or OMEs) are a frequently discussed representative of such combustibles. However, to operate compression ignition engines with these fuels achieving maximum efficiency and minimum emissions, the physical-chemical behavior of OMEs needs to be understood and quantified. Especially the detailed characterization of physical and chemical properties of the spray is of utmost importance for the optimization of the injection and the mixture formation process. The presented work aimed to develop a comprehensive CFD model to specify the differences between OMEs and dodecane, which served as a reference diesel-like fuel, with regards to spray atomization, mixing and auto-ignition for single- and multi-injection patterns. The simulation results were validated against experimental data from a high-temperature and high-pressure combustion vessel. The sprays’ liquid and vapor phase penetration were measured with Mie-scattering and schlieren-imaging as well as diffuse back illumination and Rayleigh-scattering for both fuels. To characterize the ignition process and the flame propagation, measurements of the OH* chemiluminescence of the flame were carried out. Significant differences in the ignition behavior between OMEs and dodecane could be identified in both experiments and CFD simulations. Liquid penetration as well as flame lift-off length are shown to be consistently longer for OMEs. Zones of high reaction activity differ substantially for the two fuels: Along the spray center axis for OMEs and at the shear boundary layers of fuel and ambient air for dodecane. Additionally, the transient behavior of high temperature reactions for OME is predicted to be much faster.

Experimental Research on the Macroscopic and Microscopic Spray Characteristics of Diesel-PODE3-4 Blends

Polyoxymethylene dimethyl ether (PODE) is a low-viscosity oxygenated fuel that can improve the volatility of blended fuels. In this work, the macroscopic and microscopic spray characteristics of diesel-PODE3-4 under different ambient temperatures and injection pressures (IP) are studied. The studied blends consisted of pure diesel (P0), two diesel blend fuels of 20% (P20) and 50% (P50) by volume fraction of PODE3-4. The Mie scattering and Schlieren imaging techniques are used in the experiment. The results show that with the increase in IP, the vapor phase penetration distance and the average cone angle of the three fuels increased, and the Sauter mean diameter (SMD) of the three fuels decreased. When the ambient temperature increased, the vapor phase projection area and the average vapor phase cone angle of P20 and P50 increased, and the SMD decreased, but the vapor phase projection area of pure diesel did not change significantly. The results indicate that the blended fuel with PODE3-4 has better spray characteristics than P0 at low temperature, and the SMD hierarchy between the three fuels is P0 > P20 > P50. Through the visualization experiment, it is helpful to further understand the evaporation characteristics of different fuel properties and develop appropriate alternative diesel fuel.

Gasoline spray characteristics using a high pressure common rail diesel injection system by the method of laser induced exciplex fluorescence

The liquid and vapor phases of gasoline sprays were investigated using a common rail diesel injection system in a constant volume vessel by laser induced exciplex fluorescence (LIEF) and compared with diesel sprays. The effects of injection pressure and ambient pressure on gasoline sprays were measured under evaporating conditions. The results reveal that: the liquid phase penetration has a little change as the fuel is injected, while the vapor phase penetration increases constantly with obvious branch-like structures generated at the downstream vapor phase. The spray volume and mass of entrained gas both increase roughly linearly versus the mass of injected fuel. Compared with diesel sprays in similar conditions, gasoline sprays display a significantly shorter liquid penetration, while a smaller difference between the vapor penetration lengths of gasoline and diesel sprays is observed. The maximum equivalence ratio of gasoline sprays is still more than 2 at selected conditions. As the ambient pressure increases, the penetration lengths of liquid and vapor phases both reduce, and the mean equivalence ratio also decreases with a drop of spray volume. Conversely, the mass of entrained gas rises continually. With the increase of injection pressure, the liquid phase penetration length maintains almost no change. However, the vapor penetration length shows a declined trend during the injection pressure rise at iso-injected fuel mass condition. The spray volume and mass of entrained gas give a slight reduction when the injection pressure enhances. Oppositely, the mean equivalence ratio presents an increased tendency with similar mass of injected fuel.

Study of evaporative diesel spray interaction in multiple injections using optical diagnostics

Internal combustion engines have witnessed an ever increasing stringency in emission limits and fuel economy regulations that has continuously provoked researchers to develop complex strategies that enables engines to cope with these standards. Optical techniques have been a viable method in the study of thermal processes occurring inside internal combustion engines and provides researchers with a solid understanding of the heat and mass transfer taking place. In particular, the current study utilizes two optical techniques, diffused back illumination and schlieren imaging, to visualize the spray behavior in multiple injection strategies of evaporative diesel sprays. A novel method has been developed in order to couple the two optical techniques to visualize both liquid and vapor phases of either pilot-main and main-post injections. The influence of the auxiliary injections on the main, and vice versa, in terms of spray segmentation and spray development has been studied for two different pilot/post quantities and four hydraulic dwell times under two different chamber conditions. The spray development displayed no effect of pilot quantity and dwell time on the liquid length of the second injection. On the other hand, a more pronoun effect on the vapor phase penetration and spreading angle was evidenced by the pilot injection where the main injection has penetrated farther with a higher spreading angle as compared to the case with a single injection event. The understanding of multiple injection is thus fundamental for the improvement of thermal processes in Internal Combustion Engines.

Spray penetration, combustion, and soot formation characteristics of the ECN Spray C and Spray D injectors in multiple combustion facilities

In a collaborative effort to identify key aspects of heavy-duty diesel injector behavior, the Engine Combustion Network (ECN) Spray C and Spray D injectors were characterized in three independent research laboratories using constant volume pre-burn vessels and a heated constant-pressure vessel. This work reports on experiments with nominally identical injectors used in different optically accessible combustion chambers, where one of the injectors was designed intentionally to promote cavitation. Optical diagnostic techniques specifically targeted liquid- and vapor-phase penetration, combustion indicators, and sooting behavior over a large range of ambient temperatures—from 850 K to 1100 K. Because the large-orifice injectors employed in this work result in flame lengths that extend well beyond the optical diagnostics’ field-of-view, a novel method using a characteristic volume is proposed for quantitative comparison of soot under such conditions. Further, the viability of extrapolating these measurements downstream is considered. The results reported in this publication explain trends and unique characteristics of the two different injectors over a range of conditions and serve as calibration targets for numerical efforts within the ECN consortium and beyond. Building on agreement for experimental results from different institutions under inert conditions, apparent differences found in combustion indicators and sooting behavior are addressed and explained. Ignition delay and soot onset are correlated and the results demonstrate the sensitivity of soot formation to the major species of the ambient gas (i.e., carbon dioxide, water, and nitrogen in the pre-burn ambient versus nitrogen only in the constant pressure vessel) when holding ambient oxygen volume percent constant.

Experimental and analytical study on liquid and vapor penetration of high-reactivity gasoline using a high-pressure gasoline multi-hole injector

Spray penetration length is an important parameter which is of great interest to both experimentalists and modelers. As it affects engine efficiency and emissions, measurement and prediction of spray penetration can significantly benefit engine optimization under various operating conditions. In this study, penetration length was investigated in a pre-burn constant volume combustion chamber using a gasoline multi-hole injector with high reactivity gasoline-like fuel designed explicitly for gasoline compression ignition (GCI) engines. Diffused back illumination (DBI) and shadowgraph were implemented for liquid and vapor phase penetration measurements, respectively. Different pre-burn gas mixtures are compared to investigate the influence of ambient gas properties on gasoline spray penetration under evaporating conditions. The liquid penetration under the gas composition of higher molecular weight tends to be longer. However, the vapor penetration showed insignificant effect under different gas compositions. Ambient gas temperature and gas composition were found to be an essential parameter for liquid phase penetration. Pressure difference was found to affect the vapor penetration length while its influence on liquid phase steady state penetration length at high ambient gas temperature is marginal. Statistical analysis was performed for both liquid and vapor phase penetration lengths, and a prediction model was developed with good agreement to the data under all test conditions.

Macroscopic non-reacting spray characterization of gasoline compression ignition fuels in a constant volume chamber

Recently, gasoline compression ignition (GCI) engines have become a topic of interest due to its benefits in high thermal efficiency and low emissions. Combustion in GCI engines is highly governed by the fuel stratification which is strongly associated with the spray characteristics like penetration length. Researchers have proposed both theoretical, and regression models for liquid penetration length of diesel and gasoline direct injection (GDI) spray at non-evaporating conditions. However, there are no models for gasoline sprays at elevated ambient gas temperatures, pressures, and injection pressures in literature. This research gap needs to be bridged, as it is crucial for GCI engine technology. In this study, penetration length was investigated using a high-pressure custom-made multi-hole gasoline injector. High reactivity low carbon fuel (RON 77), designed explicitly for GCI engines, and E10 certification fuel (RON 91) were used and compared. Diffused back illumination (DBI) and shadowgraph were implemented for liquid and vapor phase penetration measurement, respectively. It was found that the spray characteristics of high reactivity fuel were similar to E10 certification fuel under non-reacting conditions. Statistical analysis was performed for both liquid and vapor phase penetration lengths, and empirical models were developed with good agreements to the experimental data under high ambient gas pressure and temperature relevant to GCI engine operating conditions using GCI fuels at higher injection pressures. A ‘separation point’ was defined for the liquid phase after which it reaches a steady state, and it was demonstrated to be different from the ‘breakup time’ found in the literature.

Experimental and analytical study on vapor phase and liquid penetration for a high pressure diesel injector

In this study, a macroscopic characterization has been performed on a solenoid diesel injector (2200 bar-8 hole nozzle) under various non-reacting but evaporative conditions. For vapor penetration a two pass Schlieren visualization set up was selected. A high speed camera was used to record high speed images of the injection event to analyze the transient evolution of the vapor phase of the spray. The transient liquid penetration of the spray has been measured via MIE-Scattering imaging technique using a high speed camera as well. Unsteady RANS based CFD Simulations have been performed to simulate the experimental conditions and correlation results are presented. Built-in models from commercial code StarCD have been used to model spray formation which includes submodels for turbulence, nozzle flow, break-up and fuel properties. A novel CAE process using an automation and optimization tool has been used to achieve robust model settings, and the final model prediction are compared with the experimental observation for the injector characterization with respect to the non-reacting spray penetration with change in ambient and injection conditions. The model correlates well with the sensitivities for temperature and injection pressures qualitatively however improvements required to capture the density effects mainly related to the mesh orientation, fixed time step size where further analysis required.

Differences between single and double-pass schlieren imaging on diesel vapor spray characteristics

The use of schlieren imaging at high acquisition rate has been adopted as a standard optical technique for the analysis of vaporizing diesel sprays under engine-like conditions. A single-pass schlieren arrangement is typically used for the study of axially drilled single-orifice nozzles, as vessels with multiple optical accesses regularly allow line of sight visualization. Contrarily, for multi-spray nozzles, measurements are commonly performed through a single optical access, in which case a double-pass arrangement is employed. As a consequence, the light beams pass through the test section twice, increasing the optical sensitivity of the schlieren setup. However, the influence this has on the macroscopic spray characteristics is still unclear. The scope of this study is to analyze the differences in vapor phase penetration and spreading angle measured for the same injection event, through high-speed imaging, for both single and double-pass schlieren configurations. Experiments were carried out with a three hole nozzle with a nominal orifice diameter of 90μm, named Spray B from the Engine Combustion Network, using commercially available diesel fuel and in non-reactive conditions. The impact of different injection pressures, chamber temperatures and densities on the spray captured by each setup was assessed. On the results, vapor phase penetration and spreading angle followed the expected trend found in the literature, for the different boundary conditions tested. Comparing the optical setups, vapor phase penetration and spreading angle results obtained with the double-pass arrangement were marginally higher than those from the single-pass. The deviation was observed throughout all tested conditions. For spray tip penetration, although the discrepancy was approximately constant for different injection pressures and chamber temperature, it increased with increasing density. These results highlight the importance of a proper understanding regarding the limitations of optical diagnostics, in particular for results used in calibration of computational models.

Effects of Nozzle Geometry on the Characteristics of an Evaporating Diesel Spray

The effects of nozzle geometry on diesel spray characteristics were studied in a spray chamber under evaporating conditions using three single-hole nozzles, one cylindrical and two convergent, designated N1 (outlet diameter 140 μm, k-factor 0), N2 (outlet diameter 140 μm, k-factor 2) and N3 (outlet diameter 136 μm, k-factor 2). Spray experiments were performed with each nozzle at two constant gas densities (15 and 30 kg/m3) and an ambient temperature (673 K) at which evaporation occurs, with injection pressures ranging from 800 to 1600 bar. A light absorption and scattering method using visible and UV light was implemented, and shadow images of liquid and vapor phase fuel were recorded with high-speed video cameras. The cylindrical nozzle N1 yielded larger local vapor cone angles than the convergent nozzles N2 and N3 at both gas densities, and the difference became larger as the injection pressure increased. The vapor phase penetration values for nozzle N1 and N3 were quite similar and always lower than those for N2. This is consistent with the impingement measurements, which showed that the momentum flux of nozzle N1 was only slightly greater than that of nozzle N3, while that of nozzle N2 was substantially greater. The vapor volume fractions measured along the spray’s center line were well explained by the one-dimensional transient diesel jet model, indicating that diesel spray vaporization is controlled by turbulent fuel-air mixing.

Experimental study on spray characteristics under ultra-high injection pressure for DISI engines

In order to provide comprehensive information on gasoline spray characteristics under ultra-high fuel injection pressure for direct-injection spark-ignition engines, the macroscopic characteristics of gasoline sprays for both liquid and vapor phases, including overall spray structures, spray tip penetrations, and spray angles, were determined simultaneously via Laser Absorption-Scattering technique under non-vaporizing and vaporizing conditions. Empirical correlations of spray tip penetration for transient gasoline sprays were obtained and compared with those for diesel sprays. Experimental results showed that under non-vaporizing conditions, spray tip penetration was approximately proportional to time. Under vaporizing conditions, the spray plumes were compressed axially and expanded radially; fuel vapor was concentrated in the spray head, while fuel droplets in the tail. Vapor phase spray tip penetration shared similar values and temporal variations with liquid phase but with a subtle and regular difference. In contrast with diesel sprays, gasoline spray penetration of liquid phase showed larger dependence on ambient gas density and smaller dependence on fuel pressure drop through injector. Compared with liquid phase, vapor phase penetration showed a larger growth rate with time and presented a smaller falling slope against ambient gas temperature.

Needle lift profile influence on the vapor phase penetration for a prototype diesel direct acting piezoelectric injector

In this study, Schlieren visualization tests have been performed for a prototype diesel common rail direct-acting piezoelectric injector, to understand the influence of fuel injection rate shaping on the vapor spray development under evaporative and non-reacting conditions. This state of the art injector presents a particular feature that permits full needle lift control through a parameter referred to as piezo stack charge level, enabling various fuel injection rate typologies. A fast camera and a two pass Schlieren visualization setup have been utilized to record high speed images of the injection event and later analyze, through the vapor phase, the transient evolution of the spray. The tests have been performed employing a novel continuous flow test vessel that provides an accurate control of ambient temperature and pressure up to 1000K and 15MPa respectively. The effect of ambient temperature, injection pressure, needle lift and needle lift profile were studied. Data obtained is correlated to previous liquid length and injection rate measurements of the same injector. Results show, as expected for all cases, that instant vapor penetration rate is closely related to instant injection rate. This is confirmed by the injection pressure test results, along with those obtained for the three different piezo stack charge levels, both affecting the vapor penetration in a similar way. Nevertheless, results obtained for the three different charge levels show that the influence of the charge level and the injection pressure differ in the very beginning of the injection event, where the spray development is largely determined by needle lift and not injection pressure. Ambient temperature alone seems not to have and important effect on vapor penetration. Finally, the effects of the needle lift profile in the instant injection rate and vapor penetration are presented, confirming the strong relation between these three parameters, and confirming also that the needle lift plays a determinant role in the spray development, especially at the early stages of the injection process. Both boot and ramp shaped injections proved the ability to strongly influence the vapor penetration rate. In comparison to the square shaped injection, the effect of the ramp shaped injection delays the vapor penetration right from the start of injection while the effect of the boot shaped injection takes considerably longer to become noticeable. From the results, the needle lift control feature has proven to be a very versatile tool for engine designers to control the injection process as desired, opening a new path with plenty of room for improvement.

ENGINE COMBUSTION NETWORK (ECN): CHARACTERIZATION AND COMPARISON OF BOUNDARY CONDITIONS FOR DIFFERENT COMBUSTION VESSELS

The Engine Combustion Network (ECN) is a worldwide group of institutions using combustion vessels and/or performing computational fluid dynamics (CFD) simulation, whose aim is to advance the state of spray and combustion knowledge at engine-relevant conditions. A key activity is the use of spray chamber facilities that operate at high-temperature, high-pressure conditions typical of diesel combustion, which are operated at specific target conditions in order to leverage research capabilities and advanced diagnostics of all ECN participants. The first target condition, called A, has been defined with detailed ambient (900 K, 60 bar, 22.8 kg/m(3), 15% oxygen) and injector (common rail, 1500 bar, KS1.5/86 nozzle, 0.090-mm orifice diameter, n-dodecane, 363 K) conditions. Establishing and improving these experimental boundary conditions in unique facilities throughout the world represents a major step forward in the establishment of high-quality, quantitative data sets for engine spray combustion. This paper is a review of the methodology to characterize and control the ambient and fuel-injector boundary conditions (e.g., temperature, pressure, composition) as offered by six different participating institutions of the ECN, each targeting the Spray A conditions and quantifying experimental uncertainty. Constant-pressure flow (CPF) and constant-volume preburn (CVP) chambers with various ambient gas composition are compared for the first time. Experimental diagnostics include the use of fast-response, radiation-corrected thermocouples for spatially resolved gas and fuel-injector temperature, laser-induced phosphorescence for surface temperature, and high-speed transducers for pressure. With guidance about the uncertainty and variation that exists between facilities, simplified models are then employed to understand how these boundary condition variations may affect aspects of spray combustion. Ambient gas and fuel temperature effects on liquid- and vapor-phase penetration are examined with established one-dimensional models. Chemical kinetics modeling in single- or multi-zone reactors is used to predict the influence of different preburn environments on the major and minor species present in the ambient gas at the start of injection, and their subsequent effect on spray ignition. This review article provides recognition of the challenge in creating well-controlled high-temperature, high-pressure environments, and identifies which boundary condition variations are expected to have the highest impact on spray combustion.

ENGINE COMBUSTION NETWORK: COMPARISON OF SPRAY DEVELOPMENT, VAPORIZATION, AND COMBUSTION IN DIFFERENT COMBUSTION VESSELS

Development and mixing of Diesel sprays are long known to be key factors for combustion and pollutant emissions but the related measurements in a real engine is not an easy task. This fact led researchers to simulate engine conditions in special facilities that allow the use of high-fidelity diagnostics. The Engine Combustion Network (ECN) has focused on overcoming the variability from one institution to the next by testing nominally identical Diesel injectors in four different facilities for the first time, including constant-pressure flow and constant-volume preburn chambers. Liquid- and vapor-phase penetration, ignition delay, and lift-off length measurements are compared with similar experimental setups and processing methodologies. The consistency of the data obtained indicates a good level of repeatability between the test rigs employed, and no deviation of the results can be associated with the facility type. Comparison of liquid length measurements via Mie scattering shows that this diagnostic is sensitive to the orientation of the light source. For more repeatable results between facilities, diffused back-illumination imaging is recommended. A novel image processing method has been employed to detect spray boundaries obtained in high-speed schlieren imaging: the method showed high accuracy and robustness to the different schlieren setups employed by the institutions. High-speed broadband chemiluminescence, as schlieren imaging, shows the onset of cool flame, and moreover when the combustion is stabilized, it provides an important reference to define ignition delay and lift-off length. The methodology put in place by the ECN participants in this work allows an important step forward in two directions. The first is to understand the repeatability related to experimental data in high-pressure, high-temperature environments. The second is to advance the understanding of the different diagnostics applied, thereby providing more quantitative measurements that yield to a more suitable datasets for computational fluid-dynamic model evaluation.