The transport sector is responsible for about one third of the global CO2 emissions. To align to the net zero emission scenario, the transportation sector needs the implementation of policies aimed to reduce as much as possible the highly emitting transport options and, at the same time, the use of new technologies to reduce the environmental impact of transport methods whose emissions cannot be entirely eliminated. An exploitable solution for the internal combustion engine (ICE), even in the nearest future, would be to use hydrogen as a fuel in these engines. This is supported by the fact that H2-ICE is the only ICE technology currently capable of meeting the standards imposed by the European Union for 2035. Due to the possibility of different injection strategies as well as the variation of in-cylinder back pressure, the comprehensive knowledge of hydrogen injection jet behavior and characteristics is fundamental for improving the combustion process in direct injection H2-ICE. In this context, current study focuses on the characterization of experimental hydrogen jets in terms of mass flow rate and jet morphology under a wide range of engine-like conditions by the use of an injector appropriate for direct injection applications. A measuring system, suitable for gaseous fuels, was used for measuring instantaneous and total flow rates as well as the dynamic behavior of the entire injection system. The spatial and temporal evolution of a highly under-expanded H2 jet was studied by a Z-type schlieren optical setup. H2 fuel was injected into a constant-volume combustion vessel (CVCV) at different injection pressures (up to 50 bar) and ambient back pressures simulating typical engine conditions. Measurements of jet penetrations, jet width, and total areas of the injected gas showed a strong dependence on those parameters.

This work deals with the experimental and numerical investigation of ultra-high pressure gasoline injection against heated walls in order to characterize the fuel evaporation and distribution in gasoline compression ignition combustion chambers. Spray-wall impingement tests have been conducted in a quiescent vessel and recorded by means of the Mie scattering technique. The test conditions have been set in line with those of a reference benched GCI engine, leading to 500 bar and 700 bar for the injection pressure, 298 K, 423 K, 493 K for the wall temperature, 20 mm and 30 mm for the injector-wall distance. The same test matrix has been reproduced by means of CFD three-dimensional simulations using a proper setting of the wall-impingement model and the joint use of CFD-FEM approaches for the vapour-wall heat exchange. The time evolution of the rebound spray has been recorded and then postprocessed leading to the width and the thickness of the cloud. The CFD results are in line with the experimental ones both in terms of the overall time evolution and punctual values, proving a good accuracy of the simulation in predicting the rebound/adhered fuel mass split and the local distribution of the fuel after the impingement. Given the reliability of the simulations, insights on the numerical wall film mass and evaporated mass have been provided in order to clarify the effect of increasing pressure, temperature, and distance.

The current homologation standards in the automotive field impose the manufacturers to develop very efficient and clean engines. Low-Temperature Combustion engines have the potential to simultaneously reduce all the pollutants released while maintaining high efficiency. Among them, in Gasoline Compression Ignition (GCI) combustion technology, multiple injections allow to generate a tailored stratified charge which can auto ignite limiting the rough Pressure Rise Rate (PRR) and heat release rate typical of GCI. Therefore, the three-dimensional local distribution of the mixture becomes the key-point which the engine performance depends on. Due to emphasis on the multi-dimensional and local nature of the mixture formation phenomenon, three-dimensional CFD simulations are a promising and attractive method aiming at the design of the injection event features (timing, pattern, etc.). This paper deals with both experimental and CFD campaign on the evolution of a gasoline spray at ultra high-pressure multiple injection as well as high backpressure, typical of Gasoline Compression Ignition engines. The experimental tests have been conducted on a reference Diesel Common-Rail injector which shots in a constant-volume chamber. The hydraulic behaviour of the injector was characterized by means of the Bosch Tube principle whilst the Mie-scattering technique was used to capture the spray images. The numerical methodology is required to predict the Liquid Length Penetration and the jet morphology features (shape, area). Both experiments and simulations were conducted at different values of injection pressure (350, 500, 700 bar), back pressure (1-8 bar), energizing time (350, 600 & mu;s), according to the operations of a real reference GCI test engine. Furthermore, a dedicated sub-model which takes into consideration the effect of the spray dynamics during the injection transient opening stage has been validated. The importance of this approach when dealing with short energizing time (e.g. 350 & mu;s) is shown. Comparing both the experimental and numerical results, the model has proven to efficiently reproduce the spray penetration and morphology features, also under the hypothesis of injector ballistic phase operations, whose determination is crucial in the early development and sustainability of such combustion concept.

The combustion of fossil-based fuels in ICEs, resulting in a huge amount of greenhouse gases (GHG) and leading to an immense global temperature rise, are the root causes of the more stringent emission legislations to safeguard health and that encourage further investigations on alternative carbon-neutral fuels. In this respect, the hydrogen has been considered as one of the potential clean fuels because of its zero-carbon nature. The current development of hydrogen-based ICEs focuses on the direct injection (DI) strategy as it allows better engine efficiency than the port fuel injection one. The behavior of the fuel jet is a fundamental aspect of the in-cylinder air-fuel mixing ratio, affecting the combustion process, the engine performances, and the pollutants emissions. In the present study, comprehensive investigations on the hydrogen jet behavior, generated by a Compressed Hydrogen Gas (CHG) injector under different operative conditions, were performed. A measuring system, suitable for the gaseous fuels, was used for measuring the flow rate. The fuel jet morphology was studied in a constant volume vessel filled with nitrogen as function of the injection pressure (up to 4.0 MPa) and different backpressure in the vessel, through the measurements of the jet penetrations, total areas, and cone angles showing a strong dependence from the set parameters. The cycle-resolved schlieren imaging technique by a high-speed camera was used to follow the jet spreads while the images were processed by a home-made procedure allowed to identify the contours of the hydrogen jet in the nitrogen gas and hence to measure the main parameters characterizing the jet structure.

Among the most relevant fields of research recently investigated for improving the performance of gasoline direct injection (GDI) engines, there are ultrahigh injection pressures and the flash-boiling phenomenon. Both perform relevant roles in improving the air/fuel mixing process, reducing tailpipe emissions and implementing new combustion methods. When a high-temperature fuel is released into an environment with a pressure lower than the fuel’s saturation pressure, flash boiling occurs. Due to complex two-phase flow dynamics and quick droplet vaporization, flash boiling can significantly modify spray formation. Specifically, if properly controlled, flash boiling produces important benefits for the fuel–air mixture formation, the combustion quality and, in general, for overall engine operation. Flash boiling was broadly investigated for classical injection pressure, but few works concern ultrahigh injection pressure. Here, the investigation of the spray produced by a multihole injector was performed using both experimental imaging techniques and CFD simulations aiming to highlight the combined impact of the injection pressure and the flash boiling occurrence on the spray morphology. The shadowgraph method was employed to observe the spray experimentally. The information gathered allows for assessing the performances of an Eulerian–Lagrangian algorithm purposely developed. Breakup and evaporation models, appropriate for flashing sprays, were implemented in a CFD (Computational Fluid Dynamics) code. The experimental results and the CFD simulations demonstrate a good agreement, demonstrating that through adoption of a flash-boiling breakup model, it is possible to reproduce non-evaporating and superheated sprays while changing few simulation parameters. Finally, the results also show the significance of injection pressure in preventing spray collapse.

Nowadays, in the perspective of a full electric automotive scenario, internal combustion engines can still play a central role in the fulfilment of different needs if the efficiency will be improved, and the tailpipe emission will be further limited. Gasoline Compression Ignition engines can offer a favourable balance between NOx, particulate, operating range. Stable operations are ensured by ultra-high gasoline injection pressure and tailored injection patterns in order to design the most proper local fuel distribution. In this context, engine simulations by means of CFD codes can provide insights on the design of the injection parameters, and emphasis must be placed on the capture of spray-wall impingement behaviour under those non-conventional conditions. This paper aims to analyse the spray-wall impingement behaviour of ultra-high gasoline spray using a combined experimental-CFD approach. The fuel is injected inside a vessel through a single-hole nozzle at GCI-like injection pressure (500-700 bar) against a metal surface. At the test bench, optical measures were performed by means of the Mie-scattering technique in order to capture the impact morphology. Furthermore, some synthetic features of the impact were calculated, namely the thickness and the width of the rebound cloud. In order to focus on the wall film formation mechanism, the tests were conducted at room temperature. Then, the experimental data were used to validate the CFD spray-wall impingement methodology and tuning.

Ultra-high injection pressures, as well as flash-boiling occurrence, are among the most important research fields recently explored for improving Gasoline Direct Injection (GDI) engine performance. Both of them play a key role in the enhancement of the air/fuel mixing process, in the reduction of tailpipe pollutant emissions, as well as in the investigation of new combustion concepts. Injector manufacturers are even more producing devices with ultra-high injection pressures capable of working with flashing sprays. Flash-boiling of fuel sprays occurs when a super-heated fuel is discharged into an environment whose pressure is lower than the saturation pressure of the fuel and can dramatically alter spray formation due to complex two-phase flow effects and rapid droplet vaporization. In GDI engines, typically, it occurs during the injection process when high fuel temperatures make its saturation pressures higher than the in-cylinder one. Flash boiling significantly affects the spray structure and fuel-air mixture formation with, potentially, if spray collapse is avoided (with the consequent risk of spray-wall impingement), positive consequences for the engine performance and pollutant emissions. So, this work proposes a combined experimental and numerical characterization of the spray issued by a multi-hole device to highlight the combined role of the injection pressure (up to 700 bar) and the flash boiling occurrence on the spray morphology. Experimental observations of the spray were performed using the Mie-scattering technique. Collected data allowed to evaluate the capabilities of an Eulerian-Lagrangian code in reproducing the injection processes. CFD models for flashing and non-flashing conditions were developed featuring specific breakup and vaporization models suitable for flashing sprays. The numerical model achieves a pretty good level of agreement with the experimental data, and, in particular, it highlights the importance of injection pressure in avoiding spray collapse.

Supercritical fluid technologies are widely used in various applications ranging from pharmaceutical to food industry, from energy sector to petrochemistry and, recently, also in the internal combustion engine. The main issue associated with bringing water to supercritical conditions is related to irregular heat transfer regimes due to the continuous variations in thermodynamic properties, as the temperature increases. Induction heating systems can be used to achieve these conditions quickly and efficiently. In this study, a novel system designed to heat and pressurize a fluid above its critical condition is presented. The adopted pressurization system consists of common-rail automotive derivation devices, while the heat bringing temperature above the supercritical value is supplied through an induction heating system. For the choice of the proper power of the induction device, a numerical simulation has been carried out. The whole system has been tested with water to demonstrate the ability of the device to reach the supercritical target conditions.

Nowadays, several efforts are being made to design more efficient, cleaner, and economically accessible engines. Spray-wall interactions are strongly related with the fuel–air mixture and emission formation. As such, they are considered as the most important physical processes in engine research. In the present study, the infrared thermography coupled with an inverse heat transfer data reduction is applied to evaluate the wall heat transfer of an iso-octane spray generated by a multi-hole gasoline direct injector (Spray G) impinging on a heated thin foil. The experimental apparatus includes an Invar foil (50μm in thickness) heated by Joule effect and the injector located at 66.66 injector nozzle diameter above the surface. Thermal images of the impinging spray are acquired from the dry side of the foil at several time delays from the start of injection at two different injection pressures (10and 20MPa) and two different wall temperatures (373and 473K). The experimental data are reduced in the dimensionless form in terms of the spray cooling efficiency ξ, which represents the ratio between the spray cooling heat flux and the heat transfer capability of the fluid, by taking into account the area of impact of the spray. Results show a substantial increment of the heat flux and the spray cooling efficiency by increasing the wall temperature. Also, the increment of the injection pressure has an increasing effect on the area of impact, the heat flux, and the efficiency of the spray for both wall temperatures investigated in the experimental campaign. The spray cone angle and the plume jet axis angle were also estimated from the wall heat flux distribution.

Gasoline Direct Injection (GDI) technology has been recognized as an effective way to achieve better engine performance and reduced pollutant emissions. High-pressure injectors are demonstrating many advantages in the applications for GDI engines providing a better fuel atomization, a better mixing with the air, a consequent more efficient combustion and, finally, reduced tailpipe emissions. In this context the present work features a dual experimental-numerical characterization of the jet issued from a multi-hole injector. The numerical model has been developed by means of a Eulerian-Lagrangian CFD code and validated thanks to experimental data collected with schlieren and Mie scattering imaging techniques.

Flash boiling is the sudden change from liquid to vapour phase and in IC engines it typically occurs during the injection process with a gasoline direct injection (GDI) setup and when high fuel temperatures result in saturation pressures higher than the in-cylinder ones. The flash boiling, due to the complex evolution of a multi-phase flow and a rapid droplet vaporisation, promotes spray atomisation and affects significantly the spray structure and fuel–air mixture formation, with consequences for the engine performance and pollutant emissions. Hence, a deep knowledge of such phenomenon is required to improve the combustion process and reduce the pollutant production. The breakup mechanism of a superheated spray is quite different from a regular one, because it features the nucleation and growth of bubbles within liquid droplets. In this paper, an innovative flash-boiling breakup model was embedded in a Eulerian–Lagrangian two-phase solver using OpenFOAM library. The model assigns to the droplets a radial velocity component due to the bubble explosion, making it capable of reconstructing the spray expansion. The code was tested using experimental data of the ECN Spray G injector covering various thermodynamic conditions. The numerical model achieves a good level of agreement with the experimental data and, in particular, it is able to reconstruct the spray collapse. Besides, it provides useful information regarding parameters that are intrinsically difficult to measure experimentally.

New technologies are revolutionizing the automotive market, with innovation reshaping what it means to drive or be driven, as new vehicles are being introduced in the last years. Smart vehicles are forced to integrate various sensors, usually cameras, capable of allowing autonomous functionalities. Cameras, 360° surround-view parking assist systems, and Intelligent Advanced Driver Assistance Systems (ADAS) must be mandatorily installed on vehicles for rules issued by many countries. Those optical sensors can be partially or totally obscured by many environmental factors; thus, these sensors need to be adequately cleaned. The paper presents an experimental methodology to study water sprays used on vehicles under different injection pressure. A schlieren setup was realized and images were acquired with a high-speed C-Mos camera at a rate of 25,000 frames per second (fps) with an image window of 384 × 352 pixels. The camera was equipped with a 90 mm objective, f 1:2.8, resulting in a spatial resolution of 4.70 pixel/mm. The spray was analyzed for different injection pressure making interesting consideration about its behavior.

One of the goals of modern internal combustion engines is the NOx-soot trade-off, and this would be better achieved by a better control of the fuel injection. Moreover, this feature can be also useful for high-performance hydraulic systems. Actual fuel injection technology either allows only the control of the injection time or it is based on very complex mechanical-hydraulic systems, as in the case of piezo-actuators. This work describes the basic steps that brought the authors to the realization of a concept fuel injector based on a Terfenol-D magnetostrictive actuator that could overcome the previous issues, being both simple and controllable. The study provides the design, development, and a feasibility analysis of a magnetostrictive actuator for fuel injection, by providing a basic magneto-static analysis of the actuator, the adaptation of a suitable standard fuel injector, and its experimental testing in a lab environment, with different shapes and amplitude of the reference signal to follow.

The flexibility in managing the air-fuel mixture formation in engines equipped with Gasoline Direct Injection (GDI) has demonstrated being an effective system to pursue the growing demand of energy efficiency and reduction of pollutant emissions. This injection modality improves the spray characteristics in terms of a better atomization of the fuel, finer droplet size and better distribution in the combustion chamber to enhance the combustion efficiency. Nowadays, it is known that very high-pressure injections are adopted in GDI systems to improve the spray atomization and, subsequently, the evaporation processes in the engine combustion chamber. In this study, the investigation of the influence of the pressure on gasoline spatial spread and thermo-dynamic status was carried out for different ambient densities (from 0.2 to 11.50 kg/m3) and gas temperatures (from room to 200 °C) by a hybrid optical setup, shadowgraph and Mie scattering, to acquire in a cycle-resolved mode both the vapor and the liquid phases of the spray. The study was performed in a constant volume chamber (CVC) using a ten-hole GDI injector, 0.10 mm in diameter, with the injection pressure ranging from 40.0 to 100.0 MPa. The influences of the ambient and injection conditions on the characteristic parameters of the jets, such as tip penetration, cone-angle, and fuel spread, were extracted by a customized image-processing procedure developed in C#.

现代柴油发动机的燃烧质量严格依赖于空气-燃料的混合质量,进而取决于雾化过程的质量.空气-燃料混合受到喷射压力、喷孔几何形状和喷油器液力特性的强烈影响.提出了替代传统多孔喷嘴的喷雾概念,并认为是1种可充分增加喷射压力的解决方案,以确保活塞碗中更高、更快的空气-燃料混合,最终目标是提高燃料效率和减少发动机排放.进行了喷雾试验,该喷雾在蒸发和非蒸发条件下通过原型高压空心锥形喷嘴产生,将燃料喷射到恒定容积的燃烧容器中,该容器控制压力和温度达到类似发动机的气体密度,以便测量空间和时间上适合的燃油模式.通过2种光学技术,即纹影(Schlieren)和米氏散射(Mie scattering)表征喷雾演变.纹影考虑了液体和蒸气部分,而米氏散射则考虑液体部分.通过在MATLAB软件中开发的定制程序处理图像,以更好地勾勒出液相和蒸汽雾化区域的轮廓.结果表明,该喷嘴配置能产生均匀和周向分布的精细雾化喷雾,有助于达到更好的空气-燃料混合水平.

ARTICLE INFO Nobody escapes the importance of the air/fuel mixture preparation in internal combustion engines, whatever is the thermodynamic cycle they work on and the adopted fuel. The short time between the fueling and the start of the combustion is crucial for the best mixture formation and its burning for energy optimization and the pollutant production. The always stringent vehicle emissions rules led engine research toward the use of high-pressures and direct-injection systems for allowing a best atomization/vaporization of the fuel while, as drawback, the downsizing of the combustion system results in increasing of fuel impact on the combustion chamber and cylinder line with HC and particulate matter increase at the exhaust. A complete description of the injected fuel, its spread in the chamber with primary and secondary breakups, the vaporization, the mixture with the air and the combustion are of basic importance to govern the process and help new design architectures. Optical characterization has shown it’s powerful in describing these processes without interfering with their evolution both in stationary and reciprocating devices. Imaging and spectroscopic techniques allow us to follow the physic-chemical transformations of the initial bulk of fuel in the mixture, production of primary and secondary species and individuate the potential sites of pollutant production. Furthermore, the results constitute a data set for initializing and calibrating numerical codes for provisional, results and behavior of diverse injecting systems and at different ambient conditions, and last but not the least inside the engine. In this paper, a tracking shot of optical techniques adopted to depict the fuel spread in a quiescent optical accessible vessel at engine-like conditions is reported for practices of fuel direct injection in engines. © Iranian Society of Engine (ISE), all rights reserved. Article history: Received: 7 November 2019 Accepted: 18 February 2020