Rate of injection measurements of a direct-acting piezoelectric injector for different operating temperatures

[EN] As the regulations for pollutant emissions in diesel engines are increasingly restrictive, the introduction of the piezoelectric direct-acting injectors seeks to improve the overall efficiency of the injection system, and consequently reduce combustion contaminants. In such systems, the needle lift is governed by the charge, or voltage, applied to the piezo stack, allowing for a more precise control over the fuel injection process. Although it is known that the performance of the piezoelectric crystals depends on its temperature of operation, the effect this has on the rate of injection is still unclear. In this research, a particular setup was used to measure the rate of injection of a direct-acting injector for different operating temperatures. It was mounted into an injection discharge rate curve indicator with a particular holder that has a cooling sleeve connected to a circuit running ethylene glycol, which is driven by a thermoregulator unit. A parametric sweep of different piezo stack control voltages for three rail pressures and operating temperatures was carried out. On the results, when needle lift does not influence internal flow development, the rate of injection was controlled by the injection pressure, with minimal impact from the working temperature, resembling results from conventional hydraulic injectors. At partial needle lift, two operating regions were observed, delimited by a particular voltage level. Above it, the needle throttling was able to control mass fuel flow accurately. But below it, the stabilized rate of injection values decreased drastically. The rate of this decline was dependent only on the injection pressure. The threshold level, named critical voltage, increased linearly with increasing injection pressure and working temperature. Also, to maintain a constant fuel mass flow for decreasing operating temperature, the voltage level of the control signal had to be reduced. These results highlight the importance of monitoring and controlling the operating conditions of the direct-acting injectors, as their performance and efficiency are both influenced by the working temperature of the piezo stack.This research has been partially funded by FEDER and Spanish Ministerio de Economía y Competitividad through project TRA2015-67679-c2-1-R. Additionally, financial support to Dr. Carmen Mata was provided by Ayudas para estancias en otras universidades y centros de investigación 2017 of Universidad de Castilla la Mancha. Likewise, Alberto Viera is supported through the FPI contract 2016-S2-1361 of Programa de Apoyo para la Investigación y Desarrollo (PAID) of Universitat Poltècnica de València.Payri, R.; Gimeno, J.; Mata, C.; Viera-Sotillo, AA. (2017). Rate of injection measurements of a direct-acting piezoelectric injector for different operating temperatures. Energy Conversion and Management. 154:387-393. https://doi.org/10.1016/j.enconman.2017.11.029S38739315

Study of the influence of the inlet boundary conditions in a LES simulation of internal flow in a diesel injector

In this paper the study of the behavior of the fuel flow through the injector nozzle using CFD tools is presented. Large Eddy Simulation will be used to model the internal flow turbulence in a Diesel fuel injector with velocities over 500 m/s. More specifically, the influence of boundary conditions applied to the model will be studied. The article analyzes the influence of the inlet boundary condition upon activation and maintenance of turbulent flow during the calculation. Carefully assessing which inlet boundary condition is more trustworthy in reality, for this the outlet velocity, pressure, turbulence and level of stabilization will be studied.This work has been funded by UNIVERSIDAD POLITECNICA DE VALENCIA from Spain, in the framework of the project "ESTUDIO DE LA INFLUENCIA DEL LEVANTAMIENTO DE AGUJA EN EL PROCESO DE INYECCION DIESEL'', Reference No. PAID-06-10-2362.Payri Marín, R.; Gimeno García, J.; Marti Aldaravi, P.; Bracho León, GC. (2013). Study of the influence of the inlet boundary conditions in a LES simulation of internal flow in a diesel injector. Mathematical and Computer Modelling. 57(7-8):1709-1715. https://doi.org/10.1016/j.mcm.2011.11.019S17091715577-

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

[EN] 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.This research has been partially funded by FEDER and Spanish Ministerio de Economia y Competitividad through project TRA2015-67679-c2-1-R. Additionally Jhoan Sebastian Giraldo had a grant FPI-SUB 2 from Universitat Politecnica de Valencia.Payri, R.; Giraldo-Valderrama, JS.; Ayyapureddi, S.; Versey, Z. (2018). Experimental and analytical study on vapor phase and liquid penetration for a high pressure diesel injector. Applied Thermal Engineering. 137:721-728. https://doi.org/10.1016/j.applthermaleng.2018.03.097S72172813

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 1000 K and 15 MPa 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 a plenty of room for improvement.he authors would like to thank general motors company for their financial support and its cooperation during the project and José Enrique del Rey* and Michele Bardi* for their collaboration in the experimental measurements and setup. (*) From CMT-Motores Térmicos. Universitat Politecnica de Valencia.Payri, R.; Gimeno, J.; Viera, JP.; Plazas Torres, AH. (2013). Needle lift profile influence on the vapor phase penetration for a prototype diesel direct acting piezoelectric injector. Fuel. 113:257-265. doi:10.1016/j.fuel.2013.05.057S25726511

Study liquid length penetration results obtained with a direct acting piezo electric injector

A state of the art prototype common rail injector featuring direct control of the needle by means of a piezo stack (direct acting) has been tested. Liquid phase penetration of the sprays in diesel engine-like conditions has been studied via imaging technique in a novel continuous flow test chamber that allows an accurate control on a wide range of thermodynamic conditions (up to 1000 K and 15 MPa). This state of the art injector fitted with a 7-hole nozzle, allows a fully flexible control on the nozzle needle movement, enabling various fuel injection rates typology. The temporal evolution of the seven sprays has been studied recording movies of the injection event in evaporative conditions via Mie scattering imaging technique and using a high speed camera. The results showed a strong influence of needle position on the stabilized liquid length while the effect of the injection pressure is negligible: the decrease of the needle lift causes a pressure drop in the needle seat and thus a reduction in the effective pressure upstream of the orifices (in the nozzle sac). According to known literature the stabilized liquid-length depends mainly on effective diameter, spray cone-angle and fuel/air properties and does not depend on fuel velocity at the orifice outlet. Therefore, due to small change in the spray cone-angle, higher injection pressures give slightly lower liquid length. However, partial needle lifts has an opposite effect: when needle is partially lifted a dramatic increase of the spray cone-angle and a consequent reduction of the liquid length are observed. A deeper analysis revealed that low charges are linked also to higher hole to hole dispersion and flow instabilities. Needle vibrations caused by the fuel-needle interactions with fuel flow at partial needle lift and the onset of cavitation in the needle seat are likely the causes of this unexpected behavior. Finally, the effect of injection rate shaping on the transient liquid penetration is presented, showing the capability of the injector to control the liquid length along the injection event. This feature, when applied in a real engine, yields to develop new injection strategies to avoid fuel wall impingement.This work was sponsored by General Motors R&D, Warren, MI. The authors would like to thank Jose Enrique del Rey and David Fuertes Munoz for their precious work in the laboratory during the tests.Payri, R.; Gimeno, J.; Bardi, M.; Plazas, AH. (2013). Study liquid length penetration results obtained with a direct acting piezo electric injector. Applied Energy. 106:152-162. doi:10.1016/j.apenergy.2013.01.027S15216210

Comparison of microsac and VCO diesel injector nozzles in terms of internal nozzle flow characteristics

A computational study focused on the inner nozzle flow and cavitation phenomena has been reported in this paper in order to investigate the two most common types of diesel injector nozzles at the present: microsac and valve covered orifice (VCO). The geometrical differences among both types of nozzles are mainly located at the needle seat, upstream of the discharge orifices. In the case of microsac nozzles there is a small volume upstream of the discharge orifices which is not present in VCO nozzles. Due to these geometrical differences among both type of nozzles, differences in the inner flow and the cavitation development have been found and analysed in this research. For the study, two cylindrical nozzles with six orifices and the same outlet diameter have been experimentally characterized in terms of mass flow rate. These measurements have been used to validate the CFD results obtained with the code OpenFOAM used for the analysis of the internal nozzle flow. For the simulations, two meshes that reproduce the microsac and VCO nozzles seat geometry while keeping the same geometry at the orifices have been built. The simulations have been carried out with a code previously validated and able to simulate cavitation phenomena using a homogeneous equilibrium model (HEM) and with RANS approach for the turbulence modelling (RNG k-epsilon). For the computational study, three injection pressures and different geometries simulating different needle lifts have been used. The comparison among nozzles has been made in terms of mass flow, momentum flux and effective velocity and in terms of other non-dimensional parameters which are useful for describing the inner nozzle flow: discharge coefficient (C-d), area coefficient (C-alpha) and velocity coefficient (C-v). The analysis performed by studying and comparing the particularities of the flow in each nozzle has been useful in order to explain the experimental differences found in terms of mass flow rate and critical cavitation conditions. One of the main conclusions of this study is the higher influence of the needle on the mass flow, momentum and injection velocity results for the VCO nozzle as compared to the microsac one. Hence, whereas in the first one these variables scale with the needle lift value, in the second one there is an intermediate needle lift from which they stop being influenced by the presence of the needle. Furthermore, the study has also revealed important differences in the proneness to produce cavitation and its morphology. For the VCO nozzle, cavitation phenomenon occurs only in the upper part of the orifice inlet. However, for the microsac nozzle cavitation appears both at the upper and the lower part of the nozzle orifice entrance.This work was partly sponsored by "Ministerio de Economia y Competitividad" in the frame of the project "Comprension de la influencia de combustibles no convencionales en el proceso de inyeccion y combustion tipo diesel", Reference TRA2012-36932. This support is gratefully acknowledged by the authors.Salvador Rubio, FJ.; Carreres Talens, M.; Jaramillo Císcar, D.; Martínez López, J. (2015). Comparison of microsac and VCO diesel injector nozzles in terms of internal nozzle flow characteristics. Energy Conversion and Management. 103:284-299. https://doi.org/10.1016/j.enconman.2015.05.062S28429910

Influence of nozzle geometry on ignition and combustion for high-speed direct injection diesel engines under cold start conditions

Starting at low temperatures (below 0 °C) is an important issue for current and near future diesel engine technology. Low ambient temperature causes long cranking periods or complete misfiring in small diesel engines and, as a consequence, an increased amount of pollutant emissions. This paper is devoted to study the influence of nozzle geometry on ignition and combustion progression under glow-plug aided cold start conditions. This study has been carried out in an optically accessible engine adapted to reproduce in-cylinder conditions corresponding to those of a real engine during start at low ambient temperature. The cold start problem can be divided in two parts in which nozzle geometry has influence: ignition and main combustion progress. Ignition probability decreases if fuel injection velocity is increased or if the amount of injected mass per orifice is reduced, which is induced by nozzles with smaller hole diameter or higher orifice number, respectively. Combustion rates increase when using nozzles which induce a higher momentum, improving mixture conditions. For these reasons, the solution under these conditions necessarily involves a trade-off between ignition and combustion progress.Authors thank the Spanish Ministry of Innovation and Science for the financial support through the project OPTICOMB (reference code: TRA2007-67961-C03-C01). Authors also thank Daniel Lerida Sanchez de las Heras for his outstanding work in the facility set-up and adaptation and for his support during the tests.Desantes Fernández, JM.; García Oliver, JM.; Pastor Enguídanos, JM.; Ramírez Hernández, JG. (2011). Influence of nozzle geometry on ignition and combustion for high-speed direct injection diesel engines under cold start conditions. Fuel. 90(11):3359-3368. https://doi.org/10.1016/j.fuel.2011.06.006S33593368901

Linking instantaneous rate of injection to X-ray needle lift measurements for a direct-acting piezoelectric injector

Internal combustion engines have been and still are key players in today's world. Ever increasing fuel consumption standards and the ongoing concerns about exhaust emissions have pushed the industry to research new concepts and develop new technologies that address these challenges. To this end, the diesel direct injection system has recently seen the introduction of direct-acting piezoelectric injectors, which provide engineers with direct control over the needle lift, and thus instantaneous rate of injection (ROI). Even though this type of injector has been studied previously, no direct link between the instantaneous needle lift and the resulting rate of injection has been quantified. This study presents an experimental analysis of the relationship between instantaneous partial needle lifts and the corresponding ROI. A prototype direct-acting injector was utilized to produce steady injections of different magnitude by partially lifting the needle. The ROI measurements were carried out at CMT-Motores Termicos utilizing a standard injection rate discharge curve indicator based on the Bosch method (anechoic tube). The needle lift measurements were performed at the Advanced Photon Source at Argonne National Laboratory. The analysis seeks both to contribute to the current understanding of the influence that partial needle lifts have over the instantaneous ROI and to provide experimental data with parametric variations useful for numerical model validations. Results show a strong relationship between the steady partial needle lift and the ROI. The effect is non-linear, and also strongly dependent on the injection pressure. The steady lift value at which the needle ceases to influence the ROI increases with the injection pressure. Finally, a transient analysis is presented, showing that the needle velocity may considerably affect the instantaneous ROI, because of the volume displaced inside the nozzle. Results presented in this study show that at constant injection pressure and energizing time, this injector has the potential to control many aspects of the ROI and thus, the heat release rate. Also, data presented are useful for numerical model validations, which would provide detailed insight into the physical processes that drive these observations, and potentially, to the effects of these features on combustion performance.The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (Argonne). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.Viera-Sotillo, JP.; Payri, R.; Swantek, AB.; Duke, DJ.; Sovis, N.; Kastengren, AL.; Powell, CF. (2016). Linking instantaneous rate of injection to X-ray needle lift measurements for a direct-acting piezoelectric injector. Energy Conversion and Management. 112:350-358. https://doi.org/10.1016/j.enconman.2016.01.038S35035811

Rate of injection modelling for gasoline direct injectors

[EN] Awareness of climate change, fossil fuel availability, and pollutants has been growing which have pushed forward the effort in cleaner engines. In this aspect, the gasoline engines have more improving margin than diesel engines. To have a more efficient combustion, injection systems had evolved from old Port Fuel Injectors to modern Gasoline direct injections which are the used by engine manufacturers nowadays. In this study, within the framework of the Engine Combustion Network (ECN), the so named Spray G is modelled. This gasoline direct injector was developed by Delphi with the intention of getting a better understanding of the gasoline spray. The model is focused on the Rate of Injection (ROI) signal, whose results are presented in order to help engine calibration and modelling for an extensive range of configurations without the need for experimental measurements.This article was supported by Generalitat Valenciana through AICO/2018 under the project Nuevos conceptos en inyeccion de gasolina (NCIG) and through Ayudas de la Conselleria de Educacio, Cultura y esports para la promocion y dinamizacion de parques cientificos (PPC/2018. DOCV del 07/11/2017).Payri, R.; Bracho Leon, G.; Gimeno, J.; Bautista-Rodríguez, A. (2018). Rate of injection modelling for gasoline direct injectors. Energy Conversion and Management. 166:424-432. https://doi.org/10.1016/j.enconman.2018.04.041S42443216

Velocity field analysis of the high density, high pressure diesel spray

In this study, particle image velocimetry (PIV) measurements have been performed extensively on a non-reactive dense diesel spray injected from a single orifice injector, under various injection pressure and steady ambient conditions, in a constant flow chamber. Details of PIV setup for diesel spray measurement without additional seeding are explained first. The measured velocity profiles are compared to those obtained from other similar measurements performed in a different institution, as well as those obtained from a 1D spray model simulation, presenting in both cases a good level of agreement. In addition, the velocity fields under various injection pressures and ambient densities show the dominant effects of these parameters on the behavior of diesel spray. The self-similarity of the transverse cut profiles of axial velocity is evaluated, showing that the measurements are in agreement with the hypothesis of self-similar velocity profiles. Finally, the effect of injection pressure and ambient density on the velocity fluctuations is presented and analyzed as well. While the experimental results presented here could help to understand the complex diesel fuel-air mixing process during injection, they also provide additional spray velocity data for future computational model validation, following the main idea of the Engine Combustion Network.This work was sponsored by "Ministerio de Economia y Competitividad" of the Spanish Government in the frame of the Project "Comprension de la influencia de combustibles no convencionales en el proceso de injeccion y combustion tipo diesel", Reference TRA2012-36932. Additionally, the optical equipment used for the project was purchased with funding from Ministerio de Economia y Competitividad FEDER-ICTS-2012-06.Payri Marín, R.; Viera-Sotillo, JP.; Wang, H.; Malbec, L. (2016). Velocity field analysis of the high density, high pressure diesel spray. International Journal of Multiphase Flow. 80:69-78. https://doi.org/10.1016/j.ijmultiphaseflow.2015.10.012S69788