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A test bench for the assessment of flow meters accuracy for fuel consumption measurement in highly dynamic drive cycle tests
Full text linkExperimental and Numerical Momentum Flux Analysis of Jets from a Hydrogen Injector
No full textThe use of hydrogen in internal combustion engines is an effective approach to significantly support the reduction of CO2 emissions from the transportation sector using technically affordable solutions. The use of direct injection is the most promising approach to fully exploit hydrogen potential as a clean fuel, while preserving targets in terms of power density and emissions. In this frame, the development of an effective combustion system largely relies on the hydrogen-air mixture formation process, so to adequately control the charge stratification to mitigate pre-ignitions and knock and to minimize NOx formation. Hence, improving capabilities of designing a correct gas jet-air interaction is of paramount importance. In this paper the analysis of the evolution of a high-pressure gas jet produced by a single-hole prototype injector operated with different pressure ratios is presented. The experimental analysis is carried out using global momentum flux measurement with the support of Schlieren imaging and needle lift detection. A combined CFD analysis of the injection process is used to investigate the details of the momentum flux device operation, offering an interesting insight in the measurement mechanisms and in the jet evolution. The final goal of the combined experimental-numerical approach is to provide quantitative description of the injection process dynamics and spatial/temporal jet evolution and morphology so to support the combustion system design
Injection rate measurement of a scr injector operating in flash-boiling conditions
No full textIn the present paper an experimental campaign aimed at analyzing the hydraulic behavior of a SCR injector operated with high temperature Urea-Water Solution (UWS) is presented. In previous analyses, the effects exerted by UWS high temperature on the spray evolution were investigated in terms of spray shape and sizing. It was observed that increasing the injected liquid temperature so to approach flash-boiling conditions results in an increase of the spray cone angle and in reduced penetration. Moreover, the spray sizing is significantly reduced improving the UWS to ammonia conversion rate. The main objective of the present research is the investigation of the effects exerted by flash-boiling on the injector hydraulics in terms of mean and shot-to-shot injected mass and injection rate. In order to investigate the injector actual hydraulic behavior when injecting high temperature fluid, an innovative instrument named dINJ Injection Analyzer was developed at the University of Perugia. This instrument detects the shot-to-shot injection rate profile and injected volume while preserving the normal operation conditions for the injector, i.e. with the injected spray developing in a gaseous environment. The proposed instrument is based on the detection of the pressure time-history in a closed vessel acting as isolated fuel rail during the injection process. According to this approach the typical constraints of conventional Injection Analyzers requiring a pressurized volume (a closed vessel or a pipe) are overcome. A low pressure injector, as long as a GDI injector, can be operated with the prescribed pressure differential, maintained throughout the injection process. Moreover, the injection in a gaseous environment allows both the onset of peculiar flow conditions (flash-boiling) and the application of additional diagnostics as imaging. In the paper, after a preliminary validation of the proposed instrument with a Port-Fuel-Injection (PFI) injector, the hydraulic analysis of a SCR doser supplied with UWS at temperature ranging from ambient to 130 °C is presented and discussed, analysing the mean injected mass trend with temperature, the shot-to-shot dispersion and the injection rate profile demonstrating the effect of the flash-boiling phenomenon on the discharge process. A partial limitation of the current analysis is given by the ambient pressure and temperature conditions maintained in the vessel downstream the injector nozzle. The investigation will be completed in the future by an upgrade of the experimental setup in order to control not only the pressure and temperature of the UWS in the nozzle but also the pressure and temperature level of the gaseous environment in which the spray evolves
Impact of different droplets size distribution on the morphology of GDI sprays: Application to multi-hole injectors
No full textThe scientific literature focusing on the numerical simulation of fuel sprays is plenty of atomization and secondary break-up models, all aiming at simulating GDI sprays under possibly any engine condition in terms of injection pressure and cylinder back pressure. However, it is well known that the predictive capabilities of even the most diffused break-up models are affected by injection parameters, especially backpressure. As a consequence, model constants require usually substantial tuning based on the specific operating conditions. In this manuscript, an alternative atomization methodology is proposed for the 3D-CFD simulation of GDI sprays, aiming at reducing case-to-case tuning of the model constants for variations of the operating conditions. In particular, attention is focused on the effects of back pressure, which has a huge impact on both the morphology and the sizing of GDI sprays. 3D-CFD Lagrangian simulations of two different multi-hole GDI injectors are presented. The first injector is a 5-hole GDI prototype unit operated at ambient conditions. The second one is the well-known Spray G, characterized by a higher back pressure (up to 0.6 MPa). Results are compared against experimental data in terms of liquid penetration, PDA (Phase Doppler Anemometry) data of droplet sizing / velocity and imaging. CFD results are demonstrated to be highly sensitive to the spray vessel pressure, mainly because of the atomization strategy. The proposed alternative approach proves to strongly reduce such dependency. To confirm the improvements, such approach is combined to two different well-known secondary break-up models, namely Reitz's model and the KHRT one
Combined Experimental and Numerical Approach for the Thermal Heat Exchange Investigation of Li-Ion Cells for Automotive Applications
No full textLithium-ion (Li-ion) battery is an advanced technology in the field of electrochemical energy storage, but its management constitutes one of the most intriguing challenges for electric vehicles. Many parameters need to be controlled and managed and many aspects need to be optimised. This work presents a methodology for laboratory characterization of Nickel Manganese Cobalt (NMC) Lithium-Ion batteries suited for automotive applications. The purpose consists of obtaining a detailed description of the electrical and thermal behaviour of a single battery cell to provide an accurate model (static, dynamic, and thermal) that could ensure optimized real-time battery management by a management system for several battery packs. A battery testing system was built using a bidirectional power supply and a software/hardware interface was implemented within the National Instruments LabVIEW environment that monitors current, voltage and temperature sensors. This dedicated laboratory equipment can be used to apply and report charging/discharging cycles according to the user-defined load profile. A bidimensional CFD dynamic condition/transient simulation in the Ansys FLUENT environment was performed to study the heat thermal fluxes generated by a determined current value in the battery cells, and the results have been compared to the experimental data for validation
Experimental and Numerical Analysis of a Diesel Common Rail Fuel Spray in an Air Qiuescent Vessel
No full textCommon Rail HSDI Diesel Engine Combustion and Emissions with Fossil/Bio-Derived Fuel Blends
No full textNumerical Simulation of Non-reacting Ducted Fuel Injection by Means of the Diffuse-Interface Σ-Y Atomization Model
No full textEvaluation of the single jet flow rate for a multi-hole GDI nozzle
Full text linkFuel injectors featuring differentiated hole-to-hole dimensions improve the fuel distribution in the cylinder ensuring a more efficient and cleaner combustion for GDI (Gasoline Direct Injection) engines. A proper diagnostic system able to detect the actual fuel flow rate exiting each hole of a GDI nozzle is requested in order to optimize the matching between the spray and the combustion chamber. Measuring the spray impact force of a single plume allows the detection of the momentum flux exiting the single hole and, under appropriate hypotheses, the evaluation of the corresponding mass flow rate time-profile. In this paper two methodologies for the hole-specific flow rate evaluation, both based on the spray momentum technique, were applied to two different GDI nozzles, one featuring equal hole dimensions and one with two larger holes. Three different energizing times at 100 bar of fuel pressure were tested in order to cover a wide range of operating conditions. The results were validated in terms of injected mass by means of a proper device able to collect and weigh the fuel injected by each single nozzle hole, and in terms of mass flow rate using a Zeuch-method flow meter as reference. Both the proposed methodologies showed an excellent accuracy in the fuel amount detection with percentage error lower than 5% for standard energizing times and lower than 10% for very short injections working in ballistic conditions. The mass flow rate time-profile proved a good accuracy in the detection of the start and end of injection and the static flow rate level
Injection Strategies Tuning for the use of Bio-Derived Fuels in a Common Rail HSDI Diesel Engine
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