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Technical Paper

A Dynamic Test Bench for the Assessment of Common Rail Fuel Injection Systems Impact on CO2 Emissions over the WLTP Cycle

The internal combustion engine technological development is today driven by the pollutants and carbon dioxide (CO2) emission reduction targets imposed by law. The request of lowering CO2 emission reflected in a push towards the improvement of engine efficiency, without sacrificing performances and drivability. The latest generations of Diesel engines for passenger cars are characterized by increasing injection pressure levels (250 MPa for the current production). Enhancing the injection pressure has the drawback of increasing the energy needed to pressurize the fuel and thus the high-pressure fuel pump energy request. A small but not negligible quantity of fuel has to be burned in order to provide this energy, generating a contribution in CO2 emission. In this frame, the injector back-flow represents a significant energy loss for the fuel injection system and for the whole engine.
Technical Paper

Experimental and Numerical Analysis of Spray Evolution, Hydraulics and Atomization for a 60 MPa Injection Pressure GDI System

In recent years, the GDI (Gasoline Direct Injection) technology has significantly spread over the automotive market under the continuous push toward the adoption of combustion systems featuring high thermodynamic conversion efficiency and moderate pollutant emissions. Following this path, the injection pressure level has been progressively increased from the initial 5-15 MPa level nowadays approaching 35 MPa. The main reason behind the progressive injection pressure increase in GDI engines is the improved spray atomization, ensuring a better combustion process control and lower soot emissions. On the other hand, increasing injection pressure implies more power absorbed by the pumping system and hence a penalty in terms of overall efficiency. Therefore, the right trade-off has to be found between soot formation tendency reduction thanks to improved atomization and the energetic cost of a high pressure fuel injection system.
Technical Paper

Experimental Analysis of Fuel and Injector Body Temperature Effect on the Hydraulic Behavior of Latest Generation Common Rail Injection Systems

The present paper describes the effect of thermal conditions on the hydraulic behavior of Diesel common rail injectors, with a particular focus on low temperatures for fuel and injector body. The actual injection system thermal state can significantly influence both the injected quantity and the injection shape, requiring proper amendments to the base engine calibration in order to preserve the combustion efficiency and pollutant emissions levels. In particular, the introduction of the RDE (Real Driving Emission) test cycle widens the effective ambient temperature range for the homologation cycle, this way stressing the importance of the thermal effects analysis. An experimental test bench was developed in order to characterize the injector in an engine-like configuration, i.e. fuel pump, piping, common rail, pressure control system and injectors.
Technical Paper

Injection Rate Measurement of GDI Systems Operating against Sub-Atmospheric and Pressurized Downstream Conditions

In order to optimize gasoline direct injection combustion systems, a very accurate control of the fuel flow rate from the injector must be attained, along with appropriate spray characteristics in terms of drop sizing and jets global penetration/diffusion in the combustion chamber. Injection rate measurement is therefore one of the crucial tasks to be accomplished in order both to develop direct injection systems and to properly match them with a given combustion system. Noticeably, the hydraulic characteristics of GDI injectors should be determined according to a non-intrusive measuring approach. Unfortunately, the operation of all conventional injection analyzers requires the injection in a volume filled with liquid and the application of a significant counter-pressure downstream of the injector. This feature prevents any operation with low pressure injection systems such as PFIs.
Technical Paper

A Methodology for the Estimation of Hole-to-Hole Injected Mass Based on Spray Momentum Flux Measurement

In the present paper, a new methodology for the estimation of the mass delivered by a single hole of a GDI injector is presented and discussed. The GDI injector used for the activity featured a five-hole nozzle characterized by three holes with the same diameter and two holes with a larger diameter. The different holes size guarantees a significant difference in terms of mass flow. This new methodology is based on global momentum flux measurement of each single plume and on its combination with the global mass measurement made with the gravimetric principle. The momentum flux is measured by means of a dedicated test bench that detects the impact force of the single spray plume at different distances. The sensing device is moved in different positions and, in each point, the force trace averaged over several injection events is acquired. The global mass delivered by the injector is measured by collecting and weighing the fuel flown during a defined number of consecutive injections.
Journal Article

Experimental Assessment of a Novel Instrument for the Injection Rate Measurement of Port Fuel Injectors in Realistic Operating Conditions

In the present paper an innovative approach for the shot-to-shot hydraulic characterization of low pressure injection systems is experimentally assessed. The proposed methodology is an inverse application of the Zeuch’s method, which in this case is applied to a closed volume upstream the injector instead of downstream of it as in conventional injection analyzers. By this approach, the well-known constraint of having a finite volume pressurized with the injected liquid downstream the injector is circumvented. As a consequence, with the proposed instrument low pressure injectors - such as PFI, fed with gasoline or water, SCR injectors - can operate with the prescribed upstream-downstream pressure differential. Further, the injector can spray directly in atmosphere or in any ambient at arbitrary pressure and temperature conditions, allowing the simultaneous application of other diagnostics such as imaging, momentum flux measurement or sizing instruments.
Journal Article

Experimental and Numerical Evaluation of Diesel Spray Momentum Flux

In the present work, an experimental and numerical analysis of high pressure Diesel spray evolution is carried out in terms of spray momentum flux time history and instantaneous injection rate. The final goal of spray momentum and of injection rate analyses is the evaluation of the nozzle outlet flow characteristics and of the nozzle internal geometry possible influences on cavitation phenomena, which are of primary importance for the spray evolution. Further, the evaluation of the flow characteristics at the nozzle exit is fundamental in order to obtain reliable boundary conditions for injection process 3D simulation. In this paper, spray momentum data obtained in ambient temperature, high counter-pressure conditions at the Perugia University Spray Laboratory are presented and compared with the results of 3D simulations of the momentum rig itself.
Technical Paper

Performance and Emissions of a Common Rail DI Diesel Engine Using Fossil and Different Bio-Derived Fuels

The recent introduction of electronic controlled, high pressure injection systems has deeply changed the scenario for light duty, automotive diesel engines. This change is mainly due to the enhanced flexibility in obtaining the desired injection law (time history and injected fuel quantity), while high injection pressures also favour a suitable mixture formation. This results in higher engine performance (efficiency and power) and in better pollutant emissions control. At the same time, in order to reduce the greenhouse gases net production, research is analyzing alternative resources, such as bio-derived fuels. In particular, methyl esters derived by different vegetable oils are characterized by high cetane numbers and very small sulfur content. The present work reports the results of a comparative analysis performed on a modern DI, common-rail, turbocharged engine by using three different bio-derived fuels (rape seed, soybean, waste cooked oil) and conventional fossil diesel fuel.