Lucio Postrioti

Injection Strategies Tuning for the Use of Bio-Derived Fuels in a Common Rail HSDI Diesel Engine

The potentialities in terms of engine performance and emissions reduction of pure biodiesel were examined on a Common Rail HSDI Diesel engine, trying to define a proper tuning of the injection strategies to bio-fuel characteristics. An experimental investigation was therefore carried out on a typical European passenger car Diesel engine, fuelled with a soybean oil derived biodiesel. A standard European diesel fuel was also used as a reference. In particular, the effects of an equal relative air/fuel ratio at full load condition were analysed; further, a sensitivity study on the outcome of the pilot injection timing and duration at part load on engine emissions was performed. Potentialities in recovering the performance gap between fossil fuel and biodiesel and in reducing NOx specific emissions, affecting only to a limited extent the biodiesel emission benefit in terms of CO, HC and FSN, were highlighted.

Analysis of Diesel Spray Momentum Flux Spatial Distribution

In the present paper the results of an experimental and numerical analysis of a common -rail, high pressure Diesel spray evolving in high counter pressure conditions is reported. The experimental study was carried out mainly in terms of spray momentum flux indirect measurement by the spray impact method; the measurement of the impact force time-histories, along with the CFD analysis of the same phenomenon, gave interesting insight in the internal spray structure. As well known, the overall spray structure momentum flux along with the injection rate measurements can be used to derive significant details about the in-nozzle flow and cavitation phenomena intensity. The same global spray momentum and momentum flux measurement can be useful in determining the jet -tojet ununiformities also in transient, engine-typical injection conditions which can assist in the matching process between the injection system and the combustion chamber design. In the present paper, the potential in the internal spray structure analysis by means of local spray momentum flux distribution investigation is evaluated. To obtain such momentum flux distribution maps, a variant in the global spray momentum measurement technique is evaluated. The use of an adaptor to the momentum flux measurement rig is discussed, numerically analyzed and tested on a dedicated experimental bench. Some results pertaining to solenoid-actuated common rail injectors are presented and discussed in terms of spray distribution irregularities, momentum profiles and differences in the spray structure obtained for the different jets emerging from the nozzle.

Thermodynamic analysis of hydraulic air compressor-gas turbine power plants

Abstract Nowadays, the most common way to improve energy conversion efficiency is the integration of different systems, thus achieving a better exploitation of the available exergy potential (e.g. combined cycles, cogeneration, etc.). As a means of producing power in hydroelectric plants hydraulic energy is commonly considered to be almost completely exploited. The aim of this paper is to analyse the possible integration of hydraulic energy sources with conventional, fossil fuel based systems; in particular, power plants based on the combination of an hydraulic air compressor (HAC) and a gas turbine are considered. In an HAC, air is entrained in the water flow in a downcomer pipe and compressed. Once separated from the water in a ‘stilling chamber’ at the bottom of the downpipe, the compressed air is supplied to a combustion chamber and then to a conventional gas turbine expander. An attractive characteristic of HACs is the capability, in principle, to perform an isothermal air compression instead of an adiabatic one, as in conventional compressors. In the present work, a thermodynamic analysis is presented of HAC-gas turbine energy conversion systems, which are compared with conventional hydroelectric and gas turbine power plants. The calculated performance levels of such systems are comparable to those of combined cycle plants, making further technical and economical investigations quite interesting.

Experimental Investigation on the Effects on Performance and Emissions of an Automotive Euro 5 Diesel Engine Fuelled with B30 from RME and HVO

The effects of using blended renewable diesel fuel (30% vol.), obtained from Rapeseed Methyl Ester (RME) and Hydrotreated Vegetable Oil (HVO), in a Euro 5 small displacement passenger car diesel engine have been evaluated in this paper. The hydraulic behaviour of the common rail injection system was verified in terms of injected volume and injection rate with both RME and HVO blends fuelling in comparison with commercial Diesel. Further, the spray obtained with RME B30 was analysed and compared with Diesel in terms of global shape and penetration, to investigate the potential differences in the air-fuel mixing process. Then, the impact of a biofuel blend usage on engine performance at full load was first analysed, adopting the same reference calibration for all the tested fuels. Afterwards, the effects of a biofuel blend usage on brake specific fuel consumption and on exhaust emissions were also evaluated at 7 different part load operating conditions, representative of the New European Driving Cycle. Finally, soot-NOx trade-off obtained by means of EGR sweeps were performed in the same operating points, in order to gather detailed information about further possible emissions benefits that could be achieved through a more extensive ECU recalibration.

Dynamic behavior of a spring-powered micronozzle needle-free injector.

Conventional injection is still the leading method to deliver macromolecular therapeutics. Needle injection is considered a low compliance administration strategy, principally due to pain and needle phobia. This has fostered the research on the development of alternative strategies to circumvent the skin barrier. Among needle-free drug delivery methods, jet injection is an old strategy with great potential not yet completely disclosed. Here, the design, engineering and dynamic behavior of a novel spring-powered micronozzle needle-free injector is presented. Fluid mechanics was first studied in air to calculate jet force and speed as well as injection duration in different conditions. Polyacrylamide gel was used to simulate a soft tissue and to investigate the jet evolution over time of different injected doses. Finally, ex vivo characterization was carried out on pig skin. Results evidenced a direct dependence of the force, velocity, and duration with the injection volume. The model material allowed individuating the different steps of jet penetration and to attempt a mechanistic explanation. A different behavior has been recorded in the skin with interesting findings for subcutaneous and/or dermal delivery. Peculiar features with respect to existing jet injectors confers to this device good potentiality for a future clinical application.

Experimental Validation of Spray Breakup and Fuel Evaporation Models in High Pressure Ambient Conditions

Experimental and numerical computations of transient sprays are performed under ambient Diesel like conditions, in order to investigate on the complex phenomena that occur in the evolution of an evaporating fuel spray (like break up, fuel multicomponent evaporation, liquid gas interaction). An experimental analysis has been carried out using a single hole high pressure electronic control injection system. The investigation procedure exploits a light sheet technique based on a Nd-Yag pulsed laser and a synchronized CCD camera. The measured characteristics are the spray penetration and the spray cone angles, as the fuel jet evolves in a pressurized chamber. Furthermore, a numerical analysis of the spray development has been carried out. The numerical tool used is a modified version of the well known KIVA code in which a new break up model, developed and validated in previous works [1, 2], and a fuel multicomponent evaporation model have been included. The predictive capability of the evaporation model has been evaluated by comparison with single droplet experimental data [3].

Spray analysis of the PFAMEN injector

In an earlier study, a novel type of diesel fuel injector was proposed. This prototype injects fuel via porous (sintered) micro pores instead of via the conventional 6-8 holes. The micro pores are typically 10-50 micrometer in diameter, versus 120-200 micrometer in the conventional case. The expected advantages of the so-called Porous Fuel Air Mixing Enhancing Nozzle (PFAMEN) injector are lower soot- and CO 2 emissions. However, from previous in-house measurements, it has been concluded that the emissions of the porous injector are still not satisfactory. Roughly, this may have multiple reasons. The first one is that the spray distribution is not good enough, the second one is that the droplet sizing is too big due to the lack of droplet breakup. Furthermore air entrainment into the fuel jets might be insufficient. All reasons lead to fuel rich zones and associated soot formation. To acquire more insight into the spray of the porous injector, several PFAMEN nozzles have been produced and investigated. The momentum of the spray was found to be an order of magnitude lower compared to conventional injectors. Afterwards, the porous injector was placed in an optically accessible engine, allowing the analysis of the spray development and combustion process. The main conclusion is that the spray penetration depth is relatively low. Finally, droplet size and velocities are presented using Phase Doppler Anemometry (PDA) and from these measurements it became clear that the droplets of the PFAMEN nozzle are larger compared to conventional injectors. This is believed to be caused by the low exit velocities.

Instrument for the test of the injectors based on the measuring of spray momentum

ABSTRACT In the first part of the present paper the result of an experimental analysis of common rail high pressure Diesel spray evolving in high counter pressure conditions is reported. The global spray momentum and momentum flux measurement can be strongly useful in determining the jet to jet non-uniformities in engine typical injection conditions. The jet to jet uniformities analysis can assist in the matching process between the injection system and the combustion chamber geometric characteristic. Furthermore the knowledge of spray momentum spatial distribution allows to optimize fuel air mixing and then the combustion efficiency that is fundamental in order to fulfill the new emission rules EURO 6. The potential of spray momentum measurement technique is showed. The internal spray structure analysis by means of local spray momentum flux distribution investigation is showed too. Results are discussed in terms of spray distribution characteristic, momentum profiles and differences in the spray structure obtained for the same nozzle jets. In the second part the results of GDI gasoline injector spray evolving in counter pressure is reported. An evaluation to use the same experimental approach for testing the internal spray structure is reported for multi-holes GDI injectors.

Experimental and Numerical Assessment of Multi-Event Injection Strategies in a Solenoid Common-Rail Injector

Nowadays, injection rate shaping and multi-pilot events can help to improve fuel efficiency, combustion noise and pollutant emissions in diesel engine, providing high flexibility in the shape of the injection that allows combustion process control. Different strategies can be used in order to obtain the required flexibility in the rate, such as very close pilot injections with almost zero Dwell Time or boot shaped injections with optional pilot injections. Modern Common-Rail Fuel Injection Systems (FIS) should be able to provide these innovative patterns to control the combustion phases intensity for optimal tradeoff between fuel consumption and emission levels.In this work, a 1D-CFD model in GT-SUITE of a solenoid ballistic Common-Rail injector was firstly refined respect to the previous work [1] and then it was validated against an extensive experimental dataset of single injections, standard double pilot and multi-pilot injection patterns (up to 4 pilot events) with almost zero dwell time between two consecutive injection events. The experimental hydraulic test data used to validate the one-dimensional model were obtained by means of the UniPG Injection Analyzer based on the Zeuchs method.The comparison between the experimental and simulated volumetric injection rates showed a more than satisfactory accuracy of the model in predicting the actual behavior of the ballistic injector for all the injection patterns tested, even for relatively complex injector command strategies, characterized by reduced Dwell Time values between consecutive injection events.