1,721,006 research outputs found
The Influence of Actual Layout and Off-Axis Needle Stroke on Diesel Nozzle Flow Under Ballistic Needle Displacement
No full textThe injection of small amount of diesel fuel relies on the shortening of energizing signal. In such injection conditions, the needle does not reach the mechanical stroke-end and its displacement is defined as ballistic. Some specific experimental work has been performed on how the dynamics of injector needle is reflected on the fuel flow pattern within the nozzle. Due to the intrinsic difficulties of the field, just single axial hole injectors have been optically investigated in real time, by means of the most advanced X-ray techniques. In the current study, based on 3D-CFD modeling, the investigation has been extended to multi-hole injector layouts, under typical pilot/split injection conditions, namely high injection pressure and low needle lift. The role of different factors on the flow development within the nozzle has been shown and discussed; the investigations have taken into account actual injector tip layouts and the response to the needle off-axis operating conditions. Results are presented highlighting the flow features within the nozzle and their reflects on the hole-to-hole differences
Coupling Codes for Nozzle Flow Modeling in Diesel Injection Systems
No full textThis paper deals with a numerical investigation of a single cylinder diesel engine equipped with mechanical fuel direct injection system and focuses on the fuel injection system modelling with the aim of predicting the performance of the entire injection system, the spray characteristics, the interaction among spray-cones, combustion chamber flows and geometry. In the simulations, two different codes have been used. With the former one, AMESim code, the complete injection system has been analysed and the single components have been selected and modelled. The results obtained from the injection system simulation, in terms of injection needle lift, injection flow rate, pressure time evolution, have been used to initialize the latter computation tool, FIRE code, in which 3D flow numerical investigation of the internal injector flow has been performed. Since such a flow is directly linked to the spray modelling, the primary break-up effects have been taken into account. The details of the adopted modelling strategy have been shown and the results of each simulation step have been presented. In order to highlight the relationship among the nozzle flow condition and the spray formation-vaporization characteristics, a comparison between two different calculation setups has been shown. Moreover, a qualitative comparison among predictions and experimental data has been discussed
Vibration and acoustic characteristics of a city-car engine fueled with biodiesel blends
No full textA number of studies have demonstrated that biodiesel is a more environmentally sustainable fuel than petroleum-derived fuels since it is a renewable source of energy and it allows to reduce undesired exhaust emissions (e.g. unburned HC, CO and particulate matter). However, specialized literature highlights there is still the need to further investigate performance, emissions and NVH characteristics of engines equipped with up-to-date technologies fueled with biodiesel blend. The aim of the present paper is to investigate the vibro-acoustic behavior of a small displacement engine, mainly employed in micro-cars, fueled with blends of distilled biodiesel (obtained from used cooking oil) and ultra low sulfur diesel fuel up to 40% by volume. Demands for reducing chemical and noise pollutions, traffic congestion and parking difficulties in urban areas make the micro-cars one of the possible solutions for the future urban environment, especially if the engine is fueled with biodiesel blends for their potential of reducing the pollutant emissions. An original methodology developed by the authors for in-cylinder pressure characterization via non-intrusive measurements is here applied to evaluate the impact of biodiesel content on the combustion process and therefore on engine vibration and noise emissions. The data processing in frequency domain allowed to extract the components mainly related to the combustion events. Concerning vibration signals: for all blends, the vibration amplitudes increases with the increase of engine speed values; B40 is characterized by highest values of RMS of accelerometer signal almost in the complete engine operative field. RMS values obtained for B10 are the lowest ones in most of the investigated engine operative conditions. Concerning noise radiation: the Noise Index was used to evaluate the components of the emission where the combustion energy demonstrated to be concentrated. The results show an increase of Noise Index for all blends with the increase of engine speed. B10 is characterized by the highest values in most of the testes conditions. B40 values demonstrated the opposite behavior
Integrated Modeling of Fuel Influence on Common Rail Injection System Performance
No full textA model for the analysis of diesel engine common rail injection system has been developed and the influence that different fuels have on the injection performances has been investigated. Diesel fuel, biodiesel and kerosene have been used and the differences of injection flow rate, injection pressure time trace, nozzle flow features and break up mechanism have been highlighted. The coupling of two different codes has been used in the simulations: the former one, AMESim code, has been adopted to model the common rail system and to investigate the fuel flow rate and the injection pressure dependence on the fuel type. The latter computational tool, FIRE code, has been initialized by means of the results obtained from the injection system simulation and has been used to perform the 3D investigation of the internal nozzle flow and of the spray formation phenomena, aimed at evaluating the effect of physical fuel features on local flow characteristics and their influence on the system performances. Details of the adopted modeling strategy are described and results of each simulation step are presented
Hole Cross Section Shape Influence on Diesel Nozzle Flow
No full text"Progress in hole drilling technique is opening new perspectives in diesel nozzle design. In such a scenario, research on unconventional hole shapes looks worthwhile, in order to evaluate their influence on fuel flow features within the nozzle. In the present paper, investigations have been based on modeling. Moving from a standard hole configuration towards oval shaped holes, 3D-CFD campaigns have been devoted to highlight the hole layout influence on diesel nozzle flow. The investigations have been focused both on the fuel flow pattern at hole inlet and on the flow features at hole exit section; in such a modeling process, transient data concerning spatial distribution of velocity, turbulent kinetic energy and cavitation behavior at hole exit have been computed, highlighting the perturbations induced by the unconventional hole shape on the fuel flow; once the flow behavior has been explored, results have been resumed indicating how flow pattern properties are reflected at hole exit, quantitatively
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