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The aim of the paper is the comparison of the injection process with different fuels, i.e. a standard diesel fuel and a pure biodiesel. Multiphase cavitating flows inside diesel nozzles are analyzed by means of unsteady CFD simulations using a two-fluid approach with consideration of bubble dynamics, on moving grids from needle opening to closure. Two five-hole nozzles with cylindrical and conical holes are studied and their behaviors are discussed taking into account the different properties of the two fuels. Extent of cavitation regions is not much affected by the fuel type. Biodiesel leads to significantly higher mass flow only if the nozzle design induces significant cavitation which extends up to the outlet section and if the injector needle is at high lift. If the internal hole shaping is able to suppress cavitation, the stabilized mass flows are very similar with both fuels.

In order to evaluate the potentialities of bioderived diesel fuels, the effect of fueling a 1.9 l displacement HSDI automotive Diesel engine with biodiesel and fossil/biodiesel blend on its emission and combustion characteristics has been investigated. The fuels tested were a typical European diesel, a 50% biodiesel blend in the reference diesel, and a 100% biodiesel, obtained by mixing rape seed methyl ester (RME) and recycled cooking oil (CME). Steady state tests were performed at two different engine speeds (2500 and 4000 rpm), and for a wide range of loads, in order to evaluate the behavior of the fuels under a large number of operating conditions. Engine performance and exhaust emissions were analyzed, along with the combustion process in terms of heat release analysis. Experimental evidences showed appreciably lower CO and HC specific emissions and a substantial increase in NOx levels. A significant reduction of smoke emissions was also obtained.

A two-step simulation methodology was applied for the computation of the injector nozzle internal flow and the spray evolution in diesel engine-like conditions. In the first step, the multiphase cavitating flow inside injector nozzle is calculated by means of unsteady CFD simulation on moving grids from needle opening to closure. A non-homogeneous Eulerian multi-fluid approach - with three phases i.e. liquid, vapor and air - has been applied. Afterward, in the second step, transient data of spatial distributions of velocity, turbulent kinetic energy, dissipation rate, void fraction and many other relevant properties at the nozzle exit were extracted and used for the subsequent Lagrangian spray calculation. A primary break-up model, which makes use of the transferred data, is used to initialize droplet properties within the hole area.

In the present paper, a detailed numerical and experimental analysis of a spray momentum flux measurement device capability is presented. Particular attention is devoted to transient, engine-like injection events in terms of spray momentum flux measurement. The measurement of spray momentum flux in steady flow conditions, coupled with knowledge of the injection rate, is steadily used to estimate the flow mean velocity at the nozzle exit and the extent of flow cavitation inside the nozzle in terms of a velocity reduction coefficient and a flow section reduction coefficient. In the present study, the problem of analyzing spray evolution in short injection events by means of jet momentum flux measurement was approached. The present research was based on CFD-3D analysis of the spray-target interaction in a momentum measurement device.

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.

The 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 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.

This work involves modeling internal and near-nozzle flows of a gasoline direct injection (GDI) nozzle. The Engine Combustion Network (ECN) Spray G condition has been considered for these simulations using the nominal geometry of the Spray G injector. First, best practices for numerical simulation of the two-phase flow evolution inside and the near-nozzle regions of the Spray G injector are presented for the peak needle lift. The mass flow rate prediction for peak needle lift was in reasonable agreement with experimental data available in the ECN database. Liquid plume targeting angle and liquid penetration estimates showed promising agreement with experimental observations. The capability to assess the influence of different thermodynamic conditions on the two-phase flow nature was established by predicting non-flashing and flashing phenomena.

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.

This work aims at analyzing the fluid dynamic characteristics of a Ducati 4 valves SI engine, for racing motorcycle, during the intake and compression strokes, focusing on the correlation between steady state flow test data (experiments and simulations) and transient CFD simulation results, including the effect of variable valve actuation strategies with independent intake valve actuation. Several steady state flow test data were available in terms of maps of the discharge, tumble and swirl coefficients, at any combination of asymmetric lifts of the two intake valves. From these steady state data it can be argued that asymmetric strategies could enhance engine full load and part load operation characteristics, by exploiting favourable trade off occurring between the opposing needs for high mass flow rate and high charge motion intensity.