Search Results

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.

This paper reports investigations on diesel jet transients, accounting for internal nozzle flow and needle motion. The calculations are performed with Large Eddy Simulation (LES) turbulence model by coupling the internal and external multiphase flows simultaneously. Short and multiple injection strategies are commonly used in internal combustion engines. Their features are significantly different from those generally found in steady state conditions, which have been extensively studied in the past, however, these conditions are seldom reached in modern engines. Recent researches have shown that residual gas can be ingested in the injector sac after the end-of-injection (EOI) and undesired dribbles can be produced. Moreover, a new injection event behaves differently at the start-of-injection (SOI) depending on the sac initial condition, and the initial spray development can be affected for the first few tens of μs.

In this work an experimental analysis is performed to evaluate the influence of different flow bench test conditions and system configurations on the flow characteristics in the intake system of a high performance 4-valve, SI Internal Combustion Engine: valve lift, test pressure drop, throttle valve aperture, throttle valve opening direction in respect to the intake system layout (i.e. clockwise/counterclockwise), presence of the tumble adaptor. To this aim, experimental tests are performed on a Ducati Corse racing engine cylinder head, by measuring the discharge coefficient and the tumble coefficient. The several experimental data obtained by combining the different operational and geometrical parameters are analysed and discussed.

This paper presents the current research activity about an electro-hydraulic camless valve actuation system for internal combustion engines. From a general point of view, this system (Hydraulic Valve Control - HVC) is an open loop device for engine valve fully flexible camless actuation. In the HVC system, the valve actuation timing and duration are controlled by varying the driving signal of the pilot stage, which is governed by a solenoid, fast-acting, three-way valve; the valve lift is adjusted by varying the oil pressure of the power stage. This system uses hydraulic forces to open the engine valve while a mechanical spring is used for its closure. The HVC key element is a spool valve, which operates as a three way / three position valve. This element is designed in order to ensure the synchronization of its own motion with that of the poppet valve mass-spring system.

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 increase in the fuel price and more stringent regulations on greenhouse gases (CO2) make the engine compression ignition technology even more attractive in the context of internal combustion engines. This is because the modern turbocharged direct injection engines, with the common rail fuel system, are characterized by high combustion efficiency and power density, that make them particularly suitable both for applications on and off road. On the other hand, the compression ignition engines are subject to a heavy technological developments to meet the more stringent regulations on emissions of exhaust pollutants, especially PM and NOx. The adopted technologies have two main approaches, on the combustion and on the exhaust gas aftertreatment. The measures applied for combustion can reduce emissions, but with the risk of penalizing the other engine performances, such as noise, power output and fuel consumption.

In recent years, automotive engine manufacturers are increasingly focusing their attention on noise generated by plastic air intake manifolds (AIMs). Due to their lower density and stiffness, some deficiencies in terms of acoustical properties have been observed for plastic intake systems compared to metallic manifolds. In this framework, it seems to be very important to address not only the issue of reducing inlet noise, but also noise radiated via the coupled fluid-structure interaction. In this work three AIMs, a baseline and two modified models, nominally having equal breathing performance, have been analyzed and compared. The modified ones presented ribs and stays for strengthening the structure. The analyses were performed with concurrent experimental and numerical validated procedures.

In this paper, the intake system of the Lamborghini L804-V4 racing engine for the U.I.M. Class 1 World Off Shore Championship is analyzed. Since new rules by the Union Internationale Motonautique imposed the use of an air restrictor at the air scoop inlet, to limit the maximum engine power, it was necessary to redesign and optimize the entire air intake system. The work was carried out by exploiting both experimental and numerical approach in synergy in order to analyze the different characteristics and performance of a diffuser down stream the restrictor. The aim was to recover as much as possible kinetic energy in terms of static pressure in the air box. A further challenge to face was represented by the attempt to reduce the non-uniform air flow distribution to the different 12 cylinders, typical of this configuration.

A new camless system (referred to as Hydraulic Valve Control - HVC - system) is in an advanced state of prototyping and development. The present paper aims to support the new incoming activities concerning the possible modifications to the geometrical and mechanical characteristics of the system. The optimization of the new HVC system prototype is done using a multi-objective tool that integrates the hydraulic/mechanical simulator reproducing the physical model, with an optimization software. The latter tool can be used choosing a specific approach among different probabilistic mathematical models; the Genetic Algorithm approach was chosen to achieve the goal of the present study. The paper describes design optimization of the pilot stage of the actuator for given characteristics of the power stage and of the poppet valve.