Search Results

In the modern GDI systems, the optimization of the fuel injection process is essential to prepare an air-fuel mixture capable to promote efficient combustion and reduce fuel consumption and pollutant emissions. A key feature for a better atomization is the fuel injection pressure. The increasing of the injection pressure is considered a good way for particle number (PN) reduction due to improved spray atomization, faster evaporation and better mixture formation. In this paper, a multi-hole GDI injector was tested to investigate the effects of very high injection pressures (IVHP), in addition to different ambient densities and temperatures, on the fuel spray morphology, in a cycle-resolved images analysis. Commercial gasoline was injected at the pressures ranging between 40.0 to 70.0 MPa, at gas densities varying between 1.12 to 11.5 kg/m3, and gas temperature up to 200°C.

Though CFD methods have become very popular and widespread tools in the early as well as more advanced automotive design stages, they are still not so common in the motorcycle industry branch. The present work aims at the development of a comprehensive simulation environment, based on the open-source finite volume toolbox OpenFOAM®, for the aerodynamic and thermal fluxes optimization of a full motorcycle-and-rider geometry. The paper is divided in two parts: in the first one, the OpenFOAM® code is evaluated for a cold flow aerodynamic analysis, using a slightly simplified version of the Aprilia RSV4 motorbike geometry; in the second one, a mixed reduced scale-full scale methodology is proposed for the simultaneous assessment of aerodynamic forces and heat transfer performances of the engine cooling system. Results have been compared against other well established commercial CFD packages and, where available, with experimental measurements.

Computational Fluid Dynamics is nowadays largely employed as an effective optimization tool in the automotive industry, especially for what concerns aerodynamic design driven by critical factors such as the engine cooling system optimization and the reduction of drag forces, both limited by continuously changing stylistic constraints. The Ahmed reference model is a generic car-type bluff body with a slant back, which is frequently used as a benchmark test case by industrial as well as academic researchers, in order to investigate the performances of different turbulence modeling approaches. In spite of its relatively simple geometry, the Ahmed model possesses many of the typical aerodynamic features of a modern passenger car - a bluff body with separated boundary layers, recirculating flows and complex three-dimensional wake structures.

Alternative diesel fuels from renewable sources (biodiesels) have increased significantly interest due to their potential CO₂ emission benefits, capability to reduce unburned hydrocarbons and particulate matter emissions, biodegradability and non-toxicity. Biodiesels undergo ageing effects due to autoxidation processes of their molecular chains. Ageing leads to a variety of decomposition products like peroxides, alcohols, aldehydes and carboxylic acids. They are detectable as alterations of chemical properties, odor and taste (rancidity). The characteristics of Rapeseed Methylester (RME), RME aged and diesel sprays have been analyzed for different injection strategies in engines. The tests have been performed on a Bosch second generation common rail solenoid-driven fuel injection system capable of 160 MPa maximum injection pressure, fitted on EURO5 diesel engine for passenger car applications.

This paper reports the study of the effects of alternative diesel fuel and the impact for the air-fuel mixture preparation. The injection process characterization has been carried out in a non-evaporative high-density environment in order to measure the fuel injection rate and the spatial and temporal distribution of the fuel. The injection and vaporization processes have been characterized in an optically accessible single cylinder Common Rail diesel engine representing evaporative conditions similar to the real engine. The tests have been performed by means of a Bosch second generation common rail solenoid-driven fuel injection system with a 7-holes nozzle, flow number 440 cc/30s @100bar, 148deg cone opening angle (minisac type). Double injection strategy (pilot+main) has been implemented on the ECUs corresponding to operative running conditions of the commercial EURO 5 diesel engine.

The paper aims at performing an environmental and energetic optimization of a naturally aspirated, light-duty direct injection (DI) diesel engine, equipped with a Common Rail injection system. Injection modulation into up to three pulses is considered starting from an experimental campaign conducted under non-evaporative conditions in a quiescent optically-accessible cylindrical vessel containing nitrogen at different densities. The engine performances in terms of power and emitted NOx and soot are reproduced by multidimensional modelling of the in-cylinder processes. The radiated noise is evaluated by resorting to a recently developed methodology, based on the decomposition of the CFD 3D computed in-cylinder pressure signal. Once validated, both the CFD and the acoustic procedures are applied to the simulation of the prototype engine and are coupled to an external optimizer with the aim of minimizing fuel consumption, pollutant emissions and radiated noise.

Liquid atomisation is an important technical field for a wide range of engineering and industrial applications, particularly in the field of internal combustion engines. In these engines, in fact, the amount of pollutants at the engine-out interface is directly related to the quality of the combustion process, which is in turn determined by the quality of the air-fuel mixture preparation in Direct Injection (DI) engines. As a consequence numerical-experimental research is crucial to their development. Despite the significant amount of research that has been carried out on DI engines simulation, breakup modelling is still a challenge. In this paper we present a new numerical model for multiphase flows that could be particularly suited for liquid jet and droplet breakup simulation. The model is based on a Lattice Boltzmann (LB) solver coupled to a higher order finite difference treatment of the kinetic forces arising from non-ideal interactions (potential energy).

GM Powertrain Europe and Istituto Motori CNR have undergone a research project aimed at studying the effects on engine performance, emissions and fuel consumption of alternative diesel fuels, from both first (FAME) and second (GTL) generation. The present paper reports some of the results achieved studying the impact on injection and spray behavior of rapeseed and soybean methyl-esters, as well as of GTL diesel blends. The test were performed on a Bosch second generation common rail solenoid-driven fuel injection system capable of 1600bar maximum injection pressure, fitted on GM 1.9L Euro4 diesel engine for passenger cars. The characterization of the injection process has been carried out in terms both of fuel injection rate, as well as of spatial and temporal fuel distribution in a quiescent non-evaporative optically accessible chamber.

The modern common rail Diesel engines are normally optimised for being fuelled with the commercial Diesel fuel. Consequently, the ECU calibrations are defined to realize the best compromise between performances and emissions. If the engine is fuelled with an alternative biofuel with different characteristics (net heating value, stoichiometric A/F ratio, density, viscosity, etc.) it is clear that the calibration must be modified. Interest in fuels from renewable sources and their use in transportation has grown over the last decade. This is because of their biodegradability, potential improvements in exhaust emissions and benefits on the virtuous CO2 cycle of the earth. This paper demonstrates that it is possible to optimise emissions and performances of a light duty C.R. Diesel engine fuelled with a vegetable derived fuel (Rapeseed Methyl-Ester) pure or blended with commercial Diesel fuel.

The present paper describes a study, which can enable a small displacement (1.3 liter) turbocharged European CR-diesel engine to tolerate an important increase in EGR-level. The analysis is performed by use of a 3D virtual numerical engine model, which isolates the main parameters that must be optimized within the perimeter of the combustion chamber. The paper gives a short introduction to the physical background for NOx and soot-formation as well as a recall of the main issues related to the simulation models used in the virtual engine simulation. The analysis is performed in a 9 points load/speed test matrix. Several EGR-rates are studied as well as the impact of a precise temperature control of the exhaust gas re-introduced in the intake manifold. The paper concludes by an analysis of the cumulated impact on the EGR-level tolerated by the engine after the introduction of the suggested optimization measures.

Spray impingement on walls is an important physical process in modern DI Diesel engines as it greatly influences mixture formation, combustion process and exhaust emissions. The mixture preparation is, in fact, a crucial aspect for the correct operation of the engine as it significantly affects the combustion process. In this paper three models, among the available in literature, have been selected and implemented in the KIVA-3V code. Namely, the models by O'Rourke and Amsden (OA model) [1, 2], by Bai and Gosman (BG model) [3] and by Lee et al. (LR model) [4, 5] are compared in terms of performance and capability of representing the splash phenomenon. The model capabilities are firstly tested comparing the numerical results with four sets of experimental literature data, characterized by low injection pressures. The high injection pressures of modern Diesel engines result in droplets velocities emerging from the nozzle greater than 300 m/s.

This paper illustrates the results of an experimental investigation on the liquid fuel spray from a multi-jet common rail injection system both under non evaporative and evaporative conditions. Tests have been taken using a 5 hole, 0.13 mm diameter, 150° spray angle, micro-sac nozzle having a flow rate of 270 cm3/30 sec@10 MPa exploring different injection strategies. Experiments have been taken, under non evaporative conditions, injecting the fuel within stagnant inert gas, at different density, in a high-pressure optically-accessible cylindrical vessel with three large quartz windows. Under evaporative conditions, the experiments have been taken within a crank-case scavenged single-cylinder 2-stroke direct injection Diesel engine provided of optical accesses to the combustion chamber. It allows to study the fuel injection process under thermodynamic conditions similar to those currently reached in modern direct injection diesel engines.

The introduction of the high-pressure fully electronic-controlled injection systems has opened a number of new possibilities to optimize diesel engine performance and to reduce pollutant emissions. However greater research efforts are required to meet future European emission legislation. The control of the combustion process, which determines to a large extent the amount of pollutant emissions, requires primarily an understanding of its physics and chemistry as well as the capability to modify one or more of the interdependent process parameters in a given direction. Since many parameters have to be considered, a combined experimental-numerical approach is required.

Interest in fuels from renewable sources and their use in transport has grown over the last decade. This is because of their biodegradability, potential improvements in exhaust emissions and benefits on the virtuous CO2 cycle of the earth. Biodiesel fuels can be derived from rapeseed, sunflowers, and other kind of seeds or from UFO (Used Fried Oil). This paper analyses the results of an experimental study fuelling a Common Rail Diesel Engine with a 100% rapeseed Biofuel, with a blend of rapeseed and UFO biodiesel and compares it with commercial diesel fuel Other papers by the same authors compared the different physic-chemical characteristics of biofuels, against diesel fuel and the consequent different spray characteristics that affect the combustion phenomenon. These characteristics are correlated with the different performances and emissions obtained in the experimental activity when a modern Common Rail light duty diesel engine is adopted.

This paper illustrates the results of an experimental characterization of a high pressure diesel spray injected by a common rail (CR) injection system both under non-evaporative and evaporative conditions. Tests have been made injecting the fuel with a single hole injector having a diameter of 0.18 mm with L/D=5.56. The fuel has been sprayed at 60, 90 and 120 MPa, with an ambient pressure ranging between 1.2 to 5.0 MPa. The spray evolution has been investigated, by the Mie scattering technique, illuminating the fuel jet and acquiring single shot images by a CCD camera. Tests under non-evaporative conditions have been carried out in an optically accessible high pressure vessel filled with inert gas (N2) at diesel-like density conditions. The instantaneous fuel injection rate, obtained with a time resolution of 10 microseconds, has been also evaluated by an AVL Fuel Meter working on the Bosch Tube principle.

The paper aims at providing information about the spray structure and its evolution within the combustion chamber of a heavy duty direct injection (HDDI) diesel engine. The spray penetration is investigated, firstly under quiescent conditions, injecting the fuel in a vessel under ambient temperature and controlled back pressure by both numerical and experimental analyses using the STAR-CD code and the imaging technique, respectively. Experimental results of fuel injection rate, fuel penetration, and spray cone angle are used as initial conditions to the code and for the comparison of predictions. The experimental investigation is carried out using a mechanical injection pump equipped by the heavy duty eight cylinder engine. Only one of its plungers has been activated and the fuel is discharged through a seven holes mechanical injector, 0.40 mm in diameter.

The paper presents a study of the influence of fuel pressure supply fluctuations on the upstream side of the fuel injector atomizer. The study is performed over a wide range of pressures (70 to 130 Mpa) with two different common-rail (CR) high-pressure fuel injectors. The common atomizer is a VCO-type equipped with conically shaped atomizer bores. With the injector tip (nozzle) mounted in a counter-pressure vessel the pressure fluctuations in the fuel-rail and in the injector body are recorded simultaneously with stroboscopic Schlieren-visualization of the time-resolved spray behavior. It is demonstrated that not only the instantaneous mass flow is affected. As a function of rail-pressure, pulse-width and injection strategy the pressure fluctuations change the spray hard-core structure and its break-up behavior.

The main objective of the paper is to describe the optimization work performed to adjust direct injection (DI)-technology to SI-engines running at high (8000 to 10000 rpm.) and extremely high speeds (more than 18000 rpm). In the first category are located a certain number of small and middle displacement two-stroke series produced engines. In the second category are the typical high power racing engines used for competitions like the formula 1. The first part of the paper describes the particular requirements that an in-cylinder fuelling and mixture preparation will have to fulfill with the extremely short period available for introduction and vaporization of the fuel. The paper continues with a description of the different spray shapes, spray penetration velocities and atomization capabilities, which are optimal for the different combustion chamber architectures.

The paper presents a study of a key-element in the mixture preparation process. A typical common-rail (CR) high-pressure fuel injector was fitted with a prototype injector nozzle with atomizer bores of a particular conical layout. It is demonstrated within certain layout limits, that a considerable enhancement can be obtained for the secondary break-up of the hard-core fluid sprays produced by the nozzle. The impact on the combustion process is examined in terms of pressure and heat release as well as of the engine-out pollutant emission. The results are compared to those of an earlier developed CR high-pressure injector nozzle. The atomization behavior of the prototype nozzle is illustrated through experimental results in terms of engine-out emissions from a 1.3-liter turbo-charged passenger car diesel engine. The detailed spray behavior is visualized on a component test rig by use of specially developed optical visualization techniques.

In this paper a numerical analysis is carried out of the flow characteristics in the intake system of a high performance engine. To this aim, the experimental flow bench results - obtained in tests performed on a Ducati Corse 4 valves racing engine head and presented in the parallel work [1] - are compared with the numerical ones. In [1] an experimental analysis was performed to evaluate the influence, on the flow characteristics in the intake system of a high performance 4 stroke - 4 valve internal combustion engine Notwithstanding the macroscopic meaning of the measured global coefficients Cd (Discharge Coefficient) and Nt (Tumble Number), the comparative analysis of their respective trends allowed some hypotheses to be drawn on the flow development internally to intake system ducts. In order to confirm the conclusions drawn in [1] and to reach a deeper insight in the flow characteristics, numerical simulations were performed.