Search Results

An experimental and numerical investigation, using the Laser Doppler Anemometry (LDA) technique and a 3D fluid-dynamic code (KIVA 3V), was carried out in a prototype engine under steady-state conditions. The aim of the present activity was the flow field characterization and the effect of the intake geometry on the in-cylinder tumble flow. A new steady flow test rig designed for capturing the tumble motion within a test cylinder, made by a blower and an engine head, was assembled to simulate the intake flow. The engine head was mounted on an aluminum cylinder, having the same bore as the real engine. The cylinder was provided with optical accesses on the periphery and a flat optical window located at the bottom to a depth equal to the stroke of the engine. The cylinder was also equipped with two cylindrical ducts, used as air outflow ports.

Modeling autoignition in diesel engines is a challenging task because of the wide range of equivalence ratios over which it takes place. A variety of detailed autoignition models has been proposed in literature for different fuels. Since these models include about one thousand chemical reactions and more than one hundred species, their application to CFD engines simulations requires a very high computational time, so that they are of no practical interest. In order to lower the computational time, a number of reduced models has been developed including the shell model, which is one of the most used. This model does not take into account low temperature kinetics and consists of seven reactions and three radicals. The use of this model in engine simulations shows its limits when applied to delayed injections because of the predominant influence of the low temperature kinetics. A modified version of the shell model is proposed in the present study.

This paper describes the project of a "small' single-cylinder direct injection diesel engine (300 cc). It is equipped with optical accesses to analyze the diesel combustion process employing the most recent optical diagnostic techniques. The injection system used is a second-generation common- rail system. The optical accesses are placed on the piston and on the cylinder wall.

The improvements of the solenoid injector and of the Electronic Control Unit of the present Common Rail injection system (C.R.) allow the use of multiple sequential injections. Thanks to this feature this advanced Common Rail system is capable to perform up to five consecutive injections in one engine cycle thus improving control of the combustion process. In particular, in some operating conditions, the activation of a small injection after the main one allows the oxidation of the soot produced in the previous stages of the combustion process, without increasing nitrogen oxide emissions. This paper describes the experimental results obtained with the application of a prototype of this advanced Common Rail system both to a Fiat L4 1.9 JTD 8 valve engine and to a single-cylinder prototype, having the same combustion system and large optical access allowing investigation of the injection and combustion processes.

An experimental and numerical study has been conducted investigating Diesel spray injection phenomena. Digital images of the liquid spray were made in a steady-state pressure chamber at a constant operating pressure and temperature. 5-hole injectors with two different nozzle hole diameters were measured at an injection pressure of 800 bar. The measurements were used to study the dynamic effects of the spray injection. Three dimensional numerical simulations of the spray based on a Lagrangian stocastic spray model of discrete droplets were performed. The pressure chamber images were used to validate the numerical spray simulations. Various models for the primary and secondary droplet breakup were investigated. The simulation results are presented along with a comparison of the measured and numerical spray injection showing good correlation regarding spray penetration and cone angle.

Modern Internal Combustion Engines - especially Direct Gasoline Injection engines (DGI) - are equipped with an increasing number of actuators, thus enabling the application of new combustion systems for passenger cars. To fully take advantage of the potential of the combustion system in reducing fuel consumption, it is important to optimize these parameters simultaneously. The methodology using the CAMEO Optimization Tool supports the basic calibration as well as the optimization in the multidimensional room. Further it is important, to provide the knowledge of the engine behavior through out the whole ECU-calibration process.

A comprehensive set of computational and experimental results for high- pressure diesel sprays are presented and discussed. The test cases investigated include injection of diesel into air under both atmospheric and high pressure/temperature chamber conditions, injection against pressurized and cross-flowing CF6 simulating respectively the density and flow conditions of a diesel engine at the time of injection, as well as injection into the piston bowl of both research and production turbocharged high-speed DI diesel engines. A variety of high-pressure injection systems and injector nozzles have been used including mechanical and electronic high-pressure pumps as well as common-rail systems connected to nozzles incorporating a varying number of holes with diameters ranging from conventional to micro-size.

An AMESim model of the injection system has been developed introducing an automatic conversion of an experimental current signal into the force generated by the solenoid. The simulator realizes five multiple injections with different pauses. Using a dedicated current input, with faster rising and falling times, it was possible to realize smaller dwells between injections, optimizing the Bosch Common-Rail (C-R) system timing, without any mechanical modification. Using a commercial injector and an appropriate injection current trend, all the simulation results have been confirmed experimentally. Photographic sequences of a five holes mini-sac nozzle making five consecutive injections at 400, 800 and 1200 bar respectively were taken at ambient pressure and temperature. They showed that both spray penetration and cone angle at all operative conditions are very uniform and stable. Good agreement between experiments and simulations of needle lift has been obtained.

Quantitative measurements of the soot volume fraction and diameter performed by spectroscopic techniques within the combustion chamber of a diesel engine are employed to aid multidimensional simulation of the soot formation and oxidation processes. By changing the start of fuel injection, two different operating conditions are considered, which are characterized by different relative importance of the premixed to the diffusive stage of the combustion process. Both the reduced models by Hiroyasu et al., and the one by Nagle and Strikland- Constable are employed within the numerical simulation. The reason of the peculiar over-prediction of soot concentration of the latter model is discussed and related to the need of furnishing coherent values of the soot particle density and mean diameter.

The aim of this work is to investigate Common Rail injector behavior towards multiple injection strategies. A numerical model has been developed to simulate the electro-fluid-mechanic behavior of a Bosch mass production injector (standard injector) and validation against experiments has been performed. In order make the injector performing multiple injections, a deep investigation has been numerically carried out. The numerical study highlighted different area where injector may be improved with particular emphasis on electronic driving circuit. A new driving circuit concept, previously developed, has been successfully simulated showing promising fast-response capability for injector actuation.

Although internal combustion engines display high overall maximum global efficiencies, this potential cannot be fully exploited in automotive applications: in real conditions, the average engine load (and thus efficiency) is quite low and the kinetic energy during a braking phase is lost. This paper presents a new hybrid pneumatic – combustion engine concept, and the associated thermodynamic cycles, which is able to store energy in the form of compressed air. This energy can be issued from a braking phase or from a combustion phase at low power. The potential energy can then be restored to start the engine, or charge the engine at full load. The regenerative breaking combined with the engine downsizing should provide a great improvement in terms of fuel economy in typical slowdown – acceleration situations.

The paper deals with electric drives for road vehicles. In particular, AC drives are considered, their performances are shown and the advantages in choosing this kind of drive are made clear. An asynchronous drive is considered and its mathematical model is defined so that an energy-saving feeding algorithm can be set up. The feeding algorithm is suggested and some simulations are realized while taking the drive as operating in accordance with an ECE standard cycle.

The aim of this paper is to analyse the main concerns related to on board hydrogen catalytic production of fuel cell electric vehicles, starting from different gaseous and liquid fuels. In particular, limits and potentialities of hydrocarbons and alcohols have been examined, considering steam reforming and partial oxidation reactions with reference to emission and efficiency implications. Preliminary results of an experimental investigation on steam reforming of natural gas and liquid hydrocarbons are reported. Furthermore, a mono-dimensional mathematical model of methane steam reformer based on first order kinetics has been developed to simulate the experimental results.

In the frame of the IEA-AMF, Annex XVII project ‘Real Impact of New Technologies for Heavy Duty Vehicles’, three state-of-the-art city bus technologies were evaluated for fuel consumption and emissions in real city traffic and in a number of test cycles, both on engine and on vehicle level. One of the three buses was a natural gas bus with multi-point fuel injection, stoichiometric fuel control and three-way catalyst. Compared to the other tested technologies, this engine reached very low exhaust gas emissions. The paper will discuss the results obtained with the stoichiometric natural gas engine and compare the emissions in real traffic versus various engine test cycles, based on a number of influencing parameters. Concerning cycle characteristics it was the distribution of the engine operating points which had most effect on the exhaust gas emissions.

Previous work has shown that a novel partially stratified-charge approach can be effective in extending the lean limit of combustion and reducing the exhaust emissions from natural gas-fueled engines. The new technique provides a relatively rich mixture in the vicinity of the spark plug, while maintaining an ultra-lean homogeneous charge in the main chamber area. In order to provide the near-stoichiometric mixture near the spark gap, a small quantity of "pilot" fuel is injected through the spark plug just prior to ignition. It has been found that for most operating conditions the required pilot fuel quantity is less than 5% of the total fuel charge. This paper also reports the results of some recent one-dimensional computer modelling in which the partially stratified-charge technique has been investigated over a range of air-fuel ratios.

The paper deals with electric drives for road vehicles. In particular, AC drives are considered, their performances are shown and the adveantages in choosing this kind of drive is made clear. An asynchronous drive is considered and its mathematical model is defined co that an energy saving feeding algorithm can be set up. The feeding algorithm is suggested and some simulations are realized while taking the drive as operating in accordance with an ECE standard cycle.

One of the way for improving environmental performances of car propulsion system is the adoption of hybrid systems where the internal combustion engine (ICE) is coupled or temporary overtaken by an electric motor. The reference prototype of this article is the FIAT Multipla Hybrid where are possible three functional modes: Pure Electric mode, Serial Hybrid and Parallel Hybrid. Particularly it was approached the torque splitting algorithm applied to the parallel hybrid one; the work was first tested in simulation, after implemented in the electronic control units and finally tested on the field using the test bench of the 10 hybrid vehicles that belongs to the Atena Project [1].

An experimental and theoretical work on the low temperature oxidation of n-heptane in a jet stirred reactor has been carried out at different inlet temperatures. The presence of the typical low temperature pathologies of hydrocarbons (slow combustion, periodic and dumped cool flames) have been observed experimentally and correctly reproduced by the model. The selectivities of the intermediate and final products are also measured and compared with the theoretical evaluations. The agreement is satisfactory for all the investigated species in the whole temperature range (550–800 K). The introduction of 40% (volume) in the fuel has allowed to investigate the antiknock effect of toluene on the autoignition of n-heptane. At the same inlet temperature the n-heptane conversion shows the same general behaviour, but it is about 10% lower when toluene is fed in the mixture.

Soot formation from heavy hydrocarbons (n-hexadecane, decahydronaphtalene, N-heptylbenzene and 1-methyl-naphtalene) was studied behind reflected shock waves, using a light extinction technique. The highly diluted mixtures (99 to 99.8% of argon) were heated between 1300 and 2700 K. The pressure ranged from 650 to 1800 kPa. Soot induction delay times, growth rates and yields, were determined under pyrolysis and for two equivalence ratios (5 and 18). The effect of aromaticity, oxygen content, temperature and pressure on these parameters were investigated. Samples of soot particles formed behind shock waves and collected after experiments have been analyzed by transmission electron microscopy for a magnification of 5x10 4 in order to determine the size of elementary spheres. This parameter was studied in relation with the experimental conditions.