Search Results

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.

Combusiton of pine pyrolysis oil droplets was studied at different pressures up to a maximum of 60 bar in a single-droplet combustion chamber. Oil droplets, with diameters between 400 μm and 120 μm were suspended to a thermocouple of to a quartz fiber. Their behavior was followed by means of high-speed digital imaging based on a shadowgraph scheme. About two thousands of frames were collected during every test with acquisition speed between 400 and 4000 frames/s. Droplets were easy to ignite at normal as well as at high pressure. Increasing the pressure the intensity of swelling phenomena, undergone by droplets, decreased and completely disappeared at pressures higher than 20 bar. However, bubbling and foaming were always observed. Liquid-phase pyrolysis and the formation of cenospheres as combustion residual were observed under all the pressure conditions.

The electric storage equipment plays a relevant role in the framework of the minimum impact vehicles. Speaking about both electric and hybrid vehicles the battery still remain a necessary subsystem in order to realise an energy buffer and/or a power buffer. Normally the batteries (i.e. lead acid, Ni–MeH, semibipolar) are delivered from the manufacturers without a SOC (State of Charge) indicator. In this article it will be approached a methodology to estimate the state of charge of a battery using only the current and voltage signal. The algorithm came from a previous patent of Centro Ricerche FIAT and it will be specially modified in order to be applied to a battery system of an electric vehicle propelled by a 15 kW motor and with a 5KW fuel cell auxiliary power unit. The aim of the technology is to overtake the difficulties from the use of in-site sensors (i.e. optical or chemical).

The paper deals with on board power plants for electric road vehicles, supplied by fuel cells. As it has already been shown [1], the plants’ performances may be analysed by means of a simple equivalent electric network. The paper contributes to this performance analysis by giving some characteristic surfaces of supplied dc voltages and to the definition of control strategies by suggesting a sample structure of a digital programme for the management of the dc plant electrical energy sources.

The microstructures of atmospheric pressure, counter-flow, sooting, flat, laminar ethylene diffusion flames have been studied numerically. Aromatics growth beyond 2-, 3-ring PAH is analyzed through a radical-molecule reaction mechanism which, in combination with a previously developed PAH model, is able to predict the concentration profiles of aromatic structures formed in flames. Modelling results are in good agreement with experimental data and are used to interpret the soot volume fraction and PAH fluorescence measured in flames.

Conventional methods for combustion gas concentration measurement are typically based on gas sampling, sample treatment and subsequent analysis. These procedures could affect the species concentrations in particular when temporal variations of process parameters are under study. Moreover, in these methods, the concentration measurements are usually performed at standard temperature and pressure. In order to overcome these limitations, in-situ and real-time concentration measurement techniques are needed. In this paper, an in-situ technique with high spatial and temporal resolution, based on ultraviolet-visible absorption spectroscopy, was proposed. This technique allowed the simultaneous determination of NO and OH absolute concentrations inside optically accessible diesel combustion chamber. Temporal and spatial distribution of OH and NO was evaluated.

Downsizing is an effective way to further improve the efficiency of SI engines. To make most of this concept, the compression ratio has to be adjusted during engine operation. Thus, the efficiency disadvantages during part load can be eliminated. A fuel consumption reduction of up to 30% can be realized compared to naturally aspirated engines of the same power. After the assessment of several known concepts it turned out that the eccentric crankshaft positioning represents an appropriate solution which meets the requirements of good adjustability, unaltered inertia forces, low power demand of the positioning device and reasonable design effort. The basic challenges posed by the eccentric crankshaft positioning have been tackled, namely the crankshaft bearing and the integration of the newly developed power take-offs which have almost no influence on the base design.

The optimization of diesel engine performance and emissions can be achieved through a better understanding of the in-cylinder combustion process. Advanced non-intrusive optical techniques are providing new tools for investigating the thermo-fluid dynamics processes as well as they are contributing to develop predictive models for DI diesel combustion. High-speed images of spray and flame evolution as well as UV-visible chemiluminescence measurements were carried out in an optical 0.5-liter, single-cylinder, four-stroke, direct- injection diesel engine equipped with a prototype four valves cylinder head and a fully flexible CR injection system. In order to evaluate the effect of different injection strategies on the combustion process, measurements were performed varying injection parameters. The ignition location and time were individuated by combustion visualization and detection of radical species, obtained by chemiluminescence measurements.