Search Results

The present paper describes a calculation procedure aimed to evaluate the evaporative loss of the lubricating oil deposed on the cylinder surface of i.c. engines. The model is based on the simultaneous solution of the diffusion and energy equations referred to the liquid/gas interface. A parametric analysis has been carried out to investigate the influence of some variables on oil evaporative losses. The calculation results show that both cylinder surface temperature and lubricating oil composition are significant parameters. Conversely, the oil film thickness does not seem to play an important role in evaporative loss. Furthermore, it has been ascertained that the lubricating oil evaporation is increased during the intake stroke. In any event, the evaporative loss represents a small percentage (a few percentage points) of total oil consumption if the distillate fractions are not too much light.

The present paper describes some experiments aiming to point out the link between oil consumption and reverse blowby. Some tests have been carried out on a motored single cylinder diesel engine. The reverse blowby gas mass flow has been evaluated by a thermodynamical model that utilizes both the measured combustion and second land pressures, and the blowby gas mass flow. Oil consumption has been measured in real time using a CO2-tracer method, whereas the blowby has been measured by a fast response orifice meter. The first ring lifting has also been recorded. It has been observed that, under certain engine operating conditions, both blowby and oil consumption assume quite constant levels. On the contrary, under other operating conditions, they vary in a cyclical way. However, in both cases, a relationship between blowby, reverse blowby and oil consumption can be recognized.

Multidimensional computations of homogeneous charge spark ignition engines were made with the KIVA II code. Combustion was simulated using the Fractal Flame Model of Zhao [5]. The original code was modified to obtain better calculations of heat transfer and to take into account the mass flow in the crevices. The predictions were compared with measurements carried out on a CFR engine. The tests were carried out in stoichiometric condition with isooctane. Compression ratio, ignition timing and EGR level were selected as test parameters. The global agreement between calculations and experiments was evaluated on the basis of heat release, indicated pressure patterns and pollutants measurements. For the lower compression ratio (7.7) the predictions of pressure cycle generally were in good agreement with experiments. However the empirical constant used in this condition cannot be used at higher compression ratio to obtain acceptable predictions of the pressure cycle.

Nowadays most passenger cars are equipped with spark ignition engines with a three way catalyst. Thus, the improvement of fuel consumption of this type of engine represents a very attractive goal. In fact, it may cause a reduction of pollutant emission, and simultaneously, it may give a contribution to the lowering of global CO2 production. In this paper, a strategy to control the combustion process of stoichiometric spark ignition engines is described. It is based on the adoption of Exhaust Gas Recycle (EGR) in high compression ratio engines. The tests carried out have shown that EGR can control the knock, even at Wide Open Throttle (WOT), with a compression ratio of about 13.5. Improvements of efficiency higher than 10%, at different loads and speeds, have been achieved by the adoption of this technique. Similar improvements have been obtained for CO, while more substantial reductions have been measured for NOx.

A numerical technique, aimed to the reconstruction of the analog output of an analyzer during continuous exhaust gas analysis, is presented. To this purpose the system composed by sample line and analyzer is described as a discrete Linear Time Invariant system with Finite Impulse Response. This technique has been tested on the reconstruction of the continuous emission measurements of diluted exhaust, obtained during a driving cycle acted on a chassis dynamometer. A comparison with the results obtained with CVS bag analysis has been made. The air/fuel ratio during the test cycle has been evaluated and compared with the signal of an oxygen sensor. An attempt to evaluate the emission indices in the transients has been also made, comparing the results of reconstructed and non reconstructed signals.

In the present paper a mathematical model on ring pack behavior is presented. The program considers the aspect of gas flow into and from the inter-ring volume and the relative ring dynamic. Furthermore a proper mass balance on the oil film has been considered to automatically evaluate both starvation and the oil accumulation in front of the inlet boundary of each ring. The model can give quite accurate predictions of the gas flows and the oil film thicknesses. It may be considered the first step for the simulation of oil mist formation and evaporation that are the most important phenomena for oil consumption prediction. UBRICATING OIL gives a strong contribution to particulate formation in diesel engines. Moreover it influences the unburned hydrocarbon emission of spark ignition engines because of the absorption/desorption phenomenon between the unburned fuel and the lubricating oil films [1, 2].

An evaluation of emission levels and fuel consumption of urban hybrid vehicles has been performed. Both heavy and light duty vehicles have been considered and a comparison on specific consumptions and emissions has been carried out between the hybrid and traditional configurations. The battery behavior during charge and discharge transients has been taken into account because it is one of the most critical elements of hybrid systems. The results of this investigation indicate the possibility to reach significant reductions of consumption and emissions through the adoption of hybrid systems for urban transports.