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Downsizing by turbo charging is a current approach for the reduction of fuel consumption of Spark Ignition (SI) engines. For downsized engines compression ratio has to be set as high as possible to achieve substantial gains in thermodynamic efficiency. Unfortunately, the possibility to take full advantages offered by downsizing is limited by knock phenomenon, which imposes constraints both on supercharging and compression ratios. Quasi-dimensional and multidimensional simulation can play a role of increasing importance for the design and the optimization of future engine prototypes more and more based on advanced combustion concepts, provided that well proven tools for knock simulation may be available.

In this work the authors present a model to simulate the in-cylinder pressure oscillations due to knock. Pressure oscillations are predicted by the explicit integration of a Partial Differential Wave Equation (PDWE) similar, in its structure, to the so-called “Equation of Telegraphy”. This equation differs mainly from the classical wave formulation for the presence of a loss term. The general solution of such equation is obtained by the Fourier method of variables separation. The integration space is a cylindrical acoustic cavity whose volume is evaluated at the knock onset. The integration constants are derived from the boundary and initial conditions. A novel approach is proposed to derive the initial condition for the derivative of the oscillating component of pressure. It descends, conceptually, from the integration of the linearized relation between the derivative of pressure versus time and the expansion velocity of burned gas.

The use of Variable Valve Actuation (VVA) systems offers many advantages in terms of increased engine power, reduced fuel consumption and pollutant emissions, accomplishing a significant improvement of the global efficiency of the engine. In the last decade different devices have been proposed to implement advanced and innovative VVA managements on four-stroke engines. ElectroMechanical Valve Actuator (EMVA) formed by two opposite magnets and two balanced springs seem to be a very promising solution among several camless actuation systems. This type of valve actuator is characterized by highly nonlinear and strongly coupled dynamics which makes very difficult to govern engine valve motion during the last part of the closing and opening strokes, where an unstable behavior is exhibited. In this regard the control problem of the EMVA is tackled in this paper.

The exhaust emissions produced by the combustion of methyl ester of rapeseed oil (biofuel) have been compared with the ones obtained using a commercial diesel fuel. The tests have been carried out on a Direct Injection Turbocharged (DITC) diesel engine according respectively to the ECE 15, to a non standard STOP and GO test cycle and to the European 13 MODE test procedure. Similar engines running at the same injection timing have been adopted in performing the transient and the steady tests. PAH emissions have been measured on transient cycles. The effects of injection timing and of Exhaust Gas Recirculation (EGR) on the emission in steady state tests has been evaluated too. In particular an exhaust oxydating catalyst has been employed in presence of EGR. The tests carried out indicate that, at the same injection timing, methyl ester promotes a rise in NOx emission, a decrease in HC and CO as well as a strong reduction of smoke.

Regulated and some unregulated emissions of a medium size non catalyst vehicle obtained with different formulations of unleaded fuels have been measured. Among the unregulated pollutants, 1-3 butadiene, benzene, toluene and polycyclic aromatic hydrocarbons (PAH) have been considered because of their toxicological hazards [ 1 ]. The emission levels have been compared with the ones obtained in similar conditions using a leaded reference fuel. Cold start Europe cycle and two not standard cycles have been used as basis of comparison for pollutants measurements. The effect of a three way catalytic system, fitted on the same vehicle, on regulated and unregulated emissions has been also studied, evaluating the conversion efficiency for the different pollutants. The same fuels have been tested in the same driving conditions on a small size passenger car too, equipped by the factory with catalyst and closed loop control system.