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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].

A commercial four stroke spark ignition engine has been tested at steady conditions, with three different compression ratios, namely: 10, 11.5 and 13. Exhaust Gas Recycle (EGR) has been varied in the range 0% - 20 %. Air/fuel ratio has been maintained at stoichiometric by a closed loop control with Exhaust Gas Oxygen sensor feedback. Significant gains on fuel economy and CO emission index have been achieved at medium and high loads by the simultaneous adoption of EGR and high compression ratios. In these conditions the sum of HC and NOx emission indices attains significant reductions at any load. The tests have shown that EGR allows to avoid knock even at wide open throttle and Maximum Brake Torque timing.

A system for both ignition and ion current measurement was designed and set up at Istituto Motori. Particular attention was paid to the problem of dissipating the residual energy stored in the ignition coil, reducing the electromagnetic interferences and especially improving the response of the measurement system. In order to assess the capability of the ion current signal to give reliable and accurate information for knock detection, a number of tests were carried out at full load on a commercial PFI four cylinder engine, at various air/fuel ratios and spark timings. Some knock indices based on the ionization signal, both band pass filtered and non-filtered, were introduced, in particular: the Amplitude of the Second Ionization Peak (ASIP), the Mean not filtered Ionization Current signal (MIC), the Maximum Amplitude of Ionization Current signal Oscillation (MAICO), the Integral of Modulus of filtered Ionization Current signal Oscillation (IMICO).

3D calculations of homogeneous charge spark ignition engines were carried out using the KIVA III code. A modified wall function was introduced by an approximate solution of the one -dimensional simplified equations of energy and mass balance. The model takes into account the pressure unsteadiness and the mean rate of combustion in boundary layer. Moreover a modified turbulent conductivity law was proposed following the classical Prandtl approach. The predictions of heat transfer model were compared with the mean heat flows calculated by thermodynamic processing of pressure cycles in motored engines. Two engines with different geometry were used. Namely: a CFR engine running 900 rpm and an AVL engine, running at 2200 rpm. The results regarding heat transfer seem very encouraging. The combustion phase was simulated using a Fractal Flame Model (FFM) elsewhere describe. Simulations in firing conditions were compared with measurements carried out on a CFR engine and on an AVL engine.

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.

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.

A number of Variable Valve Actuators (VVA) has been recently proposed to improve the performances and the part load efficiency of spark ignition engines. Due to their peculiarity, these systems work with different strategies (late or early inlet valve closing, reduced lift etc.). The shape and the timing of the valve lift affect not only the pumping losses, but also air motion inside the cylinder. That influences mixture formation and combustion evolution of Direct Injection Spark Ignition (DISI) engines. The present paper compares the performances of different VVA systems with the aid of a 1D code for the simulation of the inlet and of the exhaust phases, and of a fluid-dynamic 3D code to evaluate mixing phenomena inside the cylinder.

A fuel matrix consisting of twelve gasolines was tested in presence of Exhaust Gas Recirculation (EGR). The fuels have different percentages of aromatics (20÷35% vol.), olefins (5÷15% vol.) and oxygen (0÷2% wgt). Four different oxygenated compounds (MTBE, ETBE, TAME, DIPE) were chosen as additives. Tests were carried out on a MPI premixed spark ignition engine at steady operating conditions (2000 rpm, 2 bar BMEP, 13.5% EGR) and stoichiometric air/fuel ratio. Regulated and unregulated pollutants were measured upstream the catalytic converter. Cyclic variation of Indicated Mean Effective Pressure (IMEP) in presence of EGR was also evaluated. The adoption of EGR increases PAH and aldehydes emissions, and decreases benzene emissions of unoxygenated fuels. Conversion efficiencies of CO and of total HC are lowered by EGR. An increase of aromatics content in an unoxygenated fuel leads to higher engine out NOx emission. This effect is reduced if MTBE is added.