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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).

Several methods have been proposed to use pressure signal for air/fuel ratio estimation, knock detection and optimal spark timing selection. In this paper some of these methods were compared, and their accuracy and effectiveness was checked. In order to avoid the misleading effects of measurement errors, the comparison was performed using a database of test conditions obtained by means of the WAVE code (Ricardo). New correlations physically based were introduced to evaluate the trapped air mass and the Exhaust Gas Recycling (EGR), cylinder per cylinder. These correlations can give a very important contribution to balance the air-fuel ratio in each cylinder and to improve EGR control strategies.

There is an increasing interest on innovative controls based on in-cylinder pressure measurement. However, due to current capabilities of ECUs, only a small number of pressure cycles can be sampled. Therefore suitable algorithms are required to extract from few pressure points the information useful to implement the desired control strategies. In this paper a method for the interpolation of in-cylinder pressure cycle during the constant mass phase of S.I. engines is described. It is based on the estimation of Cumulative Heat Release (CHR) in selected crank angle positions and on a simple algorithm of pressure reconstruction. To test this method, peak pressure position and magnitude have been identified on the basis of a set of experimental pressure cycles measured on a gasoline direct injection engine. In addition, a control scheme for the closed loop control of spark timing have been set up using a numerical engine (WAVE) and a numerical ECU build in the Matlab-Simulink environment.