Knock and Cycle by Cycle Analysis of a High Performance V12 Spark Ignition Engine. Part 1: Experimental Data and Correlations Assessment

In this paper, a high performance V12 spark-ignition engine is experimentally investigated at test-bench in order to fully characterize its behavior in terms of both average parameters, cycle-by-cycle variations and knock tendency, for different operating conditions. In particular, for each considered operating point, a spark advance sweep is actuated, starting from a knock-free calibration, up to intense knock operation. Sequences of 300 consecutive pressure cycles are measured for each cylinder, together with the main overall engine performance, including fuel flow, torque, and fuel consumption. Acquired data are statistically analyzed to derive the distributions of main indicated parameters, in order to find proper correlations with ensemble-averaged quantities. In particular, the Coefficient of Variation (CoV) of IMEP and of the in-cylinder peak pressure (pmax) are correlated to the average combustion phasing and duration (MFB50 and Δθb), with a good coefficient of determination. In addition, a high-pass-filtering technique is used to derive the cycle-by-cycle scattering of the Maximum Amplitude of Pressure Oscillation (MAPO) index. A similar statistical analysis is carried out to derive the log-normal distributions of the MAPO index and a methodology to asses a proper knock threshold is applied to identify the presence of knocking combustion. The above data represent the prerequisites for the implementation and validation of an advanced 1D model, described in Part 2, taking into account cycle-by-cycle variations, and finally aiming to identify the knock-limited spark advance on a completely theoretical basis.