Search Results

In this paper, an experimental and numerical analysis of combustion process and knock occurrence in a small displacement spark-ignition engine is presented. A wide experimental campaign is preliminarily carried out in order to fully characterize the engine behavior in different operating conditions. In particular, the acquisition of a large number of consecutive pressure cycle is realized to analyze the Cyclic Variability (CV) effects in terms of Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV). The spark advance is also changed up to incipient knocking conditions, basing on a proper definition of a knock index. The latter is estimated through the decomposition and the FFT analysis of the instantaneous pressure cycles. Contemporary, a quasi-dimensional combustion and knock model, included within a whole engine one-dimensional (1D) modeling framework, are developed. Combustion and knock models are extended to include the CV effects, too.

Spark-ignition engines are characterized by poor levels of thermal efficiency, it is known, especially when running at partial load. Since part-load operating points are the most commonly used in engine average life, achieving a given torque value with small displacement, high mean effective pressure engines, the so-called “downsizing”, permits, in general, to limit some typical engine losses (for instance: pumping and friction losses), improving the fuel consumption in a wide range of engine operating points. Small displacement engines, usually, achieve high toque values thanks to supercharging techniques. In this paper, knock risks for a small displacement turbo-charged spark-ignition engine have been analyzed. A parametric analysis of numerous variable influencing engine performance and knock resistance has been carried out by means of 1-D numerical simulations.