Combustion Stability at Idle: A Non-Indicated Methodology For Analysis

A non-indicated approach was performed with the aim of finding an easy, time saving, and effective analysis methodology, to evaluate the idle quality of an IC SI engine, to be used both on the engine test bed and on-vehicle by means of Engine Control Unit calibration system. A classical method of evaluating engine idle stability is based on statistical analysis of the in-cylinder pressure signal, sampled with respect to the actual crank angle. However, this approach is expensive and is sometimes difficult to apply, especially if on-vehicle activity is required. An alternative approach has been evaluated, concerning statistical analysis of instantaneous engine speed, in comparison with pressure indicated analysis. An experimental on-vehicle activity was performed in order to evaluate the subjective idle quality perception. A correlation between the engine speed-based statistical parameters and the indicated pressure measurements versus annoying events perceived on the vehicle was detected and related targets were found. On-vehicle experimental results were confirmed by engine test bed activity on different engines.