A Comparative Study on Knock Occurrence for Different Fuel Octane Number

Combustion with knock is an abnormal phenomenon which constrains the engine performance, thermal efficiency and longevity. The advance timing of the ignition system requires it to be updated with respect to fuel octane number variation. The production series engines are calibrated by the manufacturer to run with a special fuel octane number. In the experiment, the engine was operated at different speeds, loads, spark advance timings and consumed commercial gasoline with research octane numbers (RON) 95, 97 and 100. A 1-dimensional validated engine combustion model was run in the GT-Power software to simulate the engine conditions required to define the knock envelope at the same engine operation conditions as experiment. The knock intensity investigation due to spark advance sweep shows that combustion with noise was started after a specific advance ignition timing and the audible knock occur by increasing the advance timing. Therefore, the engine operation was divided into three regions; knock-free, light knock and heavy knock. The results for heavy-knock were well suited to audible knock detected by knock sensor. The simulation results from knock model divide the engine operation into two regions; normal combustion and knock region. The knock region was well suited to light-knock and heavy-knock which has been defined using experimental results. Next, an artificial neural network (ANN) model has been designed to classify the different RONs using engine rotational speed signal. The model classified different RONs accurately after starting point of noisy combustion (light-knock). This point defined from experimental results and was well suited with starting point of knock index increment from simulation results. The simulation tool ability to predict the knock envelope will reduce the experimental cost and time to generate the spark timing look-up table