Characterization of engine's combustion-vibration using diesel and biodiesel fuel blends by time-frequency methods: A case study

• Combustion characteristic for diesel-biodiesel blends was studied in this research.
• We investigate the knock and pressure changes inside cylinder by vibration signal.
• Time-frequency analysis (STFT and MSC) was used for difference in fuels combustion.
• Fuel blend was an important factor in injector spraying and creating engine knock.
• The smoothest engine working was for B40 with maximum power than other fuels.

Engine knocking and faults usually cause lower efficiency, abrasion in parts, and noise pollution. Various methods have been developed to diagnose faults and detect engine knocking. This research was conducted to study combustion, vibration, and also knocking in diesel engines produced due to the fuels, such as D100, B20, B40, B60, B80, and B100 diesel-biodiesel fuel blends. Therefore, two time-frequency representations (TFR) are used to characterize the non-stationary and noisy vibration signals measured on engine body. For an ideal combustion, the acceleration peak values were found within the frequency range of 0–7 kHz in a TFR diagram. However, each fault in valves and injection units can cause high-frequency vibrations between 7 and 25 kHz for each cylinder in the TFR diagram. It was concluded that the maximum and minimum vibrations were obtained in B40, B20, and D100, B80 fuel blends respectively during full-load engine mode. Moreover, the maximum vibration shocks were obtained for B20 and B40 fuel blends and minimum values were obtained for D100 and B80. The result achieved for B40 fuels blend showed a large amount of combustion energy loss due to the uncontrolled vibrations. However, the smoothest engine performance was obtained for B40 fuel blend.