Experimental investigation on the effect of compression ratio on detonation combustion characteristics of active pre-chamber engine

Turbulent Jet Ignition (TJI) engines show promising potential for enhancing engine efficiency. However, they differ significantly from conventional spark ignition engines in terms of in-cylinder combustion modes, rendering traditional detonation evaluation methods inadequate for accurately assessing TJI engine detonation states. This study introduces two new metrics: Before θPmax (the crank angle corresponding to peak cylinder pressure) Detonation Energy (BPDE) and After θPmax Detonation Energy (APDE) to characterize the knock behavior of TJI engines. Through analyzing the knock characteristics of the TJI engine under different compression ratio (CR), the author found that when the CR increased from 13 to 17 and the ignition angle was set to 12°CA bTDC, the engine's AMAPO increased by 0.55 MPa, and TDE increased by 0.8 MPa·°CA. However, when the CR reached 19, although TDE increased by 0.192 MPa·°CA, AMAPO decreased by 0.145 MPa. Two newly introduced metrics explain this phenomenon: when the CR increased from 17 to 19, ABPDE rose by 62.3% while AAPDE decreased by 15.5%. Knock energy primarily shifted to ABPDE, causing AAPDE to decline and resulting in the decrease of AMAPO. Additionally, no super-knock phenomena were observed at a CR of 19 and 70% load. The knock frequency distribution of TJI engines at different CRs was analyzed using Fast Fourier Transform (FFT). Statistical probability distribution (PD) and cumulative distribution (CD) were employed to estimate changes in Maximum Amplitude Pressure Oscillation (MAPO) across varying CRs. The knock characteristics of TJI engines were further detailed.