To obtain a better understanding of the effect of torch nozzle area on the turbulent flame propagation in a spark ignition engine with an unscavenged prechamber, the combustion characteristics are analyzed from ensemble-averaged pressure diagrams, and the turbulent flame propagation in both the pre- and main chambers are observed using a high-speed camera with image-processing. Also, a numerical simulation is attempted by applying a k-ε model of turbulence to the two-dimensional unsteady flow field and an one-step irreversible reaction model to the combustion process. These engine experiments and numerical calculations are performed under the same operating conditions, that is, optimum spark advance for best torque (MBT), volumetric efficiency of ηv=80±2%, air-fuel ratio of A/F≃15 and engine speed of N ≃1000 rpm, with various torch nozzle areas (An).
Consequently, the effect of torch nozzle on the flame propagation pattern become more clear. Both the maps of calculated isotherm and measured flame front are found to be in reasonable agreement, and the isotherm area fraction and flame area fraction also show a similar tendency.