This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston bowl shapes(F, B and R-type) in a optically accessible engine. The images of liquid and vapor phases were captured in the motoring engine using exciplex fluorescence method. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure was 5.1MPa. Two dimensional spray fluorescence image of vapor phase was acquired to analyze spray behaviors and fuel distribution inside of cylinder. Four injection timings were set at BTDC 90$^{circ}$, 80$^{circ}$, 70$^{circ}$, and 60$^{circ}$. With a fuel injection timing of BTDC 90$^{circ}$, fuel-rich mixture level in the center region was highest in a B-type piston. With a fuel injection timing of BTDC 60$^{circ}$, R-type piston was best. R-type piston shape was suitable under enhanced swirl ratio and late injection condition and B-type piston shape was right in a weak swirl ratio. It was found that the piston bowl shape affected the mixture stratification inside of cylinder.