Flash-boiling spray could be one promising approach to better suit for direct injection gasoline engine, since previous study demonstrated in constant chamber that flash-boiling fuel spray provides desirable spray structure with shorter penetration, more homogeneous fuel distribution, smaller droplets and quicker evaporation. However, in a real engine intake air flow have significant influence on spray development which is also one major source of cycle-to-cycle variation of engine performance. In this research, the effect of engine speed and swirl ratio on the structure of flash-boiling sprays of gasoline was investigated in an optical accessible, single-cylinder spark-ignition direct-injection (SIDI) engine with an 8-hole injector. Experiment was carried out at cold engine conditions (30oC coolant and oil temperature) under different engine speed (800, 1200, 2000 rpm). The fuel temperature was conditioned by water bath from 30 oC to 90 oC corresponding to liquid spray, transitional flash boiling spray and flare flash boiling spray respectively. Crank angle resolved spray images were recorded separately in swirl and tumble plane for 50 consecutive cycles at using high-speed Mie-scattering technique. Influence of the in-cylinder flow induced by engine speed and swirl ratio on spray transformation under both liquid and flash boiling condition was evaluated in a quantitative manner using relevance index and proper orthogonal decomposition (POD) methods. Results show that with the increase of engine speed, the structure of spray was distorted significantly with large cycle-to-cycle variation (CCV) while a more stable spray can be maintained under flash boiling condition.