Spark ignition in inhomogeneous mixtures is numerically studied using three-dimensional compressible Direct Numerical Simulations (DNS) with simplified chemistry. The thermal effect of the spark is represented by a Gaussian power distribution in the energy transport equation. Success of the spark ignition and subsequent self-sustained flame propagation is shown to be heavily dependent on the turbulent velocity fluctuation. It has been found that high levels of turbulent velocity fluctuation have detrimental effects on the spark ignition event, which ultimately may lead to misfire. It is observed that the flame shows a tribrachial structure following successful ignition. The local flame propagation speed may attain values equal to several times the laminar burning velocity of an unstrained premixed stoichiometric flame S-L, but may also be negative, in agreement with previous findings. The mean flame propagation speed decreases with increasing turbulent intensity.