The present work is a study of the problem of ignition in the boundary layer on a flat plate, where a cold gaseous fuel is injected uniformly from the porous surface into the boundary layer, diffuses and reacts with the oncoming hot oxidizer diluted with an inert gas. The effects of various physical parameters on the ignition time are examined. A one-step unopposed global reaction following the Arrhenius rate law is assumed. The unsteady non-similar two-dimensional boundary layer equations are solved for the case where the fuel injection velocity is proportional to t α ( t is the time and α is the arbitrary nonfractional number) by the series expansion method. It is found that the nondimensional ignition time at a certain location (nondimensional) is characterized by the four nondimensional quantities, i.e., the nondimensional wall temperature, injection rate, heat of combustion, and activation energy. The ignition time is shown to decrease with the increase in the wall temperature, the injection rate and the heat of combustion, and the decrease in the activation energy. The main stream temperature has remarkable influences on the ignition time as well. It is demonstrated that the trends of the effects of these parameters on the ignition time are analogous to those on the ignition length in the case of the steady injection rate.