The purpose of this study is to operate the spark ignition engine by the dual combustion cycle. The dual combustion cycle has two combustion processes, these are the constant volume combustion and the constant pressure combustion. The lean combustion and the direct fuel injection were applied to realize the dual combustion cycle for spark ignition engines. The combustion of lean mixture was corresponding to the constant volume combustion. The fuel was directly injected to combustion chamber and was burned with the remained oxygen after the lean combustion, so that this was corresponding to the constant pressure diffusion combustion. The combustion experiments were conducted by using the constant volume vessel. The lean propane-air mixture of which equivalence ratios were 0.6, 0.7, 0.8 and 0.9 were used and liquid n-heptane was injected by using the high-voltage electrical discharge.The luminous flame was observed after the fuel injection and the injected fuel was burned within the burnt gas caused by the lean premixed combustion. The luminescence from the luminous flame of diffusion combustion became weak as the equivalence ratio of lean mixture became lean. It can be considered that the oxygen remained in burnt gas increased for leaner mixture, so that the soot formation was prevented. The time at maximum combustion pressure was advanced as the fuel injection timing became early and was earlier than that of conventional combustion, because the combustion enhancement effect was caused by the fuel injection. Therefore, the dual combustion cycle could be realized for the spark ignition engine.