An experimental and comparative study on the discharge coefficients of closed-type swirl injectors, which have a swirl chamber diameter larger than the nozzle diameter, has been performed. With a range of geometric dimensions and therefore broad swirl injector geometric constants, 27 closed-type swirl injectors were designed and manufactured. Hydraulic cold-flow tests were conducted using tap water to measure the discharge coefficients, with pressure differentials through the injectors ranging from approximately 8 to 12 bar. The discharge coefficients obtained from the cold-flow tests were confirmed to follow a functional relationship to the swirl injector geometric constant. A novel simple empirical equation, which would be useful in the design of new closed-type swirl injectors for liquid rocket engines, is suggested. The present experimental results were compared with previous empirical equations to investigate their accuracy. It was found that most equations predicted well the measured discharge coefficients only in a narrow range of swirl injector geometric constants; on the contrary, an equation suggested by Russian researchers could anticipate those with great accuracy in a whole range of present swirl injector geometric