Computational and experimental investigations of a pulsed detonation engine (PDE) operating in a cycle using ethylene/air mixtures are reported. Simulations are performed for two geometry configurations, namely, an ideal tube PDE with a smooth wall fueled with premixed C2H4/O-2 and a benchmark tube PDE with internal geometry and a valveless air supply fueled with C2H4. Performance estimates of fuel-specific impulse (I-spf) of an ideal tube PDE, obtained using a two-step reduced mechanism for a C2H4/O-2 mixture, are in good agreement with existing test measurements from the literature. Realistic simulations of all processes of the PDE cycle (fill, deflagration-to-detonation transition (DDT), detonation propagation, blowdown, and purge) of a benchmark tube PDE yielded important insights into continuous cycle operation. Experimental measurements include DDT visualizations and dynamic pressure measurements. Comparisons of experimental and computational visualizations show good agreement in cycle process timescales. However, run-up distance is underpredicted, indicating a need to improve the flame propagation mechanism. The predicted decrease in the fuel-specific impulse (I-spf) for the benchmark tube when compared to the I-spf of an ideal tube may be attributed to nonuniformities in the mixture composition, the pressure drop resulting from internal geometry, and back flow in the benchmark tube due to a compression wave propagating into the upstream geometry.