<p>This work investigates cycle stability issues associated with the operation of a constant volume combustor concept applied to a pistonless gas turbine in the context of pressure gain combustion. Experimental tests are carried out on a lab-scale combustion vessel designed for cyclic operation. This facility features the turbulent combustion of air and fuel direct-injection, with a controlled overall equivalence ratio. Operating conditions are set to reach either spark-ignited flame propagation or self-ignition induced by residual burned gases or residual flame. Self-ignition events develop over two consecutive cycles, where the first (spark-ignited) cycle acts as a preparatory phase. During this phase, a slow flame propagates through the exhaust phase, establishing the conditions necessary for self-ignition in the following cycle. Chemiluminescence recordings of OH* and CH* radicals are performed to shed light onto the phenomenology of self-ignition processes. A thermodynamic model of constant volume combustion cycle is implemented to further analyze the energetic behavior of spark-ignited versus self-ignited cycles. Through the model, it is found that self-ignited cycles exhibit approximately 15% less total heat losses compared to the reference spark-ignited configuration.</p>