Time-Resolved PIV Investigation of Spark-Ignition and Selfignition in a Constant Volume Combustion Chamber

Pressure Gain Combustion (PGC) represents a disruptive approach aimed at enhancing the thermal efficiency of gas turbines. Several PGC architectures have been proposed, including the Rotating Detonation Engine (RDE) [1], Shockless Explosion Combustion (SEC) [2], Constant Volume Combustion (CVC) [3] and Wave Rotor Combustor (WRC) [4]. Among these, CVC systems have been studied extensively, with multiple research groups demonstrating measurable pressure gain through experimental prototypes [3][5]. These prototypes typically involve one or more pistonless chambers (each with a volume below 1 L), equipped with actuated inlets and either actively or passively controlled outlets [3][5]. A key requirement of the CVC cycle is consistent ignition of the fresh fuel-air mixture introduced each cycle. Most studies to date have used spark ignition to initiate combustion. However, the timescales associated with spark ignition and early flame kernel development can conflict with the short duration of the CVC cycle. This has motivated interest in achieving actuator-free, self-ignition through residual burnt gases. Several patents and wave rotor concepts propose phased transfer of hot combustion products between chambers as a means of triggering ignition in subsequent cycles [4][6][7]. One specific form of this strategy is cycle-to-cycle self-ignition (RI), in which no scavenging is performed between cycles, preserving high-temperature residual burnt gases (RBG) in chamber corners. These residuals mix with newly injected fuel and admitted air, enabling spontaneous ignition in the following cycle. Experimental and numerical studies by independent groups have confirmed the occurrence of RI events [8][9][10]. The success of this ignition mode relies on transient mixing dynamics between the RBG, injected fuel and incoming air. To gain deeper insight into this rapid combustion phase associated with RI, it is essential to understand how internal flow structures influence mixing dynamics, ignition and flame propagation. In this context, Particle Image Velocimetry (PIV) provides a powerful, non-intrusive technique to visualize and quantify the flow field. Applying PIV to both spark-ignited and self-ignited cycles enables direct comparison of intake flow behavior and its role in initiating combustion.