A conventional coil ignition system and two breakdown ignition systems with different electrode configurations were compared in M.I.T.'s transparent square piston engine. The purpose was to gain a deeper understanding of how the breakdown and glow discharge phases affect flame development and engine performance. The engine was operated with a standard intake valve and with a shrouded intake valve to vary the characteristic burning rate of the engine. Cylinder pressure data were used to characterize the ignition-system performance. A newly developed schlieren system which provides two orthogonal views of the developing flame was used to define the initial flame growth process.The study shows that ignition systems with higher breakdown energy achieve a faster flame growth during the first 0.5 ms after spark onset for all conditions studied. However, the extent to which this translates into a reduction in the duration of initial flame development period (the period from 0% to 10% mass burned) was found to be strongly dependent on the operating conditions and combustion characteristics of the engine. For the faster-burning case with shrouded intake valve, the benefits of the higher breakdown energy ceased to be significant under very lean conditions where the glow discharge ignition phase appears to play a more important role.