Investigation of CDI and TCI Ignition Charactertistics for Lean Hydrogen–Air Mixtures in a Constant Volume Combustion Chamber

The discharge characteristics of ignition systems strongly influence the formation of flame kernels under lean-burn conditions. In this study, two ignition strategies are compared. A capacitor discharge ignition (CDI) system characterized by discharge energy of 1–5 mJ with discharge current around 300 mA and short discharge duration (~50 μs). A transistor coil ignition (TCI) system delivering discharge energy of 30–50 mJ with lower discharge current (~100 mA) and millisecond-scale discharge duration. These two systems represent distinct discharge current profiles, namely “high-current/short-duration” and “low-current/long-duration.” The influence of discharge current profile on flame kernel formation and early flame development in lean hydrogen–air mixtures is investigated. Experiments are conducted in a constant-volume combustion chamber with hydrogen–air mixtures at various global equivalence ratios. Both quiescent and flow conditions are considered. High speed shadowgraph imaging is used to capture early flame kernel formation and propagation. Results show that both CDI and TCI systems provide similar ignition capability under quiescent conditions for equivalence ratios up to λ = 4. However, when λ is further increased to 6, the ignition capability of the CDI system is significantly reduced, leading to misfire events, while the TCI system successfully ignites the mixutre.