High-voltage arc plasma breakdown initiates a spherical flame kernel inside turbulent in-cylinder charge motion. Flame propagation speed dictates ignition timing advance, wall quenching hydrocarbon emissions, and alternative fuel burn rates.
The fundamentals of spark-ignited (SI) combustion appear simple: as the piston compresses the air/fuel charge, a spark plug fires shortly before Top Dead Center (TDC) to initiate a flame that expands and drives the piston downward during the power stroke. In reality, the micro-physics of in-cylinder flame propagation involve complex chemical kinetics, turbulent fluid dynamics, and surface heat transfer.
High voltage creates a ~100A microsecond breakdown arc, ionizing air/fuel molecules into a glowing ~1ms kernel.
Cooler cylinder walls extinguish flame fronts within ~1mm, leaving unburned hydrocarbon boundary layers.
High voltage creates an ionization channel between the spark gap, transitioning into a glowing arc discharge. The expanding spherical flame front is stretched and wrinkled by intake swirl and tumble turbulence. Near cylinder walls, localized heat loss exceeds flame chemical energy generation, causing thermal quenching that leaves unburned hydrocarbon layers.
In alternative fuel conversions (such as Compressed Natural Gas / CNG or LPG), lower laminar flame speeds extend combustion further into the expansion stroke. Without optimal ignition advance or intake swirl enhancement, late burning increases exhaust valve thermal stress. Focus Applied Technologies designs custom variable-swirl cylinder heads to optimize alternative fuel combustion kinetics.
Need in-cylinder pressure indication, heat release rate analysis, or CNG conversion tuning?
View Combustion Analysis