The combustion characteristics of methane fuel under different pre-chamber structures

including flame propagation velocity

flame area

flame morphology and combustion pressure

were quantitatively analyzed by high-speed photogrammetry based on the constant volume combustion bomb. The results showed that smaller aperture can lead to larger penetrations within the same time

as well as higher peak pressure

faster flame velocity

and larger flame area growth rate. As the aperture become smaller enough

the ignition mechanism will change from flame ignition (with flame in the jet) to jet ignition (flame quenches when passing through the orifice). In the case of jet ignition

ignition timing is delayed and initial flame velocity is also slowed down

while the peak pressure is almost unaffected. Similar peak pressures and pressure rise rates were observed in all pre-chamber structures

though the exit velocity in multi-stage pre-chambers was lower. The slower velocity deceleration in multi-stage pre-chambers made the flame advances that in other single-stage pre-chambers in a short time. Meanwhile

the pressure and the flame area reached its maximum value earlier.