*4.1. Cylinder Pressure*

According to the conducted tests, the in-cylinder pressure curves were obtained as an average of the 100 recorded cycles. Due to the fact that methane was always injected into the main chamber, Figure 4 only shows what type of fuel was injected into the prechamber. The blue color represents the case of fueling the pre-combustion chamber with methane, while the red color represents the case of fueling it with propane. The diagrams also include information on the share of energy contained in the fuel delivered to the prechamber. With the excess air ratio with the smallest analyzed value (λ = 1.3), feeding methane into the prechamber resulted in slightly higher values of maximum pressure in the cylinder (in the main chamber). At λ = 1.5, the maximum pressure values are very similar. Operation of the engine with an excess air ratio of λ = 1.8 results in the smallest dose of methane fed into the prechamber not igniting the fuel in the cylinder (no line in Figure 4). Only at a dose of qo\_PC = 30 J and λ = 1.8 is the value of the maximum pressure during propane combustion in the PC greater than that of methane combustion.

λ

λ

λ

**Figure 4.** In-cylinder (main chamber) pressure curves Pav\_MC averaged from 100 cycles of combustion pressure in the cylinder when the prechamber was fueled with methane or propane (methane was always supplied to the main chamber via injector placed in intake duct).
