Effects of driving gas pressure on measurements of ignition delay times in a rapid compression machine

Effects of driving gas pressure on measurements of ignition delay times of dimethyl ether (DME)/oxygen/nitration mixture and methane/(CH⁴) oxygen/argon is studied in a rapid compression machine (RCM). With a certain initial temperature 288K, experiments are conducted with driving gas pressure of 0.21 to 0.65MPa, initial pressure of 0.06 to 0.12 MPa and compression ratio of 10.65 to 13.75. The results shows that the appropriate driving gas pressure should be chosen according to the range of initial pressure and the design features of different rapid compression machine to avoid the rebound of piston. Also, with a low driving gas pressure, the top dead center (TDC) cannot be accurately defined due to the coupling of the first ignition delay and the low temperature combustion of DME/O₂/N₂ mixture in the process of compression. Additionally, both the first-stage and overall ignition delays of DME/O₂/N₂ mixture shorten with decreasing driving gas pressure due to its low auto-ignition temperature, moreover, the ignition delay is much more influenced by the change of driving gas pressure with decreasing compression ratio. In contrast, under different ignition delay, whether long or short, the ignition delay of CH⁴/O₂/Ar mixture is insensitive to the change of driving pressure within a certain range due to its high auto-ignition temperature.