Numerical Study toward Fast Intermediate Species Sampling with High Accuracy in a Rapid Compression Machine

Rapid compression machines (RCMs), as prominent zero-dimensional
homogeneous reactors, have been widely applied in autoignition chemistry
investigations. However, species sampling in these reactors is challenged
by quantitative accuracy and the limited time allowed for transient
sampling. In this study, the uncertainty of quantitative species sampling
during the autoignition of a typical fuel/oxidizer mixture was numerically
evaluated. Results show that the sampled species profiles tend to
lag behind the “true” values due to the dilution of
gases outside of the “core” region. When sampling at
a longer ignition delay time, increasing the sample duration over
2 ms has very limited improvement on the sampling accuracy, and adopting
a 10 mm probe tube is long enough to minimize the errors caused by
dilution. In the reaction chamber where nonideal gas disturbance occurs,
the sampled gases can be seriously diluted, leading to large deviations
in the results. Concentration uncertainties vary among species, while
uncertainties in the normalized time are consistent, which can be
limited to 6% with proper piston design and sampling setups.