Mixture Preparation

Reagent mixtures are prepared and stored in two high-pressure gas cylinders that are referred to as the mixing tanks. Typically, one of the tanks will be cleaned while the other is connected to the shock tube and is used to fill the driven section during each experiment.

Each mixing tank has a volume of 50 litres and typically contains up to 100 bar of the reagent mixture. Additionally, to prevent condensation of heavy species inside the tank each cylinder is wrapped with a heating jacket and can be held at temperatures up to 80 oC.

Yellow mixing tanks in the mixing rig

A reagent mixture normally contains 10-100 ppm of the reagent, 50 ppm of xenon, sufficient oxygen to achieve the desired stoichiometric ratio of reagent to oxygen with the balance of the mixture being argon. The mixture components are added to the tanks using standard manometric techniques and after all the species have been added the mixture is allowed to overnight to homogenize.

After the mixture has homogenized a sample is withdrawn from the mixing vessel and analyzed to determine the exact concentration of each species and to confirm that no impurities were introduced in the preparation of the mixture.

The xenon acts as an internal standard in the mixture and is also used to determine if there is any mixing between the driven and driver gases in the shock tube prior to samples being taken.

Sample chromatograms. Top: TCD; Bottom: FID