EMPI - Reactive Fluids

Aim

Fast gas-phase reactions are investigated in shock tubes. A shock wave caused by gas expansion heats the reactive gas mixture to temperatures of up to several thousand Kelvin within microseconds and the subsequent reactions are observed using optical methods. EMPI's high-pressure shock tube makes it possible to investigate the ignition delay times of undiluted fuel/air mixtures to describe the ignition properties of fuels for engine applications and safety considerations. The dependence of the reaction properties on the fuel composition is of interest. The data obtained support the theoretical description and modeling of the combustion process so that new fuels (e.g., based on biomass) can be used and fuels can be tailored for specific applications. Fuel gas/air mixtures are investigated to provide data for the development of low-emission gas turbines or for safety engineering.

Procedure

The shock tube has a total length of 12.5 m and an internal diameter of 90 mm. It is divided by an aluminum membrane (thickness up to 7 mm) into a high-pressure section (6.1 m) and a test section (6.4 m). The reactive gases are mixed in a pressure-resistant stainless-steel tank and filled into the test section. The high-pressure section is filled with a He/Ar mixture until the membrane bursts (max. 100 bar). Adjusting the gas mixture enables test times of up to 15 ms. The maximum pressure in the tube is 500 bar. The system can be heated up to 250 °C to test low-volatility fuels. Pressure sensors monitor the shock-wave velocity and ignition. Chemiluminescence is measured via photomultipliers and optionally with high-speed cameras through a window in the end flange and multiple windows in the side wall. A fast-opening valve enables gas sampling in the cooling phase to determine the product gas composition, e.g., after ignition of very fuel-rich mixtures. A piezo-pressure injector is used for the injection of oil droplets at reflected-shock conditions. A sliding valve 50 cm from the end flange enables so-called constrained-volume measurements, i.e., the reacting mixture is confined in this section only and after compression (reflected shock conditions) the reaction is limited to the region close the end flange. This strategy strongly reduces pressure variations and unwanted inhomogeneous ignition. A double-membrane system enables controlled breaking of the membranes.