Shock Tube Laboratory
Recent research on high-performance air breathing engines (turbojet, ramjet, and scramjet) and alternative fuels for internal combustion engines (spark and compression ignited) have created a need for research reactors capable of higher temperatures and pressures than can be reached in conventional flow reactor systems (as in our Thermal Decomposition Laboratory). In order to provide a high degree of comparability with actual engines, these reactors must be capable of employing fuel injection systems, instead of the premixed feed systems used in flow reactors. To meet these requirements, we developed a shock tube system in 1997 to study the combustion characteristics of advanced fuels.
At the core of this laboratory is a 21 foot high-pressure single pulse reflected shock tube capable of short duration exposures (~0.1-8 ms) at very high temperatures (~3,000 C) and pressures (~600 psi). This system adds significant capability in the area of exposure temperature and pressure well beyond that of the flow reactors used in our other laboratories.
Shock Tube Diagram
The shock tube features interchangeable test sections which allow the system to be readily adapted to specific research projects. The test section is mated to the tube through a pneumatically-operated ball valve which is controlled by a dedicated digital fire control system. This configuration isolates the reactants to a well-defined volume of the tube and results in superior definition of the exposure conditions. This system also provides containment for the reaction products and greatly assists in the quality of post-run sampling.
The versatile design of the test section permits the use of numerous real-time monitoring systems for pressure and radiant emissions as well as post-run sampling and analysis. The real-time sensors provide information on the shock velocity, pressure, and temperature as well as the timing of combustion events such as ignition delay and burnout.
Post-run sampling is accomplished through the use of high-volume collection systems for both particulate and gaseous products. The bulk properties of the collected samples are typically analyzed by reflectance spectroscopy and thermal desorption carbon analysis. The detailed chemical analysis of combustion products are typically conducted by high-resolution GC/FID/MS, GC/MS-MS, or multidimensional GC/MS-MS, which reside in our Thermal Decomposition and Analytical Instrumentation laboratories.
Since its completion, our shock tube facility has been in nearly continuous use to study the combustion characteristics of alternative fuels for light duty vehicles (premixed gases), alternative diesel fuels that are being formulated to reduce particulate emission (liquid sprays), and the composite ignition delay of high performance aviation fuels (liquid sprays).
To learn more about possible applications of UDRI’s shock tube facility to combustion research, please contact Sukh Sidhu or John Graham.
The UDRI shock tube as viewed from the driver section. The driver is built up of segments, which allows the exposure time behind the reflected shock to be varied as needed. The dump take on the left efficiently dampens the reflected shock and prevents cyclic reheating of the sample. The control console on the right includes a dedicated fire control system that manages all of the time critical events required by the tube's operation.
The UDRI shock tube as viewed from the test section. These test sections may be interchanged as needed for a specific research task. This particular test section has six general purpose access ports which may be fitted with a variety of sensors and samplers.
In addition to interchangeable test sections, the tube can be easily modified by changing the end plates. This particular example shows the fuel injector end plate that allows the system to study the combustion of liquid fuels. A separate analog fire control system handles the extremely important time-critical events which are required to ensure that the fuel is reproducibly injected at a fixed interval after the departure of the reflected shock and before the arrival the rarefaction wave.