60th Annual Report on Research 2015

Background and Experimental Approach: The project involves studying the formation of soot from different precursors in high pressure conditions behind reflected shock waves, and trying to observe a synergistic effect on the reduction of soot from the mixture of different precursors.  Gases and particles are continuously sampled by expansion into an endwall mounted vacuum chamber, and laser scattering is used to measure particle sizes and number density in a time resolved fashion, and also to form an indication of induction delay.  The shock tube is a 12.7 mm bore high repetition rate shock tube (HRRST), which can be used to make repeatable measurements in conditions like this, a low signal-to-noise level experimental system which requires significant signal averaging.

Technical Progress: The shock tube was completed and tested in the two months after the start of the project (Fig. 1). Besides shock tube characterization, that time was used to design the chamber necessary for the project. Fabrication was complete four months into the start of the project.  In the chamber, the detector is mounted on a custom goniometer (Fig. 2) and significant effort was expended to design this system to function inside the vacuum chamber.  The goniometer required two design iterations which caused the project to incur an unexpected delay, but the goniometer and detection system work well now.  Although initially not intended to be a significant development effort, aspects of the design of this goniometer will form the basis of journal publication.
 
Figure 1. 12.7mm bore HRRST configured for the scattering experiments of this project.
 
 Figure 2. Detector goniometer inside the scattering chamber.
 The laser source needed for the project was initially intended to be one from the department; however it was found to be unsuitable, so a suitable medical grade laser was obtained instead. This change required a new data acquisition scheme, however, as the laser is now the timing master for the experiment. By the 12^th month of the project, all the components of the experiment (shock tube, laser, and detector system) had been synced together.  Sampling of gases from the shock tube has been performed from reactive/sooty conditions.  The detector system has been tested, but not with particles formed in reacting conditions because of the delays.  The testing of particles formed in reactive conditions (pyrolysis of ethylene and toluene) will commence in Fall 2015.  

Impact of Support:
Besides the technical impact, the program has provided partial support to two graduate students working on the project.  Those students have so far been able to participate in the U.S. National Meeting on Combustion in Spring 2015. Both have presented work (one a poster on chemical thermometry in the shock tube and one a presentation on PIMS experiments on gases sampled from engines) that was performed during the periods of manufacturing delay in this project. The PI and students have already greatly benefited from the extended capabilities to the laboratory after adding the new experiment. In addition to the intended scattering experiments, the endwall mounted chamber is used for other experiments.  Those of relevance to the petroleum field include product analysis of post shock gases, and even experiments after incident shock waves.