Ignition Capability of Mechanically Generated Sparks Landing in Fuel Beds

Master of Science, Graduate Program in Mechanical Engineering
University of California, Riverside, December 2017
Dr. Marko Princevac, Chairperson

Experiments  were  conducted  to  examine  the  ignition  capability  of  mechanically  generated sparks  to  ignite  organic  matter  after  being  produced  through  grinding.  The  experiments  were performed using three different type of common metals which consisted of stainless steel, copper, and cold  rolled  steel.  The  grinding  of  these  materials  generated  hot  particles/sparks  that  were  deflected downwards  into  a  collection  box  containing  organic  matter.  The  organic  matter  consisted  of  the following types: weeping lovegrass, wild oats, timothy  grass and cheat grass. For the first set of the experiments, the interaction between the metals and the fuels at different temperatures was studied. It was found that cold rolled steel and stainless-steel particles possessed the highest ignition capabilities. For the second set of experiments, the fuel moisture was varied considerably (20%-80%) and it was determined  that  cold  rolled  steel  particles  could  considerably  ignite  the  fuels  at  decently  high  fuel moisture  percentages.  For the  last  set  of  experiments,  the  distance between  the fuel bed  and  grinder was varied to match that of real-life applications. It was concluded that cold rolled steel could ignite these  fuels  beds  up  to  distances  of  100  cm  (standing  distance).  Metal  particles  were  collected  and examined that cold rolled and stainless steel ranged from 0.0625 mm to 0.80 mm in diameter and were considerably smaller than that of copper which ranged from 0.4375 mm to 2.5 mm. Physical process concludes  that  cold  rolled  steel  and  stainless  steel  acquire  higher  initial  temperatures  than  those  of copper due to drastic difference in the toughness of the material. Both cold rolled and stainless steel are tougher metals; thus, a lot more separation energy is absorbed by the material before fracture. On the  other  hand,  copper  is  a  much  more  ductile  material  and  absorbs  less  separation  energy.  The difference  in separation  energy  dictates  the  initial  temperature  of  the  particles;  thus,  increasing  the probability  of  particle  combustion.  For  combustion  to  occur,  the  surface  temperature  of  the  particle must  exceed  the  oxides  melting  point.  This  is  supported  by  the  microscopic  images  acquired  of  the metal particles. These results were used to assess the ignition capability of all three metals.