Biodiesel may be used as recycling agent
"Mobile military bases produce a lot of garbage," said ISU professor Balaji Narasimhan. "If you burn it, you announce your presence. If you bury it, you leave evidence of how big a unit you're traveling with and in which direction you're headed." Since the next option is to carry the waste, the U.S. Army initiated research with General Atomics, Renewable Energy Group Inc. and ISU to investigate which plastic materials best dissolve into biodiesel, and how stationary engines perform when running on the polymer-rich fuel.
"If you take a Styrofoam cup and drop it into room-temperature biodiesel, it will dissolve in a couple minutes, but Polyethylene terephthalate (PET), or soda bottles, will not dissolve," Narasimhan said. Some garbage bags and containers for meals ready to eat (MREs) also dissolve into biodiesel.
ISU mechanical engineering professor Song-Charng Kong said the maximum concentration of plastics dissolved into biodiesel before fuel viscosity becomes problematic is 10 percent by weight. "Sometimes the engine fails at 10 percent, and sometimes it doesn't," he said. Specifically, the fuel injection pump can't handle plastic concentrations greater than the 10 percent threshold.
Kong used a 4.5-liter, four-cylinder John Deere engine (model No. 4045), from which emissions of soot, nitrogen oxide (NOx), carbon monoxide and unburned hydrocarbons were measured. "Because polymers are big molecules, soot emissions increased," he said. "NOx emissions also increased." Speciation of the exhaust gases wasn't examined.
While Narasimhan dissolved different types of plastics in B100, engine tests thus far have only successfully used biodiesel with polystyrene-in concentrations of 1 percent, 2 percent, 5 percent and 10 percent. A fuel with nine parts biodiesel and one part dissolved plastics has roughly the same energy content as straight B100 but requires 10 percent less fuel.