Nearly two weeks ago, Cleaire Advanced Emission Controls shut down, according to dieselnet.com...

 Cleaire was a major supplier of diesel particulate filters that were used to comply with the California Air Resources Board, CARB's, diesel retrofit regulations in order to keep older diesels in service (pre-DPF era diesel engines being outfitted with DPFs...). The closure came after the company's LongMile DPF was linked to the cause of two fire outbreaks. The first occurred in Washington back in September, 2011, where the fire consumed 3,600 acres and 29 residences. Following that fire, a school district in Humboldt, California pulled as many as 17 buses (all fitted with LongMile DPFs) out of circulation. It's rumored that lawsuits and recalls caused Cleaire to pack it in.

 An article on truckinginfo.com mentioned that a turbocharger failure on the truck's engine actually initiated the fire.

 More than likely, a turbo seal leak on the compressor side fed an uncontrolled amount of oil into the engine. From there, we're guessing that oil soaked the particulate filter, which led to the sparks and particulate matter that were seen leaving the truck's exhaust. The truck was parked next to dry grass along Highway 97, near Goldendale, Washington.