[wilfred]

"No, it won't smell like pee. Mercedes-Benz's new Bluetec diesel technology uses urea--derived from urine--to neutralize particulate emissions and make its GL320 and E320 Bluetec models the cleanest diesels in the world and fifty-state legal in the States. The urea solution must be replenished during normal maintenance stops, but there's no word yet on a rumored do-it-yourself kit based around a compact urinal..."

http://www.automobilemag.com/auto_shows/naias_2006/0601..._e320_gl320_bluetec/