There seems to be a flurry of activity going on with diesel engines. With the possibility of bikes like the Star Twin turbo diesel in the near future, emission issues are important. GM and other manufacturers are working on urea injection as a possible solution. It sounds promising but reducing the size of these technologies to work on a motorcycle could prove challenging. Finding space in a truck is easy, on a bike, not so easy.
James - Whybike.com says
Urea? I guess if you run out you can always piss in the tank.