Diesel technology is coming up big of late. First with the Audi Le Mans racer and now Yamaha developing an inline-four intercooled and turbocharged diesel engine. Yamaha has filed a patent application for various technological solutions related to the aforementioned diesel engine. The intercooler seems to be located above the engine or concealed in the frame and a turbocharger mounted adjacent to the cylinder head. This type of arrangement would ensure lesser chances of damage to the turbocharger and intercooler and will also help in reducing turbo lag. The compact design will help in packaging as well.
There is no word on when this engine will go into production. However you can check out the above document which gives more information about the engine and what Yamaha is upto. Even if Yamaha put the engine into production it won’t be the first diesel engine in a bike, because the Royal Enfield did make diesel Bullets. But surely it will be the first diesel engine in a bike which won’t rattle your bones.