Found this on Bell Performance, BTW:
Putting Gasoline In Diesel Fuel
Let’s say you accidentally drop a small amount of gasoline into your diesel fuel. The first thing it’s going to do is depress the flash point of the diesel, which can be dangerous given that pockets of higher concentrations of gasoline can develop in a tank. So the flash point wouldn’t be consistent throughout the entire tank.
Given the large difference in flash point temperature between gas and diesel, it doesn’t take very much gasoline to depress the flash temperature significantly. As little as 1% gasoline contamination will lower the diesel flash point by 18 degrees C. This means the diesel fuel will prematurely ignite in the diesel engine, which can lead to engine damage.
Gasoline contamination can also damage the fuel pump and mess up diesel injectors. This happens because of a drop in lubrication. Simply speaking, gasoline is a solvent while diesel is an oil. Diesel has enough lubricity to lubricate the fuel pumps and the injectors. Swapping in some gasoline takes away this lubrication, leading to damage.
Beyond these, you’ll get incomplete combustion, initially characterized by large amounts of black smoke. Beyond being an aesthetic problem, the vehicle’s computer will try to compensate for this combustion lack by adjusting the fuel-air mixture. This is going to cut your power and performance considerably. And if you continue to use the fuel, you can cause real damage to the vehicle’s computer sensors by either overheating them or covering them in soot such that they can’t detect anything.