Today’s diesel fuels are not what they seem. On the one hand, the new ultra low sulfur diesel would seem to burn more completely and with less emissions that the older diesel fuel. That may be true under some conditions, but more often it actually doesn’t burn as well. Old fuel is presenting more problems than ever before. I believe that the newer fuels have a much shorter “shelf life” than older fuels, not that it was that much better before.
We are seeing more blueish smoke on start up from all brands and types of diesels. Particularly, on higher performance engines (turbocharged/intercooled) the smoke is prevalent not only at start up, but at light loads even after the engine has warmed up. What is causing the smoke is a lack of cetane. The cetane rating of a fuel is somewhat like octane is to gasoline, but inversely. In gasoline, the higher the octane, the more difficult it is to make the fuel spontaneously explode due to heat. The higher the cetane rating of diesel fuel, the easier it is for the fuel to be ignited by heat.
What this means to the engine is not so easily explained. Here goes nothing. When the piston of a diesel engine rises toward the cylinder head on it’s compression stroke, the fuel is injected slightly before it reaches the top. The fuel ideally should start to burn immediately after it is injected into the hot compressed air. If it doesn’t, two things happen. First, the fuel starts to collect in the combustion chamber until the temperature reaches it’s ignition point. When that happens, all the fuel burns at once, making a “bang” in the cylinder. This makes the engine very noisy. Second, as the fuel isn’t burning, it may come in contact with the sides of the combustion chamber. The fuel that touches the metal is “quenched” and doesn’t burn with the main charge. When the exhaust valve opens and the cylinder pressure drops, this fuel evaporates, making the blue smoke that you see in the exhaust.
By adding a cetane improver, you make the fuel ignite at the proper time and all types of emissions are reduced. You engine will have more power, be more efficient, and have fewer operational problems.