Riddle me this, Batman. How do you maintain the proper stoichiometric ratio? I know how it's done with gasoline engines with both carburetors (shudder) and fuel injection. I just don't understand how it's done with diesel.
This is another BIG reason why the diesel cycle is superior to the Otto cycle: the diesel engine, by virtue of compression ignition, does not need a fixed stoichiometric air:fuel ratio. At idle, a diesel engine might has a air:fuel ratio of 60:1 - or more. At full load, a diesel engine might have about a 15:1 air:fuel ratio. In tractor pulls, when you see the tractor operator pour on the fuel, he’ll fuel the tractor “just to black” — ie, the point where the exhaust goes black. This is the point at which you’re burning the maximum amount of fuel for the air charge you’re able to push into the engine with the turbo or super charger.
The important thing to remember in a diesel is that because the air charge put into the engine is compressed to achieve a temperature well above the ignition point of the diesel fuel, and it is only at this point when the fuel is injected into the cylinder, the fuel immediately ignites and burns rapidly. The Otto cycle engine isn’t compressing the air charge to a point where the air reaches a point of being able to ignite the fuel mixture immediately upon injection. The air:fuel mixture must be maintained in a proportion where a spark can cause a rapid explosion of the mixture, and this mechanism remains the same regardless of how much load is put onto the engine.
In a diesel engine the stoichiometry is controlled by the fuel injectors, not the air intake.