Do Diesel engines have a mixture option?
For fuel, any fuel, to burn, it must be mixed with suitable amount of air. Neither too little nor too much would burn. Spark-ignition engines pre-mix the fuel with air, so they must do so in the right ratio, hence the need for mixture control (which might be automated, but it must be there).

However, compression-ignition (Diesel) engines are different. They inject fuel directly into the cylinders and as the fuel spreads from the injecting nozzle, it mixes with air and ignites at the moment it is sufficiently mixed. The cylinders always take full charge of air, otherwise the compression would not heat the air enough to ignite the fuel.

At low power, the flame is only small around the nozzle and at the large power it expands to fill the cylinder, but either way there is a point where the mixture is just right and the fuel ignites. Therefore compression-ignition engines don't need mixture control. The power lever simply controls the fuel flow into the engine and there is no throttle on the air intake (so calling power lever ‘throttle’ is inaccurate for Diesels (and turbines)).