Just say NO
Lurker here - with a dream of retirement whiles still keeping my feet wet.
While I do not have the wealth of experience with smaller Marine Engines, I have 40 years of sailing with large-slow speed (<150rpm) diesel engines as well as medium speed diesels (~750rpm).Now, having said that, petroleum expands at the same rate no matter how big the engine. Therefore, the piston linear speed is the same as a small engine.
Others have covered volatility of storage issues.
Mixing fuel is done, but with way more instrumentation than you would have. 'Normal' road diesel is 2.5 Cst (Centistokes) on the kinematic viscosity scale. At sea, our vessels ran residual fuel, heated to 280-f to obtain an ideal injection temp of 10~12 Cst on the low-speed main engine. The fuel is heated/regulated using a very sophisticated controller called a viscosimeter. It regulates the heating based on measured Viscosity in the fuel pipe being delivered to the engine.
So, again, diesel is 2.5 Cst, Gasoline is 0.88 or so. Kerosene is not so regulated and can be anywhere from 2.0~5Cst.
The fuel we were given to burn is anywhere from 380~500 Cst. 500CsT being about the consistency of road tar. Many times, a vendor will take road tar or some other 'residual fuel' and using "cutter stock" (diesel) mix it until in meets the spec that was ordered. So, I can personally attest that when you mix various grades and thicknesses of fuel and IT WILL separate in the storage tank, just like cream from raw milk. How long? Depends.
LUBRICITY - The main engines (130rpm) liked 13Cst. the Generators (750rpm) liked 8CsT. We had two Viscosimeters, one for main engine and one for the three generators. IF the operator did not get the viscosity correct, or controller failed, the fuel might get too thin, loose its lubricity from being too hot, and then the fuel pump plunger seizes within the barrel of the fuel injector. When this happens, the solid lifters below the injector have to LIFT something, and it is usually the whole injector that gets lifted off its mounts.
CETANE/OCTANE - Others have covered this well. Gasoline, even the higest octane is very explosive. So if it can get past the fuel pump, it could very well pressure-ignite in your injectors.
You would be far better off using lube oil cut with diesel than diesel cut with gas.
And yes, on the ships I worked on we 'recycled' the used lube oil into the fuel. But when you are burning 135tons of fuel a day, it might be a small percentage.
And just to make operations more interesting, changing from this heavy residual fuel (380~500/120c~150c) to regular Marine Diesel (2.5~4/ Ambient Temp) is problematic and has to be done each and every time a large ship enters (and wxits) a SECA (Sulfur Emissions Control Area) of which Europe and North America are now.
So... now you have some of the technical background.
To sum it up - Please do not do this.
