You can’t run straight diesel, but you can mix diesel with gasoline with no modifications to your engine or injectors. Try one gallon per tankful, increase until the engine either smokes, or is hard to start, then back off on the diesel per tankful. This will not harm your engine, there is the possibility of mixing too much diesel with the gas, then you’ll either foul the spark plugs, (Clean or replace them, do not use a hotter range plug) or it just won’t start, you see diesel is not as volatile as gasoline (Gasoline evaporates easily, diesel will not evaporate like gasoline, so it remains a liquid fog instead of a finer vapor. If you insist on a fuel changeover system, preheating the diesel in the line is a good idea, do it as close to the injectors as practical, but don’t get it too hot or you get vapor lock, use a water heat exchanger, (Available in the Northern states where it really gets cold) and that should be enough, but only on the diesel line and the Diesel will then vaporize easier, it will run on straight diesel (Poorly, but it will run) when the engine is hot, but not when cold starting. Be aware that the fuel systems today are intended to recirculate fuel back to the tank, so you will not only need a return line (Also switched over) but the recirculation is designed to cool the fuel, the tank mounted fuel pump, and also the injectors, you may get a burned out injector or fuel pump by heating the diesel The idea of starting on gasoline, then switching to kerosene, is a good one, and has been used since the 30’s, but the added expense of a second tank, fuel pump, lines, and changeover switch make this a costly refit.and the cost of diesel is not enough different to recover the cost. If you’re thinking that running diesel will be more efficient (Better gas mileage) you will be disappointed, the diesel engine is very different from a gasoline engine, and it’s the difference, not the fuel, that makes diesels more fuel efficient.
You have a few misconceptions about diesel running in a gas designed engine. First of all, the higher compression of a diesel is designed to raise the compressed air’s temperature above the “Flash Point” of diesel fuel (Where the fuel ignites spontaneously) This allows the diesel to be injected directly into the combustion chamber where it ignites immediately from the heat of compression without any spark plug needed to “Light the fire”. Note the injectors on diesels are in the combustion chamber itself, and squirt the diesel against about 600 PSI of back pressure from the initial compression, this requires high pressure pumps, fuel lines and different injectors.
But in gasoline engines the injectors are in the intake manifold, and squirt the gasoline not into the combustion chamber, but into the intake manifold very near the intake valve. This only requires a low pressure injector, most work around 14PSI, although 40PSI systems are on some cars.
This difference, though seemingly minor, is really a very major difference, you see, as the diesel is compressing the air trapped in the cylinder, IT IS CRITICAL TO KNOW THERE IS NO FUEL IN THE COMPRESSED AIR, then when the fuel is squirted into the hot air, it ignites.
A gasoline engine compresses both fuel and air mixture, this is why the compression ratio is lower THE AIR MUST NOT BE COMPRESSED TO THE FLASH POINT TEMPERATURE, if it is, you light the gasoline from the heat of compression and destroy your engine through detonation, also called knock, spark rattle, pre-ignition, and other names.
Gasoline engines use lower compression to prevent this ignition by air heat, then at the correct time the spark plug lights the warm (Not hot) fuel-air mixture, and away you go.
In diesels the injector timing replaces the spark timing, by squirting the diesel at the Top Dead Center (Actually slightly before TDC) the engine cannot knock, detonate, pre-ignite, etc. Remember there’s no fuel until injection occurs.
So when you tell me you intend to increase the compression of a gas engine, and/or add a turbo (Same thing) and run diesel, you’re forgetting that you are now raising the engines compressed air above the flash point of gasoline and of diesel, and are now compressing a air-fuel mixture, not just
You will destroy your engine.
I note that your tractor “Is offered with this option” the wording suggests that a factory conversion is possible, actually that is another, entirely different engine, not simply a carburetor conversion. Your garden tractor is a low compression, far more “Forgiving” engine, than any automotive engine. What works in a 6 to 1 compression, air cooled engine, will not work in a 8.5 or 9 to 1 automotive engine (Diesels commonly run 22 to 1compression ratio or higher.)
As an aside, when you increase the compression, you install colder spark plugs, not hotter ones, “Colder,” or “Hotter” refers to the spark plug’s ability to transmit the heat of combustion to the engine’s head (A heat sink) so the plug will not melt. (Yes they can and do melt.) “Colder” spark plugs can transmit more heat, allowing the plug to survive higher combustion chamber temperatures.
You worry about the EFI’s ability to handle diesel? no problem, it’s slightly thicker than gas, but automotive fuel injectors are designed for variable flow, the injector “Meters” fuel by the time it’s allowed to stay open, (richer mixture, longer “Open” time, leaner mixture, shorter time)
The system really doesn’t know or care just what fluid is flowing through it’s system, it works on a series of sensors that tell the car’s computer how hot the engine is (Coolant sensor) and whether or not there’s any free oxygen in the exhaust (Oxygen Sensor), If Oxygen is present in the exhaust stream the mixture is enriched until there is none, then leaned again until Oxygen is again detected, and repeat many times per second, the whole idea is to attain the “Perfect” fuel mixture where all fuel is burned and none is left in the exhaust.
Note, I said “Fuel” , your engine’s computer doesn’t care if the burnable stuff is gasoline, alcohol, diesel, veggie oil (I would thin it with alcohol to avoid plugging the injectors, and be sure to filter it heavily, a very tiny french fry particle will stop up an injector) or any other burnable fluid, the only thing you need to worry about is a fluid that is too thick to allow enough flow through the injector for the engine to run, and that will burn at a fast enough speed to support combustion.
While a bit extreme, an example is motor oil, you can’t use motor oil, even though it will burn, and is a liquid, it simply cannot flow fast enough, to allow enough through the injector, thin it with, any more volitile fuel, such as alcohol, gasoline, propane/butane (Bet you didn’t know propane/butane is mixed in gasoline to make gas evaporate faster) then it will burn just fine.
Was your tractor by any chance a Semi-Diesel, those engines are designed from the start as a hybrid gas/diesel engine.