Yes, never put oil formulated for a diesel in a gasoline engine.
Yes, petrol/gasoline will severely damage a diesel engine.
If you're asking what will happen if you put gasoline in a diesel engine, the engine will be destroyed if you run it on gasoline.
Gasoline in a Diesel vehicle will do some serious damage to the engine.
Don't know how much gasoline was put in or how much diesel was in the tank before gasoline was added but if you didn't run the engine after the gasoline was put in and you drained it, you should be okay.
Gasoline engine is an internal combustion engine where a diesel is an internal compression engine. Gasoline is highly flammable and explodes when an electrical spark is applied to it where diesel explodes when it is put under pressure
If it is a car that has a diesel engine, it won't break down...But if the car has a gasoline engine, you risk causing a lot of damage if you put diesel fuel into the tank instead of gasoline (aka gas or petrol) fuel... If that is what you were asking about, please see the answers to the Related Questions shown below.
If the engine is a diesel use diesel fuel. If the engine is a gasoline engine use unleaded gasoline.
Diesel engines have a much higher compression ratio than gasoline engines. Therefore, you need to drain all the fuel you can out of your tank and fill it with diesel. Gas in a diesel engine will go boom, and destroy your engine.
Who told you it is harmful? It is only harmful if it is a Diesel engine. If it is a petrol (gasoline) engine then Petrol is what it takes to run.
Flex fuel does not mean you can use diesel. It means the engine can run on pure gasoline or on E85 gasoline. If you put diesel in this vehicle it simply will not run. Diesel can only be used in a diesel engine.
Can you? Sure you can. Should you? NO! A gasoline engine will not run on diesel. You will end up having to drain the tank, flush the fuel lines, replace the filter, and possibly the injectors.