It is same as that if a human is asked to eat grass instead of their food. now result will be that he wouldn't be able to digest cellulose or other nutrients present in it because his system is not made for it. now if you will put diesel in petrol engine then it is obvious that it will get damaged. it can work for some time but its performance in various parameters will be decreased. like fuel efficiency or average, its pick up power, its sound, pollution caused by it can also be Increased.