Most pressure washer engines are designed and certified to run on regular unleaded gasoline.
Gasoline is allowed, by regulation, to contain a variety of additives. The same regulation limits how much of some additives, such as alcohol, can be included in the fuel and still allow it to be sold as gasoline. Most engines are designed for good performance and efficient operation using gasoline containing from 0 to 10% ethanol.
E85, a mixture of 85% ethanol and 15% gasoline, has been in the news recently. E85 is an alternative fuel; it is not gasoline. Most pressure washer engines are not designed or certified to run on E85 or any other alternative fuel. Always refer to your owner's manual for a list of recommended fuel and the current approved additives.