Regular engines need 87 (R+M)/2, and modern or premium cars need 91 (R+M)/2. Turbocharged and supercharged engines may require up to 93 (R+M)/2.
You should use fuel with the number of octanes that your Orion needs. Otherwise, the engine may get damaged, or you may just waste your money.
The octane rating is only applied to gasoline; Diesel does not have an octane rating.
There are a lot of manuals that still choose the amount of gasoline that your Orion requires according to their octane rating. In North America, the octane rating is stated as the average of two other measures (RON and MON) and written as (R+M)/2, which you can usually read in gas pumps. This measure is also known as Anti-Knock Index or AKI.
You can use fuel with more octanes than the required ones. However, they will not improve your engine’s condition, so you will only be spending more money unnecessarily. On the other hand, if you use fuel with lower octanes than the required amount, your engine’s performance will worsen, and you may notice that there is smoke coming out of the tailpipe since it is consuming more fuel than usual. If the amount of octanes of the fuel you use is too low, there will be mechanical troubles (like rattling sounds), and the engine may get damaged.
In the rest of the world, the octane rating is usually stated in the RON measure. There is another measure called MON, but it is not as frequently used. RON and MON are the names of the processes by which the gasoline octanes are measured in laboratories.
Generally, regular cars require 95 RON, while modern or premium cars require 98 RON.
If you want to know which fuel you should use in your Orion, you can read the following article Which type of fuel should you use in your Orion?
You should also read this guide How to improve the fuel consumption of your Orion