Simulation = For analysis and study
Emulation = For usage as a substitute
A simulator is an environment which models but an emulator is one that replicates the usage as on the original device or system.
Simulator mimics the activity of something that it is simulating. It "appears"(a lot can go with this "appears", depending on the context) to be the same as the thing being simulated. For example the flight simulator "appears" to be a real flight to the user, although it does transport you from one place to another.
Emulator, on the other hand, actually "does" what the thing being emulated does, and in doing so it too "appears to be doing the same thing". An emulator may use different set of protocols for mimicking the thing being emulated, but the result/outcome is always the same as the original object. For example, EMU8086 emulates the 8086 microprocessor on your computer, which obviously is not running on 8086(=different protocols), but the output it gives is what a real 8086 would give.