The earliest forms of engines do not come with it. But it is now being used in several engines such as the car engine, helicopters, diesel engine generators andmany more.
It seems more environment friendly in that there would be less emission and in a world where we are clamouring for less emission to mitigate
Yes i quite agree with that fact since it works immediately your engine ignites then less emissions come from the exhaust (flue gases). Its in our dear country we still use engines of over twenty, twenty five years. There have been improvements and those engines should be stopped.
Does it have any disadvantage?
The basic limitation of the engine is that it uses a percentage of the power to combust more fuel but it aids better combustion in fuel which means it brings about more energy in horsepower.