Wsalaam
@ Sohail Shuja
Sorry but the above article never says that the rocket engine is the air breathing type of engine.

@ Gr8khali
Nice contribtion bro. But the rocket engine is more efficient in terms of power production. The air breathing type is just more cost effective.
The broad categories of mechanical engines are combustion engines and the non-combustion engines.
The non-combustion engines do not use combustion as in the compressed air engine and the gravity engine.
The combustion engines are divided into two broad categories of internal combustion engines and the external combustion engine.
One of the upcoming types of external combustion engines is the breathing rocket engine, which breathes the oxygen from the atmosphere as long as it is in the atmospheric bounds. Afterwards and beyond, it is the same old Oxy-Hydrogen rocketry. This modification is done in order to reduce the cost of fuels used and thier amount also.
The future popular type of internal combustion engine is the rotary wrankle or commonly called the "wankie" engine. It does not use the conventional pumping type pistons, rather, it uses the rotary pistons to move the crankshaft. This type of engine is more fuel efficient and less in size, weight and parts. Moreover, it is a "knockless" or no vibration engine. Mazda has introduced it Rx8 in this technology, while the ever first bike with such technology was introduced by "Norton" back in 1990's