Plz clear my doubt on rocket engines.....?

As you can see by looking at any jet airplane, air-breathing engines certainly exist. The problem is that the amount of oxygen needed to generate a lot of trust is huge. The plane engines use large compressors to pull a huge amount of air into the engine. This compressor is the bulk of the jet engine and it works quite well at low altitudes. However, as the altitude increases, the amount of oxygen in the atmosphere drops dramatically as well as the air pressure. Jet engines have a hard time flying much above 50000 ft because of lack of oxygen. This is why you have to carry oxygen with you if you want the engine to work at high altitudes.