Jet engines are one of many amazing engineering marvels. They allow people to get across the U.S. in only five hours. A trip to Europe takes only six hours and thirty minutes. It is amazing to think Hans von Ohain made the first plane to fly with a gas turbine engine in only 1939. What is the real science behind them? How do these marvelous machines work? This whole process starts at the fan. The fan has many blades and is used to suck air in at the front. There are about 20 fan blades. Some of the air will skip the inner core of the engine. This air goes through a duct. The “bypass air” creates more thrust, cools down the engine, and makes the engine more quiet. In most cases the fan blades are made from strong titanium. Next is the compressor. The air flows through a series of fans with many blades. The air flows into continuously smaller spaces, slowly building up more pressure over time. The next part is where things get fiery. In the combustor the pressurized air is sprayed with fuel. In most cases their can be up to 20 spouts of fuel spraying out. The fuel ignites, giving it a much higher temperature. The air is now much more dense. The gases then shoot through the turbine, causing the many turbine blades to spin. This generates thrust. The cold air that skipped the center of the engine mixes with the hot air. The air then shoots out the nozzle at dizzyingly high speeds. There are many types of jet engines. Three of the most widely used engines are the turbofan, the turbojet, and the ramjet. Turbofans are most commonly used on today’s airliners. turbofans basically consists of a turbine and a fan. The turbofan achieves good speed just below the speed of sound. Next is the turbojet. A turbojet is basically a turbofan but with no fan at the front. Instead of a fan the air flows in through an opening in the front. It has a lower air mass flow rate than the turbofan. Last is the Ramjet. This is the simplest because it has no moving parts. Air is brought in only by the movement of the plane. This engineering marvel also has a dark side. The combustion releases carbon dioxide, a prominent greenhouse gas. Carbon dioxide is one of the many contributors to global warming. A plane emits about 53 lbs of carbon dioxide per mile. A round trip flight between New York and Los Angeles emits about 20% of the greenhouse gases your car emits in a year. Aviation is responsible for 2% of all carbon dioxide outputs. This may not seem like a lot, but in theory it is. There are also non-carbon dioxide effects. Airplanes also emit lots of water vapor. When you burn hydrocarbons in oxygen water vapor is created. At high altitude water vapor can condense to form contrails. Contrails are the white lines that follow airplanes in the sky.Jet engines have helped people in many different ways. People can visit their loved ones for just the weekend with time to spare. Militaries have faster, more maneuverable fighters while still bringing pilots home to their families. However, if our world is to survive than scientists better come up with a more eco-friendly engine. This means being more fuel efficient, less carbon dioxide output, and less water vapor. For the time being, scientists are still working on it.