The jet airplane has revolutionized travel since about 1960. It has brought people and cultures closer together. It has created environmental problems. Harmful chemicals sift down from the smoky trails of low-flying jets. The scream of jet engines is constantly heard by people who live near big-city airports.
Jet aircraft, particularly the supersonic transport (SST) could engender stratospheric air pollution with consequent changes in climate. Jet exhaust contains water, CO2 oxides of nitrogen, and particulate matter. It is speculative just how harmful these pollutants can be. For example, it is estimated that a fleet of five hundred SST’s over a period of years could increase the water content of the stratosphere by 50 to 100 percent, which could result in a rise in average. Temperature of the surface of the earth of about 0.2 Celsius degrees and could cause destruction of some of the stratospheric ozone that protects the earth from ultraviolet radiation.
It is a fact that many people prefer air travel rather than ground or water transportation. This has prompted a critical look at safety and quality control. Contributions to air pollution is a chief concern because of this revolutionary change in public transportation in the United States and around the world. The government must also establish standards for exhaust emissions. Thus manufacturers are forced to develop low-pollutant engines. Contact with government agencies will give a greater insight of this subject. Information on how to contact environmental groups in New England can be found on the reference page of this unit.
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This graph shows the dramatic increases in the air traffic since 1950, including passenger miles of U.S. airlines. (Aviation Facts and Figures 1953. Washington, DC: Lincoln Press.)
An airplane needs an energy supply and an engine, for propulsion, that will function whenever they are needed. These internal combustion engines have discharged pollutants into the air. The combustion exhaust must be dealt with. Modification of air/fuel ratios can provide a partial solution. The problem of air pollution from airplanes involve a complex set of interactions among technical, social, and economic factors.
Emission from jet aircraft, particularly on landing and take-offs, are a source of bitter complaints from nearby residents. In a few airports visibility has been dangerously restricted by particulate emissions and photochemical smog. Airlines have a considerable expense in cleaning the obnoxious odors of unburned fuel from aircraft air conditioning systems. Most pilots prefer exhaust plumes, because aircrafts are made more visible.
In a jet engine, air enters through the front and is compressed by rotating vanes as it is forced into combustion chambers arranged around the circumference. Fuel is steadily sprayed into the leading end of each chamber where it ignites in the not compressed air, burns and causes the air to expand. The burning gases push toward the rear, striking turbine blades whose rotation drives the compressor they are connected to. The burning gases are further compressed at the exhaust nozzle to provide a high-velocity exhaust. This provides forward thrust to the aircraft. The diagram below illustrates this operation.
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Reliable data on engine exhausts are difficult to obtain because engines operate under many different conditions. Engine design plays an important role in reducing pollution emissions. One engine may emit more than a comparable engine. Older aircraft have experienced a substantial reduction in hydrocarbon, carbon monoxide, and particulate emission because the fuel is more completely burned with the installation of “clean burner cans”.