Aircraft Emissions and Noise Review – Technological Paths for Pursuing Sustainability in the Aviation Industry 2020-36-0106

Environmental concerns have driven the scientific community in a continuous effort to set standards for emission and noise control in a diversity of industries worldwide. The aviation industry, which currently relies on fossil fuels, is strongly driven by a growing environmental awareness, which makes it one of those that are spending huge efforts to reduce its environmental footprint. Airplanes emit several types of pollutants, mainly Carbon Monoxide (CO), Unburned Hydrocarbon (UHC), Particulate Matter (PM), Nitrogen Oxides (NOx) and Sulfur Oxides (SOx), as well as Greenhouse Gases (GHG) and noise. These emissions, which can impact both the airport surroundings, as well as the high atmosphere layers, might affect the environment, through the modification of atmosphere’s chemical and physical properties, which ultimately might cause global, regional and local effects, as well as noise annoyance to the population near the airports. This scenario has fostered technological advances in the last decades, associated with huge improvements in the aircrafts' environmental performance, which ultimately has allowed the compliance with the continuously increasing stringent emissions and noise standards. The technological upgrade pathways have been strongly led by both aerodynamic, engine components, combustor and exhaust system improvements. However, despite the acknowledged aviation environmental performance progresses over the last years, air traffic increase, and, hence, its environmental impact, has required further advances in emission and noise emission control. This context has been translated into a continuous evolutionary trend of the stringent emissions and noise standards, in which the aviation industry is constantly challenged, in order to overcome the inherent imposed environmental and operational restrictions (environmental charges, night flying restrictions/curfews, etc.), with the use of groundbreaking technology approaches. In the field of engines, the environmental's performance improvement relies basically on the refinement of thermodynamics (including combustion technology) and aerodynamics processes. This work is supposed to present an aviation pollutant and noise emission technology review, based on the available technical literature, with a focus on the engine technology improvement pathways, as well as their inherent environmental and operational performance.