A new approach to optimizing the sound and sound quality of an aircraft engine could reduce emissions and save lives by reducing the noise produced, according to research by University of Waterloo.
Researchers have used the computer model of a modern airplane engine to investigate how the sound would change depending on the speed and thrust of the engine.
The result is an analysis of the acoustic effects of different engine speeds and thrust levels to calculate how different engine types could be used in the engine design of an airliner.
“Our work is the first to consider the effect of engine speeds on noise levels,” said Professor of Mechanical Engineering and Astronomy at Waterloo’s Department of Mechanical Science, Mark Schumann.
“Engine noise levels depend on engine type, the shape of the fuel tank and the type of combustion chamber.”
A common misconception is that the more a fuel is burned, the louder it is.
This is not the case.
The loudness of an engine depends on the fuel in the fuel system.
The louder the fuel is, the more it needs to be heated to ignite the engine.
“Engine noise is caused by the combustion of the hydrogen, oxygen and carbon dioxide molecules.”
The most obvious example is the combustion engine,” said Schumann, who is also a Fellow of the Royal Society of Canada.”
When the fuel injectors are opened, the fuel molecules collide with each other and release oxygen and gases that form hydrogen gas.
“Then the fuel gas molecules are released into the exhaust stream.”
During the ignition process, these gas molecules collide again and create more gas, which is what we think of as engine noise.
“We want to know how much engine noise is produced by a given engine type and how loud this gas emission is, so we can improve the efficiency of the combustion process.”
Schumann and colleagues found that noise levels increased as the engine speed increased, and decreased as the thrust increased.
“This indicates that there is an interaction between engine speed and engine thrust,” Schumann said.
“These effects have been studied for decades, but until now there has not been any study that was able to estimate the magnitude of this interaction.”
The researchers conducted an analysis on the sound emitted by an Airbus A380 turboprop engine at 35,000ft (10,000 metres) and a Boeing 787 Dreamliner engine at 34,500ft (8,500 metres).
“Our study is the result of a decade of research and work, which started with the development of computer models that simulate aircraft engine sound,” Schuman said.
“In our simulations, we can use the acoustic properties of a turbopropeller engine to estimate noise levels at various engine speeds.”
“Our results show that at low speeds, the sound from the engine produces a noise that is 20 times louder than that of the noise from the air surrounding the engine,” Schumans research said.
Schumann said that with improved engines, there could be a better chance of avoiding the harmful emissions from jet fuel burning.
“In our study, we also found that the noise level decreased at a very low speed, which means that it could be more difficult to avoid the harmful jet fuel emissions that can cause noise to increase,” he said.
The team said it hopes to conduct further research into the sound production process and find new uses for the noise emitted by engines.
“Using acoustic simulations to simulate sound production could help to develop better sound systems, which could potentially reduce the number of emissions generated by engines,” Schaumans said.