Summary Reader Response Draft 1

The webpage “Turbofan Engine” from NASA (2021) introduces and explains the concept of the aerospace turbofan engine. The engine produces thrust which allows an airplane to move through the air. It is a modern variation of a gas turbine engine commonly used in airliners because of its high thrust and fuel efficiency.

According to a related webpage on turbofan thrust by NASA (2021), the engine works by capturing incoming air through the inlet. Some of this air goes through the fan, core compressor, and burner for combustion. The hot exhaust then passes through the core and fan turbines before exiting through the nozzle which then produces thrust.

The nozzle serves as the engine's exhaust duct. It's where high-speed air exits the engine at the back. According to Newton's third law, this action of expelling air generates an equal and opposite reaction which results in pushing the airplane forward in the air. (Collin, 2022)

Due to engine design and noise reduction technology, the turbofan engine is the dominant choice for commercial aviation compared to other types of engines despite its high costs.

There are multiple types of engines used in aviation such as turbofan, turboprop and piston engines. A reciprocating piston engine drives a propeller by internal combustion based on the Otto cycle. Piston engines have a reputation of being reliable and affordable. However, it is impractical to be used in larger aircrafts due to the power-to-weight ratio being very low. Large aircrafts require huge power to sustain flight and the piston engine is considerably heavy when compared to their power output. In such cases, a turboprop engine is a more suitable choice if a propeller is used. (Leishman, 2023)

Despite the fact that both turbofan and turboprop engines operate the same thermodynamically, turboprop engines harness nearly all the kinetic and thermal energy through expansion turbines to power the propeller. In contrast, turbofan engines employ an expansion nozzle to generate high-speed exhaust which produces thrust. (Allen, n.d.)

One advantage of the turbofan engine is its propulsive efficiency especially when it has a high bypass ratio which is defined as the ratio of the mass flow rate of the bypass stream to the mass flow rate entering the core. (Alexander D. Baxter & Fredric F. Ehrich, n.d.) 

The propulsion system of a turbofan engine is fuel efficient due to the high bypass ratio and it produces huge thrust which is why most modern airliners use them. Due to the fans being in an enclosed structure with multiple blades, it can perform efficiently at high speeds compared to a basic propeller. On the contrary, propellers face rapidly decreasing efficiency when flying at high speeds. Therefore, turboprops are exclusively utilised for slower aircraft such as cargo planes. Due to the factors mentioned above, it explains why high-speed transports typically employ turbofans, while low-speed transports make use of propellers. (NASA, 2021)

One negative effect of aviation is the noise generated, mainly from the engines. Recent epidemiological studies indicate that prolonged exposure to aircraft noise raises the likelihood of developing cardiovascular conditions, particularly when the exposure occurs at night. During childhood, children are in a developing stage and even minor disruptions in sleep can negatively impact a child's development. (Basner & Griefahn & Berg, 2010)

According to the webpage “Aircraft Noise Levels & Stages” from the Federal Aviation Administration (FAA) (2022). The FAA enforces specific noise certification standards to limit the maximum noise output of any civil aircraft. Any aircraft seeking airworthiness certification in the U.S. must adhere to these noise level requirements. This certification guarantees the integration of effective noise reduction technology into aircraft design, leading to decreased noise levels for communities.

A technical memorandum “Noise Reduction Technologies for Turbofan Engines” written by Huff for NASA (2007) states that noise reduction is achieved through a combination of adjustments to the engine's cycle parameters and the incorporation of features designed for low noise. The most effective approach for achieving substantial noise reduction in turbofan engines involves decreasing fan tip speed, lowering the fan pressure ratio, and reducing the velocity of the jet exhaust. Design elements can be implemented to minimise noise without significantly affecting performance. Some examples of such technologies include scarf inlets, chevron nozzles, forward swept fans and applying acoustic treatment over the fan. Due to these technologies reducing the noise produced, turbofan engines are heavily utilised on commercial transports.

One huge limitation of the turbofan engine is its huge cost. According to the article “The Art of Engineering: The World’s Largest Jet Engine Shows Off Composite Curves” posted by Kellner (2016)  for General Electric, a modern turbofan engine such as the General Electric (GE) GE9X produced by GE specifically for a huge commercial aircraft Boeing 777X. GE has received 700 GE9X orders valued at a list price of US$29 billion. This indicates that a single turbofan engine cost US$41.4 Million. A turboprop engine on the other hand, could cost around US$0.5 million to US$5 million, depending on the engine’s size and power. (Hanson, 2023) Despite the high upfront cost and long term cost such as maintenance of a turbofan engine, they offer a range of benefits mentioned earlier that justify the investment for many commercial airlines.

In conclusion, types of engines such as turboprop, turbofan and piston engines are compared in terms of engine design and features, highlighting the advantages and limitations. Turbofan engines stand out for their propulsive efficiency, fuel economy and low noise compared to piston and turboprop engines. Despite their high cost, turbofan engines are the preferred choice as they are widely used in modern commercial aviation due to the advantages.