Advancements in aircraft reciprocating engines
Introduction
There is a misconception that because modern aircraft engines built by Lycoming, Continental and other companies have similar look to engines used in general aviation aircrafts of the 1970s, there have been no technological advancements in this field. Even though new engines haven’t changed much by outward appearances, aircraft reciprocating engine technologies have advanced dramatically in past two decades. The overall build quality of engine has greatly improved. Advancements in machining technologies and automatic manufacturing processes made it possible for aircraft engine makers to enhance machine’s durability. Many components of piston engines have been significantly improved, such as fuel delivery systems and coatings. The greatest technological breakthrough was the connection of aircraft engines to special aviation-grade computers. Such computerized systems can monitor almost every parameter related to engines. Today, several engine manufacturers develop engines capable of running alternative sustainable fuels or fuel-efficient diesel engines that burn jet-A fuel.
Technological advancements
Engines capable of running jet-A fuel
Jet fuel is the most readily available source of fuel on market. It is cheaper than aviation gasoline and can be used in diesel engines. One of such engines is direct-injection, turbocharged engine The Continental CD-200 or TD-300 as it was formerly called. In April 2013 CD-200 was type certified by the US Federal Aviation Administration. (Bertorelli, 2013) This 230-horsepowered engine is designed with no gear box that means that it has better reliability and reduced weight. However, it should be noted that diesel engine has its own set of disadvantages. Not just such engine weighs more, but its cost is substantially higher in comparison to most alternatives. Just the fuel delivery system of diesel engine is an order of magnitude costlier than fuel injection systems of conventional gasoline piston engines. The main reason for this is that systems based on diesel fuel must run at significantly higher pressure in order for the fuel to be atomized for a clean burn. (Pope, 2012)
Engines capable of running alternative fuels
The main idea behind this innovation is to create engines that run on a sustainable and environmental-friendly fuel in place of traditional aircraft fuel such as aviation gasoline. Today, just Boeing’s 747 aircraft use five gallons/mile of fuel that means approximately 36,000 gallons of fuel are burned in ten-hour flight. To date, the FAA authorized five types of bio-based jet fuels, which can be used for air travel. The newest fuel – Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK) was introduced in 2016. Such fuel is created from isobutanol and may be produced from feed stocks like corn, sugar or forest wastes. Another four bio-based jet fuels are: synthesized iso-parafins (SIP), Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK), and Fischer-Tropsch Synthetic Kerosene with Aromatics (FT-SKA) and hydro-processed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK). (AOPA, 2017)
Electric-powered aircraft engines
Another technology that promises to revolutionize the impact of aviation on the global environment is aircraft reciprocating engines powered by electricity. Leading companies, such as Boeing, Airbus, Safran S.A., Raytheon already works in this direction. Engineers of Boeing are developing the SUGAR Volt concept plane. Similar to a hybrid automobile, this aircraft combines both fuel and electricity to power its flight. Airbus works on project E-Fan, an aircraft powered by battery.(Airbus, 2016) Analysists predict that in next fifteen years the electric aircraft market may reach over $22 billion. (Aerotime, 2015)
Cryogenic engine overhaul
The concept of cryogenics is not new and ideas of its application in aviation have been around even before WWII. However, it was near-impossible to obtain required liquid nitrogen and liquid helium back then. Cryogenics has several manufacturing applications. Such approach may be used to make a variety of products more durable by eliminating the residual stress in machined parts.
Parts of the engine are placed in a large vacuum cryotank where a liquid nitrogen is created in non-contact atmosphere. As rule, such process consists of gradually adding the cryogen and lowering the temperature to -300 ℉. Depending on the material, tested parts should be maintained in a super-cold state for 24/48/72 hours. After that, material is either just returned to room temperature or undergo a heat treatment phase if necessary. Later the parts are tested using Rockwell hardness or X-ray diffraction ultrasonic techniques. Produced materials are less susceptible to fracturing or wear. As result, the engine constructed using such approach runs smoother, has higher efficiency and burns less fuel. (Cox, 2014, pp. 6-7)
Full-authority digital engine controls (fadec) technology
Introduction of full-authority digital engine controls or fadec marked a new stage in aircraft reciprocating engine technologies. Even though digital engine controls for aircrafts have been around since 1990s, they have undergone significant changes since then. Fadec technology provides control of fuel injection systems and over fuel flow, offers full electronic engine ignition and monitoring of all engine-related parameters. Although it should be noted that such systems are quite complex and additional wiring and modifications to the electrical system of the aircraft are needed. Fadec also requires secondary battery, that must be always kept fully charged during flights.
Innovations in the fuel delivery system should be mentioned. Lycoming’s iE2 engine technology offers a fuel injection system which controls fuel delivery with constant and high pressure. Similar systems are installed in F1. (Lycoming, 2016) If fadec system is installed, the pilot no longer needs to worry about the fuel-air mixture in the engine when altitude decreases or increases. (Pope, 2012) Another advantage is that the carburetor is no longer needed. As such, the carburetor icing cannot occur. Vapour lock is a non-event as well because of the high pressure fuel system. (EAI, 2016)
References
Aerotime. (2015). Top 10 advancements shaping the future of aviation. Retrieved 02.01.2017, from https://www.aerotime.aero/en/people/people-news/editorial/16895-top-10-advancements-shaping-the-future-of-aviation
Airbus. (2016). Airbus E-Fan: The future of electric aircraf. Retrieved 02.01.2017, from http://www.airbusgroup.com/int/en/corporate-social-responsibility/airbus-e-fan-the-future-of-electric-aircraft.html
AOPA. (2017). Five Jet Biofules Now Approved, FAA Says. Retrieved 02.01.2017, from https://www.aopa.org/news-and-media/all-news/2016/april/14/five-jet-bio-fuels-now-approved-says-faa
Bertorelli, P. (2013). Continental Extends TBOs, Certifies Diesel. Retrieved 02.01.2017, from http://www.avweb.com/avwebflash/news/Continental_Extends_TBOs_208528-1.html
Cox, B. (2014). Cryogenic Overhaul: New Technology Comes To Piston Engine Overhauls (pp. 11).
EAI. (2016). Engine Management Systems, FADEC. Retrieved 02.01.2017, from http://www.experimentalaircraft.info/articles/aircraft-engines-fadec.php
Lycoming. (2016). iE2 Integrated Electronic Engine. Retrieved 02.01.2017, from https://www.lycoming.com/engines/ie2
Pope, S. (2012). Piston Engine Aircraft Technology. Retrieved 02.01.2017, from http://www.flyingmag.com/aircraft/pistons/piston-engine-technology
