Aircraft engine design
The development of an engine is a game of compromises. Engineers create specific characteristics in engines to achieve various aims. Aircraft are one of the most difficult applications for engines, with numerous design criteria, many of which clash with one another. An aircraft’s engine must be:
- Dependable; losing power in an airplane is a far more serious concern than a car engine seizing. Airplane engines operate at severe temperatures, pressures, and speeds and must therefore work reliably and safely under all of these situations.
- lightweight; a large engine increases the aircraft’s empty weight and reduces its payload.
- strong, capable of overcoming the aircraft’s weight and drag.
- Compact and easily streamlined, big engines with a huge surface area cause too much drag, wasting fuel, and limit power production when mounted.
- repairable to keep replacement costs low. Small repairs should be reasonably priced.
- fuel-efficient to provide the aircraft with the range required by the design.
Aircraft engines, unlike automotive engines, can operate at high power levels for lengthy periods of time. In general, the engine runs at full power for a few minutes during takeoff, then slightly reduces power during the climb, and then spends most of its time at cruise power—typically 65% to 75% of full power. In comparison, a car engine may spend 20% of its time accelerating at 65% power, followed by 80% of its time cruising at 20% power. A reciprocating or turbine aircraft engine’s power is measured in units of power provided to the propeller (usually horsepower), which is torque multiplied by crankshaft rotations per minute (RPM).
The propeller transforms engine power into thrust horsepower, with thrust being a function of propeller blade pitch relative to aircraft velocity. Jet engines are rated based on thrust, which is typically the greatest amount achieved during takeoff. The reliability of aircraft engines is prioritized over performance. Extended engine operating times and high power settings, combined with the need for high reliability, necessitate engine design that allows for this type of operation. Airplane engines use the simplest elements feasible and incorporate two sets of everything required for reliability. The independence of functions reduces the possibility of a single fault causing the entire engine to fail.
The great majority of the time, aircraft move at high speeds. This enables an aircraft engine to be air-cooled rather than requiring a radiator. In the absence of a radiator, aviation engines can be lighter and more sophisticated. The amount of airflow that an engine receives is usually carefully calculated based on the aircraft’s predicted speed and altitude in order to keep the engine at the appropriate temperature.
Planes fly at greater altitudes when the air density is lower than at ground level. Because engines require oxygen to burn fuel, a forced induction device such as a turbocharger or supercharger is ideal for aircraft use. This has the normal drawbacks of increased cost, weight, and complexity.
Aircraft Systems
Aviation systems are the components required to keep an aircraft flying effectively and safely. The complexity varies according to the type of aircraft.
- Aircraft software systems: Aircraft software systems control, manage, and apply the avionics subsystems onboard an aircraft.
- Flight control systems—Airplane flight control systems and helicopter flight controls are the main articles. Flight control systems can be either manually or automatically operated. They move the flight control surfaces, or swashplate, helping the pilot maintain or change attitude as needed.
- Landing gear system: landing gear is the main topic of this essay. Larger aircraft typically use hydraulic landing gear systems for powered retraction and extension of the main legs and doors, as well as braking. Anti-skid systems are used to provide the best braking performance possible.
- Hydraulic system: For high-speed flying and big aircraft, a hydraulic system is required to transform the crew’s control system movements into surface movements. The hydraulic system also extends and retracts the landing gear, operates the flaps and slats, and controls the wheel brakes and steering systems. Engine-driven pumps, fluid reservoirs, oil coolers, valves, and actuators comprise hydraulic systems. The utilization of numerous, independent systems frequently provides redundancy for safety.
- Electrical system: A battery, generator or alternator, switches, circuit breakers, and instruments such as voltmeters and ammeters are common components of an electrical system. A ram air turbine (RAT) or a hydrazine-powered turbine can offer backup power.
- Engine bleed air system: bleed air is compressed air taken from a gas turbine engine’s compressor stage upstream of the fuel-burning sections. It is utilized for a variety of functions, including cabin pressurization, cabin heating or cooling, boundary layer control (BLC), ice protection, and fuel tank pressurization.
- Avionics-Avionics Aircraft avionic systems comprise a variety of electrical and electronic equipment such as flight instruments, radios, and navigation systems.
- Fuel systems: the airplane fuel system is the main article. An aircraft fuel system is intended to store and transport aviation gasoline to the propulsion system and, if installed, the auxiliary power unit (APU). Because of the variable performance of the aircraft in which they are placed, fuel systems vary substantially.
- Propulsion systems: Articles of primary importance: Controls for the aircraft engine and the aircraft engine Engine installations and controls are included in propulsion systems. Fire detection and protection, as well as thrust reversal, are subsystems.
- Ice protection systems: the main article is about an ice protection system. Planes that operate in icing conditions on a regular basis include equipment to detect and prevent ice formation and/or remove ice accumulation after it has developed. This can be accomplished by heating the internal structural spaces using engine bleed air, chemical treatment, electrical heating, and skin expansion and contraction utilizing de-icing boots.
How does SAF perform in aircraft?
Normal jet fuel is a kerosene-based fuel with a high density. This was created to provide the high power required by aviation engines. It has a greater flash point and a lower freezing point than regular automobile gasoline because it has longer sequences of hydrocarbon atoms. Nevertheless, because it is dependent on fossil fuels, it emits a lot of CO2. SAF (sustainable aviation fuels) are an option. They are based on renewable hydrocarbon sources that are not derived from fossil fuels. This includes waste cooking oil, municipal garbage, and forestry biomass. The driving force here is sustainability; supplies should be able to be replenished frequently. SAF was introduced in 2008. Many airlines have announced promises to utilize SAF at various levels, and this is growing. In 2019, the International Civil Aviation Organization anticipated that demand would reach 8 billion liters by 2032. (from levels then of 6.45 million liters).
SAF is not directly used as fuel. Nevertheless, it can be utilized in current jet engines after being mixed with conventional jet fuel. This guarantees that the performance and handling characteristics are comparable. Blended fuel must meet strict specifications. SAF is combined with regular fuel in up to 50% concentrations. Most fuels currently employ much lower quantities of SAF, although this is predicted to increase over time (and potentially reach 100%). United Airlines has conducted test flights with one engine powered entirely by SAF, albeit without passengers. The resulting fuel is re-certified as Jet A or Jet A-1 fuel and can be handled, transported, and used in the same manner as regular fuel. This means that (after blending), no adjustments to existing fuel infrastructure in the supply chain or at airports are required. This is a serious constraint when considering new fuel sources like hydrogen.
SAF’s current application is somewhat limited. Despite high-profile commitments from several airlines, overall adoption remains low when compared to regular jet fuel. The cost of collection and production should decrease as collection and production availability expands. Longer term, it should provide more consistent pricing than oil and will become increasingly crucial as the industry strives to meet its objective of halving global emissions by 2025. (based on 2005 levels). Similarly, manufacturing technology is evolving. Synthetic kerosene can be produced using power-to-liquid techniques, which have the potential to reduce emissions by up to 99%. Power-to-Liquid refers to the electrolytic conversion of renewable energy into fuels. There is still a long way to go before this is widely adopted, but it has the potential to offer a carbon-neutral circular system for aviation by reusing the carbon dioxide that aviation produces and converting it back into power for the planes.
Changes in aircraft to make them lighter and more fuel-efficient
Lightweight design is a widely researched and applied idea in numerous industries, particularly in aerospace applications, and is linked to the green aviation concept. The contribution of aviation to global warming and pollution has resulted in ongoing attempts to reduce aviation emissions. Increasing energy efficiency is one approach to achieving this goal. For example, a 20% weight reduction on the Boeing 787 resulted in a 10 to 12% increase in fuel efficiency. In addition to lowering the carbon footprint, the lightweight design could increase flying performance by improving acceleration, structural strength and stiffness, and safety performance.
CHOOSING LIGHTWEIGHT MATERIALS
The selection of aerospace materials is critical in aerospace component design because it affects many aspects of aircraft performance, including structural efficiency, flight performance, payload, energy consumption, safety and reliability, lifecycle cost, recyclability, and disposability, from the design phase to disposal. Mechanical, physical, and chemical properties such as high strength, stiffness, fatigue durability, damage tolerance, low density, high thermal stability, high corrosion and oxide resistance, and commercial criteria such as cost, servicing, and manufacturability are critical requirements for aerospace structural materials. According to studies, reducing density (by using lightweight materials) is the most effective technique to improve structural efficiency (approximately 3–5 times more effective than increasing stiffness or strength).
- Alloys are made of aluminum. Although high-performance composites such as carbon fiber are gaining popularity, aluminum alloys continue to account for a large amount of aeronautical structural weight. Advanced aluminum alloys are a popular choice of lightweight materials in many aerospace structural applications, such as fuselage skin, upper and lower wing skins, and wing stringers, due to their relatively high specific strength and stiffness, good ductility and corrosion resistance, low price, and excellent manufacturability and reliability. Heat-treatment technological advancements have resulted in high-strength aluminum alloys that are competitive with modern composites in many aerospace applications. By altering compositions and heat treatment procedures, aluminum alloys can provide a wide range of material qualities to fulfill a variety of application needs.
- Alloys made from titanium Titanium alloys outperform conventional metals in several ways, including high specific strength, heat resistance, cryogenic embrittlement resistance, and low thermal expansion. These benefits make titanium alloys an attractive alternative to steel and aluminum alloys in airframe and engine applications, but their poor manufacturability and high cost (often roughly 8 times higher than commercial aluminum alloys) limit their widespread use. As a result, titanium alloys are employed in applications requiring great strength but limited space, as well as applications requiring strong corrosion resistance. Titanium alloys are currently used mostly in airframe and engine components, accounting for 7% and 36% of total weight, respectively.
- Steel with high strength. Steel is the most commonly used structural material in many industrial applications because of its ease of fabrication and availability, extremely high strength and stiffness in the form of high-strength steel, good dimensional properties at high temperatures, and lowest cost among commercial aerospace materials. However, high density and other drawbacks, such as high susceptibility to corrosion and embrittlement, limit the use of high-strength steels in aeronautical components and systems. Steel typically accounts for 5%–15% of commercial airplane structural weight, with the percentage continuously reducing. Notwithstanding these restrictions, high-strength steels remain the material of choice for safety-critical components requiring exceptionally high strength and stiffness.
- Composites for the aerospace industry High-performance composites like fiber-reinforced polymer and fiber metal laminates (FML) have gained traction in aerospace applications, competing with traditional lightweight aerospace materials like aluminum alloys. At mild temperatures, aerospace composites offer higher specific strength and stiffness than most metals. Other advantages of composites include improved fatigue resistance, corrosion resistance, and moisture resistance, as well as the ability to tailor layups for optimal strength and stiffness in required directions; however, one of the major barriers to the composite application is the higher cost of composites in comparison to metals.
- The advancement of nanotechnology allows for the improvement of multifunctional properties (physical, chemical, mechanical, etc.) at the nanoscale. Unlike traditional composites, nanocomposites have the ability to improve characteristics without sacrificing density by using a tiny amount of nanoparticles (e.g., layered silicate, functionalized carbon nanotubes (CNTs), and graphite flakes). To improve the oxidation resistance of composites, nanoparticles such as silicate, carbon nanotubes (CNTs), or polyhedral oligomeric silsesquioxane (POSS) could be incorporated to generate passivation layers.
- Manufacturability is an important constraint throughout the design process, determining if a design can be produced into a genuine product. Manufacturing restrictions must be considered while selecting materials, designing structures, and optimizing them. Topologically optimal designs typically provide complicated geometry that cannot be manufactured using traditional production methods like casting and forming without modification. As a result, manufacturing processes have a considerable impact on lightweight design.
Ways that changes in aircraft design are helping reduce fuel consumption:
- Lowering an aircraft’s lift-to-drag ratio can make it more aerodynamically efficient and help reduce weight and fuel consumption. Engineers are experimenting with new designs to help minimize drag. Thicker fuselages, which improve airflow, and longer, slimmer wings are two ideas. Winglets, or small vertically lifting surfaces, are being fitted to help reduce the quantity of air that flows over the wingtip. The “double bubble” D8 idea under development at NASA relocates the aircraft’s engine to the top of the plane toward the tail, considerably reducing drag and increasing fuel economy.
- A wide-body passenger plane can gain more than 16,000 pounds due to wires and cables. Nowadays, aviation engineers are investigating the prospect of using small, lightweight wireless transceivers to replace cables in non-avionic systems such as those that regulate cabin illumination, cabin pressure, landing gear, and door sensors. The transceiver modules could be mounted on plane components using long-life batteries. The modules would collect and transmit data to router-like concentrators that would be powered by the plane’s electrical system. The pilot’s data would be shown on tablet PCs in the cockpit. Other researchers are also investigating “fly-by-wireless” systems, which would eliminate wired connections between safety-critical avionics components such as an aircraft’s engine, navigation system, and onboard computers.
- Innovative manufacturing technologies have reduced the cost of high-performance and lightweight carbon brakes to that of steel brakes. Engineers are constantly working to create lighter-weight aircraft materials that maintain strength and safety. Carbon-fiber-reinforced polymers have been utilized in airplanes since the 1970s, although only in certain elements of the aircraft, such as tail components. Carbon-fiber composites are becoming more popular among manufacturers since they are lighter than aluminum alloys. For example, using carbon-fiber composites instead of metal to make wings can reduce fuel usage by 5%.
- Aviation researchers are reducing fuel consumption by developing hybrid-electric engines and lighter-weight engines. Honeywell’s hybrid-electric turbogenerator, for example, runs partially on electricity, requiring less traditional fuel. The HTS900 engine is combined with two compact, high-power-density generators to form the propulsion system. Each generator produces 200 kilowatts, which is enough to power 40 normal American houses with full-blast air conditioning. Several electric motors situated anywhere on an aircraft could be powered by a single Honeywell turbogenerator.
Lightweight is an efficient approach to reducing energy usage while improving performance. This approach is widely accepted and used in many industries, particularly aircraft components and system design. Advanced lightweight materials and numerical structural optimization, enabled by new production technologies, are used in a lightweight design.
With every ounce of weight on an aircraft equaling dollars spent on fuel, it is vital that we continue to look for creative ways to reduce the total weight of a plane. Reduced weight means less fuel is utilized, which can save millions of dollars. Weight reduction is becoming a top focus for commercial airlines, business jet owners, armies and rescue missions, and cargo corporations due to the possible savings. Thankfully, advances in technology are making it easier for engineers to investigate and build new possibilities.
