Aerospace Engineering Propulsion

Flashcards related to the aerospace engines lecture.

Energy Sources for Propulsion

The most common form of power source in propulsion is chemical energy, released by the combustion of fuels or propellants. Other forms include solar, nuclear, and electromagnetic energy.

Airbreather Engine

Engine that uses the air itself through which it is flying as an oxidizer for the fuel in the combustion process and as a working fluid for generating power or thrust.

Operational Envelopes for Engines

Engines operate within a specific range of altitudes and Mach numbers, with limits based on lift, temperature, and aerodynamic forces.

Gas Generator

The "heart" of a gas turbine, consisting of the compressor, combustor, and turbine, which supplies high-temperature and high-pressure gas.

Turbofan Engine

Consisting of an inlet, fan, gas generator, and nozzle, this engine type is more economical and efficient than turbojets, accelerating a larger mass of air to a lower velocity.

Ramjet Engine

This engine type comprises an inlet, a combustion zone, and a nozzle, operating most efficiently at supersonic velocities.

Impact on Aircraft Performance

The previously mentioned advancements in structures and aerodynamic efficiency had a tremendous effect on flight performance, such as flight range, economy, manoeuvrability, flight speed and altitude.

External Forces on Thrust

Occurs due to fluid motion outside the engine body which exchanges momentum, where frictional and body forces are neglected static pressure forces on the exterior of the body will contribute to or reduce the net thrust.

Jet Propulsion Principle

The engine is a device which takes in air at essentially the free stream velocity V0 (or V , heats it by combustion of fuel inside the duct, and then blasts the hot mixture of air and combustion products out of the back end at a much higher velocity Ve.

Thrust Specific Fuel Consumption (TSFC)

Used to quantify and compare the efficiency of engines by measuring the fuel mass flow rate per unit thrust. Lower values indicate more economical operation.

Installed Thrust

Overall efficiency is impacted by installation losses attributed to inlet and nozzle drag, quantified using dimensionless coefficients.

Thermal Efficiency

Net rate of organized energy (shaft power or kinetic energy) out of the engine divided by the rate of thermal energy available from the fuel in the engine.

History of the Piston Engine

The first 50 years of successful manned flight the internal combustion, reciprocating, petrol burning engine was the mainstay of aircraft propulsions.

Reciprocating pistons features

Piston and cylinder to fit tightly – use piston rings to ensure the assembly is gas tight.

Wright Brothers Engine

The first Wright brothers engine used the in-line, liquid-cooled principle. They maintain a more uniform temperature between cylinders, and cooling drag can be minimized. During post Wright Engine improvements were made by applying air-cooled rotary engines.

Supercharging

Technique used to compress air for forced induction in order to boost intake airflow at altitude.

Stroke in Piston Engine

A term used to describe The distance between the TDC and the BDC is the largest distance that the piston can travel in one direction.

Mean Effective Pressure (MEP)

A measure to compare the performance of reciprocating engines of equal size. A larger value indicates better performance because it delivers more net work per cycle.

Compression Ignition (CI) engines

The air-fuel mixture is self-ignited as a result of compressing the mixture above its self-ignition temperature.

Connecting Rod

A key part is to turn reciprocating motion of the piston into a rotary motion by using a connecting rod to couple the pin to the crankshaft. Con-Rod should be able to oscillate on a pin (gudgeon or wrist pin).

Propellers in Flight

For low speed flight and short field takeoff they have a performance advantage. At speeds approaching the speed of sound, compressibility effects set in and they loses their aerodynamic efficiency.

Hooker’s Charge-Mass law

For a six-cylinder air-cooled normally aspirated four-stroke aircraft piston engine what law can you use to determine the charge-mass flow using bore and piston stroke?

Indicated Power

Individual thermodynamic processes in the cycle are necessarily non ideal. This is due to Valves taking time to open and close, and combustion/exhaust processes not being instantaneous.

Brake Power, BP

A term used to capture shaft or brake output power and a measure to determine brake effective pressure.

Thrust Power TP

This power will be lower again than shaft power SP (=BP), b y being degraded in conversion by the propulsive efficiency ηp of the propeller or rotor TP = ηp.BP

Supercharging

Method used to increase engine power, particularly sustained power at altitude. It used to compress air for forced induction, drives a centrifugal compressor at high speed.

Propellers

With an airfoil shape, this provides thrust to propel the aircraft through the air. Its shape changes with pitch angle depending on if it is nearing the root or tip of the blade.

Propeller Airflow

The airflow seen by a given propeller section is a combination of the airplane’s forward motion and the rotation of the propeller itself.

The Propulsive Efficiency

Defined as the ratio of the thrust power (thrust velocity) to the power out of the engine .

Compressibility loss

A condition in a propeller where The propeller tip speeds result in a near sonic relative wind. When this occurs, the same type of shock wave and boundary-layer separation losses act to rob the propeller of available power.

variable pitch propeller

Used to maintain maximum efficiency at all flight velocities because it Rotates the entire blade about an axis along the length of the blade. This can be visualised as riding along the peaks of the propeller efficiency curves.

Constant speed propeller

Allows the pitch angle to be varied continuously and automatically to maintain the proper torque on the engine.

Actuator Disk Model

The simplest approach to propeller theory, which replaces the propeller with an infinitely thin plane which produces an increase in the axial velocity and therefore axial momentum and propulsive force.

idealized flow

A condition where both inflow factor a = b/2 = 0.06, and the area contraction of the incoming streamtube at the disk is also 6%.

ideal Froude efficiency

There is one equation that says a Froude is always greater than the actual propulsive efficiency achieved.

CMC: Ceramic Matrix Composite

1/3 the density of Ni-based superalloys, has higher temperature capability, has hotter walls which reduces cooling needsand has a Low CTE (Coefficient of Thermal Expansion) all making it a.

Jet Propulsion Principle

The engine is a device which takes in air at essentially the free stream velocity V0 (or V , heats it by combustion of fuel inside the duct, and then blasts the hot mixture of air and combustion products out of the back end at a much higher velocity Ve.

Net thrust

To communicate a force to a solid surface nature requires surface pressure and shear stress distributions.

Enthalpy

At this point we need to define a new term which the sum of the internal energy and the flow energy of a fluid.

Isentropic stagnation state

The stagnation state is called the state when the stagnation process is reversible as well as adiabatic.

Stagnation

When the fluid is an ideal gas,. The temperature T0 is called the _(or total) temperature, and it represents the temperature an ideal gas will attain when it is brought to rest adiabatically.

Variation of fluid velocity with flow area

Can be derived (but not here!) and describes the variation of pressure with flow area.

Efficiency equation

Air/fuel ratio = ma/mf, efficiency should is Otto cycle efficiency

Thrust/weight ratio

This is to find an increase in aircraft capabilities (payload, fuel etc) or decrease the size, weight and therefore cost of a new aircraft under development

Six-cylinder air-cooled piston engine formula

A six-cylinder air-cooled normally aspirated four-stroke aircraft piston engine has a cylinder bore of 130mm and a piston stroke of 111mm. The volumetric compression ratio r is 8.5.

Combustion Engine

In a piston engine the piston (or reciprocating) engine is an engine in which combustion takes place within the engine itself, unlike a steam turbine, where steam is introduced to the turbine having been raised externally in a boiler.

clearance volume

The minimum volume formed in the cylinder when the piston is at TDC is called the_.

Operational envelopes

Each engine type will operate only within a certain range of altitudes and Mach numbers (velocities).

Developers of Gas Turbine Engine

A number of ideas were patented in the early part of the 20th century based on air breathing jet propulsion