Development of Reciprocating Engine Flashcards
___________ begins as the piston starts its downward travel from top dead center up to bottom dead center.
intake stroke
When this happens, the intake valve opens and the fuel-air mixture is drawn into the cylinder.
At what stroke does this happen?
intake stroke
The ______________ begins when the intake valve closes, and the piston starts moving back to the top dead center of the cylinder.
compression stroke
This phase of the cycle is used to obtain a much greater power output from the fuel-air mixture once it is ignited.
compression stroke
Elements of a Reciprocating Engine
- intake valve
- piston
- crankshaft
- spark plug
- connecting rod
- exhaust valve
The __________ begins when the fuel-air mixture is ignited. This causes a tremendous pressure increase in the cylinder and forces the piston downward away from the cylinder head, creating the power that turns the crankshaft.
power stroke
The ____________ is used to purge the cylinder of burned gases.
exhaust stroke
It begins when the exhaust valve opens, and the piston starts to move toward the cylinder head once again.
exhaust stroke
What are the four strokes?
intake, compression, power, exhaust
What are the five events?
intake, compression, ignition, power, exhaust
The conversion of the resultant heat energy into mechanical energy and then into work is accomplished in the __________.
cylinder
Process of Reciprocating Engine Operation
- fuel is vaporized and mixed with air
- forced or drawn into a cylinder
- compressed by a piston
- ignited by an electric spark
Two Primary Reciprocating Engine Designs
spark ignition (gasoline) and compression ignition (diesel)
What is the main difference between spark ignition and compression ignition?
process of igniting the fuel
How is the fuel ignited in a spark ignition engine?
through the use of spark plug
______________ is the ratio of the “weight” of fuel to the “weight” of air in the mixture to be burned.
Fuel-air mixture
A _____________ first compresses the air in the cylinder, raising its temperature to a degree necessary for automatic ignition when fuel is injected into the cylinder.
compression ignition engine
Reciprocating engines may operate on either a ______ or ____ cycle.
two-stroke, four-stroke
Because a to-stroke engine has a power stroke upon each revolution of the crankshaft, it typically has higher _______________ than a comparable four-stroke engine.
power-to-weight ratio
Why is the use of two-stroke engine limited in aviation?
due to inherent inefficiency and disproportionate emissions
Types of Reciprocating Engines
radial engines, in-line engines, v-type engines, horizontally opposed engines
consists of one or more rows of odd-numbered cylinders arranged in a circle around a central crankshaft
radial piston engine
Due to the small size of the crankcase, this engine type had a better power-to-weight ratio than most other designs of their day.
radial engine
The cylinder arrangement allowed for good cooling airflow and smooth operation.
radial engine
It provides the greatest drag of all the types of engines.
radial engine
It is also known as straight type engine because of its cylinder arrangement.
in-line engine
This engine mat either be liquid-cooled or air-cooled and aligned in a single row parallel with the crankshaft, which is located either above or below the cylinders.
in-line engine
In an in-line engine, if the engine is designed to operate with the cylinders below the crankshaft, it is called an __________.
inverted engine
In an in-line engine, if the engine is designed to operate with the cylinders above the crankshaft, it is called an _________.
upright engine
This type of engine has a small frontal area and is better adapted to streamlining.
in-line engine
This type of engine has the least amount of drag.
in-line engine
With increase in engine size, the air cooled in-line type of engine offers additional problems to provide _________.
proper cooling
The rearmost cylinders of an air-cooled in-line engine receive relatively little cooling air, so in-line engines were typically limited to only ________ cylinders.
four or six
This type of engine has its cylinders arranged around a single crankshaft in two in-line banks that are 45, 60, or 90 degrees apart.
v-type engine
The cylinders of a V-type engine are arranged around a single crankshaft in two in-line banks that are __, __, or __ degrees apart.
45, 60, 90
Since v-type engines had two rows of cylinders, they were typically capable of producing __________ than an in-line engine.
more horsepower
The cylinders on a V-type engine could be above the crankshaft or below it, in which case the engine is referred to as an __________.
inverted V-type engine
This type of engine is considered to provide an excellent combination of weight, power, and small frontal area.
v-type engine
most popular reciprocating engine used on light aircrafts
horizontally opposed engine
it is also considered as boxer type or flat type engine
horizontally opposed engine
It always have an even number of cylinders, and a cylinder on one side of a crankcase “opposes” a cylinder on the other side.
horizontally opposed engine
This type of engine has two banks of cylinders directly opposite each other with a crankshaft in the center. The pistons of both cylinder banks are connected to the single crankshaft.
horizontally opposed engine
This type of engine has a low weight-to-horsepower ratio because they have a comparatively small and lightweight crankcase.
horizontally opposed engine
The narrow silhouette of a horizontally opposed engine makes it ideal for horizontal installation on the aircraft wings or in ___________.
twin engine applications
An advantage of a horizontally opposed engine is its _____________ characteristics because an opposed engine’s power impulses tend to cancel each other.
low vibration
A horizontally opposed engine’s compact cylinder arrangement reduces the engine’s __________ and allows a _________ that minimizes aerodynamic drag.
frontal area, streamlined installation
Why use cooling system?
to avoid:
- failure of cylinder material
- piston seizure
- distortion of engine components
- lowering of volumetric efficiency of engine
- pre-ignition, detonation, or knocking
It is considered as the most efficient, dependable, and economical type of engine available for light aircrafts.
horizontally opposed engine
The temperature of the burning gases in the engine cylinder reaches up to _____ to _______°C, which is above the melting point of the material of the cylinder body and head of the engine.
1500, 2000
The temperature of the burning gases in the engine cylinder reaches up to 1500 to 2000°C, which is above the melting point of the material of the cylinder body and head of the engine. if the heat is not dissipated, it would result in the ___________.
failure of the cylinder material
Due to very high temperatures, the film of the lubricating oil will get __________, thus producing __________ on the surface. This will result in __________.
oxidized, carbon deposits, piston seizure
Due to overheating, large temperature differences may lead to a _______________ due to the thermal stresses set up. This makes it necessary for the temperature variation to be kept to a minimum.
distortion of the engine components
Higher temperatures also lower the _________ of the engine.
volumetric efficiency
Higher temperatures adversely affects the combustion of fuel and air charge. This includes the occurrence of _______ and _______ or ______, both resulting in the loss of engine power.
pre-ignition, detonation, knocking
ignition starts before intended time of ignition or combustion; caused by hotspots or parts of the cylinder that are too hot; the hotspots cause the ignition instead of the spark plugs
pre-ignition
two ignitions happen; before the flame is distributed, ignition happens on hotspot; abnormal combustion
detonation or knocking
Two purposes of cooling system in the working of an engine
- takes away the excessive heat generated in the engine and saves it from overheating
- keeps the engine at working temperature for efficient and economical working
Two main requirements of an efficient engine cooling system
- must be capable of removing only 30% of the heat generated in the combustion chamber
- should remove heat at a fast rate when the engine is hot
The engine cooling system must be capable of removing only about ___% of the heat generated in the combustion chamber because too much removal of heat lowers the thermal efficiency of the engine.
30
It increases the internal friction of lubricants due to the increase in viscosity of oil and reduces the ability of liquid fuel to change its state from liquid to vapor.
overcooling
For the engine to operate efficiently, it must operate at the ______________.
highest temperatures consistent with safe operation
Two main types of engine cooling systems
- air cooling system
- liquid cooling system
In this type of cooling system, the heat, which is conducted to the outer parts of the engine, is radiated and conducted away by the stream of air, which is obtained from the atmosphere.
air cooling system
In air cooling system, in order to have efficient cooling by means of air, providing _____ around the cylinder and cylinder head increases the contact area.
fins
The ____ are metallic ridges, which are formed during the casting of the cylinder and cylinder head.
fins
In an air cooling system, these are designed to force air over the cylinder cooling fins.
cowling and baffles
The _______ direct the air close around the cylinders and prevent it from forming hot pools of stagnant air while the main streams rush by unused.
baffles
_______ are built into the baffles to direct jets of cooling air onto the rear spark plug elbows of each cylinder to prevent overheating of ignition leads.
blast tubes
Some aircraft are fitted with ________ to enable the control of airflow through the engine.
cowl flaps or gills
With the cowl flaps ___, the air flowing over the engine cowling causes a pressure drop at the cooling air outlet, which accelerates the airflow, enabling it to maintain high speed over the cylinders.
open
Helps the pilot in monitoring cylinder temperature to protect the engine from excessive heat
cylinder head temperature gauge
mounted on the engine cylinder head, it sends a voltage, which is proportional to the temperature of the cylinder head, to the gauge in the cockpit
probe
The amount of heat carried off by the air-cooling depends upon the following factors:
- total area of the fin surfaces
- velocity and amount of the cooling air
- temperature of the fins and of the cooling air
during take-off, cowl flaps or gills are _____
open
during climb, cowl flaps or gills are ______
open
during landing, cowl flaps or gills are _______
closed
during descent, _______ is possible which is caused by sudden change of temperature and occurs in cylinder or cylinder heads
thermal shock
advantages of air cooling system
- simple design
- lighter in weight than water-cooled
- cheaper to manufacture
- needs less care and maintenance
- advantageous in extreme climatic conditions
- no risk of damage from frost
__________ dissipates the heat generated in the engine by pumping a liquid through passages built into the cylinder and cylinder heads.
liquid cooling system
In liquid cooling system, at the top of the cylinder head, all the channels converge to a _______.
single outlet
mounted in the slip stream of the propeller, the liquid passes through it
radiator
A _______, driven by a pulley and belt from the crankshaft, drives hot coolant out of the engine to the radiator, which is a form of heat exchanger.
pump
Unwanted heat is passed from the radiator into the _______, and the cooled liquid then returns to an inlet at the bottom of the block and flows back into the channels again.
air stream
The ________- is linked to the engine by rubber hoses or pipes and has a top and bottom tank connected by a core, a bank of many fine tubes.
radiator
The tubes pass through holes in a stack of thin sheet ________, so that the core has a very large surface area and can lose heat rapidly to the cooler air passing through it.
metal fins
In a liquid cooling system, in an engine at its ordinary working temperature, the coolant is only just ___________.
below normal boiling point
The risk of boiling is avoided by increasing the _________ in the system, which raises the boiling point. The extra pressure is limited by the _____, which has a pressure valve in it. Excessive pressure opens the valve, and coolant flows out through an overflow pipe.
pressure, radiator cap
Commonly a centrifugal type pump, it is usually driven by means of a belt
water/liquid pump
Where in the pump is the bottom of the radiator connected?
suction side
controls or monitors the coolant temperature in a liquid cooling system; a kind of check valve which opens and closes with the effect of temperature; fitted in the liquid outlet of the engine
thermostat valve
When the normal operating temperature is reached, the thermostat valve opens and allows hot water to flow towards the ________.
radiator
In a liquid cooling system, it acts as a reservoir for the coolant liquid.
header tank
It allows the liquid to flow from the header tank to the engine block, and then from the engine to the radiator, and back to the header tank.
pipes
Its purpose is to cool down the water received from the engine.
radiator
It draws atmospheric air through the radiator and thus increases the efficiency of the radiator in cooling hot water, and it throws air over the outer surface of the engine, which takes away the heat conducted by the engine parts and thus increases the efficiency of the entire cooling system.
fan
In order to prevent the water in the cooling system from freezing, some chemical solution which are known as ________ are mixed with water.
anti-freeze solutions
