Piston Engine Principles Flashcards
what is a crankcase made out of?
two halves of aluminium alloy which are bolted together. to help stiffen assembly internal webs are incorporated.
what do crankcases do?
provide support and housing for various components and a mounting phase for numerous accessories such as magnetos, oil pumps, fuel and vacuum pumps. also provides an oil type chamber for lubricating oil and a means of mounting the engine in the aircraft.
what is fitted to ensure that internal pressures are equal to surrounding atmospheric pressure?
crankcase breather
what is a crankshaft?
the backbone of a reciprocating engine at it converts reciprocating motion into rotation motion for turning the propellor.
what is a crankshaft composed of?
one or more crank throws. 1 crank throw = 2 crank webs + 1 crank pin
in addition to the crankshaft providing a drive to the propellor, it also provides a drive to what?
the valve
a connecting rod is used for what?
to link each piston to the crankshaft.
what does a connecting rod consist of?
the large end is known as the big end that attaches by a means of a two-piece bearing, a cap and attachment parts.
the opposite end is a small end bearing which is usually a bronze bush. the small end connects to the piston by means of a gudgeon pin or piston pin.
a piston pin is usually what?
fully floating, that’s free to move laterally, thus preventing uneven wear. its help in place in the piston by eng plugs.
How does a piston work and what is it made of?
As the fuel and the air are ignited inside the cylinder, the piston is pushed down by the resulting release of pressure. As it is connected to the crankshaft, the piston’s up and down movement turns the crankshaft.
usually made of aluminium alloy and consists of a crown, a side and a skirt. they typically have 3-4 grooves to accommodate the piston rings and are often internally thinned to provide extra strength to aid cooling.
what is a piston ring made of and what’s its use?
- made of cast iron or steel incorporating an expansion gap because these materials are chosen for their self-lubricating properties and springiness.
they provide a seal between piston and cylinder during all running conditions.
what are the types of piston rings?
compression, oil control and oil scraper.
what do compression rings do?
prevent cylinder head gases leaking past the piston into the crankcase and help transfer heat into the cylinder wall.
what does oil control rings do?
under compression rings, they prevent lubricating oil from leaking into the cylinder head and maintain the proper quantity of oil between piston and cylinder wall.
slots in oil control rings do what?
allow for oil to seep through the ring and return to sump by gravity.
what do oil scraper rings do?
fitted at bottom of piston skirt to remove excess quantities of lubricating oil from the cylinder walls and return it to the crankcase
what is a cylinder barrel made out of? And what do they do? (4)
made of alloy steel.
provide a working surface for piston rings
a screw thread for mounting the cylinder head
a skirt and mounting flange for attachment to the crankcase
and a series of fins for cooling.
what does a cylinder barrel do?
provide an opportunity to increase the efficiency of the engine cooling, whilst also simplifying the assembly, and reducing mass.
what are cylinder heads made of and what is their use?
normally made of aluminium alloy they are screwed and shrunk onto the cylinder barrels with fins on it.
- for heat dissipation and lightweight assemblies while fins aid with cooling
what is the valve operating mechanisms use?
the main use is to open and close inlet and exhaust valves to their respective manifolds, allowing the fuel-air charge to enter the cylinder and the burnt gases to exit.
in a valve operating mechanism, what’s the difference between inlet and exhaust valves?
exhaust valves are subjected to a great deal of heat and special provisions must be made to aid cooling.
to prevent valves rocking during their operation what is installed?
valve guides are fitted into the cylinder head which are usually pressed in and help to transfer heat from the valve to the cylinder where it’s dissipated into the air.
what is required when valves are closed?
a tight seal. it’s achieved by having ground valve inserts fitted into the cylinder head.
what do spark plugs do?
ignite the compressed fuel-air mixture in the cylinder,
