After the combustion process , only 1/3 of the heat energy from the fuel changes into mechanical energy , & the rest :• Hot exhaust gases• Frictional heat from the rubbing surfaces• Heating of the metal walls
to prevent :• Overheating and the resulting breakdown of lubricating oil film• Overheating and the resulting loss of strength of the metal itself• Excessive stresses in or between the engine parts resulting from unequal temperatures
Theformation of an oil film depends on the viscosity of the oil …And theviscosity the oildepends on TheTemperature
Will decrease the oil viscosity which will cause : metal-to-metal contact and resulting excessive wear of the load- bearing parts .
Willlead to condensation in the crankcase , causing acids and sludge to form in the lubrication oil , and condensation of corrosive gases in the cylinder walls .
At low Temp :Excessive clearances between parts will cause poundingExcessive clearances between the bearings and the Journals will allows the oil to escape .
AtHigh Temp: the parts will expand and insufficient clearances between the moving parts will result .As the clearances areReduced , inadequateLubrication will causemetal-to-metal contact.
High temperatures change the strength and physical properties of the various metals used in an engine.Excessive expansion of the metal, which may result in shearing of the cylinder-head bolts.
Thecomplete induction system for an aircraft engine includes three principal sections : The air scoop and ducting The carburetor or air-control section The intake manifold and pipes
Air Scoop is simply an opening facing into the airstream. This scoop receives ram air , usually augmented by the propeller slipstream The effect of the air scoopand ducting is inincreasing the powerin 5 percent .
Overheating can cook the seals in the engine
The ducting system comprises four principal parts : The air scoop Air filter
Alternateair valve(operatedBy means of the carburetorHeat control in the cockpit) The carburetor air heater or muff
The typical opposed-type or flat-type aircraft engine has an induction system with an individual pipe leading to each cylinder . The 2 purposes of intake manifolds are : -it cools the oil slightly -it increases the temperature of the fuel-air mixture slightly for a better vaporization ofthe fuel
The type of induction system used on a radial-type engine principally depends on thehorsepower output desired from the eingine
On a small radial engine of low output , the air is drawn through the carburetor , mixed with fuel in the carburetor, and then carried to the cylinders through individual intake pipes .
Ina typical high-output engine, an internal blower or a supercharge is located in the rear section of the engine . The fuel-air mixture passes from the carburetor through the supercharge or blower and the then flows out through the diffuser section and individual intake pipes to the engine cylinders
The portion of the intake system of an engine between the carburetor and the cylinders must be installed gastight to provide proper engine operation.the gasket should bebetween the the pipeand the cylinder , andsecured rigidly bybolts and nuts .
Icecan form anywhere from the inlet of the induction system to the intake manifold between the carburetor and the intake port of the cylinder. Thenature of the ice formation depends on atmospheric temperature and humidity
In fixed-pitch propeller , the engine rpm will decrease . Witha constant-speed propeller , the manifold pressure will decrease and the engine power will drop.
Theformation of ice in an induction system is prevented by the use of carburetor heat . Insome older installations for large engines , alcohol was sprayed into the inlet air duct to reduce the formations of ice