Apart from flight into known icing conditions the intake system of a diesel engine ?
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Source: Telepilote theorique examen 30
The thermal efficiency of a diesel engine is higher than that of a petrol engine because ?
Given the following statements about diesel engines 1 power is regulated by the throttle valve 2 there is no throttle valve 3 power is set by the fuel flow 4 thermal efficiency is lower than that ?
In liquid cooled engines compostion volume of coolant mixture 3 % ethylene glycol 7 % water. There no mixture control no throttle valve power output of a diesel engine controlled regulating quantity of fuel that injected into cylinder (the amount of air constant) diesel engines are fitted with injectors not with valves. 
The oil system a piston engine incorporates an oil cooler that fitted In return line to oil tank after oil has passed through scavenge pump. There no mixture control no throttle valve power output of a diesel engine controlled regulating quantity of fuel that injected into cylinder (the amount of air constant) diesel engines are fitted with injectors not with valves. 
Diesel engines always produce a certain amount of soot because The fuel droplets coming from atomiser do not burn completely. There no mixture control no throttle valve power output of a diesel engine controlled regulating quantity of fuel that injected into cylinder (the amount of air constant) diesel engines are fitted with injectors not with valves. 
What may happen during a continuous climb with a mixture setting fully rich Fouling of spark plugs. Carburetors are calibrated to operate with mixture control set to 'full rich' when operating at sea level as aircraft gains altitude it becomes necessary to reduce amount of fuel entering carburetor because amount of air automatically decreasing with altitude due to lower atmospheric pressure if pilot fails to decrease amount of fuel as altitude gained result will be an overly 'rich' mixture creating problems such as fouled spark plugs excessive fuel consumption. Question 30-8
Prolonged running at low rpm can have an adverse effect on functioning of Fouling of spark plugs. Carburetors are calibrated to operate with mixture control set to 'full rich' when operating at sea level as aircraft gains altitude it becomes necessary to reduce amount of fuel entering carburetor because amount of air automatically decreasing with altitude due to lower atmospheric pressure if pilot fails to decrease amount of fuel as altitude gained result will be an overly 'rich' mixture creating problems such as fouled spark plugs excessive fuel consumption. Question 30-9
When leaning mixture the most economic cruise fuel flow excessive leaning will cause High cylinder head temperature. Egt relative to temperature of charge as it burns within cylinder cht measures temperature of engine cylinder the highest egt achieved at a ratio of 15 parts of air to one part of fuel if ratio reduced ie rich charge temperature reduces due to excess fuel being left in cylinder if ratio greater than 15 1 ie lean or weak charge cooled excess air to appreciate why cht increases with lean mixtures we must consider speed at which fuel burns ie its flame rate lean mixtures burn slower than rich mixtures this means more heat transferred to engine components with lean mixtures example if you move a lighted match quickly under your hand no problem but move it slowly you will burn your hand! slow burning lean mixtures will increase cht. Question 30-10
During climb with constant throttle and rpm lever setting mixture being constant Manifold absolute pressure (map) decreases. The manifold absolute pressure (map) indicates power output of a piston engine being a measure of pressure of fuel/air mixture in inlet manifold in an unsupercharged engine reading will drop with height a given throttle setting because there less atmospheric pressure to push useful charge into cylinder. Question 30-11
Both gas turbine and piston engines use a cycle made up of induction compression combustion and exhaust phases which of these statements about a piston engine are correct or incorrect i the process in a piston engine intermittent ii theoretically combustion occurs at constant pressure I correct ii incorrect. piston engine combustion process intermittent governed the rythm of back forth movements of piston in a cylinder the combustion occurs at constant volume in cylinder turbine engine combustion process continuous occurs at constant pressure. Question 30-12
A piston engine compression ratio the ratio of Total volume to clearance volume. compression ratio = volume at bottom dead (total volume) / volume at top dead (clearance volume) the clearance volume the volume that not expelled from cylinder. Question 30-13
The purpose of a chip detector in oil system of an engine/gearbox to indicate that There are metal particles in oil. The most basic type of magnetic filter a drain plug where a magnet in shape of a disc or cylinder attached to its inside surface (typically adhesion) periodically magnetic plug removed inspected ferromagnetic particles which are then wiped from plug such plugs are commonly used in engine sumps gearboxes occasionally in hydraulic reservoirs one useful advantage of mag plugs relates to examining density of wear particles observed as a visual indication of wear rate occurring within machine over a fixed period of running time the appearance of these iron filings on magnets are often described in inspection reports using terms such as peach fuzz whiskers or christmas trees if one normally sees peach fuzz but on one occasion sees a christmas tree instead this would be a reportable condition requiring further inspection remediation. Question 30-14
The thermal efficiency of a piston engine about There are metal particles in oil. Thermal efficiency the ratio of useful work to heat put in expressed as a percentage the first law of thermodynamics states that energy may be changed from one form to another but cannot be destroyed as far as engines are concerned it means that heat mechanical work are mutually convertible that rate of exchande constant measurable however second law says (more or less) that 'heat flows from a hot substance to a cold one unaided but energy from an external source needed it to flow other way' that is you might be able to convert most of your work into heat but turning heat into work will incur serious losses which another way of saying that engines are grossly inefficient if it were otherwise exhausts would be cold! in fact engines waste as much energy in heat as power they produce approximate thermal efficiency of a four stroke engine 30%. Question 30-15
On a normally aspirated engine non turbo charged manifold pressure gauge always indicates A lower value than atmospheric pressure when engine running. devidson if engine on full power (i e butterfly valve fully open) admision pressure would be equal to atmospheric pressure on a non turbo charged engine no ? no matter how wide butterfly throttle opened there will always be some restriction hence manifold pressure will always be lower than atmospheric even if only slightly. Question 30-16
The purpose of a distributor in an ignition system to distribute Secondary current to sparking plugs. the purpose of ignition system to provide an ignition spark to proper cylinder at correct time in order to burn compressed air/fuel mixture it consists of two separate but closely related electrical circuits ? low voltage primary circuit (battery voltage) ? high voltage secondary circuit (over 20000 volts) the ignition coil the unit that takes your relatively weak battery power turns it into a spark powerful enough to ignite fuel vapor inside a a traditional ignition coil are two coils of wire on top of each other these coils are called windings one winding called primary winding other the secondary the primary winding gets juice together to make a spark the secondary sends it out door to distributor the distributor 'distribute secondary current to sparking plugs. Question 30-17
Viscosity is The tendency of a liquid or gas to resist flow. the purpose of ignition system to provide an ignition spark to proper cylinder at correct time in order to burn compressed air/fuel mixture it consists of two separate but closely related electrical circuits ? low voltage primary circuit (battery voltage) ? high voltage secondary circuit (over 20000 volts) the ignition coil the unit that takes your relatively weak battery power turns it into a spark powerful enough to ignite fuel vapor inside a a traditional ignition coil are two coils of wire on top of each other these coils are called windings one winding called primary winding other the secondary the primary winding gets juice together to make a spark the secondary sends it out door to distributor the distributor 'distribute secondary current to sparking plugs. Question 30-18
With which instrument s do you monitor power output of an aeroplane fitted with a fixed pitch propeller The tendency of a liquid or gas to resist flow. the purpose of ignition system to provide an ignition spark to proper cylinder at correct time in order to burn compressed air/fuel mixture it consists of two separate but closely related electrical circuits ? low voltage primary circuit (battery voltage) ? high voltage secondary circuit (over 20000 volts) the ignition coil the unit that takes your relatively weak battery power turns it into a spark powerful enough to ignite fuel vapor inside a a traditional ignition coil are two coils of wire on top of each other these coils are called windings one winding called primary winding other the secondary the primary winding gets juice together to make a spark the secondary sends it out door to distributor the distributor 'distribute secondary current to sparking plugs. Question 30-19
In a piston engine turbocharger boost pressure may be monitored A manifold pressure gauge only. the purpose of ignition system to provide an ignition spark to proper cylinder at correct time in order to burn compressed air/fuel mixture it consists of two separate but closely related electrical circuits ? low voltage primary circuit (battery voltage) ? high voltage secondary circuit (over 20000 volts) the ignition coil the unit that takes your relatively weak battery power turns it into a spark powerful enough to ignite fuel vapor inside a a traditional ignition coil are two coils of wire on top of each other these coils are called windings one winding called primary winding other the secondary the primary winding gets juice together to make a spark the secondary sends it out door to distributor the distributor 'distribute secondary current to sparking plugs. Question 30-20
Fixed pitch propellers are usually designed maximum efficiency at A manifold pressure gauge only. the purpose of ignition system to provide an ignition spark to proper cylinder at correct time in order to burn compressed air/fuel mixture it consists of two separate but closely related electrical circuits ? low voltage primary circuit (battery voltage) ? high voltage secondary circuit (over 20000 volts) the ignition coil the unit that takes your relatively weak battery power turns it into a spark powerful enough to ignite fuel vapor inside a a traditional ignition coil are two coils of wire on top of each other these coils are called windings one winding called primary winding other the secondary the primary winding gets juice together to make a spark the secondary sends it out door to distributor the distributor 'distribute secondary current to sparking plugs. Question 30-21
Overheating of a piston engine likely to result from an excessively A manifold pressure gauge only. Jaredleto egt relative to temperature of charge as it burns within cylinder cht measures temperature of engine cylinder the highest egt achieved at a ratio of 15 parts of air to one part of fuel if ratio reduced ie rich charge temperature reduces due to excess fuel being left in cylinder if ratio greater than 15 1 ie lean or weak charge cooled excess air to appreciate why cht increases with lean mixtures we must consider speed at which fuel burns ie its flame rate lean mixtures burn slower than rich mixtures this means more heat transferred to engine components with lean mixtures example if you move a lighted match quickly under your hand no problem but move it slowly you will burn your hand! slow burning lean mixtures will increase cht. Question 30-22
In an engine equipped with a float type carburettor low temperature that causes carburettor ice normally result of Vaporization of fuel expansion of air in carburettor. One disadvantage of float type carburetor its icing tendency the vaporization of fuel combined with expansion of air as it flows through carburetor causes a sudden cooling of mixture the temperature of air passing through carburetor may drop significantly within a fraction of a second water vapor in air 'squeezed out' this cooling and if temperature in carburetor reaches 0°c or below moisture will be deposited as frost or ice inside carburetor passages even a slight accumulation of this deposit will reduce power may lead to complete engine failure particularly when throttle partly or fully closed the formation of carburetor ice may reduce or block fuel/air flow to engine. Question 30-23
In addition to fire hazard introduced excessive priming should be avoided because It fouls spark plugs. One disadvantage of float type carburetor its icing tendency the vaporization of fuel combined with expansion of air as it flows through carburetor causes a sudden cooling of mixture the temperature of air passing through carburetor may drop significantly within a fraction of a second water vapor in air 'squeezed out' this cooling and if temperature in carburetor reaches 0°c or below moisture will be deposited as frost or ice inside carburetor passages even a slight accumulation of this deposit will reduce power may lead to complete engine failure particularly when throttle partly or fully closed the formation of carburetor ice may reduce or block fuel/air flow to engine. Question 30-24
With respect to a piston engine aircraft ice in carburettor May form at oat's higher than + °c. One disadvantage of float type carburetor its icing tendency the vaporization of fuel combined with expansion of air as it flows through carburetor causes a sudden cooling of mixture the temperature of air passing through carburetor may drop significantly within a fraction of a second water vapor in air 'squeezed out' this cooling and if temperature in carburetor reaches 0°c or below moisture will be deposited as frost or ice inside carburetor passages even a slight accumulation of this deposit will reduce power may lead to complete engine failure particularly when throttle partly or fully closed the formation of carburetor ice may reduce or block fuel/air flow to engine. Question 30-25
As flight altitude increases if no leaning made with mixture control The density of air entering carburettor decreases the amount of fuel remains constant. density decreases as we gain altitude but volume of air entering in carburettor does not change as the volume of fuel (fuel density does not change with altitude). Question 30-26
Cooling air a reciprocating engine can be obtained means of The density of air entering carburettor decreases the amount of fuel remains constant. density decreases as we gain altitude but volume of air entering in carburettor does not change as the volume of fuel (fuel density does not change with altitude). Question 30-27
The main advantage of a constant speed propeller as compared to a fixed pitch propeller a High efficiency in a much wider speed range of aeroplane. advantages of a constant speed propeller compared to a fixed pitch propeller the power setting of a piston engine defined a combination of manifold pressure (boost) rpm where separate power lever rpm lever control provided it possible to vary one while leaving other constant so optimising operation of engine/propeller combination to give best efficiency/fuel economy least engine wear tear in order to achieve this a 'variable pitch' propeller must be used enabling pilot to select a propeller pitch thus to vary rpm independently of manifold pressure provided that propeller operating between its internal fine coarse pitch stops once an rpm has been selected a control unit (csu constant speed unit or pcu propeller control unit) will automatically vary propeller pitch angle therefore its angle of attack to prevailing relative airflow in order to maintain selected rpm despite airspeed manifold pressure variations a constant speed propeller has a high efficiency in a much wider speed range than a fixed pitch propeller. Question 30-28
From cruise with all parameters correctly set if altitude reduced to maintain same mixture fuel flow should High efficiency in a much wider speed range of aeroplane. when altitude increases air density decreases to maintain a correct mixture ratio of 1 to 15 (fuel mass / air mass) if altitude reduced we need to increase fuel flow to maintain a constant ratio (air volume entering carburettor will not change but air mass will increase). Question 30-29
A turbocharger in a reciprocating engine consists of a Compressor turbine mounted on a common shaft. when altitude increases air density decreases to maintain a correct mixture ratio of 1 to 15 (fuel mass / air mass) if altitude reduced we need to increase fuel flow to maintain a constant ratio (air volume entering carburettor will not change but air mass will increase). Question 30-30
An impulse coupling inhibited at higher than normal rotational starting speeds Compressor turbine mounted on a common shaft. impulse coupling magneto the impulse coupling a spring loaded mechanical coupling which delays rotation of magneto during an engine start after a short period of rotation device allows magneto to catch up in effect spinning magneto shaft faster than engine turning it the faster it turns hotter spark the bigger voltage impulse making easier starting after engine running centrifugal forces move spring loaded arms which make impulse coupling work at low speeds out of way the impulse coupling only works at very low engine speeds. Question 30-31
The very rapid magnetic field changes flux changes in primary coil of a magneto are accomplished the Contact breaker points opening. inside primary circuit a set of contact points that make flux reversals more abrupt when they open close at critical moments when points are closed current flows in primary coil a flux field builds up around it when a spark needed they open which causes field in primary to collapse induce a current in secondary winding as field moves across it which fed to spark plugs through distributor the more suddent breaking of primary circuit is more current will be induced in secondary coil. Question 30-32
In a compressor stage of a jet engine sequence Contact breaker points opening. Compr es sor highlighted rs means correct order so rotor stator turbine stage opposite. Question 30-33
The accessory units driven the accessory gearbox of a turbo jet engine are 1 thrust reverser pneumatic motors2 ac generator through its constant speed drive csd 3 oil pumps4 hydraulic pumps5 high pressure fuel pumpsthe combination regrouping all correct statements Contact breaker points opening. the accessory gearbox driven a radial shaft that meshes with a bevel gear driven the n2 (or gas producer rotor) is used to drive essential engine components such as fuel pump oil pump fuel control unit generators hydraulic pumps the accessory gear box also used to drive engine rpm feedback tacho generators is means which starter drives engine these are systems which must operate as soon as engine starts structure containing gearbox can be utilised as a support as well each component that attaches to accesssory gearbox has its own mounting pad with its unique gear reduction speed rotational direction. Question 30-34
Consider a jet engine whose control based on engine pressure ratio epr 1 with a constant epr thrust decreases when altitude increases2 with a constant epr thrust independent of mach number3 at same environmental conditions a given epr setting maintains thrust irrespective of engine wear due to ageing 4 epr determined the impact pressure difference between turbine outlet and compressor inlet5 on take off in event of icing not detected the crew indicated epr lower than real eprthe combination regrouping all correct statements Contact breaker points opening. Engine pressure ratio (epr) a measure of thrust of a jet engine obtained dividing pressure at back of engine the pressure at front epr settings vary with altitude temperature when altitude increases thrust decreases answer 4 the epr determined the impact pressure difference between turbine outlet the compressor inlet wrong this a ratio not a difference. Question 30-35
In axial flow compressor of a turbo jet engine flow duct tapered its shape calculated so as to Maintain a constant axial speed in cruising flight. The duct in question the convergent duct formed between compressor engine compressor casing the airflow through a jet engine varies dependant on thrust selection since engine runs most of time at cruise engine designed to give correct flow rates at this thrust setting. Question 30-36
In stator of a turbine gas velocity v and static pressure ps vary as follows V increases ps decreases. If you have multiple stage turbines there a set of guide vanes between each turbine disc to redirect flow again before next turbine blade they are stationary so are sometimes called stators with turbine you want a high velocity so turbine blades are designed to extract power from hot expanding gasses to turn compressor using high velocity hitting turbine blade the guide vanes straighten flow before next set of turbine blades but in effect it decreases pressure increases velocity this also prevents excessive backpressure which could work its way forward affect combustion process the compressor on other hand designed to increase pressure through each of stages so you can deliver a good mass flow to combustion chambers however increasing pressure will try to reverse flow so convergent duct designed to keep velocity constant through whole compressor so that momentum of airflow prevents reverse flow in effect velocity therefore increased in each rotor section velocity increases decreases through each set of rotors stators by using a convergent duct velocity therefore stays constant but pressure steadily increasing through each stage. Question 30-37
Epr can be defined as ratio of The total turbine outlet pressure to total compressor inlet pressure. If you have multiple stage turbines there a set of guide vanes between each turbine disc to redirect flow again before next turbine blade they are stationary so are sometimes called stators with turbine you want a high velocity so turbine blades are designed to extract power from hot expanding gasses to turn compressor using high velocity hitting turbine blade the guide vanes straighten flow before next set of turbine blades but in effect it decreases pressure increases velocity this also prevents excessive backpressure which could work its way forward affect combustion process the compressor on other hand designed to increase pressure through each of stages so you can deliver a good mass flow to combustion chambers however increasing pressure will try to reverse flow so convergent duct designed to keep velocity constant through whole compressor so that momentum of airflow prevents reverse flow in effect velocity therefore increased in each rotor section velocity increases decreases through each set of rotors stators by using a convergent duct velocity therefore stays constant but pressure steadily increasing through each stage. Question 30-38
A gas turbine engine turbine section may employ active clearance control To provide enhanced clearances between blade tips the casing. active clearance control (acc) a method used in gas turbines to improve fuel efficiency this achieved controlling tip clearance it particularly effective on turbofans since they are required to respond quickly to changes of thrust setting the active clearance control consists of acc valve which receives air from bypass duct routes air to flow over pipes surrounding turbine casing which in turn reduces thermal expansion of turbine case maintains accurate clearance between turbine case the blade tip this clearance should be maintained accurately which essential the engine efficiency its performance the acc valve opening adjusted automatically the fadec system depending on throttle position. Question 30-39
In a gas turbine engine maximum gas temperature attained Within combustion chamber. active clearance control (acc) a method used in gas turbines to improve fuel efficiency this achieved controlling tip clearance it particularly effective on turbofans since they are required to respond quickly to changes of thrust setting the active clearance control consists of acc valve which receives air from bypass duct routes air to flow over pipes surrounding turbine casing which in turn reduces thermal expansion of turbine case maintains accurate clearance between turbine case the blade tip this clearance should be maintained accurately which essential the engine efficiency its performance the acc valve opening adjusted automatically the fadec system depending on throttle position. Question 30-40
A pressure relief valve that does not fit on its seat properly would result in Within combustion chamber. To prevent too high a pressure a pressure release valve fitted it comprises a stainless steel ball bearing a spring the ball forced the spring against an oil port when oil pressure sufficiently high ball if forced off its seat oil allowed to bypass this restriction thus making sure that pressure never gets too high if pressure relief valve not hermetic there will be a leak the pressure decreases.
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