Cap 5 Engine Fuel Systems

Question 1

Avgas

Answer 1

Avgas burns around 18-24m/s
Anti knock prooperties allowing to resist detonation (octan number says if is resistance or not)
Contains 85% carbon and 15% hydrogen

Question 2

Avgas colouring

Answer 2

Avgas 100 dyed green, Octane rating 100

Avgas 100LL dyed blue ,octane rating of 100 (more3 greener)

Avgas 80 dyed red Considered a leaded fuel

MOGAS motor gasolene authorised certain a/c only

Question 3

Detonation

Answer 3

Shockwave frown ignition triggers detonation
Esxtremely rapid combustion from detonation source
Excessevely high pressure at TDC cause mechanical shock

Question 4

Cause of detonation

Answer 4

1) Fuel with poor antiknock properties
2) incorrect mixture
3) anything that might unduly raise temperature or pressure(low rpm with high manifold absolute pressure)
4) high engine temp
5) carb heat
6) turbo/supercharge

Question 5

Principle causes of pre ingition

Answer 5

1) hot spot within cycliner (carbon deposits on valve)
And is more destruction that autodetonation
2)ignition malfunction damage spark plug
3)cylinder head temperature (CHT)

Question 6

Mixture ratio

Answer 6

Correct mixture&raquo_space;> 15:1 (Air :fuel) correct air fuel ration is the one cause the exact right amount of oxygen to the correct amount of fuel by mass .also where the exhaust gas temp is max

Rich mixture&raquo_space;8:1
Lean mixture»20:1

When is lean keep an eye on cht( cylinder head temp) it could get hot

Question 7

Additional fuel metereing

Answer 7

• it takes no account of air density
• it would result in poregressively richer mixture as engine speed and /or altitude increase
• ram air effect in the inlet would weaken the mixture with increased airspeed
• no provision for special mixture setting required at very low and very high power setings

Question 8

Ram effect

Answer 8

“Pressure balance duct “ counteracts the ram air error by balancing the same ram pressure with the inside of the carburator

Question 9

Speed squared error

Answer 9

Diffuser reduce the pressure inside carburettor to a level that cancel out the difference of 1/4pressure static pressure dropped.reastabilizing the pressure differential inside the carbuarator and the inlet when the speed is doubled

Question 10

Mixture control

Answer 10

Mixture control equalise the pressure between the chamber and the Venturi so the mixture gets leaner when pulled back

Question 11

Slow running jet

Answer 11

When the butter fly is partially closed ( when is in idle) the slow running jet is made to keep the engine in idle without shutting it down.BUT WHEN THE MIXTURE IS FULLY PULLED TO BACK THEN THEN PLUNGER IN THE SLOW RUNNING JET IS CLOSED SHUTTING DOWN THE ENGINE

Question 12

POWER ENRICHMENT

Answer 12

WHEN THE THROTTLE IS AT HIGHER END, A POWER ENRICHMENT CAM MAKES MORE FUEL TO GET INTO VENTURI SO MORE POWER IS AVAILABLE WHEN YOU PUT FULL THROTTLE FORWARD

Question 13

ACCELERATOR PUMP CAM

Answer 13

ACCELERATOR PUMP WHEN YOU NEED TO GIVE FULL POWER

Question 14

Inlet carburettor temperature

Answer 14

The temperature of the inlet carburettor can drop upto 25 degrees due to drop in press and fuel evaporation.
At moderate or high humidity ice will from in the throat
Causing stuck the throttle and /or reduction power

Question 15

Symthoms of carburator icing

Answer 15

Loss of rpm
Reduced performance
Reduced inlet manifold absolute pressure(MAP)
Decreased exhaust gas temperature
Rough running
Jammed throttle
Engine stops

Question 16

SIGNS OF CARBURATOR INLET ICING

Answer 16

FIXED PITCH PROPELLER : UNEXPLAINED DROP RPM

Variable pitch propeller : DROP IN MANIFOLD ABSOLUTE PRESSURE

Question 17

FUEL INJECTION

Answer 17

INDIRECT FUEL INJECTION
FUEL IS CONTROLLED BY THE THROTTLE LEVER.
PRESSURE GAUGE TELLS THE PRESSURE OF THE ELECTRIC PUMP OF THE FUEL .
ENGINE SHUT DOWN IS MANAGED THROUGH THE ENGINE MANIFOLD VALVE

Question 18

Pressure balancing in the carb? (Ram effect)

Answer 18

At high airspeeds the intake pressure rises because of the ram effect of
the air entering it. This increases the pressure in the throat which causes
a drop in the fuel flow from the U-tube resulting in a weaker mixture. To
avoid this problem a pressure balance duct connects the intake and the
float chamber. The duct ensures that the pressure in the intake and float
chamber remain the same

Question 19

Diffuser (due to increase in speed the pressure doesn’t reduce lineary but exponentially)?

Answer 19

Air from the pressure balance duct is fed through a perforated tube called
the diffuser. Fuel enters the diffuser from the main jet. At idle RPM the
levels in the diffuser and float chamber are almost equal. When the engine
is running, the fuel level in the diffuser falls because of the slight
restriction caused by the jet. This uncovers some of the perforations in the
diffuser allowing air from the pressure balance duct to flow in. This
additional air displaces some of the fuel and thus reduces the amount of
fuel reaching the nozzle.

Question 20

Misture control (for increase in altitude)

Answer 20

To compensate for the
effect of changing air density, a mixture control valve is fitted. The valve is
either manually controlled or operated automatically by an aneroid
capsule.

Question 21

Slow running mixture

Answer 21

The slow running jet is placed just at the edge of the
almost closed butterfly to take advantage of the strong pressure drop in
the constriction caused by the valve. This jet is designed to provide a rich
mixture at idle

Question 22

Power enrichment

Answer 22

At high power settings a power enrichment system is required to provide
the rich mixture needed to cool the cylinders.
The needle is connected to the throttle linkage so that it operates when
the throttle position is set towards high power.
The needle closes during all but high power settings and for this reason it
is sometimes confusingly referred to as an economiser system

Question 23

Accelerated pump ?

Answer 23

When the throttle is opened rapidly, the air flow to the engine increases
almost instantaneously. But there is a slight delay before reduced
pressure in the throat causes more fuel to be added to the mixture. This
can cause the engine to hesitate or even stop - a phenomenon known as
weak cut (or lean cut). The solution is an accelerator pump.
The throttle lever is connected by a suitable system of links to a small
piston type pump in the carburettor. When the throttle lever is moved
rapidly forward the accelerator pump injects a quantity of fuel directly into
the venturi