simple carburettor fuel system for a piston engine … 5...simple carburettor fuel system for a...

Simple Carburettor Fuel System for a Piston Engine

And how it works

Tank

PISTON ENGINE – Carburettor Fuel System

ExhaustInlet

Tank Cavity

Filler Cap

Filler Neck

E F1/2

FUEL

FUEL LEVEL

SENSOR

COCKPIT FUEL

GAUGE

PISTON ENGINE – Carburettor Fuel System - Tanks

PISTON ENGINE – Carburettor Fuel System - Tanks

E F1/2

FUEL

E F1/2

FUEL

WHERE ARE THE FUEL TANKS IN AIRCRAFT?

IN THE OTHERWISE EMPTY WING SECTIONS

CI30 HERCULES

PISTON ENGINE – Carburettor Fuel System - Aircraft Tanks

Tank

PISTON ENGINE – Carburettor Fuel System

Cockpit Gauge

Pump

ExhaustInlet

One-way Inlet Valve

One-way Outlet Valve

Diaphragm

Driving Cam

PISTON ENGINE – Mechanical Diaphragm Pump

One-way Inlet Valve

One-way Outlet Valve

Solenoid Windings

Switch Mechanism

Diaphragm

Magnetic Plate

PISTON ENGINE – Solenoid Diaphragm Pump

FLOW OUT

‘SPUR’ GEARS

PUMP FLOW AND RESTRICTION TO FLOW IN CONTROLLER CAUSES PRESSURE TO INCREASE

Flow Controller

PISTON ENGINE – Gear Type Pump

Air Filter

Tank

PISTON ENGINE – Carburettor Fuel System

Cockpit Gauge

Pump

Carburettor

ExhaustInlet

Air and Dirt

Clean Air

Filter element – corrugated breathable paper

Dirt trapped

by

Filter element

Basic Air Filter OperationPISTON ENGINE – Air Filter

Air Filter

Tank

PISTON ENGINE – Carburettor Fuel System

Cockpit Gauge

Pump

Carburettor

ExhaustInlet

We are now going to look at how the carburettor controls the flow to the engine

THE FLOAT CHAMBER

This is done by the: -

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

FLOAT CHAMBER

NEEDLE VALVE AIR VENTVENTURI

FUEL FEED

FUEL NOZZLE

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

FLOAT

FUEL LEVEL

AIR IS SUCKED THROUGH VENTURI BY…..

A PISTON MOVING DOWN ON INDUCTION STROKE

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

MOVING AIR HAS LOWER PRESSURE

FUEL FLOWA

IR F

LOW

AIR

FLO

W

THE LOWER AIR PRESSURE PULLS FUEL THROUGH THE JET

AIR/FUEL MIXTURE

FLOWS TOENGINE

FUEL LEVEL DROPS

PULLING AIR INTO FLOAT CHAMBER

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

FUEL LEVEL DROPS

FUEL LEVEL DROPPING LOWERS FLOAT

AND ALLOWS FUEL TO ENTER FLOAT CHAMBER FROM PUMP

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

FUEL LEVEL DROPS

FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED

FUEL LEVEL DROPPING LOWERS FLOAT

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

FUEL IS PULLED OUT OF THE FLOAT CHAMBER

ONLY WHEN ONE OF THE PISTONS IS ON THE INDUCTION STROKE

FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED

We now need to look at controlling the air/fuel mixture flowing into the engine

THE THROTTLE

Controlling the air/fuel mixture means controlling the engine

The carburettor part which controls the flow is….

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

LINK TO THROTTLE

LEVER/PEDAL

THROTTLE VALVE

VALVE SPINDLE

VALVE DISC

CARB.

THROTTLE VALVE

AIR FILTER

ENGINE

VENTURIFUEL AND AIR IS MIXED DUE TO LOWERED AIR

PRESSURE

CONTROLS MIXTURE FLOW TO

ENGINE

INLET MANIFOLD

ENGINE PULLS AIR IN DURING

INDUCTION STROKE

AND FLOW RESTRICTION THROUGH THROTTLE VALVE CAUSED BY SUCTION FROM ENGINE

BETWEEN THROTTLE VALVE AND ENGINE IS A PARTIAL VACUUM

THE INLET MANIFOLD VACUUM CAN BE USED TO HELP APPLY

THE BRAKES – CALLED ‘POWER-ASSISTING’

EXHAUSTMANIFOLD

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

THROTTLE VALVE

THIS WOULD BE A HIGH THROTTLE SETTING OR ‘FULL –POWER’

OPEN THROTTLE ALLOWS VENTURI TO WORK AT MAXIMUM EFFICIENCY

LOW THROTTLE SETTING - CALLED ‘IDLE’ OR ‘TICK-OVER’

ALMOST CLOSED THROTTLE MEANS THE VENTURI DOES NOT WORK VERY WELL

LOW AIR FLOW MEANS VERY LITTLE OR NO FUEL/AIR MIXING IN THE VENTURI

SO AN ALTERNATIVE AND EFFECTIVE VENTURI NEEDS TO BE FOUND

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

T CONTROLS FUEL FLOW

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

LOW THROTTLE SETTING - CALLED ‘IDLE’ OR ‘TICK-OVER’

EDGE GAPS BECOME THE VENTURI FOR THE LOW AIR FLOW

AT IDLE - SLOW RUNNING JET

BALANCED AIR PRESSURE AT THE MAIN JET

NEXT IS….

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

THE AIR FILTER CAN ALSO CAUSE RESTRICTION TO AIR FLOW

THIS WOULD CREATE A PRESSURE DIFFERENCE BETWEEN:-

HERE AND HERE

AND THEREFORE A SLIGHT VACUUM BEFORE CARB

FLOAT CHAMBER VENT

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

EQUALISING THE PRESSURE AT LOW SPEED

THEREFORE PREVENTING TOO MUCH FUEL MIXING WITH THE AIR

AND THE FLOAT CHAMBER IS CONNECTED TO THE CARB AIR INTAKE

SO THE VENT TO THE FLOAT CHAMBER IS CLOSED OFF

FLOAT CHAMBER VENT

MORE EFFICIENT MIXING OF AIR AND FUEL

NEXT….

MORE EFFICIENT MIXING OF AIR AND FUEL

IS ACHIEVED BY FITTING A DIFFUSER TUBE

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

HERE, ABOVE THE MAIN JET

LET’S TAKE A CLOSER LOOK AT THIS AREA

IDLE SETTING FUEL

SUPPLIED VIA IDLE JETOPEN THROTTLE

IDLE JET STOPS WORKING

CRUISE SETTINGHIGH POWER SETTING

AIR INLET

DIFFUSER TUBE

INCREASED FLOW OF MIXED AIR/FUEL

FUEL FEED FROM FLOAT CHAMBER

MAIN JET

AIR MIXES WITH FUEL

AIR/FUEL MIXING IN DIFFUSER TUBE

FUEL LEVEL IN FLOAT CHAMBER

SIMPLIFIED PISTON ENGINE FUEL SYSTEM

AUTOMATIC MIXTURE CONTROL

NEXT..….

This is required to take into account that at higher altitude there is less air, so therefore less fuel is required.

It is called a pressure bellows or pressure capsule.

This change in fuel flow is controlled by a device that can sense the change in air pressure.

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

FIXED END

MOVING END

NEEDLE VALVE

CAPSULE EXPANDS IN LOWER PRESSURES AND CONTRACTS IN HIGHER PRESSURES

PRESSURE CAPSULE

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

AT LOW ALTITUDE – HIGHER ATMOSPHERIC PRESSURE

CAPSULE CONTRACTED

HIGH FUEL FLOW

AT HIGH ALTITUDE – LOWER ATMOSPHERIC PRESSURE

CAPSULE EXPANDS

SIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEMSIMPLIFIED PISTON ENGINE FUEL SYSTEM

AT HIGH ALTITUDE – LOWER ATMOSPHERIC PRESSURE

CAPSULE EXPANDS

CLOSING FUEL ORIFICEE AND REDUCING FUEL FLOW

AUTOMATIC MIXTURE CONTROL

NEXT..….

This is required to take into account that at higher altitude there is less air, so therefore less fuel is required.

It is called a pressure bellows or pressure capsule.

This change in fuel flow is controlled by a device that can sense the change in air pressure.

BatteryFuel Tank

Pump

Warm Up Regulator

Fuel Accumulator

Ignition Switch

Filter

Primary Pressure

Valve

Air Sensor Plate

Mixture Control Unit (Fuel Distributor Valve)

Auxiliary Air Device

Cold Start ValveIdle Speed

Adjuster

Fuel Injector

Throttle Valve

Engine Temp Sensor

Safety Relay

Air Inlet

High Pressure FuelLow Pressure Fuel

Supply Pressure FuelServo Pressure Fuel

Electrical Signal

Legend

PISTON ENGINE – Hydro-Mechanical Fuel Injection System

(from Air Filter)

Air Filter

PISTON ENGINE – Electronic Fuel Injection System

Engine ECU

TankPump

Cockpit Gauge

Pressure Regulator

Injection Control

Unit

Engine TempEngine RPM/TDCExhaust TempThrottle PositionForward SpeedAir Temps – Inlet & Ambient

Fuel Injectors

‘Common Rail’

Throttle

Any Questions?