Simple Carburettor Fuel System for a Piston Engine And how it works

PISTON ENGINE – Carburettor Fuel System Exhaust Inlet Tank PISTON ENGINE – Carburettor Fuel System

PISTON ENGINE – Carburettor Fuel System - Tanks COCKPIT FUEL GAUGE Filler Cap E F 1/2 FUEL Filler Neck FUEL LEVEL SENSOR Tank Cavity PISTON ENGINE – Carburettor Fuel System - Tanks

PISTON ENGINE – Carburettor Fuel System - Tanks 1/2 FUEL E F 1/2 FUEL PISTON ENGINE – Carburettor Fuel System - Tanks

PISTON ENGINE – Carburettor Fuel System - Aircraft Tanks WHERE ARE THE FUEL TANKS IN AIRCRAFT? IN THE OTHERWISE EMPTY WING SECTIONS CI30 HERCULES PISTON ENGINE – Carburettor Fuel System - Aircraft Tanks

PISTON ENGINE – Carburettor Fuel System Cockpit Gauge E F 1/2 Exhaust Inlet Tank Pump PISTON ENGINE – Carburettor Fuel System

PISTON ENGINE – Mechanical Diaphragm Pump One-way Inlet Valve One-way Outlet Valve Diaphragm Driving Cam PISTON ENGINE – Mechanical Diaphragm Pump

PISTON ENGINE – Solenoid Diaphragm Pump One-way Inlet Valve One-way Outlet Valve Diaphragm Magnetic Plate Solenoid Windings Switch Mechanism PISTON ENGINE – Solenoid Diaphragm Pump

PISTON ENGINE – Gear Type Pump PUMP FLOW AND RESTRICTION TO FLOW IN CONTROLLER CAUSES PRESSURE TO INCREASE ‘SPUR’ GEARS Flow Controller FLOW OUT PISTON ENGINE – Gear Type Pump

PISTON ENGINE – Carburettor Fuel System Air Filter Carburettor Cockpit Gauge E F 1/2 Exhaust Inlet Tank Pump PISTON ENGINE – Carburettor Fuel System

PISTON ENGINE – Air Filter Basic Air Filter Operation Filter element – corrugated breathable paper Dirt trapped by Filter element Air and Dirt Clean Air PISTON ENGINE – Air Filter Basic Air Filter Operation

PISTON ENGINE – Carburettor Fuel System Air Filter Carburettor Cockpit Gauge E F 1/2 Exhaust Inlet Tank Pump PISTON ENGINE – Carburettor Fuel System

We are now going to look at how the carburettor controls the flow to the engine This is done by the: - THE FLOAT CHAMBER

SIMPLIFIED PISTON ENGINE FUEL SYSTEM FUEL NOZZLE VENTURI NEEDLE VALVE AIR VENT FUEL LEVEL FLOAT FLOAT CHAMBER FUEL FEED SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

AIR/FUEL MIXTURE FLOWS TO ENGINE AIR IS SUCKED THROUGH VENTURI BY….. A PISTON MOVING DOWN ON INDUCTION STROKE AIR FLOW THE LOWER AIR PRESSURE PULLS FUEL THROUGH THE JET FUEL FLOW FUEL LEVEL DROPS MOVING AIR HAS LOWER PRESSURE SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM FUEL LEVEL DROPPING LOWERS FLOAT PULLING AIR INTO FLOAT CHAMBER FUEL LEVEL DROPS SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM FUEL LEVEL DROPPING LOWERS FLOAT FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED AND ALLOWS FUEL TO ENTER FLOAT CHAMBER FROM PUMP FUEL LEVEL DROPS SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED FUEL IS PULLED OUT OF THE FLOAT CHAMBER ONLY WHEN ONE OF THE PISTONS IS ON THE INDUCTION STROKE SIMPLIFIED PISTON ENGINE FUEL SYSTEM

We now need to look at controlling the air/fuel mixture flowing into the engine Controlling the air/fuel mixture means controlling the engine The carburettor part which controls the flow is…. THE THROTTLE

LINK TO THROTTLE LEVER/PEDAL THROTTLE VALVE VALVE DISC VALVE SPINDLE LINK TO THROTTLE LEVER/PEDAL SIMPLIFIED PISTON ENGINE FUEL SYSTEM

BETWEEN THROTTLE VALVE AND ENGINE IS A PARTIAL VACUUM CAUSED BY SUCTION FROM ENGINE AND FLOW RESTRICTION THROUGH THROTTLE VALVE AIR FILTER ENGINE CARB. VENTURI THROTTLE VALVE INLET MANIFOLD EXHAUSTMANIFOLD THE INLET MANIFOLD VACUUM CAN BE USED TO HELP APPLY THE BRAKES – CALLED ‘POWER-ASSISTING’ FUEL AND AIR IS MIXED DUE TO LOWERED AIR PRESSURE CONTROLS MIXTURE FLOW TO ENGINE ENGINE PULLS AIR IN DURING INDUCTION STROKE 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 SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM 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 SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED 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 T CONTROLS FUEL FLOW SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

BALANCED AIR PRESSURE AT THE MAIN JET NEXT IS…. BALANCED AIR PRESSURE AT THE MAIN JET

SIMPLIFIED PISTON ENGINE FUEL SYSTEM THIS WOULD CREATE A PRESSURE DIFFERENCE BETWEEN:- HERE AND HERE FLOAT CHAMBER VENT AND THEREFORE A SLIGHT VACUUM BEFORE CARB THE AIR FILTER CAN ALSO CAUSE RESTRICTION TO AIR FLOW SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM AND THE FLOAT CHAMBER IS CONNECTED TO THE CARB AIR INTAKE EQUALISING THE PRESSURE AT LOW SPEED SO THE VENT TO THE FLOAT CHAMBER IS CLOSED OFF THEREFORE PREVENTING TOO MUCH FUEL MIXING WITH THE AIR FLOAT CHAMBER VENT SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

MORE EFFICIENT MIXING OF AIR AND FUEL NEXT…. MORE EFFICIENT MIXING OF AIR AND FUEL

SIMPLIFIED PISTON ENGINE FUEL SYSTEM MORE EFFICIENT MIXING OF AIR AND FUEL IS ACHIEVED BY FITTING A DIFFUSER TUBE LET’S TAKE A CLOSER LOOK AT THIS AREA HERE, ABOVE THE MAIN JET SIMPLIFIED PISTON ENGINE FUEL SYSTEM

AIR/FUEL MIXING IN DIFFUSER TUBE HIGH POWER SETTING CRUISE SETTING AIR/FUEL MIXING IN DIFFUSER TUBE INCREASED FLOW OF MIXED AIR/FUEL AIR INLET FUEL LEVEL IN FLOAT CHAMBER AIR MIXES WITH FUEL DIFFUSER TUBE IDLE SETTING FUEL SUPPLIED VIA IDLE JET OPEN THROTTLE IDLE JET STOPS WORKING MAIN JET FUEL FEED FROM FLOAT CHAMBER SIMPLIFIED PISTON ENGINE FUEL SYSTEM

NEXT..…. AUTOMATIC MIXTURE CONTROL This is required to take into account that at higher altitude there is less air, so therefore less fuel is required. This change in fuel flow is controlled by a device that can sense the change in air pressure. It is called a pressure bellows or pressure capsule.

SIMPLIFIED PISTON ENGINE FUEL SYSTEM CAPSULE EXPANDS IN LOWER PRESSURES AND CONTRACTS IN HIGHER PRESSURES FIXED END PRESSURE CAPSULE MOVING END NEEDLE VALVE SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM AT HIGH ALTITUDE – LOWER ATMOSPHERIC PRESSURE AT LOW ALTITUDE – HIGHER ATMOSPHERIC PRESSURE CAPSULE EXPANDS CAPSULE CONTRACTED HIGH FUEL FLOW SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

SIMPLIFIED PISTON ENGINE FUEL SYSTEM AT HIGH ALTITUDE – LOWER ATMOSPHERIC PRESSURE CAPSULE EXPANDS CLOSING FUEL ORIFICE E AND REDUCING FUEL FLOW SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM SIMPLIFIED PISTON ENGINE FUEL SYSTEM

NEXT..…. AUTOMATIC MIXTURE CONTROL This is required to take into account that at higher altitude there is less air, so therefore less fuel is required. This change in fuel flow is controlled by a device that can sense the change in air pressure. It is called a pressure bellows or pressure capsule.

PISTON ENGINE – Hydro-Mechanical Fuel Injection System Auxiliary Air Device Mixture Control Unit (Fuel Distributor Valve) Fuel Injector Warm Up Regulator Throttle Valve Primary Pressure Valve Air Sensor Plate Cold Start Valve Idle Speed Adjuster Air Inlet Engine Temp Sensor (from Air Filter) Fuel Accumulator Safety Relay Ignition Switch Filter Pump Legend High Pressure Fuel Low Pressure Fuel Fuel Tank Battery Supply Pressure Fuel Servo Pressure Fuel Electrical Signal PISTON ENGINE – Hydro-Mechanical Fuel Injection System

PISTON ENGINE – Electronic Fuel Injection System Injection Control Unit ‘Common Rail’ Engine ECU Engine Temp Engine RPM/TDC Exhaust Temp Fuel Injectors Throttle Position Forward Speed Air Temps – Inlet & Ambient Air Filter Cockpit Gauge E F 1/2 Throttle Pressure Regulator Tank Pump PISTON ENGINE – Electronic Fuel Injection System

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