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Fuel Hazards. Flammable and highly volatile ( vapourises easily). Fuel vapour difficult to see, has distinctive smell, burns easily. Keep forms of ignition / heat well away. Next >. Fuel Storage. Store in approved metal or plastic containers. Do not store different fuel types together.
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Fuel Hazards Flammable and highly volatile (vapourises easily). Fuel vapour difficult to see, has distinctive smell, burns easily. Keep forms of ignition / heat well away. Next >
Fuel Storage Store in approved metal or plastic containers. Do not store different fuel types together. Safety cabinets used to store containers. Next >
Working With Fuel Basic Precautions and Safety Refer to service manual before working on fuel system. Typically: • Remove negative battery cable. • Relieve pressure in fuel system. Check the fuel components for leaks, cracks, dents or other damage. Do not allow fuel to come into contact with hot engine or exhaust system. Next >
Working With Fuel Working on the Fuel System (Overview) Have fire extinguisher nearby and display fuel task sign. Wear eye protection. Clear up any spillages immediately. Empty fuel tank, before removing from vehicle, must be repaired by a specialist. Next >
Working With Fuel Heat Sources and the Fuel System Observe following when working on fuel system: • Check for leaks. • Never expose fuel components to heat sources. • Don’t use oxyacetylene cutter on rusted fuel tank strap bolts. • Protect plastic/rubber fuel pipes from heat sources. • Take necessary safety precautions. Next >
The bulk of typical petrol consists of hydrocarbons with between 5 and 12 carbon atoms per molecule. The MSDS (Material Safety Data Sheet) for unleaded petrol shows at least fifteen hazardous chemicals occurring in various amounts from 5% to 35% by volume. • These include: • Benzene 5% approx. • Toluene 35% approx. • Naphthalene 1% approx. • Trimethylbenzene 7% approx. • MTBE(Methyl Tertiary Butyl Ether) 18% approx. Next >
What are the functions of the fuel system? • store a quantity/reservoir of fuel • a system to move the fuel • a system of mixing the fuel with air as it enters the engine • ensure the fuel/air mixture is correct for all engine requirements • minimize harmful pollutants Next >
Fuel tanks. The fuel tank is the storage container to hold the fuel until the engine requires it. • What is the purpose of the separators in the fuel tank? • To prevent fuel level fluctuations and fuel surge when cornering and braking Next >
Fuel pipes and hoses • How many pipes usually come out of the fuel tank and what is their purpose? • 3 pipes • Fuel supply • Fuel return • Charcoal canister Next >
Electric fuel pumps. Next >
2 ball valves are fitted in the pump; • A pressure relief valve. • A non-return valve. • What is the operation of the 2 one-way valves fitted in this pump? • The pressure relief valve limits the maximum output pressure by allowing excess fuel pressure to return to the tank. • The non-return valve stops fuel pressure bleeding back through the pump when the engine is not running. Next >
Why does the fuel pass through the electric motor? • To cool and lubricate the electric motor. • Is there a risk of fire if the fuel comes in contact with the electric motor? • No because there is no oxygen available to complete the fire triangle. Next >
Roller-type pump element. Next >
What is the typical fuel delivery pressure for an electric fuel injection (EFI) system? • Between 2 – 4 bar. • Where is the fuel pump located? • In the fuel tank. Next >
Fuel filters What are these fuel filters constructed of? • Metal bodies and pleated paper • Why are the bodies of the filter made of metal? • To ensure it can cope with the fuel pressure Next >
Fuel Injectors • Fuel strainer • Electrical connector • Solenoid winding • Return spring • Solenoid armature • Needle valve • Pintle • Seat • What is the purpose of no1? • To keep any dirt out of the injector that has made it past the filter. Next >
The injector spray finely atomised fuel into the throttle body or inlet ports depending on the system. The electromagnetic injection valves are actuated by the electronic control unit (ECU). The signals from the ECU are of a precise duration depending on the engines operating conditions with a range of about 1.5-10 milliseconds. This open phase of the injector in known as the “injector pulse width”.
What is this components task? • To control the pressure in the fuel rail. • The fuel pressure regulator consists of a spring loaded ball and diaphragm and is set to maintain a constant pressure difference between the fuel in the fuel rail and the inlet manifold (e.g. 2.5 bar). The pressure in the manifold depends on throttle opening so when the opening is small the high manifold vacuum encourages more fuel to leave the injector when it is open. When to manifold vacuum is low, low vacuum is applied to the diaphragm so the fuel pressure increases before it can lift the ball off its seat.
State 2 places that the fuel pressure regulators can be located On the end of the fuel rail or in the tank with the pump.
Fuel Injection Timing Describes when fuel is sprayed into the inlet manifold. Intermittent (or modulated) Injectors controlled independently of inlet valve position. Timed (or sequential) Injectors controlled in time with inlet valves. Continuous Injectors open all the time, fuel pressure is controlled. Next >
Fuel Injector Opening Relationships Simultaneous Injection (all together). Sequential Injection (one at a time). Next >
A A A B B B Fuel Injector Opening Relationships Group Injection (Injectors of Vee engine operating in A and B banks). Next >
Describe simultaneous injection timing. • Simultaneous injection means all the injectors fire together, delivering half the metered amount twice per engine cycle • Describe sequential injection timing. • Sequential injection means the injectors’ fire in firing order sequence and the full metered fuel volume for the cycle is injected.
Air fuel mixture control. • The term stoichiometric ratio describes the chemically correct air-fuel ratio necessary to achieve complete combustion of the fuel. • For simple and practical purposes it’s worked out in the following way: For a petrol engine the optimal operational value of the fuel /air ratio is 14.7 parts of air, to 1 part of fuel. By mass, that’s 14.7 kilograms of air to each kilogram of fuel. • Under ideal conditions, the air/fuel ratio is 14.7:1 when ignited will burn completely to produce exhaust emissions of CO2 and H2O.
List the problems of having a richer air/fuel ratio, 12:1. • high emissions of CO • high emissions of HC • high emissions of NOX • poor running • low fuel economy • List the problems of having a lean air/fuel ratio, 17:1. • power output low • fuel more difficult to ignite • prone to detonation (cause combustion knock) • It also burns slower, so is more likely to overheat the engine.
What are the 3 systems that must work together for the EFI system to work correctly? • Fuel supply system • Air supply system • Electronic control system • What controls an EFI system? • Electronic control unit. (ECU)
System and component blocks Connection lines Direction of information flow/control Fuel System Diagrams and Schematics Fuel System Block Diagrams Each block represents a component. Lines represent connections between systems. Arrows represent direction of flow. Next >
Engine speed sensor. List the places that the engine could get engine speed from. • Ignition Circuit, Coil. • crank position sensor • cam position sensor
Positive voltage Negative voltage • Crank Angle Sensor gives informationon the speed and position of the crankshaft to the ECU to control ignition timing, and injection sequencing. The control unit can then trigger the ignition, and injection, to suit operating conditions.
The camshaft position sensor provides definitive positional information because the camshaft only rotates once per engine cycle.
Engine load sensing.Name the 2 main ways of sensing engine load • Direct, air flow or air mass sensing • Indirect, pressure/vacuum sensing system
Air flow/air mass sensors. Vane or flap type. • What is the function of the damping chamber? • The dampening chamber prevents the sensing flap being affected by the internal pumping action of the cylinders.
Engine load is sensed by the engine load sensor – e.g. air flow meter Air cleaner Air drawn into intake system Engine load is dictated by the position of the throttle butterfly – i.e. driver demands Air flow meter Flap Type.
- - v Earth terminal Signal terminal Supply voltage terminal ECU EFI components - input signal Vane type air flow sensor Oscilloscope is better!!
Pressure/vacuum sensing • This system uses a manifold absolute pressure (MAP) sensor to measure the manifold depression. Manifold depression is created by the pumping actions of the pistons. The MAP sensor measures the manifold pressure in the inlet manifold which changes with the engine’s load and throttle position. The MAP sensor consists of a diaphragm and a piezoelectric circuit.
When is manifold depression at its highest? • At idle speed, when the throttle plate is fully closed • When is manifold depression at its lowest? • At full throttle, when there is no restriction to the air flowing into the cylinders.