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Abstract: The fuel injection system can be divided into low-pressure and high-pressure sides. The low-pressure components include the fuel tank, fuel supply pump and fuel filter. The high-pressure side components include a high pressure pump, accumulator, fuel injector and fuel injector nozzle. A number of injection nozzle designs and different actuation methods have been developed for use with different types of fuel injection systems.
In order for the fuel injection system to fulfill its purpose, fuel must be transferred to it from the fuel tank. This is the role of the low-pressure fuel system components. The low pressure side of the fuel system consists of a number of components including the fuel tank, one or more fuel supply pumps and one or more fuel filters. In addition, many fuel systems contain coolers and/or heaters to better control fuel temperature. Figure 1 illustrates two examples of schematics for low pressure fuel systems, one for a heavy-duty diesel truck and one for a light-duty diesel passenger car [1590][1814].
Figure 1. Examples of Low Pressure Fuel Systems for Heavy-Duty and Light-Duty Diesel VehiclesThe fuel tank is a reservoir that holds the fuel supply and helps maintain its temperature at a level below its flash point. The fuel tank also serves as an important means of dissipating heat from the fuel that is returned from the engine [528]. The fuel tank should be corrosion-resistant and leakproof to pressures of at least 30 kPa. It must also use some means to prevent excessive pressure accumulation such as a vent or a safety valve.
The fuel supply pump, often referred to as the lift pump, is responsible for drawing fuel from the tank and delivering it to the high pressure pump. Modern day fuel pumps can be electrically or mechanically driven by the engine. Using an electrically driven fuel pump allows the pump to be placed anywhere in the fuel system including inside the fuel tank. Pumps driven by the engine are attached to the engine. Some fuel pumps may be incorporated into units that serve other functions. For example, so called tandem pumps are units that incorporate a fuel pump and a vacuum pump for the brake booster. Some fuel systems, such as those based on a distributor type pump, incorporate a mechanically driven supply pump and the high pressure pump in one unit.
Fuel pumps are commonly sized to deliver more fuel than is consumed by the engine at any particular operating system. This extra fuel flow can serve a number of important functions including providing extra fuel to help to cool injectors, pumps and other engine components and maintaining a more constant temperature of the fuel in the entire fuel system. Also, the excess fuel that is heated by its contact with hot engine components can be returned to the tank or fuel filter to improve the vehicle’s low temperature operability.
Trouble-free operation of a diesel injection system is possible only with filtered fuel. Fuel filters help reduce damage and premature wear from contaminants by retaining very fine particles and water to prevent them from entering the fuel injection system. As shown in Figure 1, fuel systems can contain one or more stages of filtration. In many cases, a course screen is also located at the fuel intake located in the fuel tank.
Two stage filter system typically uses a primary filter on the inlet side of the fuel transfer pump and a secondary filter on the outlet side. The primary filter is required to remove larger particles. The secondary filter is required to withstand higher pressures and remove smaller particles that can damage the engine components. One-stage systems remove larger and smaller particles in a single filter.
Filters can be a box-type or replacement element design, as shown in Figure 2. The box-type filter is that which can be completely replaced as needed and does not require cleaning. Filters with a replaceable element have to be thoroughly cleaned when replacing elements and care must be taken to avoid any dirt residue that could migrate to the intricate parts of the fuel injection system. Filters can be constructed of metal or plastic.
Figure 2. Two Types of Fuel Filters(a) Box type; (b) Element type
Common materials for modern fuel filter elements are synthetic fibres and/or cellulose. Micro glass fibres can also be used but because of the risk of migration of small glass fibre pieces broken off from the main element into critical fuel system components, their use in some applications is avoided [2046]. In the past, pleated paper, packed cotton thread, wood chips, a mixture of packed cotton thread and wood fibres and wound cotton have also been used [529].
The degree of filtration required depends on the specific application. In general, when two filters are used in series, the primary filter retains particles down to about 10 - 30 µm, while the secondary filter is capable of retaining particles greater than 2-10 µm. As fuel systems evolve, clearances and stresses on high pressure components increase and the need for clean fuel becomes event more critical. Both the capability of fuel filters to keep up with demands for cleaner fuel [2047] as well as methods quantifying acceptable fuel contamination levels have needed to evolve [2048].
In addition to keeping solid particles out of the fuel supply and injection equipment, water in fuel must also be prevented from entering critical fuel injection system components. Free water can damage fuel lubricated components in the fuel injection system. Water can also freeze in cold temperature conditions and ice may block small fuel injection system passages thus cutting off the fuel supply to the rest of the fuel injection system.
Water can be removed from the fuel using two common approaches. The incoming fuel can be subject to centrifugal forces that separates the denser water from the fuel. Much better removal efficiencies can be achieved with a filter media that separates water. Figure 3 shows a filter using a combination of media-type and centrifugal approaches.
Figure 3. Fuel Filter Equipped with Water SeparatorDifferent water separation media operate under different principles. Hydrophobic barrier media, such as silicone treated cellulose, rejects water and causes it to bead up on the upstream surface. As the beads become larger, they run down the face of the element into a cup under the force of gravity. Hydrophilic depth coalescing media, such as glass micro-fibre, has a high affinity for water. The water in the fuel associates with the glass fibres and over time as more water enters from the upstream side, massive droplets are formed. The water moves through the filter with the fuel and on the downstream side, falls out of the fuel flow into a collection cup.
Increased use of surface active fuel additives and fuel components such as biodiesel have rendered conventional separating media less effective and filter manufacturers have needed to develop new approaches such as composite media and ultra-high surface area coalescing media [2049][2050][2051]. Methods of quantifying fuel/water separation performance have also been affected [2052].
Fuel filters can also contain additional features such as fuel heaters, thermal diverter valves, de-aerators, water-in-fuel sensors, filter change indicators.
A fuel preheater helps minimize the accumulation of wax crystals that can form in the fuel as it cools to low temperatures. Common heating methods use electric heaters, engine coolant or recirculated fuel. Two approaches that use warm return fuel to heat the incoming fuel are shown in Figure 1.
Fuel overflow and leak-off fuel returning to the tank also carries air and fuel vapor. The presence of gaseous substances in the fuel can cause difficulties in starting as well as normal engine operation in high temperature environments. Therefore, bleeder valves and de-aerators are used to rid the fuel supply of vapors and air to ensure trouble-free engine operation.
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The car fuel system consists of a fuel tank, fuel pump, filter and injectors or carburettors. This system is responsible for delivering the required levels of fuel to the engine. All the components of the vehicle fuel system must perform efficiently to achieve the expected level of engine performance and reliability. Let’s go through the automotive fuel system in detail.
The vehicle fuel system stores and supplies required fuel levels to the engine for optimum performance. Over time, the performance of a vehicle’s engine may slow down because of buildup that clogs important parts of a fuel system. This results in reduced fuel efficiency and power. That said, the fuel system provides the required level of fuel to the engine. Let’s go through the components in detail.
The fuel injectors are the last stop for fuel in your engine before it goes into the combustion chamber. This is an electrically controlled valve that opens just long enough to supply the perfect amount of fuel needed to run the engine.
Before fuel injectors until the late-1980s, carburettors were used to supply the needed fuel to the vehicle engine. These manual non-electric devices were used for mixing vaporized fuel with air to produce a combustible or explosive mixture for internal combustion engines. That said, carburettors have been mostly replaced by electronic fuel injection in modern vehicles.
Another important component of the car fuel system is the fuel pump. This is used to pump fuel from the fuel tank, via the fuel lines into the fuel injectors. The fuel injectors then spray the fuel into the combustion chamber to create combustion. There are two types of fuel pumps. Mechanical fuel pumps (they are used in carburettors) and electronic fuel pumps (these are used in electronic fuel injection).
Make sure the fuel pump has no problems, here are some common signs of a bad fuel pump.
Another important component of an automotive fuel system is the intake valve. This valve controls the air and fuel mixture in the combustion chamber. The flow of the air/fuel mixture going into the combustion chamber can get restricted or change because of the deposits on the intake valves.
Car fuel can stick to deposits on the intake valve and not enter the combustion chamber when needed. That said, the right fuel additive helps prevent these effects and restore lost engine performance.
A properly functioning fuel delivery system happens because of a car fuel filter. Filters are more important for fuel-injection cars than carbureted cars. Fuel-injected cars use electric fuel pumps. This is because when the filter clogs, the electric fuel pump works hard to push past the filter.
Usually, vehicles use two filters. One is situated inside the fuel tank and one in a line to the fuel injectors or carburettor. Unless a large amount of fuel contamination enters the tank, it is only required to replace the filter in line. Here is how to fix fuel contamination.
The piston moves up and down in the cylinders to convert the pressure from combustion into movement. Detergent additives that help remove or reduce deposits are usually effective to reduce or eliminate deposit-related drivability and performance loss.
Combustion chambers generate power from fuel ignition. The burning of the air/fuel mixture happens inside these chambers. Deposits in the combustion chamber affect heat transfer and air/fuel compression.
Premature ignition and knocking can happen because of excess heat. To put it simply, the process of burning fuel and generating energy to power a vehicle happens inside the combustion chamber.
The purpose of the car fuel system is to store and supply fuel to the engine as needed for optimum performance. The fuel is mixed with the air, atomised and vaporized in the engine intake system. It is then compressed in the combustion chamber and ignited to produce energy or power.
Fuel systems vary from engine to engine, that said, all systems have to supply fuel to the combustion chamber and control the amount of fuel supplied about the amount of air.
The fuel is then stored in the fuel tank from where it is drawn through the fuel pump. Then it travels through the fuel lines and is delivered to the fuel injectors through a fuel filter.
The fuel pressure required depends on the type of fuel system.
Types of automotive fuel systems: return type and returnless type system.
The return-type system has a fuel pressure regulator that supplies fuel pressure based on the amount of vacuum from the intake system. Whereas, in a returnless type system the powertrain control mode (PCM) is used to regulate fuel delivery. A fuel pressure sensor mounted to the supply rail of the fuel injectors allows the PCM to monitor the pressure of fuel.
The PCM makes up for the drop in engine speed because of load or speed by increasing the injector duration and/or by the operating speed of the fuel pump.
That is all about the car fuel system. Engine efficiency is necessary for your vehicle’s performance, therefore when looking for a new or used car for sale in the UAE, check the engine thoroughly.
Stay tuned to dubizzle’s top car blog for more on the anatomy of cars.