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Fuel Injection System Components
Pump-Line-Nozzle Injection System
Common Rail Fuel Injection
Abstract: The purpose of the fuel injection system is to deliver fuel into the engine cylinders, while precisely controlling the injection timing, fuel atomization, and other parameters. The main types of injection systems include pump-line-nozzle, unit injector, and common rail. Modern injection systems reach very high injection pressures, and utilize sophisticated electronic control methods.
Basic Principles
Common Diesel Fuel Injection System Architectures
Fuel Injection System/Fuel Interactions
Electronic Control in Fuel Injection
Basic Principles
Purpose of Fuel Injection System
The performance of diesel engines is heavily influenced by their injection system design. In fact, the most notable advances achieved in diesel engines resulted directly from superior fuel injection system designs. While the main purpose of the system is to deliver fuel to the cylinders of a diesel engine, it is how that fuel is delivered that makes the difference in engine performance, emissions, and noise characteristics.
Unlike its spark-ignited engine counterpart, the diesel fuel injection system delivers fuel under extremely high injection pressures. This implies that the system component designs and materials should be selected to withstand higher stresses in order to perform for extended durations that match the engine’s durability targets. Greater manufacturing precision and tight tolerances are also required for the system to function efficiently. In addition to expensive materials and manufacturing costs, diesel injection systems are characterized by more intricate control requirements. All these features add up to a system whose cost may represent as much as 30% of the total cost of the engine.
The main purpose of the fuel injection system is to deliver fuel into the cylinders of an engine. In order for the engine to effectively make use of this fuel:
Fuel must be injected at the proper time, that is, the injection timing must be controlled and
The correct amount of fuel must be delivered to meet power requirement, that is, injection metering must be controlled.
However, it is still not enough to deliver an accurately metered amount of fuel at the proper time to achieve good combustion. Additional aspects are critical to ensure proper fuel injection system performance including:
Fuel atomization—ensuring that fuel atomizes into very small fuel particles is a primary design objective for diesel fuel injection systems. Small droplets ensure that all the fuel has a chance to vaporize and participate in the combustion process. Any remaining liquid droplets burn very poorly or are exhausted out of the engine. While modern fuel injection systems are able to produce fuel atomization characteristics far exceeding what is needed to ensure complete fuel evaporation during most of the injection process, some injection system designs may have poor atomization during some brief but critical periods of the injection phase. The end of the injection process is one such critical period.
Bulk mixing—While fuel atomization and complete evaporation of fuel is critical, ensuring that the evaporated fuel has sufficient oxygen during the combustion process is equally as important to ensure high combustion efficiency and optimum engine performance. The oxygen is provided by the intake air trapped in the cylinder and a sufficient amount must be entrained into the fuel jet to completely mixed with the available fuel during the injection process and ensure complete combustion.
Air utilization—Effective utilization of the air in the combustion chamber is closely tied to bulk mixing and can be accomplished through a combination of fuel penetration into the dense air that is compressed in the cylinder and dividing the total injected fuel into a number of jets. A sufficient number of jets should be provided to entrain as much of available air as possible while avoiding jet overlap and the production of fuel rich zones that are oxygen deficient.
The primary purposes of the diesel fuel injection system are graphically represented in Figure 1.
Definition of Terms
Many specialized concepts and terms are used to describe the components and the operation of diesel fuel injection systems. Some of the more common of these include [922][2075]:
Nozzle refers to the part of the nozzle body/needle assembly which interfaces with the combustion chamber of the engine. Terms like P-Type, M-Type, or S-Type nozzle refer to standardized dimensions of nozzle parameters, as per ISO specifications.
Nozzle holder or injector body refers to the part the nozzle is mounted on. In conventional injection systems this part mainly served the nozzle mounting and nozzle needle spring preloading function. In common rail systems, it contains the main functional parts: the servo-hydraulic circuit and the hydraulic actuator (electromagnetic or piezoelectric).
Injector commonly refers to the nozzle holder and nozzle assembly.
Start of injection (SOI) or injection timing is the time at which injection of fuel into the combustion chamber begins. It is usually expressed in crank angle degrees (CAD) relative to TDC of the compression stroke. In some cases, it is important to differentiate between the indicated SOI and actual SOI. SOI is often indicated by an easily measured parameter such as the time that an electronic trigger is sent to the injector or a signal from a needle lift sensor that indicates when the injector needle valve starts to open. The point in the cycle where this occurs is the indicated SOI. Due to the mechanical response of the injector, there can be a delay between the indicated SOI and the actual SOI when fuel exits the injector nozzle into the combustion chamber. The difference between the actual SOI and indicated SOI is the injector lag.
Start of delivery. In some fuel systems, fuel injection is coordinated with the generation of high pressure. In such systems, the start of delivery is the time when the high pressure pump starts to deliver fuel to the injector. The difference between start of delivery and SOI is affected by the length of time it takes for a pressure wave to travel between the pump and injector and is influenced by the length of line between the high pressure pump and the injector and by the speed of sound in the fuel. The difference between the start of delivery and SOI can be referred to as injection delay.
End of injection (EOI) is the time in the cycle when fuel injection stops.
Injected fuel quantity is the amount of fuel delivered to an engine cylinder per power stroke. It is often expressed in mm3/stroke or mg/stroke.
Injection duration is the period of time during which fuel enters the combustion chamber from the injector. It is the difference between EOI and SOI and is related to injection quantity.
Injection pattern. The rate of injection of fuel often varies during the injection duration period. Figure 2 shows three common rate shapes: boot, ramp and square. Opening rate and closing rate refers to the gradients in the rate of injection during needle nozzle opening and closing events, respectively.
Multiple injection events. While conventional fuel injection systems employ a single injection event for every engine cycle, newer systems can use multiple injection events. Figure 3 defines some of the common terms used to describe multiple injection events. It should be noted that the terminology is not always consistent. The main injection event provides the bulk of the fuel for the engine cycle. One or more injections before the main injection, pre-injections, provide a small amount of fuel before the main injection event. Pre-injections can also be referred to as pilot injection. Some refer to a pre-injection that occurs a relatively long time before the main injection as a pilot and one that occurs a relatively short time before the main injection as a pre-injection. Injections after the main injections, post-injections, can occur immediately after the main injection (close post-injection) or a relatively long time after the main injection (late post-injection). Post-injections are sometimes called after-injections. While there is considerable variation in terminology, a close post-injection will be referred to as a post-injection and a late post-injection as an after-injection.
The term split injection is occasionally used to refer to multiple injection strategies where a main injection is split into two smaller injections of approximately equal size or into a smaller pre-injection followed by a main injection.
Unintended post-injections can occur in some fuel injection systems when the nozzle momentarily re-opens after closing. These are sometimes referred to as secondary injections.
Injection pressure is not used consistently in the literature. It may refer to the mean pressure in the hydraulic system for common rail systems, or to the maximum pressure during an injection (peak injection pressure) in conventional systems.
Basic Fuel System Components
Fuel Injection System Components
With a few exceptions, fuel systems can be broken down into two major component groups:
Low pressure side components—These components serve to safely and reliably deliver fuel from the tank to the fuel injection system. Low pressure side components include the fuel tank, fuel supply pump and the fuel filter.
High pressure side components—Components that create high pressures, meter and deliver the fuel to the combustion chamber. They include the high pressure pump the fuel injector and fuel injection nozzle. Some systems may also include an accumulator.
Fuel injection nozzles can be categorized as hole-type or throttling pintle type and as either a closed or open. Closed nozzles can be actuated hydraulically using a simple spring-biased mechanism or using servo control. Open nozzles as well as some newer closed nozzle injector designs can be directly actuated.
Metering of the injected fuel amount is commonly carried out in either the high pressure pump or the fuel injector. A number of different fuel metering approaches exist including: pressure metered at a constant time interval (PT), time metered at a constant pressure (TP) and time/stroke metered (TS).
Most fuel injection systems use electronics to control the opening and closing of the nozzle. Electrical signals are converted into mechanical forces using some type of actuator. Commonly, these actuators can be either electromagnetic solenoids or active materials such a piezoelectric ceramics.
Basic fuel injection system components are discussed in a separate paper.
The function of the diesel fuel system is to inject a precise amount of atomized and pressurized fuel into each engine cylinder at the proper time. Combustion in a diesel engine occurs when this rush of fuel is mixed with hot compressed air.
Diesel vehicles are similar to gasoline vehicles because they both use internal combustion engines. One difference is that diesel engines have a compression-ignited injection system rather than the spark-ignited system used by most gasoline vehicles.
The fuel is injected only into the pre-chamber (where it begins to combust), and not directly into the main combustion chamber. Therefore, this principle is called indirect injection. There exist several slightly different indirect injection systems that have similar characteristics.
Your engine sounds quieter and has a better quality of sound. It also runs smoother. You will see fuel consumption benefits as well because greater injection pressure produces a finer spray of fuel (atomisation) that burns more efficiently. Better combustion efficiency is a key part of meeting emission standards.
Your vehicle can be equipped with one of the three most common injection systems on the market. GDI (Direct injection), SDI (Semi-direct injection) or TBI (Throttle body injection).
it's important to understand the differences between the two primary types of injection systems modern diesel engines use: common rail injection and mechanical injection.
Realistically, the tipping point in diesel injectors becoming so expensive was electronic control. In the old days of diesel, fuel injectors had a direct line to a high-pressure pump that was timed to the engine.
Diesel engines only use direct fuel injection — the diesel fuel is injected directly into the cylinder. The injector on a diesel engine is its most complex component and has been the subject of a great deal of experimentation — in any particular engine, it may be located in a variety of places.
They called it diesel fuel. My car can run on diesel (the fossil fuel variety), straight vegetable oil (SVO), and biodiesel (SVO that has been modified), or any combination of the three. That isn't unusual: anything with a diesel engine -- plane, boat, motorcycle -- can run on diesel, SVO or biodiesel.
Diesel fuel injectors require much higher injection pressure (up to 30,000 psi) than gasoline injectors as diesel is heavier than gasoline, and it takes much higher pressure to atomize the fuel.
Although fuel injection is by far the most effective and efficient form of fuel delivery, carburetors do offer their own set of benefits. Although fuel injection delivers more precise air-to-fuel ratios, it is significantly more costly and difficult to maintain than carburettors.
Diesel engines are also IC engines. However, in Diesel engines, there is no carburetor. Only air is compressed to much higher pressures and the fuel is injected into the compressed air. As the fuel and air are mixed, the fuel evaporates and ignites (hence called compression ignition).
Cummins offer a system complete with leakless injectors, enabling a robust and durable product. Injectors tailored to match duty cycles and provide industry leading fuel economy, delivering and delivers up to 5% efficiency improvements over our competitors.
Introduction: My name is Kimberely Baumbach CPA, I am a gorgeous, bright, charming, encouraging, zealous, lively, good person who loves writing and wants to share my knowledge and understanding with you.
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