How Does A Diesel Fuel Injector Work?

Over the last two decades of diesel growth, diesel injectors have become increasingly complicated, but their core architecture has remained quite simple. The mechanical injector body receives diesel fuel from the injection pump and begins to create pressure. A check valve in the injector is pushed off its seat once the pressure is high enough (about 4,000 psi), and fuel shoots through. After the valve is opened, any remaining fuel is sent back out via the injector body and back to the injection pump.

What is a diesel fuel injection system and how does it work?

In contrast to a gas engine, a diesel fuel injection system injects diesel fuel directly into the cylinder. In a gas engine, gasoline is injected prior to the intake stroke (outside the cylinder), where it mixes with air before entering the cylinder, using a port injection or carburetor.

The injector is the most complicated portion of a diesel engine. The pressure and heat inside a cylinder are quite high, and the injector must be able to withstand these conditions while still dispensing fuel in a tiny mist. It’s also crucial that the mist is uniformly spread within the cylinder. To swirl air through the combustion chamber, some diesel engines use induction valves, pre-combustion chambers, or another sort of device. This procedure ensures that the fuel mist is distributed evenly and that the ignition and combustion processes go smoothly.

What are the signs that a diesel injector is failing?

The fuel injection system is an important part of any diesel engine. The fuel is pressurized and injected into compressed air in the combustion chamber via this system. Feeding fuel to the injectors, regulating the fuel quantity, modifying the injection time, and atomizing the fuel are all operations of a fuel injection system.

The proper amount of fuel, at the right time, in the right condition for combustion, must be delivered.

Fuel injectors help enhance fuel efficiency, reduce the need for fuel system maintenance, and keep emissions cleaner. A diesel fuel injector has an average lifespan of 100,000 kilometers. The nozzle and the injector body are the two primary elements of a standard fuel injector. If either of these components becomes clogged or destroyed, the vehicle’s overall performance is jeopardized.

  • Uneven idling or difficulty starting the car. The engine cranks, but it won’t start unless you crank it hard enough. On idle, the engine uses a variety of rev levels.
  • Misfire. A full diagnostic of a vehicle that is misfiring on ignition entails determining which component of the combustion process is missing. This is caused by either a lack of fuel injection or a lack of combustion chamber heat in a diesel engine. One of the cylinders’ fuel charge fails to ignite, or the fuel supply to the ignition system is insufficient.
  • There’s a strong odor of gasoline. The scent of diesel within the cabin indicates that there is a leak. This could be caused by a malfunctioning injector that allows fuel to leak out while it isn’t in use.
  • Emissions are filthy. Filters that are clogged and deposits on injectors create an uneven or partial fuel burn, resulting in a polluted environment around the exhaust and the discharge of white smoke from the exhaust pipe.
  • Fuel consumption has increased, while miles per gallon has decreased. Faulty injectors waste more fuel and have a direct impact on the performance and efficiency of your vehicle.

Clean fuel injectors are essential for your diesel engine to run at its best. Any of the following signs could suggest an issue with your fuel injectors, which should not be overlooked. Injectors that are unclean, clogged, or leaky are examples of this. If you’ve driven your car for more than 100,000 miles without replacing the fuel injectors, it’s time to have them looked at by a specialist.

Purpose of Fuel Injection System

The design of a diesel engine’s injection system has a significant impact on its performance. In reality, superior fuel injection system designs were directly responsible for the most significant breakthroughs in diesel engines. While the system’s primary function is to provide fuel to a diesel engine’s cylinders, how that fuel is delivered determines engine performance, emissions, and noise characteristics.

The diesel fuel injection system, unlike its spark-ignited predecessor, provides fuel at exceptionally high injection pressures. This means that system component designs and materials should be chosen to endure larger stresses and perform for longer periods of time in order to meet the engine’s durability goals. The system’s efficiency also necessitates increased manufacturing precision and strict tolerances. Diesel injection systems are distinguished by more complex control needs, in addition to pricey components and manufacturing expenses. All of these elements add up to a system that might account for up to 30% of the engine’s total cost.

The primary function of a fuel injection system is to supply fuel to an engine’s cylinders. In order for the engine to make the most of this fuel, it must:

  • The injection timing must be managed and the fuel must be injected at the correct time.
  • To achieve power requirements, the correct amount of fuel must be delivered, which means injection metering must be controlled.

However, delivering a correctly calibrated amount of fuel at the right time isn’t enough to accomplish effective combustion. Other factors that must be considered to guarantee optimum fuel injection system performance include:

  • A fundamental design goal for diesel fuel injection systems is to ensure that the fuel atomizes into very minute fuel particles. All of the fuel has an opportunity to evaporate and participate in the combustion process because of the small droplets. Any residual liquid droplets burn inefficiently or escape the engine. While modern fuel injection systems can produce fuel atomization characteristics that are far superior to what is required to ensure complete fuel evaporation for the majority of the injection process, some injection system designs may have poor atomization during brief but critical periods of the injection phase. One such key phase is the end of the injection process.
  • Bulk mixingWhile fuel atomization and complete evaporation are necessary, ensuring that the evaporated fuel has enough oxygen during the combustion process is also crucial for high combustion efficiency and optimum engine performance. The oxygen comes from the trapped air in the cylinder, which must be entrained into the fuel jet in sufficient quantities to thoroughly mix with the available fuel throughout the injection process and ensure complete combustion.
  • Air usageEfficient air utilization in the combustion chamber is strongly linked to bulk mixing and can be achieved by combining fuel penetration into the dense air compressed in the cylinder with dividing the entire injected fuel into a number of jets. A sufficient number of jets should be available to entrain as much accessible air as feasible while preventing jet overlap and the creation of oxygen-deficient fuel-rich zones.

Figure 1 depicts the key functions of the diesel fuel injection system graphically.

Definition of Terms

The components and operation of diesel fuel injection systems are described using a variety of specific concepts and phrases. The following are a few of the more common ones:

The section of the nozzle body/needle assembly that interfaces with the engine’s combustion chamber is referred to as the nozzle. P-Type, M-Type, and S-Type nozzles refer to standardized nozzle parameters as defined by ISO regulations.

The portion on which the nozzle is placed is referred to as the nozzle holder or injector body. This item was primarily used in traditional injection systems for nozzle installation and nozzle needle spring preloading. It contains the primary functioning pieces in common rail systems: the servo-hydraulic circuit and the hydraulic actuator (electromagnetic or piezoelectric).

The time at which fuel is injected into the combustion chamber is known as the start of injection (SOI) or injection timing. It’s commonly measured in crank angle degrees (CAD) relative to the compression stroke’s top dead center (TDC). It’s vital to distinguish between the indicated and actual SOI in various circumstances. An easily measured characteristic, such as the time an electrical trigger is delivered to the injector or a signal from a needle lift sensor that indicates when the injector needle valve begins to open, is frequently used to determine SOI. The indicated SOI is the moment in the cycle where this happens. When fuel exits the injector nozzle into the combustion chamber, there may be a delay between the indicated SOI and the actual SOI due to the injector’s mechanical response. The injector lag is the discrepancy between the actual SOI and the indicated SOI.

The delivery process has begun. Fuel injection is linked with the development of high pressure in various fuel systems. The commencement of delivery in such systems occurs when the high-pressure pump begins to deliver fuel to the injector. The time it takes for a pressure wave to travel between the pump and the injector, as well as the length of line between the high pressure pump and the injector and the speed of sound in the fuel, influence the difference between commencement of delivery and SOI. Injection delay is the time between the start of delivery and the start of SOI.

The amount of fuel injected into an engine cylinder each power stroke is known as injected fuel quantity. It’s usually measured in mm3/stroke or mg/stroke.

The time it takes for fuel to enter the combustion chamber from the injector is known as injection duration. It’s the difference between EOI and SOI, and it has something to do with injection volume.

Pattern of injection. During the injection time period, the rate of fuel injection frequently fluctuates. The three most frequent rate forms are shown in Figure 2: boot, ramp, and square. The gradients in the rate of injection during needle nozzle opening and closing events are referred to as opening rate and closure rate, respectively.

There will be multiple injection events. Traditional fuel injection systems use a single injection event for each engine cycle, whereas newer systems can use several injection events for each engine cycle. Figure 3 shows a list of phrases that are commonly used to describe several injection events. It’s worth noting that the nomenclature isn’t always uniform. The bulk of the fuel for the engine cycle comes from the main injection event. Pre-injections, which occur one or more times before the main injection, supply a little amount of fuel before the main injection event. Pre-injections are sometimes known as pilot injections. A pre-injection that occurs a long period before the main injection is referred to as a pilot, whereas one that occurs a short time before the main injection is referred to as a pre-injection. Post-injection injections can happen right after the primary injection (short post-injection) or a long period after the main injection (long post-injection) (late post-injection). After-injections are another name for post-injections. While terminology varies, a close post-injection is referred to as a post-injection, and a late post-injection is referred to as an after-injection.

Split injection is a word that is sometimes used to describe various injection tactics in which a primary injection is split into two smaller injections of roughly similar size or a smaller pre-injection followed by a big injection.

When the nozzle briefly re-opens after closing, it can cause unintended post-injections in some fuel injection systems. Secondary injections are a term used to describe these injections.

The literature does not consistently employ injection pressure. In common rail systems, it might refer to the mean pressure in the hydraulic system, while in conventional systems, it could refer to the greatest pressure during an injection (peak injection pressure).

Basic Fuel System Components

Fuel systems can be divided into two basic component groupings, with a few exceptions:

  • Low-pressure side componentsThese components ensure that fuel is delivered from the tank to the fuel injection system safely and reliably. The fuel tank, fuel delivery pump, and fuel filter are all low-pressure components.
  • Components that generate high pressures, meter, and deliver fuel to the combustion chamber are known as high-pressure side components. The high-pressure pump, the fuel injector, and the fuel injection nozzle are among them. An accumulator may be included in some systems.

Fuel injection nozzles are classified as hole-type, throttling pintle-type, closed-type, or open-type. Closed nozzles can be activated hydraulically or with servo control utilizing a simple spring-biased mechanism. Direct actuation is possible with open nozzles as well as certain newer closed nozzle injector types.

The high-pressure pump or the fuel injector are widely used to measure the amount of fuel injected. Pressure metered at a constant time interval (PT), time metered at a constant pressure (TP), and time/stroke metered are all examples of fuel metering methods (TS).

The majority of fuel injection systems use electronics to manage the nozzle’s opening and closing. Using an actuator, electrical impulses are translated into mechanical forces. Electromagnetic solenoids or active materials like piezoelectric ceramics are commonly used as actuators.

What regulates the fuel injector in a diesel engine?

The newest high-pressure direct injection fuel delivery technique is common rail injection. A high-tech fuel pump delivers fuel to a common rail that also serves as a pressure accumulator. The individual injectors get gasoline from the common rail via short high-pressure fuel lines. The electronic control unit of the system carefully regulates the rail pressure as well as the timing and duration of the fuel injection. Rapid-fire solenoid valves or piezoelectric triggered actuators control injector nozzles.

What is the working pressure of diesel injectors?

The injector, the injection pump, and, in some circumstances, the engine control unit, make up the fuel system on most diesel engines (ECU). Fuel injectors are installed in the cylinder heads of most diesel engines, and the injector’s tip or nozzle sprays directly into the combustion chamber. In many cases, the injector is installed similarly to a spark plug in a gas engine. Unlike fuel-injected gas engines, which inject fuel at a pressure of 10-60 psi, diesel fuel-injection systems operate at a pressure of 10,000-30,000 psi.

What’s the most prevalent reason for injector malfunction?

The contemporary diesel engine is a complicated set of components that work together to produce the efficient power that propels our industries. The common rail fuel system, along with an electronic control unit, is the technology that started the contemporary diesel revolution. In 2001, common rail fuel systems made their debut in the United States. They represented a significant departure from existing gasoline systems such as inline and distributor pumps, eradicating all previous connections with noisy diesel engines.

Solenoid-actuated fuel injectors working at over 23,000 psi and capable of injecting several times per cylinder stroke were at the heart of these revolutionary systems. It’s not uncommon to see these original automobiles on the road today with more than 300,000 miles on them, still serving their owners. Naturally, these cars will require maintenance in order to continue to function effectively, and one component that is frequently updated is the fuel injector.

The service possibilities were limited in the early years of common rail. OEMs first sold new injectors before gradually transitioning to remanufactured options. These reman solutions were a high-quality, cost-effective repair option since they had access to both OE test equipment and low tolerance component parts.

However, in the recent decade, there has been an inflow of third-party injector manufacturers. As the number of third-parties grew, so did the number of injector issues.

Bosch recently conducted a research on a large sample of rebuilt or remanufactured common rail fuel injectors to better investigate these concerns. We put them through production testing and then dismantled them to examine the various components.

What we found was concerning

More than half of the items we evaluated failed to meet OE test criteria, and if installed, they posed a serious risk to the engine. Many of them featured corroded or ground-down reused parts. As well as new, non-OE components that caused the injector to malfunction. Exhaust system damage, odd engine noises, smoke, and power loss were all common symptoms when the device was fitted on the car. We also witnessed a 5-10% fall in fuel mileage.

With so many remanufactured injector options on the market, it’s critical for service personnel to be confident in the part they’re installing.

Common causes of injector failure

The lifespan of modern common rail networks is often quite long. They are, nevertheless, nonetheless vulnerable to problems. While numerous things might cause failures, gasoline contamination is the most common cause of premature failure. When material in the gasoline gets past the filtration and destroys the sealing surfaces, fuel contamination occurs. Consider clearances in microns, which are less than a human hair. Any dirt flowing through serves as sandpaper, wearing out a groove in vital sealing surfaces until they stop working.

Water in the gasoline is the second most common problem. Water causes corrosion since everything inside is made of metal. This can either produce trash in the system or induce sticking by reducing the micron level clearance between elements.

Finally, keep an eye out for improper installations, which is especially critical if your consumers are coming from different stores. Look for missing sealing rings, insufficient nozzle cleaning, and inappropriate tightening torque. Performance difficulties, misfiring, black smoke, and the presence of the check engine light are all possible outcomes.

What to look for in an injector

To effectively diagnose fuel injector problems, you must first have access to scan tools and OE methods. The Bosch Diesel network includes independently owned shops around the country with diesel professionals that have the knowledge and experience to diagnose these engines. A misdiagnosis can add money and frustration to a repair that is already expensive. You have a few options now that your car has been thoroughly assessed and the fuel injectors are in need of replacement.

The Bosch Diesel network also has places where you may have your injectors tested and repaired. Bosch Diesel Centers are the names given to these establishments. When compared to a similar remanufactured injector, evaluating the injectors and replacing only the components that show signs of wear can result in cost savings.

The most common service option is remanufactured injectors. As previously said, not all reman parts are created equal. During the rebuilding process, all remanufacturers must make the same selection. Is it better to keep or replace this component? Because they have access to these parts directly off the production line, OEMs will frequently replace a higher percentage of the components. As a result, the end product is of superior quality. Furthermore, it has been flow-tested on production test equipment, ensuring that it satisfies the original injector’s specifications. The last thing you want is to spend a few thousand dollars on a part and then have to wonder if it will function right out of the box.

When working with a third party, it’s common for them to offer pricing points that are far lower than OEMs. They can do this by reusing the majority of parts or even testing and reselling used injectors, which are known as core. More than half of these injectors violate basic testing standards, as we discovered before. Time is money, and some injector projects can take up to ten hours to complete. If you can’t trust the product, it’s all for naught.

What happens if one of the injectors stops working?

When fuel injectors malfunction, the engine’s performance suffers dramatically. The fuel injectors are in charge of providing fuel to your car, truck, or automobile’s engine. Obviously, if the fuel injection system fails, the engine will fail as well, and you will be unable to travel the streets of Burke, Virginia. Fuel injectors fail for a variety of causes, but here are five of the most prevalent issues.

  • A sudden loss of engine power is a fairly evident indicator of a failing fuel injector. Fuel supply will be irregular if the fuel injector is clogged. When the fuel level fluctuates dramatically, the engine will move in surges rather than moderate and gradual movements due to the high and low rpms.
  • If a clogged fuel injector struggles to spread fuel to the engine on a regular basis, it will eventually miss the fuel supply entirely, causing the engine to misfire. The misfire is immediately detectable while driving, and it frequently necessitates rapid attention from a professional automotive repair specialist. The engine can quickly overheat and pre-ignite the gasoline mixture if it misfires.
  • A faulty fuel injector will not only cause driving problems, but the consequences will last even while the engine is idle. When the gasoline supply is abrupt, the engine will idle coarsely and irregularly instead of smoothly.
  • Another indicator of a damaged fuel injector is decreased fuel economy. When the internal springs are destroyed, this might result in fuel being squandered by seeping from the body or by supplying too much fuel.

If you suspect a damaged fuel injector or that the fuel injectors are failing, contact Wiygul Automotive Clinic right away.