Why Injectors Fail and ..

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hd3

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and .. Why Do I Need Clean Diesel ?

( given the number of recent posts regarding failed injectors
( this info. posted for reference ..

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the following text taken from:

http://www.mycleandiesel.com/pages/Problems.aspx

to see the pics described in the text .. visit the link
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Clean diesel is necessary for the proper function of modern equipment. Without it, you risk increased downtime and inflated maintenance costs. This is especially true with newer equipment, which requires extremely clean fuel to prevent damaging high pressure common rail engines. Additional fuel quality challenges have arisen due to recent changes to diesel chemistry itself, further increasing the need for efficient filtration.

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Hard Particulates Damage Engines

( HPCR .. High Pressure Common Rail )

Dirty fuel will cause premature parts failure in equipment of any age. Because of the extremely high pressures, this damage is even more pronounced in newer equipment with HPCR fuel systems. Hard particulate is commonly referred to as "dirt", but is in fact made up of a wide variety of materials found at job sites (coal, iron, salt, etc.), generated by fuel tanks and lines (rust, corrosion, etc.) and inside engines (carbonatious materials and wear particles).


DAMAGE CAUSED BY HARD PARTICULATE
Hard particulate causes problems with moving parts in the fuel system. This can lead to starting problems, poor engine performance, idling issues and potentially complete engine failure.

The spray pattern generated by the HPCR injector is critical for proper combustion and overall fuel system performance. It must be extremely precise in terms of quantity, distribution and timing. Ball seat valves are sealed with balls that are only 1mm in diameter. A good seal is absolutely necessary for proper injection. Damage from erosive wear, will cause over fueling, leading to decreased fuel efficiency and eventually shut you down altogether.

Pump performance can also be compromised by scoring and abrasive wear. These issues are magnified by the tighter tolerances and extreme pressures in HPCR engines. In these circumstances, it is the smallest particles (1-5 microns in size)
that cause the most damage, virtually sand blasting part surfaces.


ALLOWABLE LEVELS OF HARD PARTICULATE

In some parts of the world, 10,000 gallons (38,000 liters) of “typical” diesel contains 1-1/2 lbs (700 grams) of hard particulate; this is 1000 times more than the 1/4 oz. (0.7 grams) per 10,000 gallons (38,000 liters) that is allowed by the cleanliness requirements of high pressure common rail fuel systems. In reality, there is no "OK" level of hard particulate. Injector manufacturers are very clear that damage caused by hard particulate reaching the engine is not a factory defect, but rather the result of dirty diesel that is not fit for use in HPCR fuel systems. At the end of the day, the end user is responsible for the fuel he puts into his equipment, and the consequences thereof.

HOW DOES DIRT GET INTO FUEL?
Dust and dirt are all around us, especially on job sites. Diesel fuel is fairly clean when it leaves the refinery, but becomes contaminated each time it is transferred or stored. Below you will find some of the key contributors of fuel contamination:

Pipelines: Most pipelines are not new, and certainly not in pristine condition. Corrosion inhibitors are added at most refineries to help protect pipelines, but rust and other hard particulate is nevertheless picked up by the fuel that flows though them.

Barges and rail cars: How often are they drained and scrubbed out? What was in the last load? Where did it come from? How much of it was still in the tank when your load was picked up? How long was it in transit? Is the tank hermetically sealed? There are lots of opportunities for contaminants to make their way into the fuel.

Terminal tanks: Terminal tanks usually see a high rate of turnover, so there is not much time for the fuel to pick-up contamination from outside ingress. Has the tank ever received a "bad load" from a pipeline or a barge? Has larger dirt had a chance to settle on the bottom of the tank? How often has it been cleaned out? Was it just filled? Did the bottom get churned up in the process? How full was the tank when your fuel was loaded into the delivery truck? There are many variables that can affect fuel cleanliness.

Delivery trucks: All the same issues that apply to stationary tanks also apply to tanker trucks, except that truck tanks never get a chance to settle. In addition, have you ever considered how much dirt gets into that tanker while it is delivering fuel to a customer, potentially a customer in an extremely dusty environment? As fuel flows out, air is sucked in to displace it. Is there anything protecting the inside of the tank from all the dust in the air? Generally not. Venting is typically completely unprotected.

Storage tanks: Onsite bulk storage tanks typically see less rapid turn-over than terminal tanks. In addition to those issues, yard and jobsite tanks can also develop serious problems with other sources of contamination, such as the ingress of dirt and water, condensation, rust, corrosion, microbial growth, glycerin fall-out and additive instability. Time and temperature become big factors affecting fuel quality.

Dispensing process: How far does your diesel need to travel between the bulk tank and the dispenser? The more pipe it runs though, the more potential there is for contamination. Are your dispenser nozzles kept clean? Are they ever dropped on the ground? Then what? What about the vehicles' fuel tank inlets, are they clean? Think about the extremely tight tolerances in your fuel system, then take another look at housekeeping issues. You will see them through new eyes.

Onboard fuel tanks: Contamination continues even after the fuel is in the equipment. What has that tank seen in the past? Has it been left stagnant for long periods? What kind of protection is there on the equipment's air intake vents? Heavy equipment does hard, dirty work.

Engines: Unfortunately, even if the fuel in your tank could be perfect, additional contamination is generated by the fuel system itself. Wear particles are created by mechanical friction. High heat and extreme pressure generated inside the modern engine, lead to coking and the creation of carbon products at the injector. Much of this internally produced particulate is returned to the fuel tank along with the unburned diesel.

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Water is the Enemy of Diesel Engines ( " All diesel contains some percentage of dissolved water. " )

Water has always caused rust and corrosion of fuel system components and infrastructure. Modern fuel systems are so much less tolerant than lower pressure systems, that manufacturers now specify zero free water must reach the engine.

DIRECT DAMAGE CAUSED BY WATER

Water causes damage to both fuel tanks and engine parts. Rust and corrosion in the tank create hard particulate that is passed along in the fuel, causing engine wear. Component life is also shortened by water etching, erosion, cavitation and spalling, such as:

injector
Rust: In contact with iron and steel surfaces water produces iron oxide (rust). Rust particles that get into the fuel, like other hard particulates, will cause abrasive wear to parts. Premature wear can cause part failures.

Corrosion: Corrosion is one of the most common causes of injector problems. Water combines with acids in the fuel to corrode both ferrous and non-ferrous metals. This is made worse when abrasion exposes fresh metal surfaces that readily corrode.

Abrasion: Water has lower viscosity than diesel, therefore providing less of a lubricating "cushion" between the opposing surfaces of moving parts. This leads to increased abrasive wear.

Etching: Etching is caused by water-induced fuel degradation which produces hydrogen sulfide and sulfuric acid that "eat" metal surfaces.

Pitting and Cavitation: Pitting is caused by free water flashing on hot metal surfaces. Cavitation is caused by vapor bubbles rapidly contracting (imploding) when exposed to sudden high pressure, which causes them to condense back into a liquid. These water droplets impact a small area with great force, causing surface fatigue and erosion.

Spalling: Occurs due to hydrogen embrittlement and pressure. Water is forced into microscopic cracks in metal surfaces. Then, under extreme pressure, it decomposes and releases hydrogen in a “mini-explosion” which enlarges the cracks and creates wear particles.

Ice: Free water in fuel can freeze, creating ice crystals that behave just like any other hard particulate. They can create wear in fuel systems and (in large volumes) clog fuel filters. A fuel filter's job is to protect the engine by stopping hard particulate. Engines and filters do not differentiate between dirt and ice. Damage caused by ice can be hard to correctly diagnose since the ice will melt and disappear long before a lab examination can occur.

INDIRECT DAMAGE CAUSED BY WATER

Water also contributes to or aggravates a number of additional issues, like the following:

Soft Solids: Water is polar. Certain chemicals in additives are polar. Hydrocarbons are non-polar. This means that water and polar chemicals are attracted to each other. In the presence of free water, the chemical molecules will sometimes disassociate themselves from the hydrocarbon chain of the additive and combine with water molecules to form a new substance. The new material is a soft solid that precipitates out of the fuel and can rapidly clog filters or create engine deposits.

Microbial Growth: Like most living organisms, bacteria and fungi (molds) need both food and water to survive. If free water is present microbial growth can proliferate, creating slimes that foul your fuel and acids that corrode your tank and fuel system.

Fuel Oxidation: Free water accelerates the oxidation process and encourages the formation of acids, gums and sediments known generally as fuel degradation products.

FORMS OF WATER IN DIESEL

saturated

All diesel contains some percentage of dissolved water. The water molecules remain part of the fuel until there are too many of them. The point at which the fuel can hold no more water is called the saturation point. The quantity of water in fuel is measured in ppm (parts per million). As long as the water stays below the saturation point as dissolved water it is typically not too much of an issue. Significant problems start when water separates from diesel and becomes free or emulsified water. Emulsified water is another form of free water; the droplets are simply so small as so well mixed into the fuel that they remain suspended rather than dropping to the bottom. There are no "droplets" when water is fully dissolved in fuel.

HOW DOES WATER GET INTO FUEL?
Water can come from a wide variety of sources, some of which can be extremely difficult to control.

On delivery from supplier
Free water fall-out (beyond saturation point)
Condensation in tank
Leakage into tank (rain, pressure washing, ground water...)
Ingress from atmosphere (humidity)
Human error (unprotected vents, fill ports, seals...)

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DIESEL ADDITIVES CAN STILL HARM ENGINES

Instability Can Create Solids in Fuel

sludge
Much of the world is required to use Ultra Low Sulfur diesel (ULSD).
With the removal of sulfur, fuel properties change radically, requiring the increased use of additive in order to meet specifications. In the
real world, maintaining these fuel properties can be a challenge. Diesel is tested at many points along the distribution channel, from refinery
to terminal to distributor to end user. Chemical additives are used to correct or enhance the fuel at each of these locations.

ADDITIVE DROP-OUT
Chemically speaking most additives are very similar to diesel itself (i.e. long chain hydrocarbons) so that they dissolve into the fuel. Additives are composed of a long hydrocarbon "tail" at the "head" of which there is another element, the one intended to have a beneficial effect on the diesel. This head typically contains atoms of nitrogen, oxygen, and/or sulfur in addition to carbon and hydrogen. Unlike the hydrocarbon tail, the head is polar. The beneficial element is intended to stay dissolved in the fuel so that it can do its job. Since head elements are polar, they have a strong tendency to want to escape from the non-polar hydrocarbons and associate with other polar substances such as water, metal, dirt, degradation particles or asphaltenes. You might think of them as being magnetically attracted to each other.

Sometimes, usually under adverse circumstances, the polar elements manage to come out of solution and form a bond with other polar elements. When this happens, there are two consequences:

The chemical may no longer be doing the job it was intended to do.
The chemical, now bonded with another substance, drops out of solution and turns into a soft contaminant in the fuel.

This phenomenon is most frequently observed in the presence of poor fuel storage conditions and fluctuating temperatures. Water, improper blending practices, and cold temperatures are leading contributors to these problems.

IMPACT ON ENGINES AND FILTERS
When unstable additive drops out of solution, it forms soft, sticky, solids which can cause rapid filter plugging and deposit formation. Engine manufacturers have observed injector deposits caused by these soilds, which are chemically identical to the substances found in many rapidly plugged filters, especially the high efficiency filters specified by OEs to protect HPCR systems.

The image to the right is of filter media at 1000x magnification under a scanning electron microscope (SEM).
The media was cut from a high efficiency filter of the type used in high pressure common rail fuel systems. This filter clogged in under 30 minutes of use. Between the media fibers you will notice a film. This kind of soft contaminant coats media as if it were covered in plastic wrap, effectively disabling the filter.

filterThe filter to the left has been completely disabled by soft contaminant. It looks clean because it did not have the time to become loaded with dirt. Instead, you will notice a sort of sheen, as if the filter media had been coated with wax. This is not due to wax (fuel gelling), but to soft contaminants that have dropped out of solution in the fuel. The pink color is red dye from off-road diesel. Upon further analysis, these soft contaminants were found to have chemical profiles identical to certain components of common diesel additives such as corrosion inhibitors, cold flow improvers, lubricity improvers and others. One thing that is important note, the root causes of this specific chemical instability are not yet completely understood. They are under rigorous investigation by Donaldson Company and other industry leaders.

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MICROBIAL BACTERIA IN DIESEL FUEL

Microbes Eat Fuel and Multiply

microbes
Microbes are present everywhere, but without food and water they cannot multiply; diesel is food. When there is free water in the tank, the microbes
have everything they need to grow, fouling fuel and damaging tanks in the process. By some estimates, a microbial colony can consume up to 1% of
your fuel investment, while destroying the rest.

MICROBES NEED FOOD AND WATER
Microbial colonies proliferate at the interface between fuel and free water
that has settled to the bottom of the tank. This creates a “rag layer” which gives them everything they need to thrive. Warm temperatures will accelerate the growth of microbial colonies. Microbial growth can occur in any diesel fuel. Biodiesel, being made from plant and animal fats, makes especially good food for these bugs and contributes to the increased incidence of biological growth problems seen in recent years. Bugs can grow in petro diesel as well. Stagnant fuel is especially at risk.

DEGRADED FUEL BECOMES UNUSABLE
With time the microbial colony proliferates beyond control. This leads to acid formation, rust, corrosion and filter plugging. Fuel degrades to the point that
it can form a slimy sludge that is unusable as fuel.
gross stuff
This process can occur in a bulk storage tank or in a piece of equipment that is left idle for a long period of time. To the right is a classic example of what is called filter “leopard spotting”, which requires the filter to be exposed to both microbes and water. The black spots are microbial colonies. Live or dead, microbes will clog filters and damage fuel systems. It is important to eliminate bugs completely and permanently.

MICROBIAL GROWTH vs. ALGAE
Microbial colonies, sometimes incorrectly referred to as algae, are actually bacteria or fungus. Algae needs light to live and grow, there is no sunlight in a closed fuel tank so algae cannot survive

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THE DEGRADATION OF FUEL OVER TIME

Diesel Fuel Has a Shelf Life

ULSD and biodiesel both have reduced stability in storage compared to traditional high sulfur diesel. While it is true that removing sulfur improves stability, the hydro-treating process also tends to destroy naturally occurring antioxidants. As a result, some ULSD fuels may require the addition of a stabilizer to prevent the formation of peroxides that lead to soluble gums. Shelf life recommendations for petro diesel and biodiesel blends are less than a year, and sometimes as low as 2 months, depending on factors below.

CONSEQUENCES OF UNSTABLE FUEL
Oxidative instability in petro diesel or biodiesel leads to the formation of fuel degradation products. These include:

Gums: sticky varnishes that contribute to corrosion and injector deposits, causing over or under fueling

Sediments: particulate that clogs filters and causes abrasive wear to fuel pumps and injector.

Acids: cause corrosion of tanks and fuel systems, leading to hard particulate formation and premature parts failure.

Thickeners: increase fuel viscosity, leading to incomplete combustion and reduced fuel economy

Common consequences of fuel degradation include loss of power, increased fuel consumption, premature filter plugging, damaged fuel pumps / injectors and increased maintenance costs. Generally speaking, fuel degradation decreases the combustion quality of fuel. You may notice symptoms such as black smoke, harder starts and reduced engine performance.

FUEL DEGRADATION IN STORAGE
Time is the enemy of diesel fuel quality. Oxidative instability can occur slowly during long-term storage or be accelerated by warm temperatures, the presence of free water and contaminants. This degradation can lead to high acid number, high viscosity and the formation of gums and sediment (fuel degradation products). Biodiesel is especially susceptible to the effects of higher temperatures. Data sets vary, but a good rule of thumb is that the oxidation rate increases 2.2 times for every 18°F/10°C.

Example: biodiesel blend stored at various temperatures
68°F/20°C: marginally OK after 6 months
77°F/25°C: degraded after 6 months
86°F/30°C: degraded after 4 months

Water in fuel can accelerate the oxidation process, but even worse are the effects of the microbial infestations that can grow as a result of water in the tank. These bacteria and fungi literally feed off your fuel, leaving behind acids and various forms of black, sticky, slimy materials that corrode your tank and plug your fuel filters. Whatever the contributing factors fuel degradation cannot be reversed, the key to success is to prevent it before it occurs with good fuel handling practices.

FUEL DEGRADATION ON VEHICLE

Fuel degradation can occur rapidly on-engine when excess diesel is heated to extreme temperatures inside high pressure common rail systems and then returned to the fuel tank along with black carbon particles created at the injector. High thermal stability is important for diesel fuel to function effectively as a heat transfer fluid inside the HPCR fuel system. Future injector designs are expected to employ even higher pressures and temperatures than today to achieve better combustion and lower emissions.

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Filters Capture More Than Dirt

frozen pipe
Cold weather operability can be a huge problem. Equipment won't start in the morning or even if it does, it might stop suddenly in the middle of a job. These issues are usually caused by solids created in the fuel as the temperature decreases.

Engines and filters do not differentiate between particles. Hard or soft, contaminant or pure hydrocarbon, solids in fuel will cause trouble. These problems are made worse by new-age fuels, the sensitivity of modern engines and the high efficiency required of filters designed to protect them.

ICE
When the weather turns cold, free water in fuel will freeze. Ice crystals will behave like any other hard particulate, loading in filters or causing abrasive wear to fuel systems. In large quantity, ice can completely block filters or pipes, preventing fuel flow. De-icers may be able to help get you running in an emergency situation, but adding alcohol to diesel is generally discouraged. Keeping free water out of the fuel is by far the best solution, learn more by reviewing solutions for water problems.

GELLING
Like water, hydrocarbons turn solid when they reach their "freezing" point. Unlike water, however, they do not turn into ice. Instead, they turn into a thick, waxy substance that cannot flow through filters. This is what is referred to as "gelling". It is a characteristic of both petro diesel and biodiesel. Diesel fuel is not one "thing". Instead, it is a complicated mixture of thousands of potential compounds, each with different chemical and physical properties. The particular formula is determined by the refinery at time of production. Typically about 250 different chemicals are included, mainly hydrocarbons. Precise freezing temperature varies widely from one hydrocarbon to another, which directly relates to winter operability issues. “Winter diesel” contains a blend of hydrocarbons with generally lower freeze points than “summer diesel”.

In some countries there is a classification of fuel called "Arctic diesel" for extremely severe conditions down to -40°F/C and below. An easy way to think of fuel "freezing" is to compare vegetable shortening to vegetable oil. Both are essentially the same thing, but shortening is solid at room temperature whereas oil is liquid. The same is true of hydrocarbons. At a given temperature, some may be liquid while others assume the soft, waxy state which is the ”frozen” or solid phase of hydrocarbons. This is commonly referred to as gelling.

WINTER FUEL
When cold weather threatens, refineries and distributors can and do improve diesel's cold weather operability properties in several different ways. They can:
Select less waxy crude oils upstream of the refinery
Extend the refining process to eliminate waxy elements with higher melt temperatures (i.e. they freeze at lower temperatures)
Dilute fuel with #no.1-D diesel or kerosene, which has lower wax content
Treat diesel with low-temperature operability additives (cold flow improvers)

Fuel suppliers manage hydrocarbon blends at the time and place of sale but cannot control unusual weather swings or fuel that is kept in storage or transported to colder climates. DO NOT add heating oil to your fuel in an attempt to lower the cloud point. This practice is strictly forbidden by most equipment manufacturers and may void your warranty.

PREDICTING COLD WEATHER OPERABILITY
There are a number of tests intended to predict the cold weather performance of a certain fuel. Their relative merits are the subject of some debate. No independent test data regarding their usefulness has been published since the advent of HPCR fuel systems, high efficiency fuel filters, ULSD and widespread biodiesel.

Cloud Point: When diesel cools, wax crystals begin to form and a noticeable white haze (or "cloud") appears. The wax drops out of solution and starts getting caught in fuel filters and lift pumps. Actual cloud temperature varies based on fuel characteristics. Some low quality fuels may have cloud points as high as 40°F/4°C, but most good quality fuels will have a cloud point around 32°F/0°C (untreated). As a rule, cold flow improvers do little to lower cloud point. There are some cloud point depressants that can significantly lower a fuel's cloud point, but their use is generally discouraged because they can actually work against the anti-gels that are intended to keep fuel flowing. The best way to lower cloud point is through the addition of a hydrocarbon with lower wax content such as #no.1-D diesel.

Cold Filter Plugging Point CFPP: This is the temperature at which wax crystals will rapidly plug fuel filters, starving the engine of fuel, preventing it from starting or stopping it cold (usually when least convenient). Cold flow improvers can depress CFPP by several degrees. They do not actually lower waxing temperature, but rather work on the wax crystal itself. They alter the size and shape of the crystals so that the fuel flows better and passes through filter pores at lower temperatures.

* A note of caution: Most cold flow improvers do not work as well in ULSD as they did in higher sulfur fuel. Be sure that performance claims are based on test results using ULSD. If not, they are irrelevant. The common test method for measuring CFPP is ASTM D6371. It was developed in 1965 and uses rapid cooling methods to determine the temperature at which 20cc of diesel will no longer flow through a 45 micron wire mesh in 60 seconds or less. A CRC (Coordinating Research Council) study in 1981 determined that CFPP is not an accurate predictor of real world performance. It tends to over-state minimum operating temperatures (i.e. cold weather performance in the real world is not as good as the test would make it appear).

Low Temperature Flow Test LTFT: This test (ASTM D4539) is considered to be somewhat more accurate at predicting the performance of additized fuels and is frequently recommended for North American heavy duty trucks. Instead of using an unrealistic rapid cooling method, this test method allows diesel to cool slowly (1°C per hour), which is much more representative of real world conditions. In this test 200cc samples are drawn through a 17 micron mesh screen using 20 kPa vacuum. The LTFT point is determined when 90% of the sample no longer passes through the screen in 60 seconds or less. Although deemed more accurate than the CFPP test at predicting cold weather performance in North America, the LTFT uses a 17 micron mesh screen in determining acceptable flow. This is finer than the 45 micron mesh used for CFPP, but one can still reasonably question its ability to predict fuel flow through the high efficiency 2 micron filters used to protect today's HPCR engines.

Pour Point: The temperature at which diesel freezes is called its pour point. At this temperature fuel will freeze solid in lines. Pour point is irrelevant in terms of predicting cold weather operability because it is lower than cold filter plugging point. If fuel cannot pass through filters to the engine, the vehicle will not run. In the absence of other complications, gelled or cloudy diesel should clear as it warms. The wax crystals will dissolve back into solution and the fuel will once again be perfectly liquid. If the fuel does not clear when warmed, then another factor is at work in addition to cold temperatures. Most likely additional chemistry is present and a reaction has taken place creating soft solids that do not melt at normal operating temperatures.

GLYCERIN
Gelled fuel and glycerin solids are frequently confused with one another. But while gelled fuel is a natural phenomenon caused by cold alone, glycerin is an entirely different chemistry that is only present in biodiesel. Glycerin and other related substances (glycerols) are byproducts of biodiesel production and are not found in petro diesel. Regulations require the removal of virtually all these materials, but even at very low levels they can immobilize a fleet. As long as glycerin remains warm and liquid, it generally causes no immediate problems. At low temperatures, however, glycerin assumes a solid waxy state. It drops to the bottom of tanks, gets caught in fuel filters, and forms sticky, corrosive engine deposits.

Glycerin can turn solid at relatively high temperatures, sometimes as high as 55°F/13°C or above. Unlike standard gelled fuel, glycerin typically does not re-liquefy when the temperature goes back up. Once solid, glycerin tends to stay solid, even at high ambient temperatures. This container of in-spec B100 was completely liquid until it was cooled off in a refrigerator at 40°F/4°C. At that temperature, a solid lump of glycerin formed and settled to the bottom. This solid did not re-liquefy, even when it was heated well beyond normal on-equipment fuel temperature. Although the origins are somewhat different, many of the consequences of glycerin and gelling are the same. Cold weather causes soft solids to form, small quantities of which clog fuel filters and prevent fuel flow. This prevents engines from starting or stops them due to fuel starvation. In cold climates, more and more indoor garages are being built so that fleets can be parked inside over night to be sure the vehicles start in the morning.

CONSEQUENCES OF SOFT SOLIDS

cold glycerin

Soft waxy solids will rapidly disable filters, regardless of the age of a filter. Where will these solids form? If fuel is delivered cold, then solids may be pumped into your tank by the supplier. If the fuel cools off in the bulk tank, then solids can fall out at that point. If your diesel doesn't get cold until it is already in the onboard fuel tank, then that is where it might solidify. Wherever they form, soft solids will quickly clog the first filter they encounter.

The image to the right is an extreme case of a filter clogged with glycerin. Usually you will see nothing this dramatic. Instead, your filter will likely appear clean, with only a faint waxy sheen to the media or a small amount of deposit in the bottom of the filter can. Here you see images of cellulose, average efficiency filter media under a Scanning Electron Microscope.

celulouse

The first image to your left is of clean cellulose media. Notice the free,
darker, areas between the fibers.
”SEM"

The second image, to your right, is cellulose and glass media of the type used in primary onboard fuel filters. The areas between fibers have been completely clogged with glycerin. It can take only a few spoonful's of solidified glycerin or other soft solids to completely disable a fuel filter.

Onboard cellulose

The final image, to your left, is relatively low efficiency cellulose media of the type sometimes used on fuel dispensers. It also is caked over with glycerin. Nothing will flow through a filter clogged with glycerin. Luckily for the equipment owner, this soft waxy glycerin was caught and prevented from reaching the engine. The unfortunate consequence, however, was that these filters likely had very short lives.

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Why Diesel Injectors Fail

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the following text taken from:

http://www.trucktrend.com/how-to/expert-advice/1211dp-why-diesel-fuel-injectors-fail

to view site included pics .. visit the above link

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Diesel injectors fail because of two main reasons. The first has to do with the mechanical soundness of the injector structure, and the second has to do with the quality of the fuel running through the injector. In order to get an understanding of the workings of an injector (and what actually makes them fail), we contacted Exergy Engineering. The company supplied us with many of the images of failed injectors you see here, taken with a microscope, to help you to keep this damage from happening to your diesel.

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Is There a Fuel Injector Problem?

If proper maintenance is performed and problematic practices are avoided, the vast majority of diesel owners will go thousands of trouble-free miles without a problem. If you’re a diesel owner with an older engine (pre-common-rail), most of this article (besides the general maintenance advice, like changing your fuel filter regularly) doesn’t apply to you. This is because older diesel injection systems only use about 1⁄2 the fuel pressure modern engines do, and older injectors send the fuel through much larger passages.

Why is there such a difference with common-rail injectors? Modern common-rail diesel injectors can fire two or three times per engine cycle—this doubles the wear on the injector compared to diesels of the past. To tell if there is a problem with common-rail injection systems fueled with ultra-low-sulfur diesel (ULSD) fuel, we need to know how many injectors have failed since its introduction. The feedback we get from our readers and online reports of failures suggests there’s always room for improvement in our fuel, too.

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Diesel Fuel Failures

According to Afton Chemical’s North American Marketing Manager, David Cleaver, there are three major causes of injector failure associated with the properties of the fuel itself: excess wear, abrasion, and deposits.


Excess Wear

One mode of injector failure is excess wear. Prior to 2006, diesel fuels in the United States contained relatively large amounts of sulfur. This sulfur is found in the crude oil that gets refined into diesel fuel. The sulfur in the fuel was used as a natural lubricant for the fuel system. Ultra-low-sulfur diesel (ULSD) was gradually introduced into the United States because sulfur ruins diesel particulate filters (DPFs). Ultra-low-sulfur diesel is now mandated in all diesel fuel segments, including on-highway, off-highway, and railroad. Ultra-low-sulfur diesel has a maximum allowable sulfur content of 15 parts per million (ppm). As refiners removed this sulfur, the lubrication benefits went away as well. As a result, diesel fuel refineries now put additives in the fuel to restore lubricity.

The standard for measuring this lubricity is called the High Frequency Reciprocating Rig (HFRR) Test, ASTM D-6079, which measures the size of a wear scar between two metal surfaces lubricated with the fuel. The less lubrication the fuel provides, the larger the wear scar. The maximum allowable wear scar in the United States is 520 microns (460 microns in Canada). Many fuel distributors add additional lubricity improvers to the fuel to limit premature wear.


Abrasion

While fuel lubricity is an important factor in determining the wear characteristics of the fuel injection system, it is not the only fuel-related cause of excess wear. The other potential cause of premature injector failure (due to wear) is caused by abrasion. All fuels contain small amounts of impurities—even the highest-quality diesel fuels. Some of these impurities include very small (a few microns in size) particles that can pass through even the tightest onboard vehicle filters. If the fuel contains a large amount of these small, insoluble particles, over time they can abrade the injectors as they pass through during normal engine operation. In extreme cases, this abrasion can significantly alter the fuel spray pattern, causing reduced engine performance. In severe cases, it can even lead to injector failure. Good housekeeping practices by the fuel supplier, and good fuel filtration, can reduce the damage caused by this abrasion.


Deposits

While excess wear (whether caused by poor fuel lubricity or abrasion) is important to consider when discussing the cause of injector failure, Afton Chemical says the major reason for injector failure today is due to excessive buildup of deposits. There are two major types of these deposits: external injector deposits and internal injector deposits

External injector deposits are generally caused by incompletely burned fuel that builds up around the injector holes. These deposits are referred to as coking deposits. While in most cases these deposits may not lead to injector failure, they can build up enough to disrupt the fuel spray, which leads to less efficient fuel combustion. This is often observed by the vehicle operator as a noticeable loss in power or lost fuel economy. Detergent additives have been used quite successfully to help control these external deposits and restore the injector to its most efficient performance—restoring both the lost power and lost fuel economy caused by the buildup of these external deposits.


Internal Diesel Injector Deposits

In the last five years, a new type of injector deposit has begun to appear, according to Afton Chemical. This deposit does not form on the external tips of the injectors, but rather on the internal parts, such as the injector needles and pilot valves. These deposits often look similar to the coking deposits (dark brown in color) but can also be very light, almost grayish to off-white in appearance. While they can form in virtually any type of diesel engine, they typically only cause operational issues in the newer engines with precision injection systems.

Engine manufacturers are now offering injection systems that operate at very high injection pressures (greater than 30,000 psi in some cases) that supply fuel to all injectors through a common fuel rail. These engines are often referred to as high-pressure common-rail (HPCR) engines. They were designed to supply the demand for more powerful diesels while still meeting ever-tightening emission regulations.
Injection pressures near 30,000 psi create a very fine fuel mist spray in the combustion chamber, resulting in more complete burning of the fuel. This more complete fuel burning yields lower emissions and can also improve fuel economy. In order to maintain these high injection pressures, the injector assemblies have been highly engineered and have very tight clearance tolerances, sometimes as small as 1 to 3 microns (a human hair is typically 70 to 100 microns thick). So you can imagine it wouldn’t take much material depositing on these parts to cause poor injector needle actuation, leading to poor engine performance. In extreme cases, these deposits can lead to complete sticking or seizing of the injector needles, particularly after the vehicle has been shut down and the engine has been allowed to cool.

As these internal deposits build up, they can cause the same symptoms as the more traditional external coking deposits, namely lost power and reduced fuel economy. In extreme cases in which the injectors begin to completely stick, they can lead to excessive vehicle downtime and high maintenance costs.

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Mechanical Failures

According to Exergy Engineering, injectors fail because of five major reasons. We listed them here, along with the indicators of the problem, the causes, and how it’s prevented.

Failure: High Internal Leakage or Return Flow

Indicators:

1. Engine is hard to start (requires increased cranking time in order to start)
2. Low common-rail pressure codes

Causes:

Worn injector ball seat
Leaking cross feed tubes (Cummins)
Blown internal high-pressure seal
Incorrect nozzle needle clearance
Cracked nozzle body
Cracked injector body

Prevention:

Keep fuel system clean, change fuel filters, purchase fuel from reliable sources, avoid filling from portable construction fuel tanks

Avoid overly aggressive tuning that increases rail-pressure and injector pulse widths and do not remove pressure-limiting devices from the system

Do not use remanufactured or aftermarket injection components that are not properly designed or manufactured

Reject all fuel system replacement parts that have metallic burrs

Use only Bosch nozzles, as they are reported to have superior crack resistance

Do not mix nozzle needles, because they are matched to the body and moving one from another can result in excessive clearance or improper needle lift

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Failure: No Injection

Indicators:

Balance rates are high (positive), indicating fuel is being added to the cylinder because the computer thinks the fuel injector is not flowing enough. The computer makes this decision based on the two things it knows: the rotational speed of the crankshaft and the amount of fuel delivered. If the crankshaft is not spinning as fast as the computer thinks it should (or is spinning faster than it should), fuel (via pulse width) is added or taken away to even out crankshaft acceleration from each injector firing.

Cylinder contribution low (cylinder contribution test is performed by shutting off one injector at a time while taking note of drop in engine RPM)

ECU fault codes

Causes:

Debris or rust in the injector plugging the nozzle
Armature and/or nozzle needle stuck
Bad stator (rare)
Loss of cylinder compression or other mechanical problem

Prevention:

Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources

Do not use remanufactured or aftermarket components that are not properly designed or manufactured

Reject all fuel system replacement parts that have metallic burrs

Avoid tying the returns from multiple high-pressure pump kits and injectors to a single return line; excessive return pressure acting on the injector stators can lift them (and in extreme cases blow them off), shutting the injector down

If a long storage time of the vehicle is expected, arrange to have it started on occasion to prevent internal varnishing and corrosion of internal components; aftermarket fuel additives specifically designed for stabilizing diesel fuel should also be added

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Failure: Excessive Injection

Indicators:

Excessive smoke at idle, poor running, and banging

Balance rates high (negative), indicating the computer is removing fuel from the injector

Cylinder contribution test is high, meaning as each injector is activated one will increase engine rpm more than normal

Excessive exhaust gas temperature

Engine damage from excessive heat or hydraulic lock from excessive fuel in the cylinder

Causes:

Worn ball seat in injector or poor end of injection cut off
Nozzle needle seat worn or damaged
Debris in control system of injector, which holds it open
Debris in nozzle needle seat holding it open
Cracked nozzle from overpressure, or overheated nozzle from improper installation of injector

Prevention:

Replace worn and high-mileage injectors; do not use these injectors as a foundation for building a high-output injector set

Replace worn nozzles
Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources
Reject all fuel system replacement parts that have metallic burrs
Do not use remanufactured or aftermarket components that are not properly designed or manufactured

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Failure: Incorrect Injection Rate

Indicators:

Rough running and poor cylinder balance

Large cylinder-to-cylinder exhaust temperature variation

Causes:

Poor nozzle flow balance
Nozzle needle lift incorrect (mixed or missing parts)
Partially plugged nozzle
Wire-brushed nozzles

Prevention:

Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources

Reject all fuel system replacement parts that have metallic burrs
Do not use remanufactured or aftermarket components that are not properly designed or manufactured

Ensure injectors are serviced or purchased from a reliable source

Do not clean nozzles with a wire brush

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Failure: Incorrect Injection Timing and Duration

Indicators:

Rough running, poor cylinder balance, and knocking
Piston damage
Large cylinder-to-cylinder exhaust temperature variation

Causes:

Ball seat wear
Incorrect injector assembly, parts mixed, or parts missing
Injector needle lift increased to increase output

Prevention:

Replace worn injectors
Ensure injectors are serviced, tested, and purchased from a reliable source

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Sources

Afton Chemical
http://www.aftonchemical.com

Exergy Engineering
http://www.exergyengineering.com
 
the following text be from ..

td4 / m47r engine faults :

http://tuning-diesels.com/75Zt/R75faults.htm

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5) INJECTOR ISSUES (relatively rare below 100k miles but have been know to occur at much lower mileage*)

These wear out and should be regarded as a potential service item and not just investigated as a 'last resort'. *They are far more likely to give problems if the car has been run with petrol in the tank or on veg oil or poor quality biodiesel.

Symptoms range from poor starting, worse when hot, uneven idle, poor performance, cutting out on full throttle, occasional white smoke & loud engine rattle. Any tuning product whether plug-in box or remap will make matters worse as it highlights the fuel pressure problem cause by worn and / or leaking injectors.

Usually a seal within an injector fails, allowing fuel to escape into the return pipe. This short circuits the rail pressure and prevents it reaching the 220bar required to activate the injectors at cranking speed. If the engine starts using Easy Start or a tow, then this can confirm injector leak back due to the higher engine speed generating enough pressure to overcome the leak. If the leak is excessive, insufficient fuel is left to supply the engine under full throttle and performance suffers and the ecu may stop the engine if the fuel pressure does reach the expected level. (usually at or over 3k rpm)

LEAKBACK TESTING

PLEASE NOTE, there seems to be some confusion on testing for leakback as opposed to checking for injector flow equality.

Leakback is unwanted leaking of fuel past the seals and out of the return orifice and causes bad starting and is done by CRANKING THE ENGINE ie not letting it start. During cranking the pressure must reach at least 300bar or the injectors will not open so there must be negligible leakback. You can often confirm leakback by tow starting or using Easystart - the higher engine speed produces a higher pressure which overcomes the leak and so the engine then starts.

When the engine is running there is always some surplus fuel issuing from the injector returns THIS IS NOT LEAKBACK hence the need to distinguish between testing during cranking and testing with the engine running.

To identify a faulty injector(s) (which can be serviced) unplug the electrical connectors and cam sensor, disconnect the returns (Tee pieces on the top of the injectors), and plug the end of the return pipe (or fuel will spray everywhere as it also carries return fuel from the injection pump and back flow from the fuel pumps).

Crank the engine and look for fuel issuing from the injector returns - there should not be any from a good injector. The fault code 'rail pressure too low' is often logged. This is the first of two known faults covered by Bosch on their common rail training course.

Checking injector flow equality is done with the engine running and collecting the surplus fuel from the returns over a period of time and comparing the volumes. They should of course be near enough equal for smooth running. If not, they need a complete service. DO NOT JUST HAVE THEM ULTRASONICALLY CLEANED THIS IS A WASTE OF TIME & MONEY.

The internal valving may also fail and the nozzle orifices can become clogged or worn so leak back is NOT the only fault. If the valving is faulty white or grey smoke smelling strongly of unburnt fuel will occur on large throttle openings and the engine can stop. Poor spray pattern gives uneven running and misfires, often the mpg will drop.

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d.i.y. LEAKBACK TESTING ..
see this pdf link:
http://www.uniteddiesel.co.uk/docs/...ecking-back-leakage-1398762965-1401121695.pdf


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from the 'Bosch' site:

http://www.choosetherightinjector.com/why-injectors-fail

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Why Injectors Fail

The key causes of injector failure are:

Poor Fuel Filtration
Fuel Contamination
Incorrect Installation
Non-OEM approved remanufactured products

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Poor Fuel Filtration

A common problem with diesel injectors is erosion of the control valve. The heart of the common rail injector is the valve through which fuel passes at extremely high pressure. The passage opening is sealed using a pressurized ball that is only 1mm in size. A proper seal is critical for exact injector performance. Abrasive contaminants, released by inadequate filtration, can erode and damage the control valve and not allowing the ball to seal.

This can lead to:

Excessive smoke
Starting or idling problems
Potential engine failure

What Can I Do?

To ensure exact performance within the designed service life of the injector, use only OE filters or filters having the same OE micron rating and follow the recommended OE filter change interval. Using anything less can cost you more in the long run.

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Fuel Contamination

The majority of diesel engine problems stem from contaminated fuel. Common problems include:

Corrosion from excessive water in the fuel. Two ways water can get into the fuel:
Through the delivery system
Through the tank vent
Micro fine particles in the fuel
Improper fuel storage, which is caused by water in the fuel

What Can I Do?

Always purchase fuel from a reputable service provider and use a proper fuel/water separator. Periodic inspection of the vehicle’s tank vent is also recommended.

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Incorrect Installation

Missing sealing rings, incorrect tightening torque, incorrect cleaning of the nozzel can cause:

Poor performance
Misfiring
Black smoke
Check engine light (MIL) to come on
What Can I Do?

Always follow the engine manufacturer’s maintenance procedures and have repair work done by a reputable shop.

Non-OEM Approved Remanufactured Products

Not all remanufactured injectors are the same. The quality of any remanufactured injector depends on the remanufacturing process and components. Some manufacturers sell refurbished/used injectors and market them as rebuilt. However, instead of being rebuilt, they are merely cleaned and polished, and the tips are not replaced. You might get a great deal on these non-OEM approved products, but you are taking a huge risk that these injectors may not be better than the one you are trying to replace.

What Can I Do?

Make sure your car is being serviced by a reputable shop and ask about the parts they use on your diesel engine to ensure they are from an OEM approved supplier.

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Bosch’s remanufactured injectors are exactly the same as OE injectors in design, engineering, materials, manufacturing and quality control. Bosch remanufactured injectors include all OE updates, so they can often be superior to the OE injectors that they replace.

If you are purchasing your own injectors, you should purchase from a reputable, OE endorsed manufacturer. If considering injectors from a non-OE endorsed manufacturer, be sure to ask the following questions to determine if the cost savings is worth the risk:

Do these injectors use new or reconditioned components?
It is preferred that the remanufactured injector use all new high-wear components vs. salvaged components.
How are the remanufactured injectors tested?
You want injectors that are tested to exact OE test specifications and not reverse engineered specifications.
What type of testing equipment is used?
It is preferable that their testing equipment is certified by the OEM.
The test equipment should not be something they build themselves.
It should be traceable back to a standard.
Is there a warranty?
Many reputable manufacturers offer at least a one-year warranty.
Are the remanufactured/rebuilt injectors upgraded to meet new OE specs?
Are component improvements added to match changes made by the engine manufacturers?

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further reading:

http://yadda.icm.edu.pl/yadda/eleme...1ac-4c1a-8f5b-a3bd7cf0073a/c/ignaciuk_gil.pdf

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my choice for the fuel system be :

using an OEM fuel filter
draining the sedimenter at least once ( or twice ) a year .. usually just before winter sets in
sourcing fuel from a reputable retailer
use of a fuel additive that .. cleans / lubricates / combats water / kills 'diesel bug' microbes

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couple more links ..

http://www.uniteddiesel.co.uk/docs/faqs/bosch-common-rail-diesel-injectors-blow-by-1398762998.pdf

regarding 'bore wash' in the above link :
in short .. that's when too much fuel gets into .. and remains in .. the cylinder bore
the fuel washes out piston ring lubricating oil resulting in advanced wear of the cylinder bore
and piston rings ..
when i got my artic-lorry (semi-truck) license (usa '76) .. we were taught that when idling the engine for long periods .. e.g. overnight in freezing weather .. to raise the idle rpm to 1000rpm or above ..
this was mainly to avoid 'bore wash' .. and to keep up the oil pressure ..

http://www.uniteddiesel.co.uk/docs/faqs/problems-with-fuel-1398763238.pdf

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( 13th nov. 2015 .. edited to add )

couple of vids showing how the bosch injectors operate :

injector internals:


How Bosch Piezoelectric Diesel Injector Works:


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