Jason Thompson @ Diesel Power Mag is working on (or already completed?) an article on why injectors fail (Most of the info pertains to CRs particularly).
Here is a link to the blog where you can see a sneak preview of the article's info (which is sourced from Exergy Performance):
http://blogs.dieselpowermag.com/6777890/diesel-engines/why-injectors-fail/
I'll copy and paste it here too, since I feel the info in the article is germane to this threads topic.
The November issue will have an article called "Why Injectors Fail." We crammed as much information into it as we could but here is a little that wouldn't fit. Fuel injector science is more impressive than rocket science. The picture was taken with a microscope. It's of a washed out ball seat caused by aggressive tuning:
Normal Injector Firings During Average Lifetime
Based on algorithm below, plug in the numbers for expected number of miles and number of injection events per engine cycle to get to number of firings in a lifetime.
# miles /lifetime x avg speed x 60min/hr x avg engine rpm x # injections per engine rev (2 stroke or 4 stroke) = Number of injections per lifetime
Example – 140,000 miles/life x 1 hr/33 miles x 60min/hr x 1300 rev/minute x 2 injections/2 engine rev (pilot and main 4 stroke) = 330,000,000 injections /life
We sometimes long for the days when diesels were simpler and less picky. We ask so much from our current diesels its amazing they last as long as they do. It's all thanks to the people who designed these systems.
Average life of various light duty Diesel Injection systems. Keep in mind this is “average” and each system has its own set of operating parameters such as number of injections per engine cycle, operating pressure, EGR or no EGR, and targeted emission standards. “Your results may vary”
5.9 and LB7 injectors – 140,000 miles
LBZ/LMM injectors – 175,000 miles (tougher injector but more injection events than 5.9/LB7)
HEUI injectors (7.3 pick-ups) 150,000 (single injection event, limited use of PRIME split injection device)
CP3 pumps – 200,000 miles
Older systems
12v/24v injectors – varies
VP44 pumps – 125,000 miles
Inline P and M Pumps – 175,000
2- Normal Temp at nozzle – Max allowed 300 deg C (572F)
3- Sled Puller temp at Nozzle - Less that 537 Deg C (1000 deg F) otherwise nozzle starts to soften (annealing point of typical Bosch nozzle material)
4- Normal pressure at nozzle (peak firing pressure of cylinder and injection pressure)
Cylinder firing pressures – 16-18 Mpa (2300 to 2600 psi)
Injection pressures at nozzle – Common Rail systems 160 to 200 Mpa (23-29,000 psi) Older systems 80 to 100 Mpa (11-15,000 psi)
Note – Heavy Duty (Class 8 trucks for example) have been running injection pressures in excess of 30,000 psi for years using Unit Injector and Unit pump systems. Cost is not as great a problem as light duty and fuel economy is king.
5 – Sled Puller pressure at nozzle (peak firing pressure of cylinder and injection pressure)
Cylinder firing pressures – We have measured over 31Mpa (4500+ psi) in dyno testing
Injection pressures at nozzle – Common Rail systems 180 to 220 Mpa (26-32,000 psi) Older systems unknown
Information Courtesy of Exergy Performance
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Information Courtesy of Afton Chemical
Q: What are the sources of the internal deposits?
A: Through cooperation with engine and vehicle manufacturers, Afton
Chemical has performed extensive engine testing and chemical analysis of field deposits from all over the world. Using sophisticated analytical chemistry techniques, two categories of deposits have been identified to
date: 1) carboxylate salts, sometimes referred to as ³waxy deposits² or ³salt deposits² and 2) organic amides, sometimes referred to as ³polymeric² or ³lacquer² deposits.
The carboxylate salt deposits are formed from the reaction of sodium ions with carboxylic acids. Sodium ions can come from the base fuel or additives put into the base fuel. For example, in certain areas of the world, sodium nitrite corrosion inhibitor may be used for pipeline corrosion protection. One way to avoid the formation of these salts is to limit the amount of sodium in the diesel fuel.
There are various sources of the carboxylic acids. Afton has concluded that DDS (dodecenyl succinic) acid and HDS (hexadecenyl succinic) acid corrosion inhibitors are the primary sources of the salt deposits found in the U.S. and some parts of Europe. A detailed summary of the investigation that led to this conclusion can be found in SAE Paper 2010- 01-2242 published by SAE InternationalTM. Afton has also concluded that sodium hydroxide, an aggressive caustic (basic) chemical present within the sodium nitrite corrosion inhibitor, will degrade lubricity improvers, biodiesel and some PIBSI- type detergent additives to form other carboxylate salts.
The source of the second type of internal deposit, organic amide, has been much more difficult to identify. Using chemical analysis and engine testing, Afton has concluded that these deposits are formed from low molecular weight, polar materials found as contaminants (production
by-products) in some diesel PIBSI-type detergent additives. Afton has been successful duplicating the organic amide deposit chemistry and diesel injector sticking on an engine test when these contaminants are added to the test fuel.
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Injectors fail because of two main reasons. The first has to do with the soundness of the mechanical structure of the injector and the second has to do with the quality of the fuel. In order to get an understanding of the workings of an injector and what actually makes them fail we contacted Exergy Engineering. They empowered us with images of failed injectors taken with a microscope and some information on how you can keep it happening to your diesel. In order to find out as much as we could about the fuel side of the equation we contacted Afton Chemical a company who specializes in fuel additives. Afton has 85 years worth of experience working with the OEMs and fuel companies. By leveraging both of these companies expertise we hope to make fuel injector problems a thing of the past.
Is There a Fuel Injector Problem?
If proper maintenance is performed and problematic practices avoided the vast majority of diesel owners will probably 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 items for example changing your fuel filter regularly) doesn’t apply to you. This is because older diesel injection systems only use about a quarter of the pressure and much wider tolerances compared to new systems. Just think of your bathtub as an example. What clogs first the shower head or main spigot? In order to tell if there is a problem with common rail injection systems fueled with ULSD (ultra low sulfur diesel) fuel we need to know how many injectors have failed since its introduction. Right now this failure rate is unknown, but from anecdotal reports of failures we know there is always room for improvement.
Sidebar: 1
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:
1. Worn injector ball seat.
2. Leaking cross feed tubes (Cummins).
3. Blown internal high-pressure seal.
4. Incorrect nozzle needle clearance.
5. Cracked nozzle body
6. Cracked injector body
Prevention:
1. Keep fuel system clean, change fuel filters, purchase fuel from reliable sources, avoid filling from portable construction fuel tanks.
2. Avoid overly aggressive tuning that increases rail pressure and injector pulse widths and do not remove pressure limiting devices from the system.
3. Do not use remanufactured or aftermarket components that are not properly designed or manufactured.
4. Metallic burrs have no place on any fuel system component and reject any component that has them.
5. Use only Bosch nozzles as they have superior crack resistance. No other aftermarket nozzle comes close.
6. Do not mix nozzle needles because they are matched to the body and moving one from another can result in excessive clearance and or improper needle fit.
Failure: No Injection
Indicators:
1. Balance rates are high (positive) indicating that 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 is added or taken away to create balance. Loss of cylinder compression is also possible with a high (positive) rate.
2. Cylinder contribution low (cylinder contribution test is performed by shutting off one injector at a time while taking note of drop in engine RPM)
3. ECU fault codes
Causes:
1. Debris or rust in the injector plugging the nozzle.
2. Armature and or nozzle needle stuck
3. Bad stator (rare)
Prevention:
1. Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources.
2. Do not use remanufactured or aftermarket components that are not properly designed or manufactured.
3. Metallic burrs have no place on any fuel system component and reject any component that has them.
4. 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.
5. 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.
Failure: Excessive Injection
Indicators:
1. Excessive smoke at idle, poor running, and banging
2. Balance rates high (negative) indicating the computer is removing fuel from the injector.
3. Cylinder contribution test is high meaning as each injector is activated one will increase engine RPM more than normal.
4. High exhaust gas temperatures.
5. Engine damage from excessive heat or hydraulic lock from excessive fuel in the cylinder.
Causes:
1. Worn ball seat in injector or poor end of injection cut off.
2. Nozzle needle seat worn or damaged.
3. Debris in control system of injector, which holds it open.
4. Debris in nozzle needle seat holding it open.
5. Cracked nozzle.
Prevention:
1. Replace worn and high mileage injectors. Do not use these injectors as a foundation for building a high output injector set.
2. Replace worn nozzles.
3. Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources.
4. Metallic burrs have no place on any fuel system component and reject any component that has them.
5. Do not use remanufactured or aftermarket components that are not properly designed or manufactured.
Failure: Incorrect Injection Timing and Duration
Indicators:
1. Rough running, poor cylinder balance, and knocking.
2. Piston damage.
3. Large cylinder to cylinder exhaust temperature variation.
Causes:
1. Ball seat wear.
2. Incorrect injector assembly, parts mixed, or parts missing.
3. Injector needle lift increased to increase output.
Prevention:
1. Replace worn injectors.
2. Assure injectors are serviced or purchased from a reliable source.
Failure: Incorrect Injection Rate
Indicators:
1. Rough running and poor cylinder balance.
2. Large cylinder to cylinder exhaust temperature variation.
Causes:
1. Poor nozzle flow balance.
2. Nozzle needle lift incorrect (mixed or missing parts).
3. Partially plugged nozzle.
4. Wire brushed nozzles.
Prevention:
1. Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources.
2. Metallic burrs have no place on any fuel system component and reject any component that has them.
3. Do not use remanufactured or aftermarket components that are not properly designed or manufactured.
4. Assure injectors are serviced or purchased from a reliable source.
5. Do not clean nozzles with a wire brush.
Sidebar 2:
Afton Chemical’s North American Marketing Manager David Cleaver responds to our question “Why Do Injectors Fail?”
There are two major causes of injector failure associated with the properties of the fuel itself: excess wear and deposits.
Excess Wear
One mode of injector failure is excess wear. Prior to 2006, diesel fuels in the United States contained relatively high amounts of sulfur. This sulfur comes from the crude oil refined into the fuel. This sulfur in the fuel acted as a natural lubricant for the fuel system. Ultra Low Sulfur Diesel (ULSD) was gradually introduced into the market and is now mandated in all diesel fuel segments including on-highway, off-highway, and railroad. ULSD has a maximum allowable sulfur content of 15 ppm. As refiners removed this sulfur the lubrication benefits went away as well. As a result additives are now used to restore lubricity. The standard for measuring this lubricity is 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 on-board 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 them during normal engine operation. In extreme cases, this abrasion can significantly alter the fuel spray pattern, causing reduced engine performance, and even increased downtime and maintenance due to severe abrasion. 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, the major reason for injector failure today is due to excessive buildup of deposits. There are two major types of deposits: external injector deposits and internal injector deposits. External injector deposits generally are 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 (IDID)
In the last 5 years, a new type of injector deposit has begun to appear. This deposit does not form on the external tips of the injectors, but rather on the internal parts like the injector needles and pilot valves. These deposits often look similar to the coking deposits (dark brown in color), but also can 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 highly engineered 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 help meet the ever-tightening emission regulations engine manufacturers must meet. The extremely high injection pressures 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 – 3 microns (a human hair is typically 70 – 100 microns thick). So, you can imagine that it would not 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 where the injectors begin to completely stick, they can lead to excessive vehicle downtime and high maintenance costs.
