All experienced technicians will likely agree that modern diesel fuel injectors and filters have not kept pace with developments in diesel fuel injection technologies, since injectors and filters don’t seem to last as long as they used to. However, the fact is that diesel filters clog and injectors fail because the cleanliness of diesel fuel has not improved during the last two decades, and while there is not much that we as technicians can do about that, there is much we can do to minimise the impact of dirty diesel fuel on our customers’ vehicles. In this article, we will take a closer look at some best on-board diesel fuel filtration practices to follow to keep our customers’ vehicles running, starting with-
Most jurisdictions subscribe to the ISO 4406:1999 diesel fuel cleanliness standard, which was adopted when the Worldwide Fuels Charter was established in 1998. However, while most vehicle manufacturers now subscribe to this standard, several enormous technological advances in both engine and fuel injection technologies require fuel cleanliness standards that exceed current standards by several orders of magnitude. Consider the facts in the table below-
|
Injection Method |
Injection Pressure |
Fuel Viscosity |
Fuel Injector Clearances |
Cleanliness Standard |
|
Electronic Unit Injection |
1 100 bar |
1-4 Centistokes |
5-8 microns |
18/16/13 |
|
High Pressure Common Rail |
2 400 bar |
1-4 Centistokes |
1-4 microns |
18/16/13 |
From this is it clear that even though injection pressures have more than doubled and injector clearances have reduced by about 50%, fuel cleanliness standards have remained the same. Here is what this particular cleanliness code means-
The ISO 4406:1999 standard includes a wide range of codes, each consisting of three numbers that are used to quantify, or describe the maximum allowable range of sizes of solid particle contaminants in a 1-millilitre sample of diesel fuel. In the example above, the three numbers mean the following-
According to the ISO 4406:1999 standard, this particular set of numbers means that each millilitre of fuel can contain between-
Modern diesel fuel injectors inject fuel through laser-cut orifices that are considerably bigger (about 100 microns and smaller) than the biggest allowable particles in this example. However, the clearances between moving parts in modern diesel fuel injectors and injection pumps are as small as, or smaller than the smallest allowable particles (4 micron) in diesel fuel, which means that if fuel filtration is poor, both injectors and pumps are almost certainly damaged on a continuous basis.
In fact, the majority of diesel fuel injector manufacturers recommend ISO cleanliness codes of between 15/12/10 and 12/9/6, which as a practical matter, is more than 60 times cleaner than our 18/16/13 example. This level of filtration is only possible to achieve with OEM diesel filters, or very high quality aftermarket diesel filters such as those supplied by Ryco, which brings us to-
In order to understand the need for diesel fuel filtration best practices, we first need to understand how diesel fuel filters are rated, and what these ratings mean. In practice, diesel fuel filters come in three varieties-
OEM equipment
As a rule, when car manufacturers design a diesel filter, engineers take into account factors like the internal clearances in the engine and injection system components, component compatibility, fuel flow and pumping rates, vibration frequencies and amplitudes, under-bonnet temperatures, and the fuel return rate, among others. This ensures that OEM diesel fuel filters operate at very high levels of efficiency, since all the factors that affect their efficiency have been taken into account.
High quality aftermarket filters
Suppliers like Ryco often cooperate with car manufacturers to ensure that the filters they supply to the aftermarket and independent repair trade meet, and often exceed the performance levels of original equipment.
“Will fit, should work” filters
These are often unbranded, and invariably cost much less than both OEM and high quality aftermarket filters. These filters should be avoided at all costs, since there is a very good reason why they are as cheap as they are; they do not work.
However, neither OEM, nor high quality aftermarket diesel fuel filters are created equal, which is why the number one best practice to follow is to know and understand what diesel fuel filter ratings mean in the real world, starting with-
Absolute ratings
All diesel fuel filters are rated according to their ability to prevent particles of a specified maximum size from passing through the filter media into the injection system. Thus, if you have a filter with an absolute rating of say 15 micron, you would assume that no particles bigger than 15 microns would be able to pass through it.
However, the pores in filter media are not perfectly uniform, and under real-world conditions, heat, vibration, pressure fluctuations, and deformation of some filter media can force particles larger than 15 microns through the filter media. Of course, this is not to say that particles twice or three times the rated size will get through the filter, but the word “absolute” implies that NO particles larger than 15 microns can pass through the filter, which is not always the case under real-world operating conditions.
Nominal ratings
The nominal rating of a filter refers to that filters’ ability to filter out a percentage of particles of a certain size. This value is always expressed as a percentage; for instance, 90% of say, 10-micron particles. While this means that 90% of particles that are 10 microns in size will be filtered out, it also means that 10% of the total number of 10-micron (and sometimes larger) particles in the fuel will pass through the filter.
Like the absolute rating, the nominal rating should not be relied upon in isolation, since some filter manufacturers manipulate the parameters of the test, such as the flow rate and test pressure as well as the composition and relative concentrations of the particles in the test fuel.
Beta ratings
To obtain a beta rating, a known number of particles of a known size are passed through a filter, and particle counters count the number of particles on both sides of the filter. For instance, if a filter has a beta rating of say, “4 at 15 microns”, it means that the filter is designed to filter out particles of 15 microns (and larger) in diameter, and based on the number of 15-micron particles that made it through the filter, a beta ratio is calculated for that filter.
If in this example, the fuel test sample contained 8 particles that were 15 microns in diameter, and four particles were detected before the filter and four after the filter, this particular filter would have a beta ratio of 50%, since it had filtered out 50% of particles that were 15 microns in diameter. Thus, the higher the beta ratio of any given filter is, the more efficient that filter is at removing particles of a specified diameter, which brings us to-
Consider the damage to this piston from a small displacement diesel engine in the image below-
What appears to be impact damage to the crown is in fact evidence of abnormal combustion that produced extreme temperatures, which in turn, partially melted the edges of the bowl in the crown. This type of damage is common in diesel engines, and is usually the result of chaotic spray patterns caused by damaged or partially clogged diesel fuel injectors. Here is how to avoid this from happening to your customers-
Install a pre-filter
Since there is direct correlation between the cleanliness level of diesel and the length of the fuel distribution chain, customers in remote locations may benefit greatly by the installation of a pre-filter. Moreover, since more than 90% of the fuel flow is returned to the tank, a pre-filter will continuously filter out most of the gunk, which includes water and bacterial colonies in the fuel.
However, as the name suggests, a pre-filter must always be installed between the tank and the primary factory filter, and with as little modification of the existing fuel system piping as possible. In addition, a pre-filter must always be rated to remove particles that are several times as big as the particles that are removed by the factory filter to maintain a proper and adequate fuel flow rate.
NOTE: Bear in mind that the rated micron size of a fuel filter has a direct bearing on its efficiency, which in turn, has a direct bearing on the filter’s maximum flow rate. Thus, if you are installing a pre-filter to any vehicle, make sure that the rating of the pre-filter will not cause a restriction in the fuel system. Therefore, most reputable manufacturers of aftermarket pre-filter kits recommend a 30- micron rating for the pre-filter, which must also include a water separator to relieve the load on the factory filter.
Avoid post-filtration
Since most factory-fitted diesel fuel filters are rated at between 2 and 5 microns, adding an additional filter after the factory filter may actually do more harm than good. Factory filters are increasingly being fitted with flow restriction sensors, whose purpose it is to monitor the fuel flow rate through the filter as an indication of how clean (or otherwise) the filter is.
Thus, adding an additional filter after the factory filter could have the effect of creating an artificial restriction, which a modern ECU will interpret as a clogged factory filter. Moreover, a post filter could also restrict the fuel flow to the point where the engine is starved of fuel.
Minimise the effects of water contamination
While the Fuel Standard (Automotive Diesel) Determination 2001 prohibits the presence of free water in all diesel sold in Australia, there is nothing the law can do to prevent dissolved, or emulsified water in diesel fuel, which in time, settles out of the fuel and collects at the bottom of the fuel tank, to initiate and spread corrosion throughout the entire fuel system.
An associated problem is the presence of several species of microorganisms that live and thrive in the interface between the (now) free water and the fuel. Most of these organisms are between 1 and 10 microns in size, and if they are not removed, or prevented from establishing colonies in the fuel in the first place, they can clog fuel filters and /or fuel injectors in very short order.
To combat this, many fuel and oil companies have developed additives known as “surfactants”, which include rust inhibitors, lubrication enhancers, and anti-wear agents. Collectively though, surfactants interact with both fuel and water molecules in such a way that the interfacial tension of both water and fuel molecules is reduced, thus causing free water in the fuel to dissolve into the fuel. In practice, this deprives microorganisms of the interface between fuel and water they depend on to exist.
However, adding too much surfactant to diesel fuel, and especially to biodiesel blends, has the effect of reducing, or even destroying the filter media’s ability to separate water from the fuel, so always follow the manufacturer’s instructions exactly when adding any additives to diesel fuel.
Replace diesel fuel filters regularly
Never exceed recommended diesel fuel filter replacement intervals, and if needs be, err on the side of caution in dusty or remote locations. Where possible, use high quality aftermarket filters from reputable suppliers such as Ryco, whose products are known to meet or exceed OEM standards in terms of efficiency and reliability.
Moreover, don’t follow the common (bad) practice of filling up the new filter with the contents of the old filter to save the few minutes of work it takes to purge the air out of the new filter. If you do this, you are adding all the collected gunk, water, and other contaminants trapped by the old filter to the new filter, which you will agree, defeats the purpose of replacing the fuel filter in the first place.
As diesel engines evolve, their need for clean fuel will become increasingly more important to keep them performing at their best. In fact, proper on-board diesel fuel filtration has already become a critically important factor in the maintenance of these engines. As experienced technicians, we have the responsibility of both recognising this fact, and to adhere to accepted fuel filtration best practices- after all, it’s really not that difficult or complicated.
