Fuel-related customer concerns are always near the top of warranty claims. Fuel quality and cleanliness can have considerable impact on fuel system components and filters are a vital last line of defence, blocking dust, dirt and other harmful contaminants. Failure of this critical component can lead to power loss, breakdowns and leave you seriously out of pocket. The issue of diesel filter blocking has been plaguing the fuel industry for years and has been the subject of a serious amount of head-scratching.
However, industry stakeholders that are surprised by increased filter-plugging rates often fail to consider that modern, high-pressure commonrail injector systems have far less tolerance for particulate contamination than diesel engines had historically. Consequently, fuel must pass through smaller pore-sized filters before reaching the injectors. For a given particle load (combination of both total particle count and particle size distribution) a smaller pore-sized filter will plug faster than a larger-pore-sized filter. That said, fuel chemistry does play a significant role. Severe hydrotreating needed to produce ultra low sulphur diesel (ULSD) also degrades the fuel’s lubricity, corrosivity and oxidative stability.
The American Chemistry Council’s (ACC) Fuel Additive Task Group (FATG) is a task group of the Petroleum Additives Panel, comprised of fuel additive manufacturers. Members include Afton Chemical, BASF, Chevron Oronite, Infineum, Innospec and The Lubrizol Corporation. In March 2018, FATG released a publication entitled “Overview of Diesel Additives & Filtration Issues” to help increase the understanding of diesel additives and common filtration issues.
Undeniably, the modern fuel distribution system is multifaceted and complicated as fuels are transferred from refinery to pump via a myriad of terminals, pipelines, delivery trucks and tankage. For almost a century, diesel fuel additives have been used throughout the entire diesel distribution system to improve fuel quality, performance, achieve basic specifications or to protect critical components of the distribution chain or vehicle’s engines.
An increase in filtration is evident throughout this complex distribution system as companies make every effort to minimize contaminants in fuel. The FATG document notes that many diesel fleets and large end-user groups have increased filtration at intermediate diesel bulk storage facilities in order to reduce particulates upstream of vehicles. Filtration on the inbound side of an onsite fuel tank is also increasingly prevalent to augment outbound filters.
The subject of controlling particle contamination at various points in the fuel system, especially as the diesel engine base continues to implement less dirt-tolerant high-pressure common rail injection technology, has been discussed numerous times at various industry meetings. In June 2015, ASTM Subcommittee D02.14 on Fuel Cleanliness and Stability even organized a Diesel Cleanliness Workshop to address this enduring problem.
More recently, questions are being asked about the potential role diesel additives play in the blocking of filters throughout the diesel distribution chain.
The FATG report states, that “additives may be observed during surface analysis of slow-running or blocked filters,” however, the task group says “they are likely not the root cause of the filter blocking issue.” Water, dirt, biomass, metal salts and biodiesel impurities are more commonly fingered as complicit in filter blockages at various points along the diesel fuel distribution chain. Rick Chapman, senior vice-president at Fuel Quality Consultants, leader of the Coordinating Research Council (CRC) Fuel Cleanliness Panel and co-chair of ASTM Subcommittee D.02.14 Particulate Contamination and Particle Counting Work Group, advises that the most prominent diesel filter blocking problem is probably wax build-up when fuel is attempted to be used below the cloud or CFPP point.
But why, if diesel fuel additives are not the cause of blockages, is there a need for guidance via the FATG document? When it comes to the use of diesel additives, Frederick Passman, president of Biodeterioration Control Associates, Inc., and sub-vice-chairman of ASTM Subcommittee D.02.14, suggests that the primary link between additive use and filter plugging is on vehicle filters and is most often caused by the use of aftermarket additives. When used, these can boost total additive concentration to levels above those which are stable in fuel. This overdosing can cause filter plugging, says Passman.
The FATG document does identify multiple possible causes of filter blocking associated with the use of diesel fuel additives. Most appear to be preventable, stemming from incorrect fuel and additive management. Passman says, “theoretically” the impacts of diesel additives on filter blocking are 100% avoidable. Though, he acknowledges valid challenges that can cause problems. “The key issue is that communication between market tiers is insufficient,” he says.
Insufficient mixing of diesel additives into fuel, the impact of fuel temperature fluctuations and additive treat rates are all identified by FATG as primary factors in the build-up of particulates, and the document issues guidance on how to prevent these from occurring. ACC is however quick to caveat the guidelines as a “general composite of best practices” that users may wish to follow “where appropriate for their own needs and circumstances.” The document should not be considered as an industry standard, they advise.
Insufficient mixing of diesel additives into fuel can lead to inadequate solubilization of diesel additives resulting in the build-up of total additive concentration and subsequent filter blocking issues. Unsatisfactory mixing can occur right throughout the distribution network — including bulk fuel treatments, downstream fuel terminals, and even through the addition of aftermarket additives directly into a vehicle’s fuel tank.
The FATG document recommend “co-current diesel additive injection in the direction of fuel flow via a quill at the pipe center point while the fuel is in turbulent flow” to alleviate additive concentration build up. Proportional additive injection is recommended in transit to storage tank or delivery tank-wagon. In some cases, “splash blending” — a blending process done by manually pouring products together, is the only available option. In this instance, closely matching diesel additive viscosity and density to the fuel viscosity and density is suggested.
Temperature reductions can have a notable influence on diesel additive solubility and higher diesel additive viscosity may also affect dispersion and blend homogeneity. Filter blocking, or degradation, can occur with the injection of winter fuel and cold flow improvers into fuel below cloud point. Application of flow improver additives can exacerbate these issues as opposed to improving cold flow performance.
The FATG report favours diesel additive injection into warm fuel (~30°C/~80°F). However, in locations faced with severe temperature fluctuations — clearly this can be untenable. In this case “select the highest diesel additive dilution to provide good mixing at the lowest expected temperature.” With respect to cold flow improvers, injecting additives into fuel with a temperature that is at least 10°C (18°F) above its cloud point is optimal to ensure superior filterability performance.
A common misconception within the fuel industry is “more is better” when it comes to additive treat rates. The “Overview of Diesel Additives & Filtration Issues” clearly outlines that this is not the case. When used at prescribed concentrations, additives do a great job of maintaining fuel’s fitness for use. Problems arise when additives are overused or when fuel infrastructure is not maintained according to best practices. FATG confirms that a diesel fuel additive is most effective when injected into the fuel, so it is thoroughly dispersed and mixed, and the additive supplier’s recommended treat rate is achieved homogeneously throughout the entire batch of the fuel. To diminish filtration problems and achieve optimum performance levels it is critical that treat rates do not exceed the additive supplier’s maximum registered U.S. EPA (Environmental Protection Agency) treat rates.
The report is available at www.americanchemistry.com/fatg.