By Peter Bartl and Johannes Bader
Armed forces are equipped to operate in any environment under severe conditions. High mobility in robust and protected vehicles is a major prerequisite. Solid logistics of fuels and lubricants contribute significantly to this mobility by strictly limiting the number of products. Admittedly this concept represents in some applications a compromise. However, it has proven its feasibility over decades. To work flawlessly, it needs to be supported by a collection of several routine measures e. g. adequate specifications, approval procedures, quality assurance and equipment tests.
The approach is backed by several sophisticated complementary options. Failure investigations addressing the entire system are used as feedback to evaluate potential deficits in the overall performance of a lubricant.
Framework conditions and logistics requirements of a military operator differ significantly from civilian requirements. Size and diversity of the fleet on the one hand and operational as well as environmental conditions stressing vehicles and the crew to the maximum on the other hand constitute a big challenge in many respects. Fuels- and lubricants-related issues are one of them.
In principle, there are two options to keep logistics simple and robust. One would be a fleet of vehicles of the same type running on a manufacturer-approved list of products. In the armed forces we are faced with the opposite, a multi-supplier vehicle fleet representing different technological levels to make it even more demanding. The second option is to keep the lowest possible number of types of fuels and lubricants (Figure 1). This concept of standardisation was introduced as a North Atlantic Treaty Organisation (NATO) policy from the beginning . At that time, most of the product specifications were issued by the U.S. armed forces. In addition, vehicles were specifically designed and developed for military missions over longer periods of time.
This has changed in the meantime. The specification business is now driven by civilian applications and requirements. Another important factor is the trend to buy equipment more often off-the-shelf to save time and financial resources.
As a consequence, the implementation of a logistics-driven small list of products for a larger fleet representing the variety described above has become a major task.
This paper outlines first the framework conditions and the concept of standardised fuels and lubricants used by NATO/Bundeswehr. The second part will deal with the efforts to guarantee the validity of the approach, including research activities.
Figure 2 summarises the most important factors which have to be met and considered to operate and support a fleet of military vehicles reliably.
For obvious reasons, it is essential keep the number of products to as few as possible. It not only facilitates transport and storage, it also reduces the danger of interchanging products and possibly causing system failure. The latter is further supported by the colour and marking of the trading units. The former demand of “NATO-olive” painted containers with a large and clear depiction of the NATO code is now relaxed. Today, the supplier can offer his standard container when labeled according to our requirements (Figure 3).
Another important aspect of NATO policy is the capability of nations for joint operations including cross servicing, often described by the term interoperability. This is totally based on the use of common standards.
Public procurement introduces some complication. To promote competition in the market, goods are purchased via a tender process where normally the lowest bidder gets the contract. So, as a rule, there are different brands of the same type on the shelf. As a consequence, mixtures cannot be avoided. So the brands have to be miscible and compatible (no precipitations or antagonistic effects) for safe operation.
To guarantee the safe and steady operation of vehicles, the manufacturer has to be aware of the limited list of products set by the customer. Therefore STANAG 1414  is an essential document in any contract.
STANAG 1135  defines the fundamental requirement of interchangeability and lists in Annex C all NATO-coded products and their substitutes under regular and emergency conditions (Figure 4). Usually, member-nations use a subset adapted to their specific needs, e.g. Betriebsstoffliste der Bundeswehr .
MAJOR PRODUCTS USED BY BUNDESWEHR
Aviation lubricants represent the closest analogy to the commercial side, with the approval of the same types against the same specifications.
More details for the support of ground vehicles are provided in table 2. Until recently, only motors up to emission level Euro 3 were in use at the Bundeswehr. It is Bundeswehr’s strategy to keep this robust motor technology for all combat and armoured vehicles as long as possible. Fortunately, major truck manufacturers have indicated that they are willing to provide and support this standard in the foreseeable future. O-236 engine oil represents a reliable standard for this environment. With its medium ash content, it can cope with higher sulphur levels in the fuel which are typical for conflict areas. It implies improved corrosion inhibition, in addition to the ACEA E3/B3 requirements, to address usual prolonged downtime periods of military vehicles. Low temperature demands (below -20 °C) are covered by O-1178.
A different situation came up with high-protected patrol and logistic vehicles for special applications. They were established in the armed forces within a short time frame because of mission-related immediate need. These vehicles equipped with commercial Euro 4, or in some cases Euro 5, diesel engines have to be operated with Low SAPS (Sulphated Ash, Phosphorus, Sulphur) engine oils.
Because we carefully observe the development of different exhaust aftertreatment technologies and their interaction with engine oils, as well as with fuel quality in missions abroad, we were able to provide suitable engine oils. Several full-scale engine tests show that most selective reduction catalyst (SCR) systems and flow-through diesel particulate filters (DPF) cope with our medium ash engine oil O-236.
For wall-flow DPF application, we established the Low SAPS engine oil with NATO Code O-1180. In addition to the fundamental requirements of the NATO guide specification STANAG 7091 , Bundeswehr O-1180 meets not only ACEA E6 or E9 for DPF application. With respect to higher sulphur or/and poly-aromatic content of fuels in places like Afghanistan, it fulfills API CI-4 additionally. The latter assures the backward compatibility with older pre-chamber diesel engines and their higher soot and waste input into engine oil.
A different situation applies to medium-weight trucks coming now as protected vehicles with automatic transmissions as a common feature. This provides significant relief to the driver in operations and is very welcome. Efforts have been initiated to clear the demand for a further automatic transmission fluid (ATF) on Bundeswehr’s list of lubricants. One option could be to adopt the commercial specification and choose from approved brands and permit mixing of them.
MEASURES SUPPORTING THIS APPROACH SPECIFICATIONS
Historically coming from a strict concept of military specifications, the strategy has changed to integrate civilian standards wherever adequate.
QUALITY ASSURANCE IN THE PROCUREMENT AND STORAGE OF FUELS AND LUBRICANTS
NATO-coded lubricants normally run through an approval process and are procured from a list of successfully qualified products/brands. This is the first step of a total quality approach described in detail in STANAG 3149 . The second is quality control upon delivery. Essential parameters of the specification are tested on every batch. Knowledge of the formulation and long-term experience with a product help to select meaningful parameters and keep time and efforts in acceptable limits. Retesting, common in former times with large quantities in stock, is becoming obsolete now with procurement on demand in short intervals.
In addition to laboratory equipment, Bundeswehr has access to its own full motor, gear and other system test facilities. The Bundeswehr Technical Center for Automotive and Armored Vehicles is able to carry out performance tests of equipment and lubricants in different environments.
An example is given in figures 6 and 7. It proves adequate performance of O-236 and O-1180 in motors of the newest technology. Using EN 590 diesel fuel, the configuration met Euro 4 requirements. The expected fail in Euro 4 emission limits caused by sulphate particles was observed with jet fuel. Sulphur content of the utilised kerosene met nearly 1,200 mg/kg.
NATO’s single fuel policy (SFP) is based on the capability of diesel motors to run on kerosene, either neat aviation fuels or with added lubricity and cetane number improvers (F-63).
VERIFICATION OF KEY PERFORMANCE FACTORS
The changeover from specifications with predefined chemistries to performance-related demands had an impact on this topic. Because the chemistry in successfully approved brands might differ significantly, we have to consider miscibility and compatibility of qualified lubricants.
As mentioned before, unlike most civilian operators the Bundeswehr runs its vehicle fleet on mixtures of brands, because several products are approved. The feasibility of this approach is sometimes questioned.
In addition to the reference to commercial specifications it requires a good knowledge of formulations, valid test procedures and sometimes deeper investigations to understand interactions and avoid difficulties. Hydraulic fluid H-540 is an example. Brands with different base oils and additive packages were individually approved. Filterability, foaming and appearance over a temperature range were found to be good indicators for problems in practice, especially if they are not only running at ambient temperature, but also at +100 °C and -40 °C. Therefore, these tests are integrated in the respective specification TL (Technische Lieferbedingungen) 9150-0035.
More often, the compatibility of elastomers with unknown fluids is in question. All specifications comprise respective tests, mostly with reference elastomers in short-term tests.
However, equipment manufacturers often subject their technical elastomers to the fluids in expensive investigations suitable to guarantee long-term stability in the field. Such an approach is absolutely impractical in our situation. Figures 8 and 9 show first results of a recently started program. It is our intention to gain a fundamental understanding of factors that govern the interaction of fluids and practice elastomers.
Key elements are the use of model elastomers, close to commercial products, with known ingredients and the development of analysis techniques giving full insight into the materials and the interactions when they are in contact.
ADJUSTMENT OF PERFORMANCE CHARACTERISTICS
Commercial glycol-based brake fluids are formulated to the requirements of the respective configuration of the system. Modern designs with integrated ESP for example need a DOT 5.1 fluid with a wet boiling point >180°C and a viscosity below 900 mm2/s at -40°C. Older vehicles need higher viscosities and get along with wet boiling points around 150°C. Running a vehicle fleet under very severe conditions, requiring both types of brake fluids, a fluid with high wet boiling point and medium viscosity, is best suited for service. The quality is described as DOT 4+ (table 3).
A very important source to gain and build expertise on the performance of fluids is failure analysis. In case of a failing tribosystem, lubricants are always part of the investigation as they carry information on liquid and solid contaminants, wear particles, thermal stress and the additive status. A systematic approach includes a thorough investigation of failed mechanical parts with data of the materials and their surface treatment and condition, as well as a close look at the system and its load limits in general.
The example in figure 10 depicts friction pads of an automatic transmission from an off-road vehicle. The upper pad representing the original status is contrasted with the black one below. The latter exhibits characteristic signs of a burned surface due to over-heating.
The oil analysis showed a complete degradation of the antioxidant and oil oxidation, which was not typical for the lubricant in an automatic transmission. This indicates an unusually high temperature caused either by high friction or prolonged travelling in a mode generating too much heat, which the system could not dissipate fast enough.
The most obvious interpretation of the failure is an overload of the pads responsible for shifting gears 2 and 3. Clutch pads are configured to carry out the speed shift within a short time frame. If this is prolonged by vehicle overload or terrain profile, the pad temperature increases. The clutch disk coating reacts with increasing hardness and a decreasing friction coefficient. This provokes slip effects between the disks and further increasing temperatures and finally, overheating and burning of the friction coatings. The transmission fluid has little or no influence on this effect.
In a commercial operation, for which the transmission is designed, it runs quickly through gears 2 and 3 into modes of higher speed and better long-term durability.
As a result, under these conditions, the lifetime of this part of the transmission is rated to be within expected limits.
LIMITING THE NUMBER OF PLATFORMS
In these days, procurement of protected vehicles is driven by urgent demand, budget constraints and deadline pressure. Concerns about maintenance costs are second priority until significant problems occur.
In the Bundeswehr, a working group has been established to address this issue, with the objective of reducing the number of different platforms. The supportability with lubricants is just one aspect of the task.
The operation of a very heterogenic vehicle fleet with a small list of standardised lubricants and hydraulic fluids is a proven concept. However, it has to be backed by quality assurance measures exceeding a general level and guided by a team of experts.
- NATO Petroleum Committee – Terms of Reference
- NATO Standardisation Agreements – STANAG(s)
- Nr. 1135
- Nr. 1414
- Nr. 3149
- Nr. 7091
- Betriebsstoffliste der Bundeswehr: www.baain.de ->Auftraggeber Bundeswehr -> Betriebsstoffliste
- The European Automobile Manufacturers Association (ACEA): European Oil Sequences for Service-Fill Oils Edition 2002