On-site power systems driven by diesel engines are commonplace as the “last resource” backup power source for mission-critical facilities. Hospitals, public safety operations, municipal utilities, and all sorts of private businesses incorporate diesel-powered generators to help avoid loss of life, lost production time and/or lost profits.
It is not uncommon to find several million dollars spent in the design, construction and commissioning of on-site power systems for a new hospital, a municipal water plant or an emergency operations center that must have reliable power under the most adverse conditions. These facilities might have multiple generators, redundant electrical power distribution systems, uninterruptible power systems (UPS) and tens of thousands of diesel fuel on site. All of this to help ensure power continuity in the event of an extended outage by the local power utility.
When designing diesel-powered on-site power systems, the design engineer should be attentive to the “facility fuel systems” portion of his/her design work, and specifically to the subject of fuel quality. Most designs focus on whether there will be sufficient fuel, and how it is to be delivered reliably to the engines, but sometimes lost in the process is whether the fuel will be in usable condition. Diesel fuel, in the typical power generation application, is received, stored in the fuel tanks, and left on its own. This is where future problems begin to grow, literally!
Let’s step back for a minute and consider: Why is fuel quality seldom paid the attention it deserves?
- Lacking an extended utility outage, standby power generators, while regularly exercised, simply do not run for a long-enough period of time, or with sufficient load, to display issues associated with fuel quality.
- Designers of emergency power source systems believe they have little control over the long-term maintenance of the sophisticated equipment that was designed and installed for a client.
- Facility managers are not always full-time positions for many of the facilities that are equipped with on-site power generation systems. The lack of a trained, full-time person, charged with looking after the equipment, often leaves the equipment ignored.
- Service organizations, hired to perform preventive maintenance on emergency generators, have only recently begun to present “fuel polishing” as part of their portfolio of services. Even then, facility owners are generally not educated on the reasons why fuel quality is crucial, and often skip the proposed fuel maintenance services.
So what exactly happens when fuel is contaminated, or aged beyond its usefulness?
- Long-term storage of diesel fuel in vented tanks will lead to water contamination. Moisture from the air enters the tanks via the vents. With temperature changes, this moisture turns into condensation which will settle to the bottom of the tank. The interface of fuel and water leads to bacteria growth, which eventually attaches itself to the walls and bottom of the tank. As colonies of bacteria form, some will become suspended in the fuel, ready to be sucked into the engine’s fuel supply.
Bacteria Growth in Diesel Fuel - Fuel aging is a critical factor with on-site power systems. As fuel is not consumed quick enough, many of its chemical properties change over time. Aging fuel can lose properties critical to lubricity, cold-starting performance and proper combustion for low emissions.
What are the symptoms of poor diesel fuel quality on diesel engines?
- Clogged filters are often the first indication of poor fuel quality. Consider that water is more dense than diesel fuel, and therefore will settle to the bottom of the tank. Once the water contamination reaches the engine fuel supply suction tube, or the fuel level drops to a level close to the water contamination, the filters will begin receiving a higher ratio of contaminated fuel. Clogged filters will reduce fuel flow and will increase the pressure drop across the filters. These conditions can lead to an unexpected engine shutdown.
Microbial Induced Corrosion in Fuel Tank - Depending on the quality of the filters, some contaminants can pass through and on to the engine fuel pump and injectors. At pressures over 20,000 psi, these contaminants can cause damage to the fuel pump and pitting of the fuel injectors, which in turn leads to erratic fuel spray patterns, inefficient fuel combustion and increased emissions.
- Microbial contamination can lead to corrosion of the tank’s internal walls, as well as any sensors, valves or fuel lines in the system. From the bulk storage tank to the engine fuel system components, corrosion is an unwelcomed problem that can be very costly.
- Untreated fuel that is stored for a long period will provide less lubricity to the engine’ fuel system, as well as less energy content. These problems lead to component damage and output power losses.
What can a design engineer do when long-term diesel fuel storage is expected? A design engineer can provide a useful service to his client by taking these steps:
- Educate the client on the importance of purchasing clean fuel from a reputable supplier, and the requirements for long-term fuel quality maintenance.
- Specify that any fuel tank be treated with an appropriate stabilizer that contains an antioxidant, biocide and corrosion inhibitor. Most facilities require that the contractor be responsible for the initial fuel fill. Additive treatment should be made part of this initial fuel fill requirement.
- Specify a permanent, automatic, fuel maintenance system to periodically filter the stored fuel to remove water and solid contaminants.
Fuel Maintenance System - Specify a fuel maintenance training session for the facility owner, after the equipment is commissioned. This training session should involve a local third-party, which may offer its services to periodically sample and test the stored fuel.
Maintaining diesel fuel quality is not a difficult task, but it is one that requires collaboration between the design engineer, the general contractor and the facility owner. The engineer and contractor can ensure that the facility has the equipment and necessary provisions for regular fuel maintenance and testing. With this equipment in place, and with a basic understanding of the steps to proper fuel maintenance, the facility owner is now well-equipped to take responsibility for the quality of the stored diesel fuel.
Would you like to read more on this subject? Here are some additional resources to expand your knowledge of fuel and how to maintain its quality in mission-critical applications:
- Chevron – Diesel Fuels Technical Review – a good source of technical details and common sense guidelines to proper fuel handling and storage.
- Fuel System Design Considerations for Critical Power Generation Installations – a review of common issues found in facility fuel system designs.
- Fuel Maintenance System – Sample Specification
Do you have a fuel quality maintenance program in place? Any success stories or helpful tips? Please share your comments and questions below. We appreciate your feedback!