How to avoid using low-quality diesel fuel
| August 08, 2012 |
To kick off a webinar hosted Tuesday by the Association of Equipment Management Professionals, Ken Hill said he has heard a lot of complaints over the past few years about poor diesel engine performance and inquiries from operators about what they can do about it.
Hill, the vice president of sales & marketing at oil analysis firm WearCheck USA, said a common cause of poor engine peformance is the use of low-quality diesel fuel in equipment. He then spent about 45 minutes going over the properties of diesel fuel, proper fuel quality checks and finally, storage maintenance checks to ensure operators are using quality fuel.
“The important thing to remember is that diesel fuel quality deteriorates every time it is handled,” Hill said before tracing the path diesel takes before entering your equipment. Of course, diesel begins its life in the oil well before traveling to a refinery. It’s then transported to a terminal through a pipeline, Hill said.
“But what was in that pipeline perviously?” Hill wondered aloud. “And remember, a terminal sees multiple reciepts of diesel fuel that your fuel has come into contact with.” From the terminal, the diesel is handed over to a fuel jobber, “someone you trust in to bring the proper fuel you’ve ordered,” as Hill put it. The jobber fills a tank that Hill says has likely been used to transport other fuels before delivering it to you and your storage tank.
“Always be cognizant of the fact that by the time it goes into your equipment that fuel has been trasferred seven to eight different times,” Hill said.
Hill then defined several important properties of diesel fuel. Opeators can gain a better understanding of fuel quality by sending samples of diesel fuel for testing in a labratory to find these measurements.
Heat Value – This is the amount of energy stored in one gallon of diesel fuel. It is measured in BTUs and indicates how well the engine converts the heat energy of combustion into actual work. The higher the heat value per gallon of fuel, the more power that will be derived from each gallon of fuel used.
Cetane Index – Typically diesel fuels have a cetane number between 40 and 55. A cetane rating of 40 or above is currently the standard for all on-highway diesel engines. A higher cetane number is beneficial during engine starting and warm-up as well as in cold weather and in service with prolonged low engine loads.
API Gravity – This measurement determines fuel density and, along with Distilation (defined below), is used to calculate the Cetane Index. Diesel fuel normalls ranges from 20-45 API Gravity. Another name for this measurement is specific gravity which refers to the ratio of the density of the fuel versus the density of water. Specific gravity can be measured with a common hydrometer and ranges in diesel fuels from 0.8 to 0.94.
Flash Point – This is the temperature where the vapors that form above the surface of a liquid fuel will ignite when exposed to an open flame. The minimum Flash Point of diesel is 125 degrees Fahrenheit . Flash Point has a minimal effect on engine performance and moreso informs the proper handling and storage of the fuel. Flash Point allows operators to check fuel quality becuase it indicates if the fuel has come into contact with any lower-quality fuels.
Viscosity- The measurement of a fuel’s resistance to flow at a given temperature. Diesel Viscosity typically falls within a range of 2.4 to 4.1 cSt. When Viscosity is outside of this range, fuel injector performance may be affected. Diesel fuel can be too thin or too thick for proper engine operation, so viscocity is a critical property in blending diesel fuel.
Distillation- Measures the initial boiling point and separation of distillates at different temperatures and identifies dangerous or damaging gasoline contamination to diesel fuel. Diesel fuel volatility is represented by a 90 percent Distillation temperature which is the temperature at which 90 percent of the diesel fuel is distilled off with an acceptable range of 282-338 degrees Celsius.
Sulfur Content (parts per million) – To minimize potential problems and reduce exhaust emissions, Environmental Protection Agency regulations require a Sulfur Content no greater than 15 parts per million in highway diesel fuels. However, lowering the sulfur content of diesel fuels reduces its lubricity, its ability to lubricate moving parts, especailly those in the fuel injection pump and injectors. Most fuel providers have added a lubricity additive into the blend and there are aftermarket lubricty enhancers available. Fuels with lubricity additives are more expensive.
Cold Weather Analyses
Hill then went over some worthwhile properties to remember and tests to run when the cold season comes.
Cloud Point – Diesel fuels contain paraffin wax and in cold temperatures the wax begins to congeal and solid wax crystals can form in the fuel which plug fuel lines and engine filters. Cloud point is the temperature at which these crystals of paraffin wax begin to appear in the fuel. You can actually detect the presence of these wax crystals by a cloudy look to the fuel.
Pour Point – If the temperature continues to drop below the Cloud Point, the fuel will reach and exceed its Pour Point, becoming too thick to flow and eventually becoming a solid. Pour Point determines the temperature at which this happens. There are additives available which can improve fuel flow and lower the Pour Point in extremely cold temperatures.
Cold Filter Plugging Point – Measures the temperature at which wax crystals form in a fuel to the extent that they plug filters.
Hill then moved on to detail various types of fuel contamination. “This will be one of your biggest pains in your rear end,” he said.
Water and Sediment – Both can clog fuel filters and cause significant power loss, corrosion, fuel system component wear and promote microbiological growth. The amount of water in fuel should not exceed 500 ppm or .05 percent. Sediment should be no greater than 100 ppm, or .01 percent.
Bacteria, fungi and mold – The presence of bacteria, fungi and mold indicates that fuel storage tanks have not been properly maintained. When present, water separates from fuel and accumulates at the bottom of storage tanks creating an excellent breeding ground for biological growth. Initially, diesel fuel is sterilized thanks to the high temperatures involved in refinery processing, but fuel can quickly become contaminated with microorganisms presnt in air or water that contain bacteria and funci.
With all of this information in mind, Hill went over several maintenance tips to ensure these problems don’t slow you down. First, he suggested ensuring that you purchase fuel from a reputable supplier. To do so, ask the supplier to provide a certificate of prior analysis for each shipment. This should cover sulfur content, color (dye) if any and assurances regarding the transport vehicle, whether or not their tank was cleaned of other products before storage or transport.
Hill also suggested inspecting each delivery you receive and each fuel compartment of the shipment to ensure it meets the certificate of analysis and is free of excess water and sediment. Afterward, it is a good idea to take a sample of the shipment and send it to a lab for testing.
When it comes to storing your diesel, Hill recommended inspecting storage tanks and fuel systems at least once monthly. Drain water from the tank(s) as needed, which helps to prevent microbial contamination. Keep tank(s) as full of fuel as possible in order to reduce the volume of outside air from entering. This reduces moisture as the air condenses. Finally, install desiccant air breathers to reduce mositure and sedmient from entering the fuel system.