Fuel Purification Systems
"The Engineer's Choice"
Poor Fuel Quality: Cause of Generator Failure
This article first appeared at www.datacenterjournal.com
Poor Fuel Quality: Cause of Generator Failure
Written by Frank Wood, on Tuesday, 31 July 2007
Published in : Facilities, Mechanical
If your data center's standby power source is a diesel generator, the odds are one in eight that the fuel that's supposed to operate the engine fails to meet oil-refinery specifications. Furthermore, if the fuel has been stored at your data center for more than three months, there's a 50-50 chance that the fuel is seriously contaminated with water or algae, posing a threat to the generator as well as to essential functions that are supposed to be protected by the engine during an emergency.
Today, it is common for purchasers to buy fuel that's contaminated up to 20 percent by water from condensation or by particulates from inadequate transportation and storage. Such contamination affects all diesel-powered equipment.
In short, diesel fuel quality is at an all-time low, and there appear to be no prospects for immediate improvement.
Why the decline? Changing oil refinery standards contribute to the problem. To get more products per dollar, diesel fuel is now being refined from more marginal portions of the crude-oil barrel. Ultimately, this results in a lower-grade product that is inherently thicker and more susceptible to acute water contamination.
Mainly, however, the decline in fuel quality is due to the greater popularity of diesel power and the resulting increased demand for diesel fuel. In the past, such fuel remained in an oil refinery's storage tanks long enough for water to naturally separate and settle, allowing it to be drawn off; now, with demand up, diesel fuel seldom remains stationary long enough to separate. With global demand showing no signs of slowing down, this problem is likely to persist.
The result: suspended water is passed along to the purchaser.
How much water must be present before damage is likely to occur? Manufacturers set a general limit of 16 ppm to 18 ppm, but water in any amount is a serious threat to machinery and must be eliminated, if possible.
Why bother? Understanding the threat that water poses to a diesel generator means realizing the added burdens that are placed upon diesel fuel (as opposed to gasoline). Gasoline acts as a fuel only; diesel fuel, on the other hand, acts not only as a fuel but also must cool and lubricate injection-system parts.
Such parts are engineered to incredibly precise tolerances (up to 0.0002 inches) and any type of contamination means rapid wear or seizure. Water not only displaces diesel fuel as a coolant and lubricant for the components; it also acts as a cutting agent, scouring and damaging injection system parts.
Water that enters the combustion chamber results in even more equipment damage. For example, when water comes in contact with the heat of the combustion chamber (more than 2,000 degrees F), it immediately turns to steam and often explodes the tip of the injector.
Keep in mind that the injection system is the heart of the diesel engine and represents, on average, 30 percent of the cost of the unit. Repairing these parts is measured in thousands of dollars in replacement costs.
Water is heavier than diesel fuel and will separate from it if the storage container remains relatively undisturbed for a period of time in an end-user's bulk-storage tanks, for example. Furthermore, the less frequently the fuel is used (as in standby applications), the more likely water will separate and cause damage.
This characteristic of water (that it is heavier than diesel fuel) is the key to its removal because water cannot be separated from diesel fuel by conventional filters. The only way to remove it, and to keep water out of the engine, is through the use of a fuel/water separator.
Removing water is important not only to improve combustibility, but also to prevent corrosion in tanks, lines, and injectors. Such corrosions contribute to diesel fuel deterioration by enhancing the environment for bacteria that feed on nitrogen, sulfur and iron oxides.
In fact, diesel fuel begins to deteriorate as soon as it is produced, a problem that poses no real threat if the fuel is consumed quickly. However, such fuel may be stored for years in a standby power system; such deterioration affects the fuel's pumpability and combustibility as well as the degree of damage that it could cause to the engine.
Catalytically cracked diesel fuels, which are common today, are especially susceptible to deterioration. As catalytically cracked diesel fuels age, they tend to repolymerize, forming sub-micronic particles that scour expensive fuel-metering injectors.
As the process continues, the repolymerized molecular chain becomes longer and longer, forming agglomerates and sludge. This sludge plugs filters and causes injectors to "drool" or "slobber," thereby diluting the crankcase oil with fuel.
Diluted crankcase oil leads directly to bearing failure and shortened engine life.
Bulk-storage quality maintenance systems (such as those manufactured by Fuel Purification) for diesel and biodiesel fuel are very effective in reducing contaminants in fuel-storage tanks.
However, if your data center cannot afford such assistance, the steps outlined below will help to ensure that when it comes time for your data center's standby power generator to start and come on-line, it will do just that.
Fuel Tank Maintenance Program for Data Centers Lacking Diesel Fuel Quality Maintenance Systems:
Step 1 :
Periodically check the fuel volume in the tank with a measuring stick and compare the reading to the tank gauge's value to determine whether the gauge is accurate. Also, by comparing previous volume readings with past fuel delivery dates and amounts, you can tell if the tank's volume is increasing by an unusual amount, a sure sign of condensation.
Step 2 :
Determine the depth of the water at the bottom of the tank with a measuring stick that changes color in the presence of water.
Step 3 :
Manually pump the water from the bottom of the tank with a clear hose to observe when oil starts flowing.
Semiannually, transfer the entire contents of the bulk-storage fuel container to a tanker, and then clean the interior of the tank.
Step 5 :
Take fuel samples on a monthly basis and have them heat-aged in an electric oven; note spectrometric readings both before and after aging. This information will allow you to determine the fuel's heat stability as well as the type of additive that may be needed to keep the fuel in a stable condition.
Step 6 :
Add special additives to the fuel on a monthly basis to keep it in a pumpable, combustible condition and to control bacterial growth.
About the Author:
Frank Wood is President of Fuel Purification (www.fuelpurification.com). He was also co-founder and President of Power Distribution, Inc and the former owner of Clean Fuel, Inc.