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Part 3: Proper Heater Temperatures, Fuel Ramp-Up Speed Can Help Limit Generator Smoke
February 2013 -
Power & Communication Article Use Policy
In older gensets, prolonged cranking while fuel is being injected eventually generates the heat necessary for ignition, but uses excessive diesel fuel and results in large amounts of black smoke. "Diesel engines use air compression, creating heat that generates the fire to combust the fuel," explains Piske.
To speed up that process, a jacket water heater can be installed on the block. "The block heater circulates warm water through the engine so that it starts faster," explains Pope.
"The colder the environment, the more that heater has to work," says Piske. "Some gensets have dual heaters."
With jacket water heaters, it's important to use a thermostat that senses increases and decreases in temperature or to adjust the temperature manually to compensate for ambient temperature changes. "Ideally, the block water heater operates at about 100 degrees Fahrenheit," explains Piske, "which is warm to the touch. If the block heater is running at 180 degrees, it will shorten the life of the hose and waste electricity."
The engine's governor controls the speed at which the engine ramps up to 1,800 rpm at start-up. On older systems extra fuel was injected at start-up to achieve the fastest start possible. Unfortunately, much of this extra fuel does not get burned and exits the exhaust as smoke. The extra fuel also spills over the engine's cylinders, taking some of the cylinder lubricating oil with it. A qualified technician can slow down the ramp-up speed, thus reducing smoke but still meeting the NFPA 110 10-second rule, notes Tim Hinde, application engineer for Woodward, Inc., and an EGSA volunteer school instructor for several years.
Fortunately, older governors can be replaced with modern electronic governors.
"Replacing old governors with new electronic governors will more precisely control the engine speed and burn the diesel fuel more efficiently," says Hinde.
"Modern electronic fuel injection and electronic engine management systems ensure that precisely the right amount of fuel is injected into the cylinders to produce the power needed by the generator for the facility load, frequency is steady (at 60 Hz), and optimal fuel economy is maintained," Pope explains.
To reduce wet stacking around the exhaust, Kathy Plunkett, vice president of engineering at GT Exhaust, part of the IAC Group, suggests lagging the exhaust pipe, which means insulating it. "Insulation that tolerates temperatures of 900 to 1,000 degrees Fahrenheit and that is not flammable is the least expensive way to correct wet stacking," says Plunkett.
"The insulation keeps the exhaust hot, so no condensation occurs," Plunkett explains. "It does not get rid of the issues, but it helps from creating more."
Another option for addressing smoke and wet stacking is the installation of load banks. "When you're exercising the gensets but not actually putting a building load on them, the genset engine is idling," explains Kurt Summers, president of Austin Generator Service, Load Banks of America. "When the engine is idling, the combustion chamber is not burning all the fuel and some crankcase oil is getting into the exhaust system." The result is wet stacking, the collection of that unburned fuel and oil as spillage around the generator.
To replicate building load during testing, a number of facilities are installing or renting load banks. Most distributors offer load bank service, according to Pope.
Typically, load banks replicate 75 to 80 percent of the genset's full electrical load, says Summers. Load bank testing generally runs four to eight hours. In addition to reducing wet stacking and testing the engine thoroughly, load banks allow operators the chance to double-check many genset functions. Electrical output at the generator can be verified, the voltage regulator can be checked and the governor, cooling system, radiator, thermostat and water pump performance also can be evaluated during the load bank run, according to Summers.
Part 1: EGSA-Certified Technicians Can Offer Solutions To Smoking Generators
Part 2: EGSA Member Recommend Solutions To Prevent Older Generators From Smoking
Part 4: Diesel Oxidation Catalyst, Diesel Particular Filter Can Prevent Generator Smoke