TACA Conveyor - Winter 2007 - (Page 9) B ack in 1994, when the Environmental Protection Agency announced stringent new requirements for particulate or soot control for diesel truck engines, some industry experts predicted the end for diesel engines. At the time, the emissions limit for these engines was .1 gram particulate per horsepower hour, but the EPA was demanding that engines manufactured starting January 1, 2007, reduce that by 90 percent, to .01 gram per horsepower hour. Many thought those limits were unreachable. But engine manufacturers met the challenge. The new diesel truck engines introduced this past January are virtually soot free. “In these engines, the exhaust is so clean, that after you’ve run 100,000 miles – you can take a white handkerchief and rub inside the exhaust and never get any black on it. It is amazing how they clean up the exhaust,” says Zack Ellison, director of customer support at Cummins. The best news for diesel truck owners and operators is that the engine and truck manufacturers have managed to develop a system that is easy to use. In many cases, truck operators will not have to do anything different with these trucks than what they are doing today. filters without the particulate getting through.” Three types of filter cleaning The particulate matter captured in the DPF is burnt off through a process called regeneration. “Over time, the black soot will build up in the particulate filter, but once the exhaust gets up to a certain temperature, it’s just like a self-cleaning oven,” says Ellison. “It actually starts to oxidize and convert that black soot into nitrogen and carbon dioxide (CO2).” There are no byproducts from the regeneration process; the soot converts completely. When the engine is working very hard, under heavy loads or at high speeds, it will generate enough exhaust heat to allow regeneration to take place without additional fuel or heat. This is called passive regeneration. But when the truck is running at lower speeds or with lighter loads the engine is not working hard enough to generate the exhaust gas temperatures necessary for passive regeneration. To overcome this difficulty, most engine manufacturers use active regeneration to burn off the soot. In active regeneration, the engine system injects a small amount of diesel fuel into another ceramic cylinder (a diesel oxidation catalyst) through which all the exhaust gases pass before reaching the DPF. The inside of this ceramic cylinder is coated with platinum and palladium. The chemical reaction between these elements and the injected fuel elevates the temperature of the exhaust gas as it passes through on the way to the DPF, making the exhaust hot enough for regeneration to occur. This process is called dosing and it generates heat without any flame. (Caterpillar has taken a different approach, using a small, auxiliary natural gas burner mounted on the engine to heat up exhaust gases when needed.) Passive and active regeneration take place automatically. But when a dieselpowered vehicle is used primarily in stop and go situations it may not generate exhaust gas temperatures high enough for regeneration even with additional heat. The soot builds up in the DPF, and a warning light on the dashboard tells the operator that the DPF needs to be cleaned out. The operator must then begin a process called stationary regeneration. “The driver parks the equipment in a safe location, sets the parking brake and then hits the regeneration start button,” says Ellison. “The engine RPM picks up to 1100 rpm, and it generates the exhaust heat and adds fuel to it. About 20 to 30 minutes later the DPF has been completely regenerated or cleaned. “Stationary regeneration gives people who have lighter duty cycles, such as pick up and delivery, a way to clean the filter,” he adds. The frequency with which an operator needs to do stationary regeneration varies with the vehicle’s usage, he says. “But I believe that most of the customers in the concrete business will have a heavy enough duty cycle, that they’ll go through a regeneration process on their own without having to do stationary regeneration.” Ash removal Not all engine byproducts are burned off in the DPF. Over time the particulate filter will start to fill up with the ash from the engine oil. Ash, which neutralizes the acid in the motor oil but it does not oxidize, so it must be removed from the DPF through the use of a special pulse air machine available at the dealer or distributor’s service center. Ash removal will need to be done every 200,000 to 300,000 miles. To alleviate the ash buildup, oil manufacturers have developed a new, reduced ash oil classification—CJ-4—to be used with 2007 engines. Introducing the DPF The heart of the new emissions reduction systems is the diesel particulate filter (DPF). A DPF is a ceramic cylinder, sometimes referred to as a ceramic brick that is about 30 inches long and 16 to 18 inches in diameter. A DPF looks like a slightly oversize muffler and actually replaces the muffler on the truck, handling its sound reduction work. But the DPF’s primary role is emissions control. “The DPF is a ceramic substrate with small passages through it, with every other passageway plugged up. The exhaust gas goes from the engine into every other passageway, and then the gas passes through the ceramic wall into the neighboring passageway, which opens to the outlet side,” explains Mike Powers, who works in product developmenthighway engine for Caterpillar Inc. “You’re capturing the soot coming from the engine in every other passageway, and the gas is then allowed to pass out the alternating The costs of cleaner air The biggest drawback to the improved diesel truck engines is probably their increased cost. With all the new equipment required plus the billions of dollars that engine manufacturers spent TACA Conveyor • Winter 2007 9
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.