Diesel engines are undergoing an overhaul in the face of stringent regulations. While design changes will make them cleaner, they may also affect performance and life cycle, as well as your wallet.
Sometimes, it feels like a war is going on over diesel-powered trucks. For starters, the Environmental Protection Agency (EPA) has tightened emissions regulations so much that by 2007, diesel engines may actually be cleaner, in some respects, than those powered by natural gas.
California's Air Resources Board (CARB), threw more fuel on the fire in 1998 by labeling the particulate matter in diesel exhaust a Toxic Air Contaminant.
Then the U.S. Dept. of Justice and EPA teamed up to land an enormous body blow to the diesel engine manufacturing community two years ago. Seven diesel engine makers were forced to pay $83.4 million in civil penalties and collectively spend more than $850 million to develop new, cleaner engines and rebuild older engines to cleaner levels.
Yet the haze of battle surrounding on-highway diesel truck emissions obscures some critical developments where engines are concerned.
First, diesel engines provide one of the most fuel-efficient forms of vehicle transportation today, especially when it comes to hauling heavy loads of freight. Second, a quiet revolution in engine technology has occurred over the last two decades, helping cut diesel emissions levels between 80% and 90%. Even greater technological innovations are waiting in the wings.
In fact, diesels provide 45% to 60% better fuel economy per mile than their gasoline counterparts. According to Allen Schaeffer, spokesman for the Diesel Technology Forum (DTF), Herndon, Va., " they consume less fuel, burn less fuel, and therefore lessen the need for oil imports."
Yet these benefits are largely overshadowed by the perceived negatives. "Diesel has the benefit of being everywhere and the curse of being everywhere. Garbage trucks, buses, locomotives and even ships are powered by it. Yet there's a `so-what' attitude towards diesel power by the general public," he says.
Even CARB admits that diesel engines are important to the economy. Michael P. Kenney, CARB's executive officer, says: "Diesel is the lifeblood of California commerce." But that doesn't stop the organization from fighting for tighter emissions standards.
The major drawback to diesel is its exhaust residue. According to DTF, the emissions of greatest concern are oxides of nitrogen (NOx), sulfur dioxide (SO subscript 2) and particulate matter (PM), or soot, smaller than 10 micrometers.
Environmental groups believe that soot can cause cancer in humans, and NOx is considered a major contributor to smog and ozone depletion. According to the Natural Resources Defense Council (NRDC), diesel exhaust contains 100 to 200 times more fine particulates than gasoline exhaust, and on-road diesel engines were responsible for 26% of the NOx pollution produced in the U.S. in 1996.
EPA tightened emissions restrictions for diesel engines throughout the last decade, mandating a number of reductions in sulfur, oxides of nitrogen, non-methane hydrocarbons (NMHC) and PM levels.
This year, the agency proposed even tighter standards for emissions from model-year 2007 heavy-duty engines. The regulations mandate that PM levels drop to 0.01 g/bhp.-hr., NOx to 0.20 g/bhp.-hr., and NMHC to 0.14 g/bhp.-hr. While PM standards will take effect immediately in 2007, NOx and NMHC levels will be phased in between 2007 and 2010.
On top of that, the sulfur content of diesel fuel will be cut drastically by 2006, dropping from 500 ppm to 15 ppm. As far as cost is concerned, the Engine Manufacturers Assn. (EMA), working with the American Petroleum Institute and National Petroleum Refiners Assn., says the price of low-sulfur diesel fuel should only rise by 5 to 7 cents a gallon.
Yet Schaeffer says diesel engine makers have long worked toward the goal of providing a cleaner environment. "The (1998) consent decree and tighter emissions regulations have simply accelerated standards the manufacturers were already working towards," he explains.
Now those improvements will be put to the test as the 2007 emissions standards draw closer. "That's the last great horizon for diesel engine technology," Schaeffer says. "Meeting those standards will make the engines so clean, their emissions levels will approach zero."
According to DTF, engine makers will have to make changes in four areas in order to meet the 2007 standards:
1. Cleaner diesel fuel. Although EPA has mandated 15-ppm low-sulfur diesel, several engine manufacturers say 5-ppm fuel is needed to meet the 2007 goals. "The top thing we need is ultralow-sulfur fuel," says Patrick E. Charbonneau, vp-engineering for International's truck engine subsidiary. "If we don't have the fuel, we don't have the aftertreatment technology to get us to the near-zero emissions level required." According to EMA, 5-ppm ultralow-sulfur fuel would cost 7 to 9 cents more per gallon.
2. Fuel injection systems. The advent of electronic engine controls has given diesel engine manufacturers almost pinpoint control of fuel delivery to the combustion chamber. This control is necessary to avoid temperature spikes during the combustion process, which create higher levels of NOx.
3. Air intake management and exhaust gas recirculation (EGR). Better air intake management results in better fuel combustion, leaving fewer particles to remove from the exhaust. EGR takes it a step further by rerouting exhaust through the high-heat combustion process, literally `burning' away more hazardous exhaust chemicals.
4. Aftertreatment technology. This includes catalysts and particulate traps that either convert or capture emissions before they leave the exhaust pipe.
Engine makers are pursuing a variety of technical angles to meet the 2007 emissions goals. Right now, however, most don't know what the final cost to fleets will be.
GREEN DIESEL International Truck & Engine Corp. combines ultralow-sulfur fuel and a continuously regenerating particulate trap with its "green diesel technology" to cut diesel emissions below current EPA standards, making them even cleaner than natural gas engines.
International equipped one of its 4900 6x4 dump trucks with a modified 530E 300-hp. green diesel engine. The truck weighed in at 21,250 lb., and its green diesel engine produces 3.01 g/bhp.-hr. worth of NOx and 0.005 g/bhp.-hr. worth of PM. That's well below the 4.0 g/bhp.-hr. NOx and 0.1 g/bhp.-hr. PM levels mandated by EPA. It also beats natural gas engines, which record 3.2 g/bhp.-hr. NOx and 0.07 g/bhp.-hr. PM levels, says Charbonneau.
"Our first focus is to get this green diesel technology into school bus fleets in California, which will use ultralow-sulfur fuel, to get real world data," he says. "The technology in our green diesel engine will be the technology to help us meet the 2007 standards. We'll need to add an ultra-high NOx absorber to reach the lower NOx requirements."
Charbonneau adds that International's green diesel technology will work in all of its engine products, from Class 8 tractors down to 8,500-lb. GVWR pickups.
Another piece of the clean diesel puzzle comes from International's camless engine technology. Instead of using a mechanical camshaft and pushrod assembly to control the flow of air and fuel to the combustion chamber, International would use electro-hydraulically controlled actuator pistons to open and close the engine valve. Developed in conjunction with Sturman Engine Systems, International's camless technology would allow microsecond valve control to optimize the combustion process.
SCR Mack Trucks is in the midst of a two-year aftertreatment project using Selective Catalytic Reduction technology to cut emissions from its Class 8 diesel engines.
"SCR is an aftertreatment not unlike the catalytic converters used in cars over the last two decades," says Chuck Salter, executive director of engine engineering at Mack. "We imagine SCR will be a principle solution for reaching 2007 NOx and PM emissions levels. We've demonstrated it in the lab and now we're using it on one of our inter-plant trucks running from Allentown, Pa., to Hagerstown, Md., to see how it works in the real world."
According to Salter, aftertreatment catalysts are used in cars to reduce incompletely burnt remnants of hydrocarbons, creating water and carbon dioxide while burning off carbon monoxide. In a diesel engine, however, NOx makes that process more difficult. Chemicals must be added to the diesel exhaust stream to separate the oxygen and nitrogen in NOx.
SCR involves spraying Eurea, a common nitrogen-based fertilizer, into the exhaust ahead of the catalyst. The high heat of the exhaust stream causes Eurea to react with NOx, creating ammonia gas, which contains nitrogen and hydrogen. The hydrogen then bonds with oxygen within the exhaust catalyst, leaving just nitrogen and water coming out the tailpipe.
Using Eurea to clean diesel exhaust is not new; Salter says it's been used for six years on big power-plant diesel generators. But while power plants run on a steady engine load at a consistent rpm, truck engines vary rpm all the time. That means the amount of Eurea sprayed into the exhaust must be constantly adjusted, or ammonia will end up coming out of the tailpipe. "That's worse than the original problem," says Salter.
So far, Mack has achieved 70% effectiveness with its SCR system and plans to boost its real-world tests. The company will add 10 trucks to its test fleet over the next 12 months. This time, they will be vocational vehicles, mostly garbage trucks in city operations.
Salter says Mack is also working with a variety of particulate filters to reduce PM exhaust levels. These filters will use precious metals, such as platinum, to eliminate particulates. Though effective, these filters are expensive and could increase engine costs.
He echoes Charbonneau's concerns that without ultralow-sulfur fuel there will be no chance to reach the EPA's 0.01 g/bhp.-hr. PM requirement by 2007. "Ultralow-sulfur fuel is a key component for PM reduction," he says. "A 10- to 15-ppm range should work."
EGR According to Salter, Mack is also experimenting with EGR systems to help cut down on PM exhaust levels. But this solution would require the addition of extra valves and manifolds for recirculating the exhaust back into the engine to `burn' away excess PM. That would require engine computers to meter the flow of exhaust as a function of speed and load on the engine, which can get complicated.
Another concern with EGR is that it can increase sulfur and water levels within the engine. "The sulfur oxides in diesel exhaust can combine with water to make sulfuric acid, and if that condenses within the engine during EGR, you're at serious risk of starting a chemical attack on the engine," he says. "You must keep the sulfur and water from condensing in the engine cylinders, especially; we're working with strategies that would prevent that from happening."
EGR can also increase soot levels, which can compromise the engine's oil, if you're not careful. "High levels of EGR use often provide an opportunity to drive more soot into the engine oil," Salter says. "One solution is to create an oil additive package to compensate for higher soot levels. That way, the service intervals for oil don't change."
David Semlow, marketing manager for Caterpillar Truck Engine Div., says that EGR remains the system of choice for his company to attack diesel emissions, both for heavy- and medium-duty trucks.
"Our technology center is spending $3 million a day looking at emissions control systems, but we believe EGR is still our prime path to reducing emissions," Semlow says. "Right now, we don't have any concern that we can't get to the 2007 levels with the technology we're working with."
Again, ultralow-sulfur fuel remains a critical starting point, regardless of the emissions technology. "Without it, we aren't going to get there, and we believe 5-ppm fuel is the best option for the customer and the economics of emissions reduction technology," Semlow says.
PERFORMANCE AND COST But regardless of the way engine manufacturers reduce exhaust emissions, the end result must not affect current performance factors, says Salter.
"The devil is in the details with these systems," he explains. "We need to iron out those details to achieve near-transparency for the customer. The oil must remain in good shape, fuel economy must be maintained and the truck must operate the same - without throttle lag or other performance inhibitors.
"The cost of using EGR, catalysts, filters and other emissions control technology must also be dealt with," Salter adds. "These are not $100 devices you just attach to the exhaust stack. We're looking at thousands of dollars worth of additions in today's production costs."
According to Semlow, Caterpillar believes providing the best total engine value will be the key calculation for engine makers as new emissions control technologies come into play.
"We can't say what new emissions controls will cost the customer. We still have two years of work ahead of us," he explains. "We will need, however, to concentrate on several factors - reliability, low operating cost, good fuel economy and best life to overhaul - all in one package. That means we have to do everything we can so there are little or no negative effects from new emissions controls."
Reducing the overall weight of diesel engines and stretching their life cycles will also remain priorities, says Salter. "We have a multi-year plan to take 10% of the weight out of our engines, regardless of the emissions debate," he says. "We're also aiming at one-million-mile overhauls, so typical new truck customers, who own their vehicles for three to four years, will never need an overhaul."
Yet to stay focused on those priorities, engine makers must first tackle - and solve - the emissions question, says Salter. "Once we get past emissions concerns, we can get back to wholly concentrating on those issues," he adds. "But we have to get emissions behind us first."