New technologies will be needed to meet the next round of federal diesel emissions standards. Here are the details on the strengths and weaknesses of the most likely near- and long-term candidates currently under evaluation by engine makers.
Recent disagreements between the Environmental Protection Agency (EPA) and engine manufacturers have created a good deal of uncertainty over the timetable for introducing stricter diesel engine emissions standards. No matter what the outcome of those discussions (see sidebar), one thing is certain diesels will soon be required to make another major contribution to cleaner air. Engineers are currently struggling with a variety of technologies to meet the stricter emissions requirements, and the issue for fleets is what the various solutions will mean in terms of cost, efficiency, durability, and overall operating characteristics.
In general terms, EPA is concerned about two components of diesel emissions particulates, which are solids created by unburned fuel and by-products, and oxides of nitrogen, which are called NOx for short and are linked to ozone-layer damage. Over the last decade, EPA requirements have largely addressed particulate emissions, which, according to the Engine Manufacturers Assn. (EMA), are now 90% below levels commonly seen in 1987. The next major drop in emissions, scheduled for 2004, focuses on NOx emissions, requiring that they drop 50% from current levels. NOx is already 70% below 1987 levels, according to EMA.
The problem is that particulates, NOx, and fuel consumption form an interrelated triad. Reducing one usually results in increased levels for the other two. For example, lowering combustion temperatures in the cylinder cuts NOx but boosts particulates, and may or may not have a negative impact on fuel consumption. Despite the interrelation, EPA is demanding that both emissions components be cut sharply, while the market is also demanding better fuel efficiency.
As stringent as those requirements for 2004 may be, they are still five years off. Theoretically, that should give engine makers enough time to make an orderly transition to the new technologies that will be needed to cut NOx while maintaining current particulate levels without sacrificing fuel efficiency. But that timetable has been thrown into doubt by the current negotiations between EPA and all of the major diesel engine manufacturers. While both sides have agreed to avoid all public comment until they reach a final agreement, the most likely outcome is that the 2004 deadline for NOx will be moved up perhaps to as soon as 2000 or even the coming year.
What can the engine companies do to satisfy the more stringent standards? The following chart outlines some of the technologies that are most likely to be used within the next four years and those that might be developed in five years or more as long-term solutions.
The chart is based on research by Steve Berry, manager of advanced engineering and materials for Mack Trucks. It quickly describes each of the major technologies, outlines benefits and potential shortcomings, and gives a relative indication of cost. Given the trade-offs involved in controlling engine emissions, in all likelihood the short- and long-term solutions that are eventually chosen by engine makers will include some combination of these individual technologies.
In general, these are the major technologies being evaluated now, says Berry. Some may eventually fall by the wayside and others may be introduced, but these are the ones getting most of the attention right now.
Why it matters Every diesel engine sold in the United States has been certified by the Environmental Protection Agency (EPA) that it meets federal emissions standards. Despite that approval, earlier this year EPA notified heavy-duty diesel engine manufacturers that it believed they were violating the Clean Air Act by selling engines that, in effect, made an end run around its certification tests.
At issue is the EPA-mandated testing procedure that manufacturers are required to use in certifying their engines. It appears that the test cycle accurately predicts engine emissions under urban stop-and-go conditions, but todays electronically controlled diesels produce significantly higher nitrogen oxide (NOx) levels under real-world highway conditions.
EPA says the electronic controls are defeat devices intentionally designed to pass the tests while sacrificing NOx reduction for better fuel economy in normal operating conditions. Such devices are illegal under the Clean Air Act, which specifies stiff penalties for anyone selling them. For their part, the manufacturers point out that they must use the EPA tests to get the needed certification and that they never intended to defeat the emissions requirements.
Under pressure from environmental groups to address the situation, the agency has been trying to negotiate a settlement since February with the individual manufacturers, including Cummins, Caterpillar, Detroit Diesel, Mack Trucks, Volvo Truck, and Navistar. Just as this issue was going to press, EPA announced that it had reached agreements with the engine makers.
Initial reports indicate that the engine companies will pay over $1 billion in fines, contributions to alternative fuel demonstration projects, and efforts to produce cleaner engines sooner. Introduction of engines meeting lower NOx emissions standards originally scheduled to take effect in 2004 is now scheduled for October 2002. Thosestandards will lower the present 4-gram NOx standard by nearly 50%, to 2.5 grams. The engine makers will not have to recall electronically controlled engines already on the road, however.
Clearly the revised deadline will require engine makers to adopt new technology solutions like those outlined in the accompanying chart.
The agreement also calls for current engines to be upgraded during overhauls. Although how that would be accomplished and who would pay for those upgrades was not clear, chances are some of the technologies described in the chart would also be retrofitted during overhaul.
(For early fleet and engine supplier reactions to the EPA settlement, see Point of Departure on page 6.)
(Please refer to pages 44-45 of FLEET OWNERs November 1998 issue to view detailed charts.)