Emissions picture clears, aftertreatment ahead for nearly all engine categories

Diesel Progress North American Edition, Dec, 2004 by W. Addy Majewski

In our emission forecasts in previous years, we always discussed emission regulations with special focus on new diesel emission standards that have been visible on the horizon. This year we arrived at the point where "aftertreatment-forcing" emission standards are final for nearly all engine categories and few new regulations remain to be adopted in 2005 or over the next decade.

The Tier 4 regulation, finalized in May of this year, established emission standards for mobile non-road engines--such as those used in construction, agricultural and industrial equipment--which are similar to the 2007-2010 emission standards for heavy-duty highway engines. What this means is that non-road engines above 25 hp will have to be fitted with diesel particulate filters and non-road engines above 75 hp with some kind (it is not yet certain what kind) of N[O.sub.x] reduction catalysts, as summarized in an accompanying table.

The Tier 4 standards will be accompanied by the introduction of ultra-low (15 ppm) sulfur diesel for non-road engines from June 2010.

In Europe, Stage 3/4 non-road standards were also finalized in 2004, which also force the use of PM filters and N[O.sub.x] catalyst technologies, largely in harmonization with the U.S. Tier 4 regulation.

It should be perhaps noted that the PM limits to be implemented in 2007 for highway and in 2011-13 for non-road engines on the order of 0.01 to 0.02 g/bhp-hr--will bring the definite solution to the problem of diesel particulate emissions and the black diesel smoke, making both of them historical issues. (In fact. these limits are stretching the capability of current PM measurement methods: if more stringent PM emission limits are to be ever established in the future, they would require that the current gravimetric technique be replaced with some form of instrumental PM measurement.)

One might ask how "final" are these final regulations, or if they could be challenged by interest groups that will be eventually bearing the costs of added emission controls and the development of low emission engines, such as the trucking industry? There are two answers, one for PM and one for N[O.sub.x] emission standards.

Diesel particulate filters can be considered a relatively mature technology. At least in light-duty vehicles. DPFs have been used in high-volume applications in diesel passenger cars in Europe. with over 850.000 system sold since 2000. In the U.S., several heavy-duty engine manufacturers have been testing their 2007 truck prototypes and expressed confidence in the DPF technology. Therefore. it is very unlikely that the PM standards could be delayed or relaxed. On the regulatory side. many states have already adopted California standards--which in this case are identical to the federal ones --in order to make the regulation more resistant to possible challenges.

N[O.sub.x] control technologies, on the other hand. are far from being established. The U.S. Environmental Protection Agency (EPA) has voiced its support for the N[O.sub.x] adsorber catalyst (NAC) technology, for both highway and non-road engine use. But N[O.sub.x] adsorbers, despite intensive development effort since the late 1990s. have not vet been demonstrated as a durable technology on heavy-duty engines. If N[O.sub.x] adsorbers are to be commercially used from 2010. improvement in the catalyst durability and the cost of the system must be demonstrated.

The competing urea-SCR catalyst is a more mature technology, with first commercial heavy truck applications being implemented in Europe and Japan. Perhaps the biggest drawback of urea-SCR is the need to establish urea distribution infrastructure. Urea-SCR supporters, however, have argued that SCR is also more cost-effective when compared to NACs (which utilize high loadings of platinum catalyst), even when considering the cost of establishing nationwide urea infrastructure.

Finally, it is also possible, although uncertain in the 2010 time frame, that significant in-cylinder N[O.sub.x] reductions will be achieved through the use of homogeneous charge compression ignition (HCCI) or "massive EGR" concepts, thus lowering or even eliminating the required N[O.sub.x] reduction through aftertreatment.

In summary; timely implementation of the U.S. 2010 N[O.sub.x] standard depends on the progress in N[O.sub.x] adsorber technology.

To complete this forecast, we should focus again on the coming year 2005 and comment briefly on what will likely happen:

* Technology--Some U.S. engine manufacturers may be required (by the 1998 consent decrees that mostly dealt with highway engines, but did also include certain non-road provisions' to supply Tier 3 non-road engines starting in 2005. one year ahead of the regulatory deadline. While the Tier 3 standards close to 40% N[O.sub.x] reduction and no PM reduction relative to Tier 2) represent not nearly as much challenge as the future that we just discussed. In many cases manufacturers will take this opportunity to introduce new engine platforms that will be the basis for meeting Tier 4 limits in the 2011-15 timeframe.