Mazda Delivers First Hydrogen Dual-Fuel Rotaries to Customers
UK Exploring Use of Biodiesel and Straight Vegetable Oil in Commercial Fishing Vessels

EPA Tweaks Tier 2 Light-Duty Diesel Standards

The U.S. Environmental Protection Agency (EPA) is making minor amendments to the Tier 2 emissions standards to be applied to light-duty diesel vehicles. The changes relax a very limited set of standards for nitrogen oxides (NOx) for only high-altitude and high-speed/high-acceleration conditions.

These alternative compliance options will last for only three model years—2007 through 2009—during which time the agency expects advancements in diesel emissions control technologies to further develop to addresses the covered situations.

EPA designed these temporary alternative compliance options to be environmentally neutral, Manufacturers choosing them will be required to meet more stringent requirements in other aspects of the Tier 2 program including tighter particulate matter standards and a longer regulatory useful life.

The Tier 2/Gasoline Sulfur rule, enacted in 2001, phases in a single set of exhaust emission standards that applies to all light-duty vehicles (LDVs), light-duty trucks (LDTs) and larger passenger vehicles. To enable Tier 2 vehicle emission control technologies to be introduced and to maintain the programs’ effectiveness, EPA also requires reduced gasoline sulfur levels nationwide.

Under the Tier 2 program, manufacturers have the flexibility to certify Tier 2 vehicles to different sets of exhaust emission standards that EPA refers to as “bins.” The Tier 2 program implements a structure that has eight emission standard bins. Manufacturers have to choose the bins so that their corporate sales-weighted average NOx level is no more than 0.07 grams per mile (g/mi).

Because diesel vehicles still face some very specific technological challenges in meeting the full suite of Tier 2 requirements, EPA is providing very limited relief with the just-announced changes.

These two narrow areas of operation are the most challenging for diesel vehicles due to the relatively high engine loads of the high-speed/high-acceleration test cycle (known as the US06 test cycle) and the relative lack of oxygen at high altitudes.

The new technologies that have been applied to bring these vehicles into Tier 2 compliance will require further fine-tuning fully to address emissions under these conditions. EPA is projecting that, with only a few more interim years of refinement, these technologies will be able to achieve full compliance under these narrow conditions, as they have already demonstrated under typical operating conditions.

The new ruling contains two voluntary alternative compliance options for 2007 thru 2009 model year diesel vehicles: the US06 Option and the High-Altitude Option.

In the US06 Option, LDVs could meet a slightly higher 4,000 mile US06 standard (0.25 vs. 0.14 g/mi). As an offset, any such vehicles must meet the 50,000 mile Supplemental Federal Test Procedure (SFTP) composite standard equivalent for a full useful life of 150,000 miles (as opposed to 120,000 miles under the base Tier 2 requirements).

In the High Altitude Option, Bins 7 and 8 vehicles, at high altitude only, are allowed to meet a slightly higher in-use NOx standard of 1.2x the Federal Test Procedure (FTP) standard to which they are certified. In return, any such vehicles must comply with the bin 5 PM standard of 0.01 g/mi (vs. bin 7/8 PM standard of 0.02 g/mi), and certify to FTP standards for all regulated pollutants standards for a useful life of 150,000 miles (vs. 120,000 miles under the base Tier 2 requirements).


Rafael Seidl

Of these, the US06 option is the more significant as modern diesels are all turbocharged anyhow, making them fairly insensitive to altitude.

With oxydation catalysts standard issue and particulate filters now available for most Euro 4 cars, this voluntary option should make it easier for carmakers to increase the range of turbodiesel vehicles available to customers in all states except CA, NY, MA, VT and ME (which follow the stricter CA regs).

The longevity requirement is >2x that imposed by Euro 4. The engines and turbos themselves are very durable but the DPF recuperation parameters might have to be tweaked a little.

The expectation is that by 2009, SCR and/or DeNOx technology will be made available in passenger cars. Right now, SCR is available but quite expensive. The operator must also regularly fill up on a consumable catalyst called AdBlue (a 35% aeqeuous solution of pure urea). A distribution infrastructure is being set up in Europe since Euro 4 trucks all use SCR. DeNOx does not need an extra fluid but it reduces fuel efficiency, is not yet effective enough at scrubbing NOx and does not yet have the required longevity.


Kills me how EPA is allover future tailpipe emissions but so lax on present ULSD implementation.

Rafael Seidl

What makes you say the EPA is lax? There was concern that a few retail outlets might not make the original deadline, so erring on the side of caution EPA gave them an extra 45 days to ensure a smooth transition. Ok, maybe that is not ideal but it's hardly the end of the world after many decades of dirty diesel.!OpenDocument


Because Euro has had ULSD since '94 and its not mandated here until basically hours before '07 models that require it roll. Oh and then DOT and EPA regs that cause "confusion" sheilding US automakers from true competition.

The comments to this entry are closed.