Engine manufacturers reach agreement on NTE limits and in-use testing with US EPA and California ARB

12 June 2003

The Engine Manufacturers Association (EMA) announced that they have reached an agreement with the US Environmental Protection Agency (EPA) and the California Air Resources Board (ARB) that will settle several outstanding lawsuits on engine emission standard issues, brought by EMA and/or its members.

One of the major issues on the negotiation table were the “Not-To-Exceed” (NTE) emission limits. No technical details were revealed, but the EPA and ARB will issue guidance documents on NTE testing, which will address the manufacturers’ concerns. In particular, the guidelines will explicitly specify the requirements that manufacturers must meet during engine certification testing.

As part of the agreement, engine manufacturers volunteered to develop and implement a manufacturer-run program to test emissions from heavy-duty vehicles that are being used on the road today. This “in-use” testing program will provide information on the effectiveness of new technologies and controls in reducing emissions from heavy-duty vehicles under real world conditions. The program also will encourage further development of advanced portable emissions testing equipment that will make it easier to confirm that in-use vehicles continue to comply with all applicable emission standards throughout their useful lives. EPA will develop regulations to enforce the new in-use testing program, which will initially be implemented in model year 2005.

The NTE limits were first introduced by the 1998 Consent Decrees between the EPA and engine manufacturers. Since then, NTE limits have become a part of all new US emission standards for heavy-duty engines, including the 2007-2010 regulation. The NTE limits were designed to be an additional instrument to make sure that heavy-duty engine emissions are controlled over the full range of speed and load combinations commonly experienced in use. The NTE approach establishes an area (the “NTE zone”) under the torque curve of an engine where emissions must not exceed a specified value for any of the regulated pollutants.

The NTE test procedure does not involve a specific driving cycle of any specific length (mileage or time). Rather it involves driving of any type that could occur within the bounds of the NTE control area, including operation under steady-state or transient conditions and under varying ambient conditions. Emissions are averaged over a minimum time of thirty seconds and then compared to the applicable NTE emission limits. Engine manufacturers have argued that such a loose definition of test requirements makes it impossible to demonstrate engine compliance during certification testing, because one cannot test the engine under all operating conditions.

Source: EMA