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How are Diesel Emissions Measured and Regulated?

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Emission standards compliance is measured with engine or vehicle test cycles. These test procedures are used to verify that diesel engine designs meet the current existing standard. These tests are intended to create repeatable emission measurements and simulate actual driving conditions. Further, the methods to analyze captured data are regulated by the emissions standard.

The test cycles are a series of load and speed conditions performed on a dynamometer. Emissions measured on a vehicle (chassis) dynamometer are expressed in grams of pollutant per unit of distance traveled (ie. grams per mile). Emissions measured on an engine dynamometer are expressed in grams per unit of power delivered by the engine (for example grams per brake horsepower per hour).

Depending upon intended application for a particular engine, test cycles are divided into a series of steady (constant load and speed) and transient (dynamic load and speed) states or modes. Individual exhaust gas samples are collected and measured, or a stream of data is continuously analyzed from electronic sensors. Emissions are calculated for each mode, and then an overall result is calculated from weighted averages of all test cycles and modes.

Standards are separated and classified by tiers—and then bins within those tiers.

  • Tier Level 1 standards were published in June of 1991 and completely phased in as of 1997.
  • Tier Level 2 standards were adopted in 1999 with phase-in slated to be completed in 2009.

Tier 2 regulations have been extended to a broader range of vehicles including heavier medium duty passenger vehicles (MDPV) that were not covered in Tier 1. Additionally, Tier 2 includes an average fleet NOx as well as Certification Bins that have different levels of stringency. Think of them as drawers in a cabinet, with each one holding a particular document. Manufacturers can choose to certify particular vehicles to any of the bins; however, those vehicles are limited to use within the parameters set within that particular bin.

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