Is Your Generator Set Meeting EPA Tier 4 Emissions Standards?

More than 15 years ago – in 1996, to be exact – the U.S. Environmental Protection Agency (EPA) began to enforce limits on emissions of diesel exhaust from non-road diesel engines and stationary diesel-engine generator sets. These new standards limit the amount of nitrogen oxides (NOx), carbon monoxide (CO), particulate matter (PM), and non-methane hydrocarbons (NMHC) emitted by diesel engines. By 2015, these emissions will have been reduced by 99% since the 1990s – an impressive accomplishment!Diesel generator

The EPA diesel emissions standards have followed a “tiered” progression to greater reductions, starting with the initial Tier 1 standards in the late 1990s. The standards became more stringent in 2004, when the EPA’s Clean Air Nonroad Diesel Tier 4 standards were passed. According to this article, the phase-in schedule for Tier 4 standards began in 2008 and continues until 2015, starting with “Tier 4 Interim” standards and ending with “Tier 4 Final” standards. As of today, this leaves less than two years for industries to bring generator sets into Tier 4 Final compliance.

Additionally, in 2013, the EPA has added a “Not to Exceed,” or NTE test standard for Tier 4 diesel-regulated engines. Regardless of how an engine is operated, according to the NTE standard, an engine should not exceed maximum emissions.

What generator set applications are required to comply with Tier 4 standards?

  • Demand-response applications.
  • Prime power applications.
  • Applications involving mobile rental power units.

The Tier 4 standards are only required for generators in prime power applications (ones that run instead of a utility), and for generators that are in demand-response programs.

Generator sets can be brought into compliance to meet Tier 4 standards through in-engine improvements and with exhaust after-treatments add-ons. In-engine improvements may include:

  • More precise injection timing.
  • Advanced engine controls.
  • High-pressure common-rail fuel injection.
  • Advanced turbocharging.

Exhaust system add-ons include:

  • Selective Catalytic Reduction (SCR).
  • Diesel Particulate Filter (DPF).
  • Exhaust Gas Recirculation (EGR).

Whether you decide to purchase a new generator or update your existing one to meet these new standards, it’s important for all those in the power generation and emissions industries to understand and meet these new tiers.


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