Diesel Oxidation Catalyst (DOC) Retrofit

Phased Emission Generator Tier Ratings

The EPA implemented emissions reductions in phases to allow scientists, manufacturers and the market to develop technologies, knowledge and funds necessary for compliance. Each tier level provides a cap at which point emissions must be restricted, and each advancing tier builds off of the last.

Each tier level also has a certain standard with regard to harmful emissions and provides a cap at which point emissions must be limited. The standard progresses over the years in accordance with the tier level.

The intended and primary emissions to be reduced include:

• Nitrogen oxides (NOx)
• Hydrocarbons (HC)
• Carbon monoxide (CO)
• Particulate matter (PM)
• Non-methane hydrocarbons (NMH

Tier 1 & Diesel Generator Emissions

Though Tier 1 standards were published in 1991, the implementation for diesel engines and generators did not begin until 1996 with the intention that all diesel engines and generators be in compliance by 2005. Initially, Tier 1 standards focused on diesel equipment under 37 kW (50 hp) with the phase-in period from 1996 to 2000. The below table identifies Tier 1 standards related to diesel engine power and harmful gases to be limited.

Tiers 2 & 3 Diesel Generator Emissions

Tier 2 standards were published in 1999 and Tier 3 standards were published shortly thereafter. These phases, however, did not begin until 2001 with all engines to be in compliance by 2008. These two levels required engines that were more sophisticated in design and advanced in performance in order to meet the criteria set out in the regulations. The below table identifies Tier 2 and 3 standards related to diesel engine power and harmful gases to be limited.

To note, sulfur content was not originally limited by environmental regulations in Tier 1 for non-road diesel fuels but was later mandated and required to be met by 2007 in Tiers 2 and 3.

Tier 4 – The Current Emissions Standard For Diesel Generators

Tier 4 is in effect today, so all new prime power and portable diesel generators should be manufactured to meet this tier requirement. Tier 4 is, of course, the strictest of all previous regulations and requires the most advanced technologies to achieve the greatest reduction in emissions available today: near-zero emission levels.

Tier 4 emission standards began being phased-in in 2008. The regulations set out to reduce NOx, particulate matter, and hydrocarbon emissions substantially with respect to all off-road and on-road engines and generator sets. Carbon monoxide standards, however, remain relatively similar to those established in Tiers 2 and 3.