Tier 4 Diesel Emissions Regulations

Tier 4 Diesel Emissions Regulations

For many years, researchers, engineers and scientists have spent much time and funds improving diesel-powered engines to be not only more efficient in gas usage but also in power output. However as with every engine, particularly with ones used by construction companies, rules must be set in order to maximize the output while at the same time putting less strain on the engine. On the downside, this increases the price further when sold to consumers and will greatly affect the demand.

TIER 1-3. Tier 1 or the first federal standards for off-road diesel engines were adopted in 1994 for engines over 37 kW (50 hp) and phased-in from 1996 to 2000. A stricter Tier 2 covered the period 2001 to 2006. Tier 3, for engines 37-560 kW, took effect from 2006 to 2008. Engines manufactured with tougher emissions standards could earn them a title “Blue Sky Series”. Smoke standards of 20/15/50% opacity at acceleration/lug/peak modes, respectively are required of all engine sizes.

Table 1. Their 1-3 Emissions Standards


Table 2. Standards for earning “Blue Sky Series”.


With evolving technology come improvements. The most recent round of off-road clean-diesel sanctions, or Tier 4, will eliminate the engine that runs most construction equipment. A new guard of sophisticated, clean-burning, electronic engines are rendering the old, smoke-belching, mechanical diesels obsolete. Cleaner power costs more up front, but the long-term returns more than make up for it.

TIER 4 (2008 to 2015). Signed by the EPA for final ruling on May 11, 2004, Tier 4 standards require a 90% reduction of NOx (engines over 56 kW) and PM (over 19 kW), and stiff HC limits. CO emission limits stay constant from the Tier 2-3 stage.

Table 3. Tier 4 Emission Standards for engines UP TO 560 kW, g/kWh (g/bhp-hr)


Manufacturers may accredit all their engines to an alternative NOx limit in each model year within the phase-in period as an alternative to the required percentage of Tier 4 compliant engines. The following are the alternative Nox standards:

  • 56-130 kW engines:
    • Option 1: NOx = 2.3 g/kWh = 1.7 g/bhp-hr (Tier 2 credits used to comply, MY 2012-2013)
    • Option 2: NOx = 3.4 g/kWh = 2.5 g/bhp-hr (MY 2011-2013)
  • 130-560 kW engines: NOx = 2.0 g/kWh = 1.5 g/bhp-hr (MY 2011-2013)

Table 4. Tier 4 Emission Standards for engines ABOVE 560 kW, g/kWh (g/bhp-hr)

Nonroad Engines. Nonroad engines are all internal combustion engines, excluding stationary engines (> 12 months in one location), highway motor vehicle engines, engines exclusively used for competition, or aircraft engines.

Effective May 14, 2003, nonroad engines include ALL diesel powered engines, including stationary engines, used in agriculture in California. But in other states, stationary engines are not classified as nonroad.

EPA Reductions in Nonroad Diesel Fuels:

  • 500 ppm for nonroad, marine (NRLM) and locomotive diesel fuels effective June 2007
  • 15 ppm (ultra-low sulfur diesel) for nonroad fuel ffective June 2010, and June 2012 for marine and locomotive fuels

Nonroad engine categories EXEMPTED from nonroad diesel emission regulations:

  • Railway locomotive engines (Subject to separate EPA regulations)
  • Marine vessel engines (Subject to separate EPA regulations). Marine engines below 37 kW (50hp) are subject to Tier 1-2. Other marine engines exempted from marine standards may be required to comply to nonroad regulations.
  • Underground mining equipment engines.
  • Hobby engines (per cylinder<50 cm3)

Examples of Regulated Applications:

  • Forklifts
  • Skid steer loaders
  • Excavators
  • Portable generators
  • Bulldozers
  • Diesel lawn tractors
  • Road graders
  • Wheel loaders
  • Backhoe loaders
  • Logging equipment
  • Farm tractors

The diesel’s transition from mechanical to electronic operation is similar to a period in the 1970’s – a challenging decade of efficiency and reliability problems – when new fuel and emission rules began disabling gasoline engines. It took engineers years to fix these problems.

Diesel underwent heavy regulation in the last decade that will continue through 2015. It is therefore necessary for users to learn and master new technological improvements such as selective catalytic reduction (SCR), diesel particulate filters (DPFs), and diesel exhaust fluid (DEF). Nevertheless, the advancement of computer controls enables the engines to move into the digital age.


According to Chris Knipfer, a marketing manager of Bobcat Company, manufacturer’s engines that have 25 horsepower and below have met final Tier 4 requirements since 2008, while engines in the 25- to 75-hp range won’t even be subject to final Tier 4 until 2013, and engines such as Bobcat’s 99-horsepower product won’t be subject to final Tier 4 until 2015. Meanwhile 75-horsepower engines that meet interim Tier 4 (the stage before final Tier 4) are as what Knipfer pointed out “just getting out there”.

A small number of manufacturers were reluctant to discuss whether there would be price increases resulting from technological enhancements they were making to their products to satisfy the final requirements. But it was noted that the need for price increases, if any, varies by model, horsepower, and level of additional technology required to meet emissions regulations. And according to them, maintaining Tier 4-compliant equipment is not expected to require major changes to existing maintenance practices and procedures.

General maintenance operation and frequency, such as oil changes, inspections, and lubrication, differ by model, but they will not change specifically and in conjunction with the introduction of Tier 4 models. Some Tier 4-compliant tractors equipped with a diesel particulate filter will require removal and professional cleaning of that filter periodically, but not more frequently than every 4 months. Some companies will offer a filter exchange service through its dealers to accommodate this need.


Meeting Tier 4 in the lower horsepower ranges isn’t a discouraging challenge. For engines with 25 horsepower and below, it’s a matter of small internal adjustments such as changes in the air and fuel mixture to attain cleaner fuel combustion. That’s why manufacturers were able to meet the requirements for those engines four years ago.

While Tier 4 compliant lower-horsepower engines may be available in the market today, requirements for higher quality horsepower engines will grow exponentially over time and even more difficult to accomplish.

Engine costs will not be cheap and resale prices would take a plunge. Tier 4 engines are expected to be 25% more costly than Tier 3 versions by 2015. Another issue is the question of selling used Tier-4 equipment to unregulated markets such as South America, where clean diesel fuel is not readily available. Curt Hinkelman, Ritchie Bros senior vice president, stated that the market will adapt, and that low sulfur diesel will start to find its way. Manufacturers are also working on kits for overseas technicians to “de-tier” the machines so they can operate in countries that are slower to adapt, such as Africa and other 3rd world countries.

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