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Mechanics Corner: Clean diesel technology – Tier 4 and more

Diesel Technology Forum Published on 28 February 2011

The following information was obtained from the Diesel Technology Forum. The article reviews what Tier 4 is, how it emerged, and the differences among Tier 4 engines.

Clean diesel technology is now the standard for all new technology, everything from new passenger cars and pick-up trucks to highway commercial trucks. Clean diesel is a system of three key parts: cleaner diesel fuel, advanced engine technology and aftertreatment.

Now, starting in 2011, this new generation of clean diesel technology for off-road engines and equipment known as Tier 4 will be making its way onto the construction and industrial jobsites and farm fields around the country.

What is Tier 4?
Tier 4 refers to a generation of federal air emissions standards established by the U.S. Environmental Protection Agency (EPA) that apply to new diesel engines used in off-road equipment.

Essentially it requires manufacturers to reduce the levels of particulate matter and oxides of nitrogen (NOx) to a level that is 50 to 96 percent lower than the existing generation of diesel engines.

It is important to note that Tier 4 emissions requirements apply to new products only and do not apply retroactively to any existing machines or equipment.

How were the “tiers” established? What are the other tiers?
The “tiered” series of emissions regulations has been in effect over the last 13 years governing new off-road engines and equipment. These standards establish progressively lower allowable emissions of nitrogen oxides and particulate matter.

It is a complex system and its compliance dates are based on the size of engine (in hp and kW-hr) and other factors.

The Tier 4 standards provide manufacturers with a flexibility provision and include an interim step – Tier 4 interim – which requires substantial reduction in PM emissions and flexibility in lowering oxides of nitrogen.

A Tier 4 final step includes additional reductions in NOx and HC emissions.

A Tier 0 engine has basically no modern emissions controls, may be referred to as unregulated and is likely to be a mechanically controlled engine rather than electronic. Each progression of standard level – Tier 1, Tier 2 and Tier 3 engines – all are lower in emissions and more advanced technologically than the previous generation.

The use of electronic engine controls, new higher-pressure fuel injection systems and advanced turbocharging are all technologies that reduce emissions and aid performance.

How will Tier 4 engines be different from previous engines?
While each manufacturer will pursue their own technology path and emissions compliance strategy, there are a number of new technologies coming on many Tier 4 engines and equipment.

For the equipment, the changes likely to be most noticeable are in the packaging and placement of the aftertreatment system and the increased size of the air intake system to accommodate the needs for increased airflow and cooling.

New changes to the engine will likely mean that engine compartments may be reworked to manage the new systems.

Some OEMs have indicated they will package any new exhaust system configuration inside reworked sheet metal skin, while others will place the systems in their traditional locations with additional shielding and mounting hardware to accommodate the heavier exhaust system components.

Most Tier 4 engines will be electronically controlled, meaning that a computer will monitor and adjust the fuel and air mixture to optimize emissions and performance for the engine on a real-time basis.

In addition, changes in the engine will include new and different systems to accommodate the increased heat rejection of the new engines. For the first time, most off-road equipment will likely incorporate emissions control technology in the exhaust system, such as a catalytic converter and/or particulate filter, typically in place of the existing muffler and exhaust system.

Some of these new exhaust aftertreatment systems mean that the pipes and placement of the muffler and exhaust may be different than previous generations of equipment, or potentially larger in size to accommodate the new functions and in some cases, hotter temperatures of the exhaust.

There are two primary technology pathways for meeting the Tier 4 requirements: exhaust gas recirculation (EGR) or selective catalytic reduction (SCR).

EGR is a technique that recirculates a portion of the exhaust gases back into the combustion chamber, which has the effect of lowering the combustion temperature and reduces formation of NOx. This system will add additional manifolds and plumbing around the engine.

One of the biggest changes for engine and equipment dealers is that some engines/machines will utilize a new emissions control technology system known as selective catalytic reduction (SCR). This technology is also designed to reduce emissions of nitrogen oxides.

Widely used in Europe on heavy-duty trucks and in some U.S. stationary industrial and power generation settings, SCR technology is new to the U.S. for mobile on-road and off-road applications in 2010.

The majority of heavy-duty truck manufacturers began using SCR technology in their 2010 products, along with a number of light-duty diesel car manufacturers, and some manufacturers will use this in their off-road equipment offerings.  FG

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