A Sensible Introduction to Tier 4 from Volvo Construction Equipment

What is Tier 4? How does it work? Why do we need it? When must we have it in our construction equipment? How will Tier 4 affect you, an off-road equipment owner? This is a complex subject, one full of technology and engineering detail that we probably do not need - nor understand -but must bear the burden of trying to comprehend.

The information on Tier 4 provided in this document will ease that burden and answer specific questions you have raised. And the source is quite reputable. Volvo built its first internal combustion engine in 1893, and since then the company has become the world's second largest manufacturer of heavy-duty diesel engines in the 9 to 18 liter category. The new generation of Volvo diesel engines, featuring Volvo Advanced Combustion Technology - V-ACT - has been engineered for off-road applications and to meet the specific needs of each Volvo machine. They are solid proof of the company's high level of engine technology and experience in successfully applying innovative solutions for performance and productivity - and to meet the requirements of Tier 4.

How and when will the tighter emissions standards impact off-road customers?

Engines 25 to 75 hp (19 to 56 kW):

Tier 4 started in 2008 for engines less than 75 hp (56 kW). In this power range Volvo has achieved 2008 Tier 4 emissions levels without the need for exhaust aftertreatment. 2013 will see another significant reduction in emissions.

For Engines 75 hp (56 kW) and greater Tier 4 is comprised of two significant stages. First is Tier 4a - sometimes referred to as interim Tier 4 or Tier 4i and second is Tier 4b - sometimes referred to as Tier 4 final. The Tier 4 standards require significant emission reductions of both particulate matter (PM) and Nitrogen Oxides (NOx).

Tier 4a - is a significant PM or black smoke/soot reduction along with a significant NOx reduction. NOx is defined as nitrogen monoxide (NO) and nitrogen dioxide (NO2).

Implementation:

  • 2011 for 175-750hp (130-560kW)
  • 2012 for 75-175hp (56-130kW)

    Tier 4b - a further but substantial NOx only reduction

    Implementation:

  • 2014 for 75-750hp (56-560kW)

    The Emissions Box: In general what is done within the engine to reduce NOx creates PM. What is done to reduce PM creates NOx. As high temperatures burn off the black soot or PM, it creates NOx. Conversely, cooler temperatures reduce NOx but increase soot (PM). This creates the problem of "getting in the box" that the engine developers fret about. Below is a graph of the different "boxes" showing how the levels of PM and NOx emissions have been drastically reduced over the years. The smallest red box shows the levels in 2014.

    Moving forward we will see "in-cylinder" solutions and "external" solutions to emissions reductions. In cylinder solutions take care of emissions (either all or part) within the cylinder or combustion chamber. These solutions may have external help, like cooled exhaust gas recirculation (EGR) but ultimately what leaves the cylinder through the exhaust port meets the specific goal of the manufacturer. If only part of the emissions equation is solved in cylinder, what is left must be treated externally. In the case of particulate matter treated externally, the use of a particulate filter may be used. NOx can be addressed through the use of an SCR catalyst. There are arguments about which solutions provide the best efficiency, convenience and performance.

    Also new:

  • Tier 4 emissions certifications require that the entire system of engine and any aftertreatment system be certified together. Emission controls are no longer confined to the engine itself.
  • Tier 4 also ushers in a new test cycle to better simulate actual off-road operation referred to as the Nonroad Transient Cycle (NRTC).
  • Not-to-exceed standards (NTE) also come into effect with Tier 4 to help assure emission standards are met and maintained.

    Crankcase Emissions:

    Emissions from the crankcase will now also be included in the total emissions calculation. Crankcase emissions come from the hose that in the past has typically run from the top of the engine and positioned to vent blow-by (combustion gasses that slip by the pistons) containing oil mist directly to the atmosphere. This also allowed oil to drip directly on the ground. Crankcase breather systems are evolving to separate the oil and return it to the crankcase. The gasses themselves are counted within the overall emissions.

    What it is like around the rest of the world?

    For customers and engine/machine manufacturers that operate on multiple continents, there will be new challenges. For North America and Europe, Tier 4a is very similar to Stage III B in Europe and Tier 4b is similar to Stage IV. NA and Europe are what is referred to as "harmonized" - when the emissions and implementation timeframes are the same (or close enough). Japan will likely introduce regulations similar to and in the same timeframe as the EU and North America.

    Tier 4 regulations require the use of Ultra Low Sulfur Diesel (ULSD) (15ppm down from 500ppm sulfur). This of course is the same fuel required by 2007 on-highway truck and becomes effective for off-road in June 2010. Lower levels of sulfur produce less PM and sulfur dioxide. Generally ULSD is also required to allow the use of catalysts in some emissions control system. Emissions and fuel regulations are not the same and can very greatly around the world. As we move into Tier 4a, we will be forced to have different solutions in different parts of the world due to fuel availability.

    How will we get there and meet our customer's needs?

    Off-road regulations lag on-road regulations, by about four years in recent times. 2007 on-road saw the implementation of diesel particulate filters and ULSD. We on the off-road side will likely see the same type of technology make the transfer to off-road beginning in 2011 for engines 175 hp (130 kW) and above.

    Similarly, on-road will see further emission reduction and new technology introduced in 2010. Off-road is poised to see another round of emissions reductions for Tier 4b in 2014. We will carefully evaluate all technology to access its fit in off-road applications.

    Volvo is a leading global manufacturer of engines for both on-road and off-road. This positions us incredibly well to transfer our vast experiences and technologies already developed, tested and productionized in the global on-road sector and apply it to our off-road development. Top competitors cannot offer this level of experience. Let's talk about some of the technology.

    Technology

    Particulate Filter:

    A particulate filter is used to collect the PM generated by combustion. Often called a particulate trap, it does just that - traps the PM. As more and more material is collected, backpressures increase and the filter must be cleaned. The filter cleans itself by oxidizing the material in a process called regeneration. A separate muffler is typically not needed, as the particulate filter adequately silences the exhaust.

    Regeneration:

    Cleaning of the particulate filter is accomplished by regeneration. Regeneration of the filter cleans it of PM by converting it to NO and H2O.The temperature within the filter must be at a certain level to make this happen. Regeneration can happen passively, actively or a combination of both. Passive regeneration is accomplished through the use of a catalyst and requires a minimum exhaust temperature to make the reaction happen. Active regeneration is done by adding heat through the use of a burner in the exhaust. A small amount of fuel can also be injected across a catalyst, raising the temperature and oxidizing the PM. All this happens while the engine is running and results in no loss of production.

    Just like the on-road particulate trap, ash is generated through the burning of small amounts of engine oil. Ash cannot be oxidized and therefore it collects and the trap will have to be cleaned at regular intervals. The use of low ash oils and advancements in engine oil control technology help to greatly reduce the need for ash cleaning.

    Cooled Exhaust Gas Recirculation (EGR)

    Cooled EGR is very effective at lowering combustion temperatures, therefore reducing NOx. Controlled amounts of exhaust gas are routed through a cooler and routed back into the engine mixing with the fresh air in the cylinder. The process reduces the oxygen concentration and lowers the combustion temperature. The amount of EGR varies from mild to massive.

    Air Handling and Turbo Charging

    Turbo charging is part of the emissions design equation and results in the capability to deliver the optimum pressure in the intake and exhaust manifolds. This makes it possible to tailor the EGR flow back to the inlet manifold and also have optimum performance and fuel economy. Wastegated and Variable Geometry Turbo (VGT) options allow specific tuning based on performance requirements. V-ACT (Volvo Advanced Combustion Technology) continues to evolve, enhancing fuel injection and air handling, along with a new generation of engine management systems with greater speed and precision.

    SCR

    To get the significant reduction in NOx for Tier 4b, we will see some different approaches in the market. One of the solutions to NOx reduction is Selective Catalytic Reduction (SCR). SCR technology utilizes an additive called Diesel Emission Fluid (DEF) which is a non-toxic liquid (urea) currently produced and used in agriculture, food and cosmetics. DEF is injected into a catalytic converter which converts the NOx to harmless Nitrogen. If SCR technology is chosen, distribution of the additive will already be well established in the on-highway market due to the majority of engine manufactures introducing it in 2010.

    Construction equipment requires specific engine performance characteristics. Volvo Construction Equipment has long recognized this, tailoring engine technology to optimize all aspects of machine operation and ownership. Other Volvo Group companies will ultimately choose the right technology from the vast array of tools in our tool box to optimize engines to meet their customer needs and the demands to meet the ever increasing environmental challenges.

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