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).
- 2011 for 175-750hp (130-560kW)
- 2012 for 75-175hp (56-130kW)
Tier 4b - a further but substantial NOx only reduction
- 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.
- 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.
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.