Since 2008, the Environmental Protection Agency (EPA) has been phasing in a series of “tiered” emission regulations to reduce harmful exhaust gas for diesel powered equipment. The standards require significant emission reductions of particulate matter (PM) and nitrogen oxides (NOx).
Today’s Tier 4 Final emission standards represent a 95% reduction in emission levels compared to non-regulated amounts. As government mandates, all new products must meet these requirements, but machine owners can still elect to use existing equipment.
Therefore, the responsibility solely falls on engine manufacturers to not only meet these requirements but do so while maintaining qualities that are advantageous to the rental power industry such as performance, reliability, productivity and cost.
PM is defined as the black smoke or soot found in diesel engine exhaust, and NOx is defined as nitrogen monoxide and nitrogen dioxide. Tier 4 standards require that both be significantly reduced; however the two work independently and against each other. There are technologies that lower PM, but often increase the NOx levels and vice versa.
As a result, engine manufacturers implement various strategies to meet stringent Tier 4 standards while also bringing enough added value to encourage rental operations to actively select these solutions.
Tier 4 solutions often offer advanced fuel injection systems, which precisely control the fueling process through a series of carefully timed microbursts. This injection timing provides greater control of combustion for the cleanest, most efficient fuel burn. In a rental setting, generator sets are often utilized in remote or unattended locations. But increased fuel efficiency can result in less frequent refueling charges, which saves the customers costs over the rental period.
Exhaust gas recirculation (EGR) may also be utilized to lower the engine’s combustion temperature. The EGR valve allows a small amount of non-combustible exhaust gas to re-enter the engine cylinder and combine with the combustion air. This lowers the combustion temperature and reduces the level of NOx output. By optimizing combustion, fuel consumption is lowered thus reducing the amount of diesel exhaust fluid (DEF) required.
Beyond in-cylinder advancements, a variety of aftertreatment components are available to complement engine optimization to exceed customer expectations for productivity, fuel efficiency and service life. In this process, gases flow through the canister and are brought in contact with the catalyst that oxidizes the unburned hydrocarbons (HC) to reduce emissions.
A diesel particulate filter (DPF) is a device designed to capture diesel particulate matter or soot from the exhaust stream of a diesel engine. The device uses a series of alternately block channels within the filter to force exhaust gas to flow through the walls and capture PM.
Selective catalytic reduction (SCR) is a technology that injects a small amount of DEF into the exhaust upstream of a catalytic chamber. An electronic controlled DEF injector sprays a precise amount of DEF into the exhaust stream. Most engines have a targeted flow rate of 2-3% of diesel fuel consumed. When the DEF and exhaust enter the catalytic chamber, a chemical reaction occurs that converts NOx to nitrogen (N2) and water (H2O). In a rental application, SCR allows for lower fuel consumption through combustion optimization and increased productivity.
As previously established, Tier 4 Final solutions require that PM or soot must be removed from the DPF to ensure emissions criteria are achieved. The process is called regeneration and there are two available options for engine manufacturers.
The first method of regeneration is passive regeneration. In a passive regeneration system, the DPF restores on its own during normal operation. Most passive regeneration systems introduce an oxidation catalyst into the process to oxidize the PM, but to create the oxidation the exhaust temperature must be raised. Because of this, passive regeneration is not preferred by rental applications, as many operations are lightly loaded and do not reach the optimum temperature for regeneration to occur. Some manufacturers that rely on passive regeneration have incorporated an on-board load bank to increase the load in order to meet the required exhaust temperature for regeneration to occur. This adds increased cost and components to the generator set.
A more efficient regeneration method for rental applications is active regeneration. In an active regeneration system, the soot level of the DPF is monitored and it triggers regeneration when thresholds are reached. When the system requires regeneration, it will induce it and utilize a fuel burner that will burn or oxidize the soot over the catalyst. This strategy will be more efficient in rental applications, where load levels may fluctuate. Regeneration will occur independently of the load variation and ensure optimal performance of the DPF.
A built-in fuel efficiency benefit of Tier 4 Final solutions is the required use of ultra-low sulfur diesel fuel (ULSD). The improved fuel blend reduces the sulfur content from 500 ppm in low sulfur diesel fuel to 15 ppm in ULSD. Although ULSD fuel comes at a higher cost, this will be somewhat offset by the increased fuel efficiency of up to 5%. Improved fuel efficiency can translate to thousands of dollars over a given rental period. Plus, using fuels with higher levels of sulfur often results in operational problems and jeopardizes component life. ULSD can be utilized in all legacy engines as well, so there is no need to purchase multiple fuels.
With today’s Tier 4 Final standards, engine manufacturers are going above and beyond to strategically and systematically implement technologies that not only meet stringent requirements but also establish these solutions as beneficial assets to any rental operation.
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How are you impacted by Tier 4 Final emission standards?
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Does improved fuel efficiency play a role in selecting a solution?