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CARB holds a public workgroup on Tier 5 emission standards for off-road engines

8 August 2022

The California Air Resources Board held today a public workgroup meeting to discus the development of Tier 5 emission standards for new off-road diesel engines. The topics included (1) the development of a Low Load Cycle, (2) emission credits for hybrid vehicles, (3) GHG emissions standards, and (4) small volume manufacturer provisions. All of these concepts represent ideas under consideration—no regulatory proposal has yet been released.

Other components of the Tier 5 regulation were discussed at earlier meetings—the structure of the standards and the targeted emission reductions at a workshop in November 2021; and the Tier 5 in-use testing program in May 2022.

CARB staff confirmed at the meeting that the US Environmental Protection Agency (EPA) is not currently developing a corresponding federal-level Tier 5 emission regulation. CARB intends to adopt the Tier 5 standards in 2025, to become effective around 2030. However, in the absence of a federal rule, California-only Tier 5 standards will have a rather limited scope, because California has been pre-empted from regulating emissions from new farm and construction equipment under 175 hp—a category that represents some 50% of off-road engine emissions in the state. Furthermore, current regulations do not prevent California residents from bringing off-road engines and equipment from other states.

Off-road Low Load Cycle. Current test cycles do not adequately represent emissions during low load engine operation, particularly in engines equipped with SCR aftertreatment. Testing over the Low Load Application Cycle (LLAC)—developed by the Southwest Research Institute (SwRI) based on proprietary data—showed NOx emissions that were up to 19 times higher than during the NRTC.

CARB—in cooperation with the SwRI and the University of California Riverside—is now developing a new off-road Low Load Cycle (LLC) to be used for Tier 5 certification and compliance testing, in addition to the existing off-road tests. The objective is to develop an LLC applicable to variable speed off-road diesel engines between 56 and 560 kW that is indicative of engine operations under low load and low exhaust temperature conditions. The development is based on long-term monitoring data from 240 off-road diesel engines in different applications, and on short-term testing data from 130 engines. Cycle translation and engine dynamometer testing at the SwRI is scheduled for late 2022, and testing results will be available in early 2023.

Hybrid vehicle credit. According to CARB staff, most off-road hybrids are reporting fuel savings of 20-25% (manufacturers’ claims), while there are no reports of any NOx emission benefit. Under the considered hybrid credit, hybrid vehicles that can achieve a minimum of 20% fuel consumption reduction would be eligible for a NOx emission credit. Manufacturers would have to provide either (1) fuel consumption data and an engineering argument supporting the potential for NOx emissions reductions based on the reductions in fuel consumption from the hybrid system compared to an equivalent conventional equipment, or (2) emissions data demonstrating NOx emission reductions of the hybrids.

The default NOx credit would be equal to 5% of the existing emission standard (Tier 4 final or Tier 5). Higher credit levels, up to a a maximum of 10% of existing NOx emission standard, could be considered if the OEM provides actual NOx emission test data demonstrating higher NOx emissions.

GHG emission standards. New GHG emission standards are envisioned that would apply to non-preempted off-road Tier 5 diesel engines above 19 kW, measured over the NRTC and the steady-state certification cycles. The following GHG reducing or capping standards have been considered (a reducing standard requires an emission reduction from the current levels; a capping standard is intended to prevent an emission increase in future engines):

Small volume manufacturer provisions. As was the case with the Tier 4 regulation, small volume manufacturers would be granted certain compliance flexibilities during the initial two years of the Tier 5 program. These flexibilities would include more relaxed NOx emission standards, minimal or no change in useful life periods, and no LLC certification requirements. Additionally, options are being considered in lieu of off-road in-use testing and in lieu of full OBD compliance

California regulations define a small volume manufacturer as an OEM who had annual US-directed production of no more than 2,500 units in 2002 and all earlier calendar years, and has 1000 or fewer employees. As the Tier 5 standards would apply only in California (at least in the initial period), a new California-specific definition is proposed, with California-based sales volume criteria, including a total annual CA-directed off-road diesel engine sales ≤ 200 total units and ≤ 60 non-preempted units prior to 2020.

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CARB has also been developing a program to further reduce emissions from in-use off-road diesel engines. The in-use program—which is separate from the Tier 5 new engine standards—is to be adopted as amendments to the existing In-Use Off-Road Diesel-Fueled Fleets Regulation (Off-Road Regulation). These amendments are intended to help achieve the goal of reducing California NOx emissions from the construction and earth moving sector by 7.5 tpd by 2031, which was set out by the Draft 2020 Mobile Source Strategy.

Source: CARB