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US EPA adopts 2027 emission standards for heavy-duty engines and vehicles

20 December 2022

Today, the US Environmental Protection Agency (EPA) adopted a final rule, “Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards,” that sets stronger emission standards for heavy-duty vehicles and engines starting in model year 2027. This action follows a proposed rule that was released in March.

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The final program includes new, more stringent emission standards that cover a wider range of heavy-duty engine operating conditions compared to today’s standards. The final rule also includes provisions for longer useful life and warranty periods and requires that manufacturers to design more tamper-proof engines by limiting tamper-prone access to electronic pollution controls.

In addition, the final rule includes other limited amendments to emission regulations for other sectors, including light-duty vehicles, marine diesel engines, locomotives, and various types of nonroad engines, vehicles, and equipment.

The adopted rule is a federal counterpart of the California ‘Omnibus’ low NOx regulation that introduces an FTP NOx limit 0.02 g/bhp-hr effective 2027. The EPA proposal included two options for the NOx program. The more stringent Option 1 included a 0.035 g/bhp-hr NOx standard from 2027, followed by a 0.02 g/bhp-hr standard from 2031. The less stringent Option 2 was a one-step approach with a NOx standard of 0.050 g/bhp-hr in MY 2027.

The final rule is a compromise between the two proposed options. It is a one-step program effective from model year 2027, with a certification NOx standard of 0.035 g/bhp-hr (FTP) for all engine categories and an effective in-use NOx standard of 0.050 g/bhp-hr for medium and heavy heavy-duty engines (HDE). The 0.035 g/bhp-hr standard represents an 82.5% reduction in NOx emissions from the current NOx standard of 0.2 g/bhp-hr.

The regulation introduces new NOx, PM, HC, and CO emission standards for heavy-duty engines, including standards for the existing SET and FTP laboratory test cycles, as well as new standards based on the Low Load Cycle (LLC).

Final emission standards for Light HDE, Medium HDE, and Heavy HDE for MY 2027 and later
Duty Cycle NOxa HC PM CO
mg/hp-hr mg/hp-hr mg/hp-hr g/hp-hr
SET & FTP 35 60 5 6.0
LLC 50 140 5 6.0
a An interim NOx compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy HDE

A NOx ‘compliance allowance’ of 15 mg/hp-hr applies to any in-use testing of Medium HDE and Heavy HDE. This compliance allowance is added to the NOx standard that applies for each duty cycle and for off-cycle testing, with both field testing and laboratory testing (except for ‘bin 1’ off-cycle standard). With the allowance, the in-use NOx emission standards for Medium HDE and Heavy HDE effectively become 50/65 mg/bhp-hr over the FTP/LLC tests, respectively. Light HDE and Spark Ignition HDE must meet the 35/50 mg/bhp-hr FTP/LLC NOx standards in both certification and in-use testing.

The new low load certification cycle is intended to address deficiencies in the current certification duty cycles and the NTE field testing program with respect to emission control at low load. The LLC test adopted by the EPA is consistent with the test cycle introduced by the California Omnibus regulation. However, the EPA procedure requires the use of auxiliary load during the test.

Future Regulations. The final rule is one of three major actions being taken under EPA’s “Clean Trucks Plan.” By the end of March 2023, EPA intends to release proposals for the remaining two steps in the Clean Truck Plan. This includes a proposal for the heavy-duty “Phase 3” GHG emission standards for Model Years 2027 and later, and a multi-pollutant standards proposal for light- and medium-duty vehicles for Model Years 2027 and later.

The EPA also intends to issue final decisions in early 2023 regarding several California waiver requests for California’s heavy-duty vehicle and engine emission standards. Importantly, the list of California emission regulations that still await an EPA waiver includes the Heavy-duty Omnibus Low NOx regulation and the Advanced Clean Trucks (ACT) rule.

Source: US EPA