CARB developing in-use testing program for Tier 5 off-road engines

3 May 2022

As part of their Tier 5 emission standards work, the California Air Resources Board (CARB) started the development of an in-use emission testing program for new Tier 5 off-road engines. An online workshop on the Tier 5 in-use program concepts was held on May 2, 2022.

Under the existing off-road in-use compliance (ORIUC) program, CARB has the authority to test in-use engines up to 75% of their useful life (UL) period, using the test procedures used for certification (transient, steady-state, and not-to-exceed). At the Tier 5 stage, CARB intends to implement a manufacturer-run ECU/sensor-based and PEMS in-use testing program—similar to the existing in-use testing requirements for onroad heavy-duty diesel engines and for large nonroad SI engines.

The changes to the ORIUC program would include off-cycle test procedures using PEMS, updated emissions calculations and evaluation methods, and changes to expand the UL limits for ORIUC engines.

The new in-use program would be applicable to engines with a power rating of ≥56 kW, which at minimum would require SCR aftertreatment to comply with emission standards. The program concept involves three steps:

1. Engine Control Unit (ECU)/sensors data—NOx emission data from the vehicle NOx sensor and ECU is collected with telematics. Manufacturers submit data annually for 75% of engine sales per engine family (EF). Emissions data is binned into idle, low load, and high load bins. If data for an EF raises no alerts, then the in-use testing requirements for the EF is fulfilled.
2. Triggered PEMS testing—If 20% or more of the ECU/sensor reports for an EF have events in any bin with emissions greater than 2 times the emission standard, in-use PEMS testing is required. The PEMS testing involves 5 to 10 engine tests and is conducted for NOx and for other criteria pollutants. If compliance is determined, then the in-use testing requirements is fulfilled.
3. Corrective action—If PEMS testing shows that an EF is not compliant, then the manufacturer must take steps to correct the non-compliance.

A number of challenges with the use of PEMS on off-road equipment were identified at the workshop, such as the large size of PEMS systems and mounting/safety considerations. CARB has requested feedback from the stakeholders on these and other pertinent issues.

Source: CARB