California Air Resources Board

Useful Life

Engine manufacturers wishing to certify engines in California must first demonstrate that the engine and aftertreatment system (ATS) are durable and comply with emission standards for the useful life (UL) of the engine. Manufacturers confirm engine durability and emissions by aging the engine (either in the field or on an engine dyno) to the full useful life or age the engine to a percentage of the engine useful life then linearly extrapolate emission level to full useful life.

The table below shows the engine useful life of on-road engines (see 13 CCR 2112), categorized by gross vehicle weight rating (GVWR):

Heavy-Duty/Medium-Duty Engine Useful Life (UL)

The table below shows the useful life for Off-Road Compression-Ignition engines (see 40 CFR 1039.101(1)(g)).

OFCI Engine Useful Life 

Engine Durability Plan

Before engine certification, the manufacture must submit to CARB a Durability Demonstration Plan (durability plan), which describes how the manufacturer will age the engine and calculate pollutant Deterioration Factors (DFs). It is the manufacturer's responsibility to have its durability plan reviewed and approved by CARB. 

The Durability Demonstration Plan validates that the engine complies with emission standards for the entire engine useful life, and the engine/aftertreatment system are durable for the entire useful life. The manufacturer must perform emissions tests at the "low-hour" point (immediately after engine break-in) and at evenly-spaced intervals until the durability test is complete. 

Manufacturers have the choice of aging an engine to its full useful life or aging an engine to a percentage of the useful life then extrapolating emission levels to the end of the useful life. Once the emissions at the end of useful life are determined, the fully aged emissions levels may be directly used as the certification values or the Deterioration Factors (DFs) for all pollutants are calculated and applied to emissions tests conducted on an emission data engine (EDE) to produce certification values. Manufacturers may determine the emissions during aftertreatment regeneration events in order to calculate the IRAF values needed for certification while conducting a durability program so long as the representative nature of the aging process is not affected. Manufacturers may elect to use an engine aging acceleration factor to decrease the time required to complete the durability test. However acceleration factors must be approved by CARB before engine testing can begin. 

A durability plan should include (at a minimum) the following:

1. Engine family name
2. Useful life
3. Carry Across Sheet
4. Engine emissions stabilization procedure
5. Aging cycle procedure and cycle details (aftertreatment temp, engine load, etc.)
6. The justification that the aging cycle is representative of real-world engine operation 
7. Accelerated factor calculation (if applicable)
8. Timeline with emission test points
9. Emission test procedure
10. DF extrapolation 
11. Engine maintenance schedule
12. Other information as needed or requested

Please note that the upcoming Heavy-Duty Omnibus Regulation will update and standardize many requirements for durability demonstration for on-road engines. Effectively, the Omnibus regulation will supersede many aspects of the current Durability Demonstration Plan process and procedures for on-road engines. While written for on-road engines, off-road compression-ignition engines (OFCI) may incorporate aspects of the Low NOx Omnibus regulation.  Manufacturers are highly encouraged to follow the Omnibus Regulation and attend any relevant workshops. 

Bench aging may be an option for Durability Demonstration for Otto and Diesel Cycle Engines (typically seen on Otto Cycle Engines). However, the manufacturer must obtain CARB approval before starting testing. 

DF validation Program (for SCR Engine Families only)

CARB and USEPA have reviewed the results of a DF test program conducted by the Truck and Engine Manufacturers Association (EMA). The results showed that while engine out emissions for SCR equipped engines were consistent over the test period, calculated DFs were higher using all data points through the end of Useful Life (UL) when compared to DFs extrapolated to UL using lower service accumulation aged test points (35%, 50% or 75% UL). One engine’s UL emissions exceeded emissions standards even though its extrapolated DFs represented it as passing. The agencies have also been analyzing base-line test results provided by manufacturers as part of On-Board Diagnostic (OBD) Manufacturers Self Testing (MST) requirements for on-road heavy-duty engines. A significant number of engines and after-treatment systems tested at 70-80% UL have shown non-compliance with the applicable emissions standards.

As a result, CARB and USEPA believe that DFs generated by manufacturers using less than full useful life service accumulation may not be representative of full useful life emissions deterioration. Therefore, both agencies are requesting manufacturers who generated DF’s with less than UL demonstrations to undertake additional steps to confirm their established DFs.

CARB and USEPA will consider methods proposed by individual manufacturers to validate their DFs for use in certifying future model year engines. To aid manufacturers in this effort, the information offered in the attachment identifies and describes example methodologies for validating DFs on SCR equipped engines that will be considered acceptable by the agencies. The examples have been discussed with EMA and are being presented to all interested manufacturers

For more information please review the DF Validation Workshop Presentation from July 8th, 2020, DF Validation Workshop Mail-Out, and DF Validation Methods Mail-Out.

Assigned DFs

Assigned deterioration factors may be used on engines produced by small-volume manufacturers. However, the manufacturer needs to obtain approval from EPA or CARB and include documentation in the certification application. Manufacturers do not need explicit approval to use assigned DFs from the following EPA letters. For on-road engine assigned DF information see the On-Road EPA Assigned DF Letter. For off-road engine assigned DF information see Off-Road EPA Assigned DF Letter. 

Relevant Regulations for On-Road Engines

• The break-in period for on-road engines is 125 hours (see CFR 40 86.004-26). However an alternative break-in period may be used if approved by CARB.
• For information on DF and IRAF calculations for on-road engines see 40 CFR 86.004-28.

Relevant Regulations for OFCI Engines  

• The break-in period for OFCI engines must not exceed 300 hours. In addition, the manufacturer must provide justification (engineering judgment or data) that the break-in period is sufficient for emissions stabilization (see "low-hour" under 1039.801).
• For information on DF calculations and IRAF calculations for OFCI engines see 40 CFR 1039.240 and 40 CFR 1065.680 respectively.