California Air Resources Board

This study was the culmination of a continuing effort aimed at demonstration of the capability of certain diesel emission control technologies to reach Low Nitrogen Oxide (NOx) levels on an off-road diesel engine. This study used incremental improvements and technology additions that were available within the time and budget available without resorting to the further tools afforded by fundamental redesign of the block, heads and rotating assembly. The study objective was to demonstrate the feasibility of technologies to reach tailpipe NOx emission reductions of up to 90% from the current Tier 4 standards, and particulate matter (PM) emission reductions of at least 75% from the current Tier 4 standards. Two different systems were developed to meet these targets, the first of which was intended to meet the target NOx and PM levels with no impact on greenhouse gas (GHG) emissions. The second system was intended to meet the target NOx and PM levels while also demonstrating a 5% to 8.5% improvement in carbon dioxide (CO₂) emissions.

This study report focused primarily on the development and performance of the second system, which was designated as Package 2. The demonstration was targeted primarily at off-road engines rated between 56 kilowatt (kW) and 560 kW. The off-road Low NOx demonstration reported here builds on previous extensive studies to demonstrate Low NOx technologies for on-highway engines. As well as previous off-road test studies, such as Off-Road Low NOx Demonstration Stage 1 and Off-Road Low NOx Demonstration Stage 2, for the California Air Resources Board (CARB) that were intended to lay the groundwork for the current study. The focus of this Stage 3 study was on a final robust performance demonstration of an optimized system configuration and durability out to a full-useful life (FUL) of 8,000 hours. The final emission control systems developed and evaluated in this program demonstrated levels 25% to 50% below the target emission levels at end of life (EOL) with technologies generally suitable for implementation in production, allowing for a reasonable potential compliance margin. In addition to these efforts, a Low Load Cycle (LLC) representative of off-road engine operation was developed by CARB and SwRI using field data provided by CARB and other stakeholders, and the performance of the emission control system mentioned above over this cycle was also demonstrated.