California Air Resources Board

Given the ongoing air quality challenges in California, there has been significant interest extending the efforts of recent on-highway Low Nitrogen Oxide (NOx) technology demonstration efforts into the off-road sector. Off-road engines account for a large and increasing percent of statewide NOx and PM emissions. This study, and subsequent demonstrations of Low NOx technology focusing on the off-road sector, wasintended to providetechnical support for the promulgation of more stringent standards to reduce NOx and PM emissions from these engines with relatively little impact on carbon dioxide (CO₂) emissions, or potentially to leverage additional engine technology to pursue both NOx and CO₂ reduction, albeit at higher system cost and complexity levels.

The study detailed in this report include gathering off-road market information, detailed baseline testing of Tier 4 engines, and modeling efforts to examine potential approaches to reaching NOx levels up to 90% below the current Tier 4 standards, and PM levels 75% below the current Tier 4 standards. These efforts included examination of engines under low load conditions than are currently regulated under the Tier 4 standards.