UC Davis Institute of Transportation Studies

Heavy duty engines are substantial contributors to NOX and PM emissions inventories in urban areas, and stringent emissions standards have been adopted as a consequence. CARB has passed very strict emissions standards for heavy duty engines beginning in 2007. Meeting these standards, especially for NOX emissions, may be difficult for conventional transit bus technologies. The purpose of the Hydrogen Bus Technology Evaluation Program was to develop and evaluate hydrogen enriched natural gas (HCNG) engine technology in transit buses and to demonstrate NOX emissions reductions below the CARB 2007 standards. Collier Technologies, Inc. modified a John Deere 8.1 liter natural gas engine to operate on a mixture of 30% hydrogen and 70% natural gas. The engine was tested on a dynamometer to determine emissions and fuel economy, and these values were compared with data from conventional CNG engines. UC Davis developed both an HCNG combustion model to understand the processes inside the engine and a dynamic vehicle model to understand the benefits of HCNG buses. The results indicate that HCNG bus NOX emissions can meet the CARB 2007 standards. Based on information from this program, Collier Technologies has developed a prototype HCNG engine which can be used to retrofit CNG buses.