Heavy-duty trucks rely on diesel engines because they are powerful, durable, and more fuel efficient than gasoline engines. However, with more stringent emissions standards and the greater availability of low-cost, compressed natural gas (CNG), the market opened for trucks powered by engines fueled with CNG. Compressed natural gas combustion engines have been commercially demonstrated and deployed with their supporting fueling infrastructures. These CNG-fueled engines are available today with NOx emissions certifications 90 percent lower than the mandatory diesel engine standard. When fueled with renewable natural gas, these vehicles can also provide substantial greenhouse gas (GHG) emission reductions.
This project designed, developed, and demonstrated a prototype control system integrated into a CNG hybrid electric Class 8 truck, optimized to achieve both near-zero NOx emissions and significantly reduced GHG emissions. The truck used a 239 kW 8.9-liter near-zero CNG engine, a 222 kW electric motor, 31 kWh Lithium-ion battery pack, and electric accessories to provide equivalent performance to a larger 15-liter diesel engine while adding a 20-mile zero-emission range.
By comparing the emissions test results with similar engines’ emissions on other projects, the research team found that a hybridized near-zero power train can offer fuel economy benefits of 40 percent and NOx emissions 22 times lower than the current 0.02 g/bhp-hr standard. Moreover, the team found that 90 percent of NOx emissions can be attributed to cold start operations. The CNG hybrid electric vehicle technology can provide range, reliability, and refueling convenience for certain fleet operations. Further research, optimization of the system, and support from the component manufacturers could yield additional improvements.
