Developing, Demonstrating, and Testing Advanced Ultra-Low-Emission Natural Gas Engines in Port Yard Trucks

This project demonstrated two precommercial liquefied natural gas-powered Capacity Trucks yard tractors with low-nitrogen oxides (NOx) 6.7-liter natural gas engines (B6.7N) from Cummins Westport Inc. at Everport Terminals in the Port of Los Angeles. Capacity Trucks previously developed liquefied natural gas tractors using the Cummins Westport Inc. 8.9-liter natural gas engine (L9N), which was primarily designed for onroad heavy-duty vehicles but determined to be oversized for yard tractors. This project demonstrated these liquefied natural gas tractors using the emerging “right-sized” B6.7N engine while comparing performance, efficiency, and emissions to an L9N-equipped tractor and a diesel tractor. University of California, Riverside engineers also developed an advanced gas composition sensor technology to measure gas quality and potentially enable automatic engine adjustments in real-time. The university tested chassis dynamometer emissions on both types of liquefied natural gas yard tractors and a baseline diesel tractor. The university also performed multiple emissions tests on the B6.7N unit with gas blends of variable composition to evaluate the potential benefits of the gas composition sensor.

Both types of liquefied natural gas tractors had lower NOx emissions than the diesel tractor. Cummins Westport Inc. was able to certify the B6.7N engine to the most stringent 0.02 grams per brake horsepower-hour NOx heavy-duty on-road emission level. Demonstration results corroborated that the two B6.7N-equipped tractors performed as well as the L9N-equipped yard tractors while improving fuel efficiency by 15 to 20 percent. Capacity Trucks indicates that commercialization of near-zero emission natural gas yard tractors will focus on the B6.7N rather than the larger L9N. This project has shown that liquefied natural gas yard tractors with the B6.7N can provide an operationally feasible, low NOx alternative to diesel units for use by California marine terminal operators.