On-Road CO 2 and NO x Emissions for a Heavy-Duty Truck with Hydrogen-Diesel Co-Combustion

Abstract

Heavy-duty diesel trucking is responsible for 25%-30% of the road transportation CO₂ emissions in North America. Retrofitting class-8 trucks with a complementary hydrogen fuelling system makes it possible to co-combust hydrogen and diesel in the existing internal combustion engine (ICE), thus minimizing the costs associated with switching to non-ICE platforms and reducing the barrier for the implementation of low-carbon gaseous fuels such as hydrogen. This retrofitting approach is evaluated based on the exhaust emissions of a converted truck with several thousand kilometres of road data.

The heavy-duty truck used here was retrofitted with an air-intake hydrogen injection system, onboard hydrogen storage tanks, and a proprietary hydrogen controller enabling it to operate in hydrogen-diesel co-combustion (HDC) mode. The hydrogen controller operates on the J1939 network, similar to the OEM Controller Area Network (CAN) and determines the hydrogen injection rate from hydrogen energy share ratio (R_H2) tables based on engine-related parameters.

The cycle-total R_H2 for the considered in-use operation ranged from 15% to 28%, with a maximum instantaneous value of close to 40%. This range of R_H2 has been explored in engine-dynamometer studies in the literature showing promising results without negative combustion anomalies. Here, the real-drive exhaust CO₂ and NO_x emissions during the HDC operation were compared to those for the neat diesel operation. The OEM sensors were used for on-road exhaust NO_x measurement, and their accuracy and cross-sensitivity to interfering gaseous species were examined in controlled laboratory experiments. The road data shows that the exhaust NO_x emissions during the HDC operation are reduced compared to the neat diesel baseline, and the tailpipe CO₂ reductions are directly correlated to the hydrogen substitution rates.