Onboard Natural Gas Reforming for Heavy Duty Vehicles

Powertrain simulations and catalyst studies showed the efficiency credits and feasibility of onboard reforming as a way to recover waste heat from heavy duty vehicles (HDVs) fueled by natural gas (NG). Onboard reforming involves 1) injecting NG into the exhaust gas recycle (EGR) loop of the HDV, 2) reforming NG on a catalyst in the EGR loop to hydrogen and carbon monoxide, and 3) combusting the reformed fuel in the engine. The reformed fuel has increased heating value (4-10% higher LHV) and flame speed over NG, allowing stable flames in spark ignition (SI) engines at EGR levels up to 25-30%. A sulfur-tolerant reforming catalyst was shown to reform a significant amount of NG (15-30% conversion) using amounts of precious metal near the current practice for HDV emissions control (10 g rhodium). Engine simulations showed that the high EGR levels enabled by onboard reforming are used most effectively to control engine load instead of waste-gating or throttling. This leads to 3% efficiency gain due to reduced pumping losses and enables the engine to run while the catalyst is inactive, such as during a cold start or regeneration. Several powertrain layouts were assessed to show that a net efficiency gain of 10% is achievable when reforming occurs in a reactor that allows heat exchange with the non-recycled exhaust. The size of the heat exchange reactor was shown to be (4 ft. length, 7-10 in. diameter). The next steps to achieve onboard reforming include the development of the heat exchange reactor and validation with real engine testing.