On-board Fuel processing for a Fuel cell-heat engine hybrid system

Fuel cells operated with hydrogen are more efficient than internal combustion engines, because the combustion in the internal combustion engine is less reversible than the electro-oxidation of hydrogen in the fuel cell. Hydrogen can be produced out of hydrocarbons, such as natural gas, or renewable resources at stationary facilities, but fuel cells operated with pressurized hydrogen stored on board require advanced hydrogen infrastructure for commercialization. An alternative to on-board storage of hydrogen is on-board processing of a liquid hydrocarbon to hydrogen via steam reforming. However, on-board reforming of hydrogen is less energy-efficient than centralized production of hydrogen. Moreover, on-board reforming, purification, and subsequent oxidation of the reformate in a fuel cell is not more efficient than a hybrid electric vehicle technology assisted internal combustion engine. We propose a fuel cell-heat engine hybrid system, which consists of a membrane reformer, a fuel cell, and a reciprocating internal combustion engine, and estimate the efficiency of the proposed hybrid system. Steam reforming of a hydrocarbon requires additional heat input, which can be recovered from the waste heat of an internal combustion engine. On the other hand, the retentate of the membrane reformer can be used in the internal combustion engine to further increase the system efficiency. Methanol is proposed as the fuel for the membrane reformer because the temperature level required is low enough to recover waste heat of reciprocating internal combustion engines for steam reforming of methanol. The hybrid system proposed is more flexible than a fuel cell with an on-board reformer, because additional fuel can be directly combusted in the internal combustion engine at cold start or rapid load increase. Because fuel cell efficiency decreases with load and internal combustion engine efficiency increases with load, the overall system efficiency is less load-dependent compared to the efficiencies of each of these technologies. The power of an automobile engine is considered as a benchmark for the system proposed.