Use supplemental hydrogen in spark ignition engines: Simulation of Impact on Performance Emissions

摘要

A two-zone spark ignition engine cycle simulator with multi-fuel capability has been developed and used to study effects on performance and emissions expected from partial substitution of a hydrocarbon fuel with small amounts of hydrogen. In the simulation, the hydrogen may be supplied in pure form or in combination with other gaseous fuel species (generated by partial oxidation (POX) of the original hydrocarbon fuel). The base fuels include methane, propane, ethanol and gasoline and these may operate in combination with products of partial oxidation (H_2, CO, CO_2, CH_4, C_2H_2, C_2H_6, H_2O and N_2). Predicted results applicable to a methane-fuelled spark ignition engine (0.35 litre / cyl.), operating at 2000 rpm, 6.0 bar IMEP and MBT ignition timing, are presented for a range of equivalence ratios. These show that pure hydrogen (at 5percent energy fraction) increases NO_x and slightly reduces indicated thermal efficiency under stoichiometric conditions. If retarded timing is elected instead of MBT, the NO_x level does not increase with hydrogen usage. The same energy fraction of hydrogen supplied in combination with other POX products yielded the opposite predicted result (reduced NO_x and increased efficiency), again at stoichiometric air-fuel ratio. The indicated thermal efficiency with hydrogen addition was predicted to increase at leaner mixtures. The predicted NO_x reductions were 54percent for POX-derived H_2 supplement and 38percent for pure H_2 (at lean conditions).