He, Z., Xu, Z., Zhu, L., Zhang, W. et al., "The Performances of a Spark Ignition Natural Gas Engine Coupled with In-Cylinder Thermochemical Fuel Reforming (TFR)," SAE Technical Paper 2016-01-2239, 2016, doi:10.4271/2016-01-2239.
In-cylinder thermochemical fuel reforming (TFR), which involves running one cylinder rich of stoichiometric and routing its entire exhaust back into the intake manifold, is an attractive method for improving engine performances. Compared with other hydrocarbon fuels, the chemical structure of methane is more stable owing to much shorter carbon chain. As ethanol contains hydroxyl in chemical structure, it potentially generates OH radical during the combustion. Therefore, adding ethanol into natural gas (NG) might help the thermochemical reforming process in engine cylinder. This paper focused on researching the effects of ethanol-NG combined in-cylinder TFR on engine performances, before which the effect of NG in-cylinder TFR was examined in detail. Cylinder #4 (TFR cylinder) was running rich and its cooled exhaust was coupled to the intake manifold of a four-cylinder engine during the experiments. For NG in-cylinder TFR, a rapid decrease of brake specific fuel consumption was found when equivalence ratio of TFR cylinder reached about 1.2-1.3, at which substantial fraction of H2 and CO were confirmed in the reformed gas, under low load. However, compared with the case without TFR, global engine operation stability was worsened and distinct IMEP discrepancy between cylinder #2 (typical of cylinder #1, 2, 3) and TFR cylinder was resulted. For ethanol-NG combined in-cylinder TFR, results proved higher H2 and CO concentration in reformed gas and comparable fuel economy compared with NG in-cylinder TFR. Besides, more stable engine operation and lower NOx emission as well as smaller IMEP discrepancy between cylinder #2 and TFR cylinder was obtained.