Effects of natural gas, ethanol, and methanol enrichment on the performance of in-cylinder thermochemical fuel reforming (TFR) spark-ignition natural gas engine

In-cylinder thermochemical fuel reforming (TFR) process, which involves running one cylinder with a rich equivalent ratio, generates hydrogen and carbon monoxide to be all rebreathed by the intake manifold. Both the thermal efficiency and the emissions can be optimized by the TFR mode. However, when natural gas is used as the single enrichment fuel, there are still some limitations such as the indicated mean effective pressure (IMEP) discrepancy between the reforming cylinder and normal cylinders, combustion instability. To overcome these and further improve the engine performance, a more suitable enrichment fuel, instead of natural gas, should be identified to help the reforming process. In this paper, methane, methanol, and ethanol are studied to enrich the reforming cylinder. The results show that methanol not only maintains the thermal efficiency and further reduces the engine-out emissions, but also provides the best engine performance stabilization, followed by ethanol and methane. In addition, engines functioning with methanol enrichment can maintain stable operation on a wide range of rich equivalent ratios in the reforming cylinder.