This study uses a port-injection spark-ignition four-cylinder natural gas engine to achieve TFR (Thermochemical fuel reforming) mode. To study the effects of fuel reactivity on combustion, reforming process, emissions and fuel economy, chemicals including n-heptane, PRF50 and isooctane are respectively used as enriched fuel. The results show that the higher the reactivity of the enriched fuel, the better the combustion and cycle stability of the reforming cylinder. However, n-heptane enrichment with high reactivity has the problem of knocking at large equivalence ratio. The enrichment limit of PRF50 is the highest, which combines the properties of n-heptane and isooctane. The H-2 production abilities of three enriched fuels are similar, but that of isooctane is slightly lower under large equivalence ratios. In terms of fuel economy, the three perform similarly at small equivalence ratios. Whereas it's lower with isooctane enrichment at large equivalence ratios, which is at the expense of increased NOx emission. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.