In the current investigation, the carbon nanomaterials, mainly graphene oxide (GO), graphene nanoplatelets (GNPs), and multiwalled carbon nanotubes (MWCNTs) were added into diesel fuel, 20% (by volume) n-heptanol + 80% diesel fuel (H2OD), and 40% (by volume) n-heptanol + 60% diesel fuel (H40D) to investigate the combustion and exhaust emission characteristics of a common rail diesel engine and rapid compression-expansion machine (RCEM). The dose level of 50 mg/L of GO, GNPs, and MWCNTs was dispersed into diesel fuel, H2OD and H4OD mixtures utilizing ultrasonication system. The common rail diesel engine was operated under different loads and a fixed speed of 1000 rpm while the RCEM was run under diesel engine condition with fixed inlet air properties. The findings for H2OD and H4OD blends illustrated that the brake specific fuel consumption was increased by approximately 10%, while soot and NOx emission were reduced by about 40% and 12% respectively compared to pure diesel fuel. Moreover, the addition of carbon nanomaterials into diesel fuel, H2OD, and H4OD led to a substantial reduction in the specific fuel consumption by about 15% and the common rail engine soot emission was decreased by 60% whereas NOx was increased by 20% compared to base fuel. Combustion parameters for RCEM confirmed that there was a reduction in flame temperatures for H2OD and H4OD blends compared to diesel fuel. Additionally, there was a significant enhancement in the flame temperatures with the addition of carbon nanomaterials. According to combustion and emission results, the recommended blending ration of n-heptanol and diesel fuel is H2OD.