The purpose of this study is to examine the effects of bioethanol and gasoline as a premixed injection source on the combustion performance and exhaust emissions characteristics of a dual-fuel combustion engine. The ignition source of dual-fuel combustion was biodiesel derived from soybean oil. The premixing ratio was calculated based on the total input energy and was varied from 0.2 through 0.8. Experiments were conducted using a single cylinder diesel engine with a re-entrant geometry type combustion chamber. Experimental results show that dual-fuel combustion has a higher maximum combustion pressure (P-max), shorter ignition delay, significantly lower NOx and soot emission, but it has higher HC and CO emission when compared to single-fuel combustion. In a comparison of bioethanol and gasoline during dual-fuel combustion, biodiesel-bioethanol dual-fuel combustion showed lower P-max longer ignition delay, and higher IMEP than biodiesel-gasoline dual-fuel combustion. The increase in the premixing ratio for both dual-fuel combustion modes increased the ignition delay and IMEP, and decreased P-max With the increase in the premixing ratio, fuel consumption increased during biodiesel-gasoline dual-fuel combustion, but decreased during biodiesel-bioethanol dual-fuel combustion. NOx significantly decreased during biodiesel-bioethanol dual-fuel combustion; however, biodiesel-gasoline dual-fuel combustion had a limited effect on NOx reduction. HC and CO emissions were increased by bioethanol or gasoline premixing. The biodiesel-bioethanol dual-fuel combustion mode showed higher HC emission than the biodiesel-gasoline dual-fuel combustion mode, and the CO emission level was similar in both combustion modes. (C) 2014 Elsevier Ltd. All rights reserved.