Biodiesel is identified as a likely alternative fuel for Compression Ignition (CI) engines as it leads to an effective reduction in consumption of petroleum diesel, and of engine exhaust emissions. In the current study, the effects of preheating of intake air on performance, emissions and combustion behavior have been studied for various compositions of cottonseed oil biodiesel–ethanol blends in a compression ignition engine. The characteristics were compared for intake air temperatures of 30°C and 80°C, respectively. An increase in the air intake temperature caused variations in the ignition delay period of the biodiesel–ethanol blend by improving the vaporization characteristic of ethanol, and provides a better combustion. It was found experimentally that the carbon monoxide (CO) as well as the unburned hydrocarbon (HC) emissions decreased with an increase in the preheat temperature, and were found to be slightly lower than those of biodiesel-fueled CI engines. An increase in the relative amount of ethanol blended with the biodiesel was also found to decrease CO and HC emissions. However, in comparison with biodiesel fuel, the ethanol–biodiesel blends resulted in higher emissions of oxides of nitrogen (NO x ). © 2017, © 2017 Informa UK Limited, trading as Taylor & Francis Group.