As a promising alternative fuel, biobutanol, i.e. n-butanol, can be utilized to reduce fossil fuel consumption and carbon dioxide emissions from spark ignition and homogeneous charge compression ignition (HCCI) engines. In this work, the HCCI operation was achieved by the negative valve overlap strategy through variable exhaust and intake valve timing and lift devices on a single cylinder port fuel injection four-stroke engine fuelled with n-butanol when indicated mean effective pressure (IMEP) was kept constant at different relative air-fuel ratios. The results show that the onset of autoignition advances with engine speed while autoignition timing moderately delays and combustion duration slightly changes with the increase of relative air-fuel ratio at the same operating conditions. In addition, acetaldehyde and ethanol emissions are much higher than formaldehyde and methanol emissions, respectively. (C) 2013 Elsevier Ltd. All rights reserved.