In this study, n-butanol (port fuel injection) PFI was investigated in a direct injection compression ignition engine while at idling speeds, and loads, 1-3 bar IMEP (indicated mean effective pressure) in order to determine the effects on combustion, efficiency, emissions, and specifically, a modified tradeoff of soot and nitrogen oxides. As a result, the engine entered into (low-temperature combustion) LTC regions, for selected loads and speeds. Compared with the baseline taken with ultra-low sulfur diesel no. 2, the heat release with n-butanol in (premixed charge compression ignition) PCCI mode, has resulted in a 75% reduction from the maximum values, while a secondary peak appeared where the diffusion combustion typically occurs in the power stroke. At 3 bar IMEP an early, (bottom dead center) BTDC low-temperature heat release was found that began 6 degrees earlier than for the diesel reference cycle, and corresponding to 1200 K. Soot emissions showed a massive decrease of about 98%, concurrently with a 74% reduction of nitrogen oxides at 3 IMEP by controlling the combustion phases and by modifying the classical NOx-soot tradeoff. The results of this work prove that biodiesel combined with n-butanol PFI in PCCI and LTC are very effective in simultaneously reducing soot and NOx at idling speeds. (C) 2013 Elsevier Ltd. All rights reserved.