Experimental testing was done with a modern compression ignition engine to study the effect of the engine load and the effect of different fuels on the post injection characteristics. Two different fuels were utilized; ultra-low sulphur diesel and n-butanol. The results showed that a post injection can be an effective method for increasing the operating range of the engine load. Engine operation at high load can be limited by the peak cylinder pressure but the test results showed that an early post injection can increase the engine load without increasing the peak in-cylinder pressure. Neat butanol combustion may have a very high peak in-cylinder pressure and a very high peak pressure rise rate even at low load conditions. The test results showed that a butanol post injection can contribute to engine power without significantly affecting the peak pressure rise rate and the peak in-cylinder pressure. The test results indicated that high load conditions were more favourable for the combustion of delayed post injections. For diesel fuel post injection with exhaust gas recirculation, the earliest post injection timing was limited by high smoke emissions but this was not the case for butanol. However, the delayed post injections with butanol fuel were limited by the loss of ignition of the butanol post injection. An early post injection reduced the exhaust carbon monoxide emissions for the neat butanol tests but not for the diesel fuel tests. The hydrocarbon speciation analysis indicated that the butanol post injection tended to produce mostly formaldehyde, ethane, and unburned butanol hydrocarbons and that there were no detectable quantities of hydrogen, methane, ethylene, and propylene at these test conditions. It was found that the formation of these latter species was sensitive to the post injection timing when diesel fuel was used with reduced intake oxygen.