The optimal fuel for partially premixed combustion (PPC) is considered to be a gasoline boiling range fuel with an octane number around 70. Higher octane number fuels are considered problematic in respect with low load and idle conditions. In previous studies the intake air temperature do not exceed 30oC. Possibly by increasing intake air temperatures the load range could be extended. In this study primary reference fuels (PRF) (iso-octane and n-heptane blend) with octane numbers of 70, 80, and 90 are tested on an adapted commercial diesel engine under partially premixed combustion mode to investigate the potential of these higher octane number fuels in low load and idle conditions. During testing combustion phasing and intake air temperature are varied to investigate the combustion stability, combustion characteristics, emissions and efficiency under low load and idle conditions. The results show that for low load condition combustion occurs for all fuels, with intake air temperatures above 60oC, with a coefficient of variation (COV) of the indicated mean effective pressure (IMEP) below 3%. Emissions display similar behavior only PRF90 has a much shorter burn duration resulting into relative high NOx emissions. For the idle condition stable combustion occurs for all fuels with intake air temperatures above 60oC, with a COV of IMEP below 4.5%. PRF70 and 80 display similar emission behavior while PRF90 requires higher intake air temperature to get comparable emissions with respect to the other fuels.