This work capitalizes on the investigation of the effect of injection pressure and timing on the in-cylinder soot formation performance of low CR GTL-fueled DI diesel engine. An optically-accessed Rapid Compression Machine capable of simulating compression and expansion strokes of diesel engine was deployed allowing the application of optical diagnostics. For the detection of flame zones aiming mainly at determining the Lift-Off-Length, imaging of flame self-luminescence technique was used, while for the assessment of in-cylinder soot formation the photodiode-based non-imaging soot incandescence acquisition optical technique has been applied. Through in-cylinder installed pressure transducer and piston position sensor, the rate of heat release was calculated for the analysis of the combustion development. It was found that soot formation rate and peak decrease with increasing injection pressure. The former decreases, however, non-linearly, while the later decreases linearly. Such linear relation is attributed to the linear dependency of Lift- Off-Length on injection pressure. Start of soot appearance seems to be independent of injection pressure probably due to stable ignition of GTL fuel under low Compression ratio conditions. The more injection timing is retarded, the later soot inception is and the higher the decrease in its formation. Thus, by retarding injection timing, the portion of sootless combustion increases. This suggests that for the case of GTL fuel, the combination of low CR, sufficiently high injection pressure and late injection, the combustion mode of Highly Premixed Late Injection or HCCI-like combustion are quite attainable. It seems that under the operating conditions deployed in this work, late injection or retarded injection timing strengthens the effect of cylinder charge cooling brought about by heat lost from the cylinder charge to fuel evaporation which in return lowers local temperatures decreasing as a result the propensity for soot formation. It seems that by retarding injection timing, the portion of heat released towards the expansion stroke increases and combined with higher mixing energy due to flow induced by piston motion, soot oxidation rate apparently increases yielding overall lower soot concentration.