Experiments were performed in an optically accessible DI diesel engine to investigate the effects of the addition of dimethoxymethane (DMM) to diesel fuel. The DMM was blended into the baseline diesel fuel to obtain 2% and 4% oxygen by fuel mass. Laser light extinction was used to measure soot variation during combustion as well as exhaust soot levels; NOx, CO2 and CO concentrations in the exhaust were measured using gas analyzers. In addition heat release analysis and direct photography were used to characterize the combustion process. The addition of DMM led to significant reductions in soot, but heat release analysis showed that it also caused significant changes in combustion characteristics, with increases of up to 1.7 degrees of crank angle in ignition delay as well as increases in the fraction of premixed burn. Then, 2-ethylhexylnitrate was used to compensate for the effects on heat release characteristics to determine the relative importance of chemical and heat release effects in reducing soot. A fuel blend of 2,2-dimethylbutane in the diesel fuel was studied to estimate the effects of boiling point on soot and combustion characteristics.