A study was performed in which the effects on the regulated emissions from a commercial small DI diesel engine were measured for different refinery-derived fuel blends. Seven different fuel blends were tested, of which two were deemed to merit more detailed evaluation. To investigate the effects of fuel properties on the combustion processes with these fuel blends, two-color pyrometry was used via optically accessible cylinderheads. Additional data were obtained with one of the fuel blends with a heavy-duty DI diesel engine.California diesel fuel was used as a baseline. The fuel blends were made by mixing the components typically found in gasoline, such as methyl tertiary-butyl ether (MTBE) and whole fluid catalytic cracking gasoline (WH-FCC). The mixing was performed on a volume basis. Cetane improver (CI) was added to maintain the same cetane number (CN) of the fuel blends as that of the baseline fuel. However, other fuel properties, such as density, distillation temperatures, and viscosity were not controlled.The effects of the fuel blends on engine performance were similar for both the small and large engines. Ignition delay was increased with the fuel blends for both engines. The transition from premixed-burning to diffusion-burning phases was difficult to discern with the small engine. However, premixed-burning phase was dominant at low load; diffusion-burning phase dominated at high load. The fuel blends showed slightly higher premixed-burning peaks and lower diffusion-burning peaks than the baseline fuel. Decreases in smoke, CO, and THC emissions were observed with MTBE-mixed diesel fuel (MD). The effects of oxygenate- and gasoline-blending components on NOx were negligible at high load. Two-color pyrometry showed different combustion characteristics between fuels. Flame temperature and soot KL factor of MD were uniform. Major differences in flame temperatures between fuels were observed from 5∼35° aTDC. A decrease in soot KL factor was observed with MD for both engines after approximately 30° aTDC.