Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) method was used to comprehensively evaluate performance and emission characteristic of DI diesel engine with fumigation gasoline under different engine operating conditions. Diesel and B20 fuel were considered as baseline fuels and gasoline was inducted as fumigation in intake manifold at two different ratio, so that at each operation point, six cases of fuel were tested. The experimental results showed that gasoline fumigation method for both baseline fuels of diesel and B20 results in a significant increase in UHC and CO emissions, and decrease in exhaust gas temperature, smoke opacity and NO and CO2 emissions. Also, gasoline fumigation increased the brake thermal efficiency at medium and higher loads to about 5% for diesel baseline fuel, while the brake thermal efficiency decreased slightly in case of the B20 baseline fuel with gasoline fumigation. Moreover, the using B20 as an alternative fuel to diesel fuel in modes of with fumigation gasoline reduced the UHC and CO emissions, smoke opacity, exhaust gas temperature respectively to about 20.5%, 16.4%, 9% and 1.1% on average throughout engine loading. While, NO emission of B20 was up to 5% higher than diesel at modes with fumigation gasoline. Finally, all criteria of performance and emission were considered and the evaluation process done to obtain final ranking and choosing the best alternative or the best combination of fuel. From the analytical results it was determined that case of B20 with fumigation gasoline results in desirable performance and minimum emissions at some operation points.

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