This study examines the effect of concentration and flow-rate of CeO2 nano-fluid to reduce smoke emissions from a diesel engine. Taguchi-Grey relational-based multi-response optimization method was employed for test-plan. Results revealed that nano-fluid flow-rate and its concentration have a positive impact on smoke emissions reduction in a diesel engine. It is confirmed that the results obtained in the experimentations are in line with the calculated values obtained Taguchi technique. The usage of nano-fluid in the tailpipe is an effective way of reducing Smoke emissions from a diesel engine. [ABSTRACT FROM AUTHOR]