Metal‐based fuel additives have been promising alternative choice to improve diesel engine performance and emission characteristics. Many studies have been performed on use of metal‐based fuel additives such as magnesium, platinum, titanium, and cerium in diesel engine. Unlike conventional metal‐based additives, Acetylferrocene and Ruthenium polypyridyl complex may be alternative metal‐based additives for diesel. This study intends to investigate performance and emission variations of a diesel engine powered by diesel blended with Acetylferrocene and Ruthenium polypyridyl complex additives. In accordance with this purpose, a single cylinder, direct injection diesel engine was used to test these alternative metal additives. Results showed that Acetylferrocene and Ruthenium polypyridyl complex were effective to improve emission characteristics without causing degradation in performance. CO and Soot emissions were showed decrease up to 40% and 32%, respectively, and the fuel consumption characteristic of engine was improved with additives. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019