To assess the applicability of methane gas in the context of a methane injection strategy in dual fuel concept, it is crucial to evaluate not only the engine performance but also the exergetic performance and the enviro-economic analyses. In this experimental study, a comprehensive investigation was performed to explore the impacts of a methane injection strategy, involving the timing and quantity of methane gas injection, on the combustion and emission characteristics of a diesel/methane dual-fuel operation. Also, an assessment of energy, exergy, environmental impact, and cost analyses on methane injection strategy using data obtained from experimental results was performed. In the literature, there is a deficiency regarding the evaluation of methane injection strategy in terms of energy, exergy, and enviro-economic analyses. This study will not only address the current research gaps but also serve as a reference for future investigations. The experiments were conducted on a single-cylinder, air-cooled, diesel engine with a common rail fuel system, operating at a fixed engine speed and load. In the experiments, methane injection timing (MIT) was advanced from 20 CAD aTDC to 60 CAD aTDC in 10 CAD increments. The methane injection duration (MID) was increased from 2 ms to 4 ms in 0.5 ms increments. The results have demonstrated that delaying the MIT increases combustion stability compared to early MIT and shortens ignition delay time. High HC and CO emissions resulting from early MIT have been reduced by up to 26 % and 19 %, respectively, with the delay of MIT. Through the delayed MIT application, the diesel/methane study yielded higher exergetic efficiency, lower exergy destruction, and entropy generation compared to the only-diesel operation. Additionally, lower environmental impact and cost values were obtained due to combustion at lower temperatures compared to diesel.