The uncertainty in the supply of crude oil, increasing the number of vehicles and rising air pollution, especially in urban areas, has prompted us to look for alternative fuels. It is understood that using Compressed Natural Gas (CNG) in IC engines could be a mid-term solution to these problems. It is well established that CNG has better combustion characteristics and low emissions compared to conventional gasoline and diesel fuel. In the present study, an experiment was conducted to evaluate the engine performance and exhaust emissions using various percentages of CNG in dual fuel mode. CNG was mixed in the intake manifold’s air stream, and diesel was injected after the compression of the CNG air mixture. This paper presents experimental results of 40%,60%, and 80% CNG in the air stream. Engine performance and emissions are presented and discussed at a speed of 1200 rpm to 1500 rpm in steps of 50 rpm. The results of the experiments showed that adding CNG to diesel engines in dual-fuel combustion significantly impacted performance and emissions. Compared to single diesel fuel combustion, dual fuel combustion increases brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) at all CNG energy shares and engine speeds. Carbon monoxide (CO) and hydrocarbon (HC) emissions were increased, while nitrogen oxide (NOX) and smoke opacity were decreased in dual fuel combustion compared to single diesel fuel.