A comprehensive review of compressed natural gas (CNG)-fueled engines under different operating conditions and combustion strategies on performance and combustion characteristics

Climate change and stringent emission regulations are driving the search for sustainable fuels for internal combustion engines. To address growing urbanization, increased vehicle use, and environmental concerns, researchers are exploring alternative fuels that reduce greenhouse gas emissions and air pollution. Compressed natural gas (CNG) is one of the most promising and ecologically friendly alternative fuels since it can be exploited in both compression ignition and spark ignition engines. Thus, this review article broadly and comprehensively focuses on the global background of CNG usage, aiming to attain the ambition of mitigating greenhouse gases and environmental pollution. Indeed, CNG projects carried out around the world and the suitable properties of CNG for internal combustion engines are critically presented. More importantly, the performance, combustion, and emission attributes of the CNG-fueled engines are evaluated and compared with those of conventional diesel and gasoline engines. The brake thermal efficiency of CNG is greater than that of gasoline, but it drops when compared to diesel because of the disparity in calorific value. Compared with conventional fuels, CNG has a lower peak cylinder pressure and heat release rate because its laminar flame speed is slower. In addition, the effects of operating parameters on CNG-fueled engines are also completely analyzed. Finally, the combustion strategies, limitations, and perspectives of CNG are discussed in detail.