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The current study seeks to greenhouse gas emissions reduction in an existing engine under dual-fuel combustion fueled with diesel fuel and natural gas due to great concerns about global warming. This simulation study focuses on the identification of areas prone to the formation of greenhouse gas emissions in engine cylinders. The simulation results of dual-fuel combustion confirmed that the possibility of incomplete combustion and the formation of greenhouse gas emissions in high levels are not far from expected. Therefore, an efficient combustion strategy along with replacing natural gas with hydrogen was considered. Only changing the combustion mode to reactivity-controlled compression ignition has led to the improvement of the natural gas burning rate and guarantees a 32 % reduction in unburned methane and 50 % carbon monoxide. To further reduce engine emissions, while changing the combustion mode, a part of natural gas replacement with hydrogen to the complete elimination of it was evaluated. Increasing the share of hydrogen energy in the intake air-natural gas mixture up to 54 % without exhaust gas recirculation does not lead to diesel knock. Moreover, improvement of engine load and efficiency can be achieved by up to 18 % and 6 %, respectively. Natural gas consumption can be reduced by up to 67 %. Meanwhile, the unburned methane and carbon dioxide mass, known as greenhouse gas emissions, can be reduced to less than 1 % and up to 50 %, respectively. Continued replacement of natural gas with hydrogen until its complete elimination guarantees a reduction of 92,000 cubic meters of natural gas per year in one engine cylinder. Although, the engine efficiency and load face a decrease of 0.8 % and 5.0 %, respectively; the amount of carbon dioxide can be decreased by about 4.5 times. Unburned methane, carbon monoxide and nitrogen oxides can be reduced to below the relevant EURO VI range while the amount of unburned hydrogen compared to the hydrogen entering the engine is about 0.5 %.

The main purpose of this study is to determine the appropriate operating conditions for Iranian national heavy-duty diesel engines under RCCI combustion fueled with natural gas and diesel fuel. Therefore, in the RCCI combustion simulation, based on the DOE concept, the effect of changing six major parameters namely the IVC pressure, the IVC temperature, the diesel fuel SOI timing, the engine speed, the natural gas/diesel fuel mass ratio, and the effective compression ratio on the engine performance and combustion characteristics were assessed. The simulation results show that considering the IVC pressure between 2.3 and 2.7 bar, the IVC temperature between 350 and 380 K, the diesel fuel SOI timing between -30 and -50 ° ATDC, the NG/diesel fuel mass ratio between 70/30 and 90/10, and the engine speed between 1300 and 1600 rpm lead to optimal D87 engine operation. Where the GIE can be improved to more than 40% compared to the D87 engine operation under the dual-fuel mode of combustion. Although, the engine output power is noticeably reduced up to 17%, , the NOx emission level gets close to the EURO V level and the CO emission level gets close to the EURO VI level. At the same time, the UHC emission level is far from the EURO VI level and the Formaldehyde emission level is far from the EPA 2007 level.