Abstract:Under the "dual-carbon" strategic goal, ammonia, as a carbon-free fuel, is one of the most promising options for the industrial and transportation sectors. The use of ammonia fuel in automotive engines can effectively reduce carbon emissions in transportation. This study investigated the combustion and emission characteristics of gasoline/ammonia dual-fuel engines under different intake valve opening (IVO) conditions using a modified engine test bench and three-dimensional combustion simulation software. The IVO was adjusted within the range from −30°CA to 10°CA, with IVO = −356 °CA ATDC as the reference point. The results show that as IVO advances, the peak in-cylinder pressure and heat release rate decrease gradually, and the combustion phases corresponding to the peak are delayed gradually. This is due to an the increase in residual gas in the cylinder as the valve overlap angle increases, which suppresses in-cylinder combustion. As IVO advances, the combustion phase CA10, CA50, and CA90 first delay and then advance, which is caused by the combined effect of valve overlap angle and intake-exhaust pressure difference. The advance of IVO affects the intake valve closing angle, resulting in a gradual decrease in pumping mean effective pressure, which reaches its minimum value at IVO=−30°CA. Notably, the effect of IVO on thermal efficiency is small. Meanwhile, the emissions of unburned hydrocarbons, carbon monoxide, and nitrogen oxides increase gradually with the advancement of IVO, while the change in IVO has little effect on the emission rate of unburned ammonia. This is because the decrease in cylinder temperature reduces the opportunity for hydrocarbons and carbon monoxide to be oxidized, and the increase in valve overlap angle raises the concentration of nitrogen oxides contained in residual gas in the cylinder. Meanwhile, the decrease in pumping mean effective pressure (PMEP) also increases the cylinder temperature, promoting the generation of nitrogen oxides. IVO constrains the performance and emissions of gasoline ammonia dual fuel engines. When the exhaust valve timing is fixed, in order to improve emission characteristics, IVO should be adjusted to 10°CA. At this point, total hydrocarbons, nitrogen oxides, and carbon monoxide all reach their minimum, but the brake thermal efficiency (BTE) is relatively low, at only 32.1%. To improve combustion characteristics, IVO should be adjusted to −30°CA. At this point, the BTE reaches 32.7%, but total hydrocarbons, nitrogen oxides, and carbon monoxide all reach their maximum, leading to a deterioration in the emissions. By using multivariate optimization methods to find the optimal valve timing combination, overall optimization of engine performance and emissions can be achieved. Close-