<p>This study employed three-dimensional numerical simulation methods to investigate the combustion and emission characteristics of three fuels—B0 (pure diesel), B15 (a mixture of 15% n-butanol and 85% diesel), and B30 (a mixture of 30% n-butanol and 70% diesel)—under the coupled effects of different injection pressures and injection timings. The results indicate that an increase in injection pressure significantly improves fuel atomization, promotes the transition to premixed combustion, and shortens the ignition delay time (ID) and combustion duration (CD) by 0.25, 0.51, and 0.73°CA, and 8.13, 8.19, and 8.26°CA, respectively. As injection pressure increased, the indicated thermal efficiency improved by 0.4%, 0.7%, and 1.2%, respectively, but NOx emissions increased by 107.4%, 84.7%, and 63.7%, respectively, while soot emissions showed the opposite trend. Furthermore, injection timing has a significant impact on the combustion atmosphere within the cylinder; delayed injection leads to prolonged ID and CD, adversely affecting indicated thermal efficiency. The study found that the injection timing yielding maximum thermal efficiency for B30 fuel is 9°CA, which is slightly earlier than that for B0 fuel. When the fuel injection timing was delayed from 11°CA BTDC to 3°CA BTDC, NOx emissions for all three fuels showed a decreasing trend to varying degrees, but soot emissions increased by 45.1%, 38.3%, and 35.2%, respectively. It is worth noting that soot emissions from B30 fuel remained at a relatively low level across different injection timings. The results of this study provide a theoretical basis for optimizing the combustion performance and emission control of biodiesel-diesel blends.</p>