A Study on Combustion and Emission Characteristics of an Ammonia-Biodiesel Dual-Fuel Engine

Internal combustion engines, as the dominant power source in the transportation sector and the primary contributor to carbon emissions, face both significant challenges and opportunities in the context of achieving carbon neutral goal. Biofuels, such as biodiesel produced from biomass, and zero-carbon fuel ammonia, can serve as alternative fuels for achieving cleaner combustion in internal combustion engines. The dual-fuel combustion of ammonia-biodiesel not only effectively reduces carbon emissions but also exhibits promising combustion performance, offering a favorable avenue for future applications. However, challenges arise in the form of unburned ammonia (NH₃) and N₂O emissions. This study, based on a ammonia-biodiesel duel-fuel engine modified from a heavy-duty diesel engine, delves into the impact of adjustments in the two-stage injection strategy on the combustion and emission characteristics. The research findings indicate that as the pre-injection timing advances, the ignition delay increases, and the first-stage heat release is delayed, the indicated thermal efficiency initially increases and then decreases, reaching a maximum of 48.5%, surpassing the indicated thermal efficiency of pure biodiesel combustion. With the advancement of the pre-injection timing, nitrogen oxides (NO_x) emissions exhibit an overall declining trend, while nitrous oxide (N₂O), total hydrocarbons (THC), and carbon monoxide (CO) emissions increase, and there is an optimal pre-injection timing for reducing unburned ammonia emissions. Adjusting the main-injection timing can modulate the phase of ammonia-biodiesel combustion to improve the indiated thermal efficiency. Compared to the pure biodiesel mode, the equivalence CO₂ emissions from the ammonia-biodiesel mode are significantly reduced by approximately 40%. Furthermore, this study compares the combustion and emission performance of ammonia-biodiesel and ammonia-diesel combustion modes, revealing that using biodiesel for ammonia ignition results in better performance, with reduced unburned ammonia emissions and higher indicated thermal efficiency. This research offers guidance for optimizing ammonia-biodiesel dual-fuel engine combustion and provides a pathway for further energy efficiency and carbon reduction in internal combustion engines.