Numerous research studies have been conducted to enhance fuel economy and reduce emissions by converting diesel engines to run on aqueous ammonia-diesel (AAD) blends. However, only a few studies have investigated the effect of the piston bowl geometry on combustion efficiency and emissions from AAD blends. This study investigated the effect of piston bowl geometry on the combustion efficiency of a diesel engine fueled with AAD blends. Five different types of piston bowls, namely the Double lip (Case 1), 10D100 (Case 2), Mexican hat (Case 3), Inveco F1C Rollbuch (Case 4), and Peugeot DW 10 (Case 5), were used. Diesel-RK software was used for modeling and simulating the fuel combustion inside the diesel engine. Based on the numerical findings, with the same combustion chamber, the results show that the NOx emission, smoke level, and peak pressure reduced with increased engine speed from 2000 to 3000 rpm, whereas peak temperature, CO₂, and PM emissions increased. Moreover, among all designs, Case 5 achieved the highest combustion performance, with peak pressure and temperature, along with the lowest PM and smoke. However, it produced the highest NOx emissions. In contrast, Case 1 yielded the lowest NOx, peak pressure, and temperature, but the highest PM, indicating poor combustion. Case 3 achieves the second-highest peak pressure (53.13 bar at 2000 rpm and 52.61 bar at 3000 rpm) and second-highest temperature (1886.8 K at 2000 rpm and 1914 K at 3000 rpm), and only moderately elevated NOx. Case 3 offers the best overall emission balance while maintaining high combustion efficiency, making it the most suitable piston bowl geometry for sustainable operation with AAD blends.

The current work investigated the combustion efficiency of biodiesel engines under diverse ratios of compression (15.5, 16.5, 17.5, and 18.5) and different biodiesel fuels produced from apricot oil, papaya oil, sunflower oil, and tomato seed oil. The combustion process of the biodiesel fuel inside the engine was simulated utilizing ANSYS Fluent v16 (CFD). On AV1 diesel engines (Kirloskar), numerical simulations were conducted at 1500 rpm. The outcomes of the simulation demonstrated that increasing the compression ratio (CR) led to increased peak temperature and pressures in the combustion chamber, as well as elevated levels of CO₂ and NO mass fractions and decreased CO emission values under the same biodiesel fuel type. Additionally, the findings revealed that the highest cylinder temperature was 1007.32 K and the highest cylinder pressure was 7.3 MPa, achieved by biodiesel derived from apricot oil at an 18.5% compression ratio. Meanwhile, the highest NO and CO₂ mass fraction values were 0.000257524 and 0.040167679, respectively, obtained from biodiesel derived from papaya oil at an 18.5% compression ratio. This study explained that the apricot oil biodiesel engine had the highest combustion efficiency with high emissions at a compression ratio of 18:5. On the other hand, tomato seed oil biodiesel engines had low combustion performance and low emissions of NO and CO₂ at a compression ratio of 15:5. The current study concluded that apricot oil biodiesel may be a suitable alternative to diesel fuel operated at a CR of 18:1.