Comparative analysis of water injection and EGR effects on combustion, performance, and emission characteristics of a diesel engine using diesel-biodiesel blends

The pollutants emitted from diesel engines, especially nitrogen oxides (NOx), are one of the fundamental challenges for designers and manufacturers of internal combustion engines. Exhaust gas recirculation (EGR) and water injection are two essential methods for reducing NOx emitted from the engine. The comparison of these two methods when simultaneously utilizing biodiesel in the engine can be considered the most significant gap in previous research. This study investigates the effects of water injection and EGR, along with the application of various diesel-biodiesel blends, on the performance, combustion, and NOx emissions of a Caterpillar 3401 diesel engine. The AVL Fire CFD software package was utilized along with a three-zone extended coherent flame combustion model and k - ζ - f turbulence model for evaluating the impacts of water injection at percentages of 15 %, 30 %, 45 %, and 60 %, and EGR at rates of 0 %, 10 %, 15 %, 20 %, and 25 % for the B0, B10, B20, and B50 (50 % diesel-50 % biodiesel) blends. According to the results, increasing water injection by up to 45 % reduces the maximum in-cylinder pressure by 4.4 % and engine power by 3.2 %–4.4 % for different fuel mixtures. However, a slight increase in power is observed when the water injection percentage reaches 60 %. Additionally, the specific fuel consumption (SFC) rises by 6.4 % for these mixtures. Similarly, as the EGR rate increases, the maximum in-cylinder pressure decreases by up to 5.5 %, with power declining by 3.5 %–4.3 %, comparable to the water injection scenario. The SFC also increases by 3.7 %–4.6 % across different fuel blends, though slightly less than with water injection. The results also reveal that a water injection of 60 % reduces specific NOx by about 57 %; furthermore, increasing the EGR rate to 25 % reduces nitrogen oxides by approximately 78 %. It was found that a 0.18 mm diameter is the most suitable for water droplets to reduce NOx emissions during water injection. Based on the results, considering both engine performance and the reduction of nitrogen oxides, the EGR method is recommended over water injection.