Evaluation of the combined impact of injection pressure and EGR on a diesel engine running on waste-recovered plastic biodiesel for environmental benefits

• Modified fuel delivers diesel-like efficiency with cleaner performance. • Early injection boosts BTE, but smart tuning needed to manage NOx. • 20% EGR slashes NOx effectively—cleaner emissions achieved. • Optimal settings cut CO and smoke, making modified fuel eco-friendly. • Peak pressure and HRR at 23° bTDC, 0% EGR show strong combustion. The present study investigates the performance and emission characteristics of a diesel engine operating on a 50% waste plastic biodiesel blend (WPB50D50), evaluated under varying injection timings (19°, 21°, and 23° bTDC) and exhaust gas recirculation (EGR) rates of 10% and 20%. This study presents a novel exploration of the combined effects of injection timing variation and exhaust gas recirculation (EGR) on the performance and emission behavior of a WPB50D50 blend. The findings indicate that advancing injection timing enhances brake thermal efficiency (BTE), with the maximum efficiency of 32.61% achieved at 21° bTDC with 0% EGR. However, further advancing the timing to 23° bTDC results in marginal efficiency losses due to increased heat dissipation. Brake specific energy consumption (BSEC) follows a decreasing trend with advanced injection timing, reflecting improved combustion, but rises with increasing EGR due to oxygen depletion. The emission analysis reveals a reduction in CO and HC emissions with advanced injection timing, with the lowest levels recorded at 23° bTDC and 0% EGR. However, NOx emissions increase with advanced timing due to elevated combustion temperatures, peaking at 1924 ppm at 23° bTDC and 0% EGR. The application of EGR effectively mitigates NOx emissions, with the lowest concentration (1513 ppm) observed at 19° bTDC and 20% EGR. Smoke opacity is similarly reduced with both advanced injection timing and higher EGR rates, reaching a minimum of 35% at 23° bTDC and 20% EGR. Combustion analysis indicates that the highest peak pressure and heat release rate (HRR) occur at 23° bTDC with 0% EGR, suggesting improved premixed combustion under these conditions. Overall, the WPB50D50 blend exhibits performance and efficiency comparable to diesel fuel, with significantly reduced smoke and CO emissions. The optimal combination of injection timing (21°–23° bTDC) and low EGR (0%–10%) balances combustion efficiency and emissions control. These results highlight the potential of WPB50D50 as a sustainable alternative to conventional diesel, aligning with the objectives of Sustainable Development Goal (SDG) 7 by promoting affordable and clean energy through the use of waste-derived biodiesel. Additionally, by reducing fossil fuel dependency and lowering harmful emissions, the study contributes to SDG 13 (Climate Action), supporting global efforts toward climate mitigation.