A comprehensive study on the effects of multiple injection strategies and exhaust gas recirculation on diesel engine characteristics that utilize waste high density polyethylene oil

The present study utilized the catalytic pyrolysis method for extracting oil from waste high-density polyethylene (WHDPE) plastics. Experiments were carried out with D70H30 (diesel-70%, WHDPE oil-30%) blend under the influence of three start of pilot injection (SoPI) timings [45 degrees before top dead center (bTDC), 50 degrees bTDC, and 55 degrees bTDC] and three pilot fuel injection quantity (PFIQ) (10%, 20%, and 30%) at the engine's rated power output. Later, the impact of exhaust gas recirculation (EGR) (0%, 10%, and 20%) was studied with the optimum SoPI and PFIQ. Experimental results indicated that at SoPI timing of 55 degrees bTDC and at PFIQ of 30%, the brake thermal efficiency (BTE) increased by 8.5%, nitrogen oxides (NOx) increased by 19.25%, while smoke, hydrocarbons (HC), and CO emission got lowered with baseline operation of the blend and found to be best among other modifications. In the next phase of the work, exhaust gas is recirculated at 10% and 20%. The results portray that inclusion of 10% EGR in the intake at SoPI 55 degrees bTDC and at PFIQ 30% has shown 1.7% higher BTE, with 3.7% and 28.9% lower NOx and smoke emission compared to the single main injection of the blend. It is concluded that pilot injection strategy with 30% PFIQ and SoPI timing of 55 degrees bTDC at 10% EGR rate can be adopted to utilize WHDPE oil/diesel in diesel engines effectively.