Hydrogen-assisted combustion of pyrolysis oil derived from mulch-film agricultural waste in a diesel engine

Plastic mulch films are extensively used in modern agriculture for improving crop productivity, moisture retention and weed control. However, the disposal of used mulch films has emerged as a critical environmental challenge due to contamination with soil, agrochemicals, and organic residues, which makes conventional recycling difficult. In many regions, these waste mulch films are commonly disposed of through open burning or landfilling, practices that contribute to air pollution, greenhouse gas emissions, and long-term degradation of fertile agricultural land. To address this issue, the present study investigates a sustainable waste-to-energy approach by converting discarded agricultural mulch films into liquid fuel through a controlled pyrolysis process. The pyrolysis was carried out under controlled oxygen environment to thermochemically decompose the plastic waste into valuable fuel fractions. The analysis of the pyrolysis oil showed that its properties were comparable to that of d\Diesel and the spectral analysis indicates the presence of aliphatic and aromatic hydrocarbon group which makes it viable to use in compression ignition (CI) engine. Pyrolysis oil derived from the used mulch film for CI engine use has not been reported earlier. The pyrolysis oil thus produced was blended with Diesel in varying proportions from 10 to 50% (by volume). The trials on a CI engine indicates that 50% blend of pyrolysis oil in Diesel (W50) resulted in the highest brake thermal efficiency of 30% a substantiative increment of 6.85% over Diesel. To reduce carbon emission from CI engine, the best blend of W50 was partially substituted with hydrogen gas. The hydrogen was inducted into the intake manifold at flow rates of 2.5, 5 and 7.5 litre per minute (LPM). Engine experiment reveal further improvement in engine performance with the highest flow rate of hydrogen. The thermal efficiency at maximum load condition with W50 + 7.5LPM improved by 5.7% as compared to W50 blend. The in-cylinder pressure and heat release rate were higher compared to base fuels with slightly delayed start of combustion. The unburnt hydrocarbon (HC) emissions reduced by 32%, carbon monoxide emission reduced by 45%, smoke opacity reduced by 15% while NOx emissions were increased by 34% with hydrogen. Overall, the waste mulch-films are a potential candidate for conversion to liquid fuel through pyrolysis. This study highlights a viable circular economy strategy for agricultural plastic waste along with efficient and cleaner engine operation.