Influence of pinene isomerism on combustion and emissions in a heavy-duty diesel engine

The heavy-duty transport and maritime sectors require decarbonisation to reduce fossil fuel-derived CO 2 emissions and mitigate air quality impacts from exhaust pollutants such as particulate matter (PMx) and ( NOx ). This study investigates the combustion and emissions of the bio-derived bicyclic isomers α -pinene and β -pinene, which can be sourced from pine resin and waste paper pulp, while systematically assessing the effects of isomerism to understand the impact of minor structural changes on combustion behaviour. Both isomers were blended at 10% (volume/volume) into EN590-B0 diesel fuel and also at 10% and 50% (v/v) into hydrotreated vegetable oil (HVO), then tested in a Volvo 7.7 L D8K heavy-duty compression-ignition engine, bracketed with repeat tests of B0 diesel, at fixed load and speed under two injection timings. Nearly identical ignition delay and apparent peak heat release rates were observed for α - and β -pinene in both base fuels. At a 10% blend level, ignition delay increased by 0.2–0.3 crank angle degrees (CAD), while 50% β -pinene in HVO led to a longer delay (1.1–1.2 CAD), matching the delay observed with B0 diesel. Increasing pinene blend level elevated the peak heat release rate, particularly in the 50% HVO blends, which corresponded with higher NOx emissions. Total particulate mass remained similar across all blends, and 10% pinene addition had negligible impact on total particulate number (PN). However, PN increased significantly at a 50% blend level in HVO, reaching levels comparable to EN590-B0. Particle size distributions shifted toward smaller diameters, with greater PM 0.1 fractions at higher pinene content.