Tyre pyrolytic oil blends in a state-of-the-art compression ignition engine: Towards fuel-optimised combustion

Abstract

The end-to-end efficiency and environmental impact of tyre pyrolysis oil (TPO) are currently high on the agenda of worldwide research. However, most knowledge regarding combustion and emissions of TPO fuels comes from legacy (pre-Euro standard) engine platforms, operating in non-optimal combustion conditions. The few tests on modern automotive engines have used factory, diesel-optimised calibration maps and focus on only small TPO admixtures to diesel fuel (DF). The present work aspires to tackle these knowledge gaps by testing higher TPO admixture diesel blends in a state-of-the-art research engine realising low nitrogen oxides (NOX), partially premixed compression ignition. Measurement campaigns focus on accuracy in establishing fuel-to-fuel differences in emissions, also with consideration of unlegislated species. A combination of thorough combustion analysis and accurate fuel property characterisation allows evaluation of a calibration strategy that harnesses multi-pulse injection and a fully controlled air-path to mitigate emissions. This strategy enables an engine fuelled with a 40% TPO blend to realise low-temperature combustion in a wider area of the calibration map than is possible with DF. The most favourable NOX/particulate matter (PM) mode is extended towards high exhaust gas recirculation and early injection regimes. Adopting this dedicated engine control for TPO allows best-point NOX/PM emissions of 1.22 g/kWh and 0.18 g/kWh respectively, while maintaining the baseline indicated thermal efficiency target of 42%. Carbon monoxide and hydrocarbons emissions are elevated, but in terms of current EU Non-road Mobile Machinery Stage V limits, differences between TPO and DF are insignificant. However, regardless of calibration, TPO's chemical make-up causes increased emissions of sulphur oxides and aromatic hydrocarbons.