Tyre pyrolytic oil fuel blends in a modern compression ignition engine : A comprehensive combustion and emissions analysis

Abstract

There is abundant worldwide research into combustion engine applications for tyre pyrolysis oil (TPO). However, most studies are methodologically outdated in terms of their assumed technology, either with regard to TPO production or engine application, or in their analytical approaches. The variety of radically different studies produce conflicting or ambiguous results, rendering TPÓs role as a feasible future fuel uncertain. This study is the first to provide state-of-the art combustion analysis results for thoroughly-evaluated TPO fraction optimised in a modern, industry-grade pyrolytic reactor. The fuel blends are selected for engine tests, taking into account the overall availability/compatibility of their TPO fractions with diesel. Testing with a modern, sophisticated single-cylinder research engine provides detailed analysis of combustion and both regulated and unregulated emissions. Emissions results are supported by FTIR analysis of exhaust gases, including identification of 23 species. The results show that contemporary Tier 4-compliant combustion systems with multi-pulse injection can handle high TPO-content fuels without needing re-calibration. With diesel/TPO blends of up to 40% TPO admixture, combustion phasing is substantially delayed (by 3CAD) only at near-idle loads and particularly when using heavy exhaust gas recirculation. The consequential differences in performance and emissions diminish over the test cycle. Current US EPA Tier 4 emission limits are not particularly challenging for TPO, even at 40% blending rate, but its elevated levels of particulate matter (25% increase over test cycle versus diesel baseline), sulphur oxides, aromatics and formic acid present health concerns and potential maintenance issues. These should be considered when assessing the fueĺs life-cycle environmental impact. The increase in emissions of those species correlates directly with fuel sulphur content (0.5% for neat TPO fraction), polyaromatic hydrocarbons fraction (0.49%) and acidity. Further optimisation of TPÓs composition in the reactor and via improved fuel post-processing can address these issues.