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• First study to compare low blend ratio MF20 and MTHF20 with neat ULG in a DISI engine. • MTHF20 exhibits improved specific fuel consumption over MF20 across all load conditions. • MTHF20 achieves the highest thermal efficiency at most mid-range loads. • Unburned furan emissions from MF20 and MTHF20 accounted for only 3 % of total HC at 280 °CA BTDC. The nearing depletion of fossil fuels and the possible consequences of its emissions on the global climate has prompted a worldwide probe for their alternatives. 2-methylfuran and 2-methyltetrahydrofuran are considered promising alternative fuels for spark ignition engines. In this study, the combustion and emission characteristics of low blending ratio MF20 (2-methylfuran 20 %, gasoline 80 % by volume) and MTHF20 (2-methyltetrahydrofuran 20 %, gasoline 80 % by volume) were first implemented and compared to neat gasoline in a single-cylinder direct injection spark ignition engine. The combustion performance of the test fuels was analyzed across a range of loads from 3.5 to 8.5 bar indicated mean effective pressure and fuel injection timings between 180 and 280 crank angle degrees before top dead center. Meanwhile, the compositions of the hydrocarbon emissions were experimentally investigated using the Fourier Transform Infrared Spectroscopy technique. Results show that MF20 exhibits advanced spark timing flexibility of 8 and 7 crank angle degrees before top dead center compared to the unleaded gasoline and MTHF20 respectively at the peak load. MTHF20 exhibits the highest maximum cylinder pressure at medium load compared to other fuels but drops sharply at peak load accompany with the audible knock. Additionally, MTHF20 exhibits specific fuel consumption advantage over MF20 across the entire load range. The unburned furan of the total hydrocarbon emissions was recorded to be 3 % of total hydrocarbon emissions. The concept of low blending ratio furan-based fuel proposed could provide a solution for the transition period of carbon neutrality. [ABSTRACT FROM AUTHOR]

Kinetic analyses were performed based on the experimental results of ignition delay times of 2-methyltetrahydrofuran (2-MTHF) using shock tube technique at temperatures of 1050–1800 K, equivalence ratios of 0.5–2.0, fuel mole concentrations of 0.25–1.0%, and pressures of 1.2–10 atm. A new kinetic model of 2-MTHF oxidation named Mech III was established according to the analysis of simulation using two published models (Mech I from Ravi Fernandes group and Mech II from Battin-Leclerc group) and the experimental data in this work. Comparison between simulation and experimental data indicated that Mech II shows remarkable under-prediction while Mech I gives a good agreement with ignition delay times under most conditions except for underprediction on fuel-rich mixtures at relative low temperature around 1250 K. Sensitivity analysis indicated that both models underestimated ignition delay times for the reactions of C 0 -C 4 molecules, so Mech III was formed by introducing such reactions and can demonstrate improved simulation performance under all conditions. Reaction pathway analysis of Mech III showed that 2-MTHF is mainly consumed through fuel decomposition at high temperatures (around 1550 K), and H-atom abstraction reactions at lower temperatures (around 1250 K), respectively. The comparative experimental and kinetic study between 2-MTHF and 2-methylfuran (MF) indicated that 2-MTHF has higher ignition delay times under the same conditions in this work, while the disparity decreases as the temperature increases, and 2-MTHF produces less soot precursors under high temperature conditions. [ABSTRACT FROM AUTHOR]

• The dilution effect on laminar flame characteristics of 2-MTHF was investigated. • The effect of CO 2 , N 2 and helium on LBVs of 2-MTHF-air was compared. • The stabilizing abilities of CO 2 , N 2 and helium were compared and analyzed. • The dilution effect of CO 2 , N 2 and helium on critical flame size was evaluated. Recent investigations have indicated that 2-methyltetrahydrofuran (2-MTHF) can be a potential alternative fuel, owing to its renewability and environmentally friendly properties. In this study, the effects of carbon dioxide (CO 2), nitrogen (N 2), and helium (He) dilution on the laminar burning velocity (LBV) and cellular instability of 2-MTHF-air flames were investigated experimentally and kinetically at a temperature of 423 K, a pressure of 5 bar, equivalence ratios (ϕ) of 0.7–1.5, and diluent ratios of 0–15%. The results illustrated that CO 2 exhibited the strongest ability to reduce the LBVs, followed by N 2 and He. The effective Lewis number ( Le eff ) of the He diluted 2-MTHF-air flames increased as more He was added to the reactant mixture, thereby indicating that the intensity of diffusive-thermal instability could be diminished by He dilution. In contrast, Le eff was insensitive to CO 2 and N 2 dilution. The flame thickness increased and the density ratio decreased as the diluent ratio increased, indicating that all three diluents suppressed the hydrodynamic instability of 2-MTHF-air flames. The relative magnitudes of the stabilizing abilities of these diluents were in the order CO 2 > N 2 > He. The stability analysis indicated that the monotonically decreasing critical Péclet number and non-monotonically altered flame thickness caused a non-monotonic variation in the theoretical critical flame radius of 2-MTHF-air flames versus ϕ. The most chaotic state occurred at approximately ϕ = 1.3 under all test conditions. Notably, CO 2 and He exhibited a similar ability to delay the onset of cellular instability, whereas N 2 demonstrated a weaker ability to do so. [ABSTRACT FROM AUTHOR]

• A highly compact and robust tetrahydrofurans chemical kinetic mechanism was developed with 56 species and 183 reactions. • Genetic Algorithm was introduced to achieve self-adaptive tuning of Arrhenius pre-exponential factor of reactions. • Good performance was highlighted by the optimized mechanism against existing experimental results. This work presents a compact and robust chemical reaction mechanism for modeling the combustion of saturated furans including tetrahydrofuran, 2-methyltetrahydrofuran and 2-buthyltetrahydrofuran under engine relevant conditions. A decoupling method is adopted to construct the mechanism. The oxidation reaction for the small species is described by a mature and detailed H 2 /CO/C 1 sub-mechanism, based on which the skeletal sub-mechanisms for tetrahydrofuran, 2-methyltetrahydrofuran and 2-buthyltetrahydrofuran are incorporated via a compact yet robust C 2 -C 3 sub-mechanism. The sub-mechanisms for the three tetrahydrofuranic fuel components are selected from the detailed chemical mechanisms in the literature via a series of species rate of production analysis, sensitivity analysis, isomer lumping and reaction lumping. The Arrhenius pre-exponential A factors for these selected reaction pathways are then optimized via a single objective genetic algorithm. The resulting mechanism is rather compact consisting of only 56 species among 183 reactions. The performance of the developed mechanism for predicting the combustion chemistry for the three fuel components has been evaluated against the experimental measurements in the literature. Reasonable agreement between the predicted ignition delay times, speciation profiles and laminar flame speeds with the experimental data is achieved for all the cases considered, indicating the high accuracy and robustness of the developed mechanism. [ABSTRACT FROM AUTHOR]