| The direct application of i-propanol-n-butanol-ethanol(IBE)as the next generation biofuel of n-butanol in internal combustion(IC)engines and to get rid of the high recovery cost and extra energy consumption associated with n-butanol production has been gaining popularity.During the fermentation process of nbutanol,IBE is one of the intermediate products,contains some water.If the inherent water content in IBE can be blended with diesel to create diesel micro-emulsions for use in internal combustion engines,the energy required for water removal will be reduced and could reduce engine emissions and enhance thermal efficiency simultaneously.To research on water-emulsified IBE and provide experimental and numerical findings on the combustion and emission behavior of the fuel,IBE was prepared in a volume ratio of 3:6:1(I: B: E)and the samples of pure diesel(D100),IBE10(10 vol.% IBE and 90 vol.% diesel),IBE30(30 vol.% IBE and 70 vol.%diesel),IBE29.5W0.5(29.5 vol.%,IBE 0.5 vol.% water and 70 vol.% diesel)and IBE29W1(29 vol.% IBE,1 vol.% water and 70 vol.% diesel)were prepared.The physico-chemical properties of the fuel blends were determined and compared with European standard(EN590).The experiment using the water-in-diesel/IBE emulsion blends was carried out on a Kirloskar diesel engine and the numerical simulation was realized using a computational fluid dynamic(CFD)approach by developing and validating a novel reduced i-propanol-n-butanol-ethanol(IBE)/diesel mechanism for engine combustion and emissions prediction.In China and across the world,studies on the impact of water addition in diesel-alcohol fuel have been reported.However,the trade-off between engine power and emissions still exist.The key findings and innovative contributions of this research are itemized as follows:(1)Experiments were performed to solve the trade-off between the engine thermal efficiency and the emissions,by adding a small amount of water to the IBEdiesel blends.The effect of IBE10 and IBE30 blends without water addition resulted in the decrease of the engine emissions except for nitrogen oxide(NOx)and showed decreasing brake thermal efficiency(BTE)and brake specific fuel consumption(BSFC).The BTE and BSFC have been improved by the water addition with further reduction in the emissions level.In comparison with IBE30,IBE29W1 has shown decreasing peak in-cylinder pressure and increasing ignition delay and combustion duration by 0.13–4.80 %,0.50–12.40% and 0.26–3.80% respectively.As for the engine performance,BTE has been enhanced by 2.60 – 14.10% and BSFC decreased by 0.10–15%.The emissions of unburned hydrocarbon(UHC),smoke,carbon monoxide(CO)and nitrogen oxide(NOx)have been decreased by 21– 42.60 %,0–21.70%,5.40–11%,and 0.64–9%,respectively,at varying engine loading conditions.(2)To mitigate the high computational cost associated with the use of the detailed chemical kinetic mechanisms,a reduced mechanism of n-heptane/toluenei-propanol-n-butanol-ethanol(HT-IBE)including 151 species and 775 reactions to track the combustion and emissions behavior of engines fueled with IBE/diesel blends has been proposed for the first time and applied for engine simulation in the present research.The redundant species and reactions of i-propanol,n-butanol and ethanol detailed mechanisms have been removed accordingly using the algorithms of directed relation graph(DRG),directed relation graph with error propagation and sensitivity analysis(DRGEPSA),computational singular perturbation(CSP)and reaction path analysis(RPA)using CHEMical KINetic software(CHEMKIN)and Senkin codes.At the end of the DRGEPSA stage,the species and reactions of ipropanol,n-butanol and ethanol were downsized to 55 species and 310 reactions,97 species and 447 reactions,and 25 species and 113 reactions,respectively.The overall mean absolute errors for i-propanol,n-butanol and ethanol reduced mechanisms at the DRGEPSA stage were 13.75%,9.08% and 9.45%,respectively.The CSP further removed the unwanted species and reactions that could not be fully identified in the DRGEPSA stage.This gives rise to a reduced mechanism of ipropanol,n-butanol and ethanol with 54 species and 238 reactions,97 species and355 reactions,and 25 species and 60 reactions,respectively.The overall mean absolute errors for i-propanol,n-butanol and ethanol mechanisms at the CSP stage were 20.65%,19.3% and 22.60%,respectively.After the DRGEPSA and CSP stage,the reduced mechanisms of i-propanol and n-butanol were still large for numerical simulation,and thus the RPA was employed to further reduce the mechanisms.This further reduced the n-butanol and i-propanol mechanism to 76 species,283 reactions and 48 species,199 reactions respectively.The maximum induced errors recorded at this stage were 24.40% and 21.39% for n-butanol and i-propanol,respectively.The HT-IBE mechanism has been meticulously developed based on the coupling of the reduced mechanisms of i-propanol,n-butanol,ethanol and diesel surrogates and the simplified NOx and soot formation models.(3)On the basis of the functional requirements of the developed mechanism,the mechanism has been validated using experimental results from other researchers’ literature against ignition delay,laminar flame speed,and species mole fractions over a wide range of engine relevant conditions.Another functional requirement of the developed mechanism is a convincing response to 3D numerical simulation.The reduced mechanism and the CFD models were embedded into the KIVA3-2V–Cantera code for 3D simulation studies.Several numerical models alongside the reduced mechanism were used to simulate the in-cylinder pressure,heat release rate,NOx and soot emissions.The KIVA-3V-2 code functions based on the conservation of mass,momentum,and energy equations.The experimental results for the 3D validation were obtained from a researcher’ literature having a configuration of a single-cylinder direct injection diesel engine(AVL 5402)fueled with IBE0,IBE15 and IBE30 with a typical component proportion of I:B: E=3:6:1 in volume.(4)To investigate the combustion and emissions characteristics of the water-indiesel/IBE blends,a numerical simulation was carried out using a one-sixth sector mesh of the Kirloskar diesel engine chamber geometry alongside the verified novel diesel-IBE mechanism.The experimental results obtained from the configuration of the Kirloskar diesel engine were used to validate the simulated results with water addition impact.The combustion characteristics considered were the in-cylinder pressure and the heat release rate(HRR)and the emissions of the test fuels mainly CO,UHC and NOx were simulated and compared with the experimental results at full load and at the exhaust valve opening timing.Other important combustion and emissions precursors simulated were temperature distribution and equivalence ratio distribution.The evolution and spatial distribution of NOx and soot emissions.Based on the computational results,longer spray penetration length and greater spray volume were achieved for the blended fuels.As the water content increased,the spray distribution performance was affected due to the increase of the kinematic viscosity but improved the fuel atomization characteristics. |
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