Synergies between aliphatic bio-alcohols and thermo-chemical waste heat recovery for reduced CO2 emissions in vehicles

• Published in: Fuel (Guildford) Vol. 304; p. 121439
• Main Authors: Singh, J., Nozari, H., Herreros, J.M., Tsolakis, A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.11.2021; Elsevier BV
• Subjects: Alcohol; Alcohols; Aliphatic compounds; Bio-alcohols; Carbon dioxide; Chemical wastes; Ethanol; Exergy; Exhaust emissions; Flow mapping; Flux density; Free energy; Gasoline; GDI engine; Gibbs free energy; Heat; Heat recovery; Heat recovery systems; Hydrogen production; Isooctane; Mass flow; Nuclear fuels; Octane; On-board hydrogen production; Reactors; Reforming; Renewable fuels; Steady state; Thermodynamics; Vehicle emissions; Waste heat; Waste heat recovery; Renewable fuels; On-board hydrogen production; Bio-alcohols; Exergy; Waste heat recovery; GDI engine
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.121439

[Display omitted] •C1–C5 renewable alcohols were investigated for on-board thermochemical heat recovery system.•An AVL CRUISE M vehicle model was created and validated for exhaust exergy prediction.•A methodology was developed to couple the vehicle and reactor models to compute heat recovery.•Heat recovery of up-to 9% of engine power was observed in the high-speed phase of WLTC.•In WLTC a CO2 reduction of up-to 8.4% was observed for the Vehicle-Reformer system. The impact of aliphatic (C1–C5) bio-alcohols for on-board thermo-chemical exhaust waste heat recovery, H2 production and hence fuel savings for a gasoline direct injection (GDI) engine has been investigated with iso-octane as reference. Gibbs free energy analysis was conducted to establish which reaction pathways for fuel reforming were dominant and how these reactions are influencing H2 and CO yield. To obtain engine exhaust temperature and mass flow maps for several steady-state engine operation conditions, an engine model was created in AVL CRUISE M and validated with real GDI engine data. A methodology was developed to couple the thermodynamic reactor results and engine model results to compute waste exhaust heat recovery by accounting limited available exergy in exhaust and optimising reforming reactor’s operational parameters to maximise exergy recovery and reforming efficiency in the reformer. Under steady state engine operation, iso-pentanol was more effective overall due to its high hydrogen content by weight (8.3% and 4.3% higher than methanol and ethanol respectively), high energy density of 34.6 MJ/kg (42.2%, 22.3% 13.2% and 4.3% higher than C1-C4 alcohols respectively), high reforming endothermicity and the versatility for heat recovery under all engine operation conditions with heat recovery of at-least 2% of engine power even under low-load conditions. Subsequently, the engine model was evolved into a full AVL CRUISE M vehicle model and was studied over a duty-cycle to evaluate the fuels further. Iso-pentanol and iso-propanol were most effective concerning average heat recovery over the duty cycle. For the high-speed regions of the cycle, up-to 9% of waste heat recovery is observed for C4 and C5 bio-alcohols. In terms of vehicle’s carbon emissions, iso-pentanol, n-butanol, and ethanol exhibited maximum CO2 reduction of 8.4%, 7.7% and 7.1% respectively. The results presented herein indicates versatility of bio-alcohols for cleaner and more efficient powertrains.