Thermochemical exhaust waste-heat recovery using bioalcohols for cleaner, efficient and decarbonised powertrains

Singh, Jasdeep (2023). Thermochemical exhaust waste-heat recovery using bioalcohols for cleaner, efficient and decarbonised powertrains. University of Birmingham. Ph.D.

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Abstract

Gasoline direct injection (GDI) engines power a significant portion of road transport powertrains. Due to concerns regarding global warming and deteriorating air quality, research community is seeking pathways for cleaner and decarbonised road transport. Partial substitution of gasoline with hydrogen can improve engine’s thermal efficiency and reduce engine out pollutant emissions. On-board hydrogen production is an attractive solution to mitigate limitations associated with hydrogen fuelling/storage.
This thesis investigated how use of different bio-alcohols as fuels for thermochemical heat recovery process affects fuel savings, exhaust heat recovery, CO2 emissions and gaseous pollutant emissions under range of different conditions. Lifecycle analysis of CO2 emissions was also conducted. The research was carried out using thermodynamic, kinetic, and experimental studies.
The research began with the analysis of five aliphatic bio-alcohols using a thermodynamic reactor model. By varying various parameters, maps of predicted product compositions were created for each examined fuel. Using a novel method, potential heat recovery maps were computed for each fuel. Fuel chain length affected specific exergy availability and hence energy recovery. Production of hydrogen peaked at higher temperatures for longer chain bio-alcohols. All the studied bio-alcohols showed heat recover potential whereas, iso-pentanol showed superior performance with potential heat recovery of 7.9% of engine power.
Iso-pentanol was further parametrically examined for fuel reforming at typical GDI engine exhaust conditions to understand how hydrogen production, fuel conversion and energy recovery varies with reactor temperatures and fuel injection rate with ethanol utilised as a reference fuel. From the study it was found that the fuel chain length influences fuel conversion which in turn influences hydrogen production and energy recovery. From the obtained results, a global kinetic mechanism for exhaust gas reforming was developed. Iso-pentanol’s reforming exhibited maximum calorific value increase of 23%.
Both the bio-alcohols were further examined in a prototype fuel reformer integrated to a modern GDI engine at two different GHSVs (gas hourly space velocity) and three fuel injection rates. The reformer was instrumented to identify regions of exothermic, autothermal and endothermic nature.
Finally, the performance of GDI engine was investigated when fed with reformate produced from the two bio-alcohols’ reforming process. The reformate introduction increased thermal efficiency and reduced engine out pollutant emissions and greenhouse gas emissions.
Life cycle analysis revealed maximum CO2 reduction of 11% with iso-pentanol reforming. The findings of the thesis reveal that carbon neutral bio-alcohols are a viable solution to simultaneously abate internal combustion engine emissions and decarbonise transport sector for a transition into a net zero society.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):