Properties and Performance of Model Lignocellulose Derived Biofuel Mixtures as Low Carbon Replacements for Diesel Fuels

The decarbonisation of heavy-duty vehicles and other compression ignition (CI) engine applications is pivotal to meeting global climate change targets. Since these engines are likely to rely on liquid fuels, there is a need for low-carbon alternatives. One potential option could be the product blend from alcoholysis of lignocellulosic biomass. The main products include an alkyl levulinate, a dialkyl ether, and the alcohol used. The blend composition could be tailored to ensure compliance with existing fuel standards and to favour comparable engine performance and low emissions, whilst maximising the use of the main product, the alkyl levulinate. In this work, experimental and computational techniques were used to investigate the influence of the biofuel blend composition and carbon chain length on the fuel properties, engine performance, and emissions when utilising the blends in an unmodified engine. Physical properties of ethanol, n-butanol, and n-pentanol alcoholysis derived three-component blends with and without diesel were tested, along with their miscibility. A design of experiments (DoE) approach was used to effectively cover the desired design space. Accurate predictive models were produced using the DoE methodology for the flash point, density, and kinematic viscosity, for the blends, with R2 values >0.900. Blends with diesel and biodiesel were also tested to establish blend boundaries and their compliance with existing fuel standards. Tailoring the physical properties of butyl-based blends showed more favourable engine performance compared to when tailoring the combustion properties of the ethyl-based blends. The butyl-based biofuel blends could be added up to 25 vol% in diesel whilst remaining compliant with fuel standards. The blends of diesel and biofuel three-component blends were tested in a Yanmar L100V single-cylinder CI and their engine performance and emissions were determined. Emissions indices were calculated to investigate if the fuel blends would enable the engine to maintain compliance with the Euro Stage V emissions standard. The CO and total hydrocarbon (THC) emissions increased relative to diesel for all biofuel blends, whereas the particulate matter (PM) and particle number (PN) emissions reduced. The nitrogen oxide emissions were stable relative to the diesel baseline. At maximum load, the butyl-based blends reduced the THC, PM, PN, and volatile organic compounds emissions. Whist the blends were compatible with the engine in terms of their overall performance, there would need to be optimisation or the retrofitting of aftertreatment systems to ensure their compliance with the emissions standard. Chemical kinetic simulations of the gas phase combustion highlighted the need to include the fuel spray and turbulent mixing when modelling CI engine combustion in order to capture trends in combustion behaviour on blending. Chemical ignition delays followed the expected trends for the biofuel blends but did not match those from the engine, demonstrating the combined influence of chemical and physical effects on ignition delays and heat release properties.