The tremendous increase in the worldwide consumption of fossil fuels in the last decades
has led to several environmental issues, for example, greenhouse gas (GHG) emissions and
deteriorating air quality. It is urgent, therefore, to find alternative and sustainable fuel sources
for society and industry. Lignocellulosic biomass is the most abundant renewable source
of carbon, with the potential to support the sustainable production of renewable biofuels.
This study focused on experimentally investigating the effect of utilising a range of fuel
molecules from pyrolysis of lignocellulosic biomass, with different chemical compositions
and properties, as fuel blending components on combustion and emissions in a spark-ignition
engine.
In this work, a modern gasoline direct injection (GDI) engine (BMW B48) was utilised
to test various molecules, which were representative products of biomass pyrolysis, at
different fuel injection timings and air/fuel ratios. Initially, a group of short-chain oxygenated
molecules, including acetic acid, hydroxyacetone, and propylene glycol, were tested at two
different conditions with different IMEP, injection timings and λ values. Subsequently,
engine experiments were undertaken on oxygenated aromatics and furans from biomass
pyrolysis at 4 bar IMEP, with four different operating conditions achieved by varying the
injection timing and λ value to simulate the homogeneous and stratified modes of modern
GDI engines.
The major of the molecules investigated saw stable engine operation at a variety of
conditions, with the exception of anisole, 1,2-dimethoxybenzene and 2,5-dimethylfuran at
the stratified condition. A significant influence of the physical properties of the oxygenated
fuel molecules on the engine combustion characteristics was observed, especially at the
late injection timing. For example, the significantly higher viscosity of propylene glycol
compared to ethanol resulted in later heat release and a longer combustion duration at the
semi-stratified condition. Effects of the oxygenated fuel molecule structure on the engine-out
emissions were also observed. For example, the methoxyl functional group on anisole,
guaiacol, and 1,2-dimethoxybenzene contributed to the formation of particulate matter at
the homogeneous lean condition. At the stratified condition, molecules such as guaiacol
and 1,2-dimethoxybenzene with more than one oxygenated functional group reduced CO
emissions. Furthermore, the addition of a second methyl group to 2-methylfuran to form
2.5-dimethylfuran reduced NOx emissions through reduced rates of heat release.