Researchers from Belgium and France are exploring the use of a tri-component blend of biofuels derived from low-value biomass wastes—ethyl acetate (EtAc), ethyl propionate (EtPr), and ethyl butyrate (EtBu)—in homogeneous charge compression ignition (HCCI) engines. In a paper published in the ACS journal Energy & Fuels, they report that fuel blends of various proportions of EtAc, EtPr, and EtBu are all exploitable in an HCCI engine.
Not only does the HCCI engine offer the promise of efficiency improvement
and emission reduction, but it can also be run on a large variety of fuels, including low-grade fuels, given that the appropriate operating conditions are chosen, the team from Université catholique de Louvain (Belgium) and Université d’Orléans (France) notes. This enables the use of simpler and more efficient bioconversion process; other researchers have used hydrous ethanol, for example.
This paper focus on the products that can be obtained by
acidogenic fermentation (acidogenesis). Acidogenesis is commonly
used to decrease negative ecological effects of polluting
compounds. This simple and efficient process produces volatile
organic acids (including acetic, propionic, and butyric acids) from
low-value biomass wastes. Therefore, it has been identified as an
attractive alternative for bioenergy or chemical production.
The volatile organic acids are generally not used in internal
combustion engines because of the resistance of materials. Therefore,
they are combined with ethanol (also produced in small
proportions during the first stages of the acidogenic fermentation)
to produce ethyl acetate (EtAc), ethyl propionate (EtPr), and
ethyl butyrate (EtBu).
The process produces a mixture of various esters in proportions
that vary with the fermentation conditions and biomass
sources. Removing unwanted components or maintaining a
precise formulation of the biofuel require more energy-consuming
separation processes. Therefore, to use the fuel blends
directly in an engine, their effects on the combustion timing
need to be characterized.—Contino et al.
In a prior study, the team characterized experimentally the
ignition timing and the HCCI zones of EtAc, EtPr, and EtBu
compared to ethanol. Their results showed that these fuels ignite
more slowly than ethanol. For the given conditions, the upper
HCCI limit was increased while maintaining the lower limit for
EtPr and EtBu. However, the ignition of EtAc was so delayed that
the lower limit was modified because of more instability.
The current study had two main objectives: to provide information
to direct the fermentation process toward a portion of the
mixture region that is the most suitable; and to understand
the impact of these esters to improve the control and the
operating zone of the HCCI engine.
They evaluated 12 blends of the three fuels in a single-cylinder HCCI mode engine based on the
PSA DW10 model that has a displacement of 0.499 L/cylinder. The lower heating value (LHV) of the stoichiometric mixture for all fuel blends was in a very small range (below 1.5% of
the mean value), with a low impact on the combustion. The range of the air/fuel ratio (AFR), however, was larger
(14% of the mean value) and had an impact on the specific
heat of the mixture.
Among the findings were:
-
The ignition delay is mainly determined by
the proportions of EtBu and EtAc. It decreases when the proportion
of EtBu increases or when the proportion of EtAc decreases. -
EtPr has nearly no direct effect on the ignition timing but has an
antagonistic effect on the other components. It mitigates the
impact of the proportion variability on the ignition timing.
These results suggest that, on one hand, the smaller ignition
delay of EtBu could help reduce the inlet temperature and make
the use of these esters as transportation fuels easier. However, on
the other hand, the dilution effect of EtPr could maintain a
prescribed timing, while the blend composition changes. Directing
the fermentation process toward the optimal blend would
therefore depend upon these aspects. Moreover, the successful
implementation of these fuels may require to blend them with
other fuels or to use various compositions to control the engine.
These subjects will therefore remain the focus of future studies.—Contino et al.
Resources
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Francesco Contino, Fabrice Foucher, Christine Mounam-Rousselle, Herv Jeanmart (2011) Combustion Characteristics of Tricomponent Fuel Blends of Ethyl Acetate, Ethyl Propionate, and Ethyl Butyrate in Homogeneous Charge Compression Ignition (HCCI). Energy & Fuels doi: 10.1021/ef200193q]