The increasing energy demand and more stringent legislation on engine
pollutant emissions with the use of carbon-neutral fuels have motivated the
use of bio-alcohols such as butanol (B). Because butanol-acetone (BA) and
acetone-butanol-ethanol (ABE) are intermediate mixtures in bio-butanol
production, they present cost benefits compared to butanol production as a
consequence of reduced energy consumption and recovery processes. This study investigated the effect of using bio-alcohol additives with neat
diesel (D) or biodiesel (Bd) on macroscopic spray characteristics, engine
performance and emission concentration. The spray tests were carried out in
a constant volume vessel (CVV) under different injection conditions using a
high-speed camera. Engine tests were conducted using a single-cylinder
direct injection (DI) diesel engine at three engine speeds (1400, 2000 and
2600 rpm) and two compression ratios (18:1 and 19:1) at full load. Spray characteristics were altered to provide for more favourable combustion
using bioalcohol
as an additive to D or Bd due to the low viscosity of bioalcohol
which resulted in increasing both the spray penetration length and
spray volume. Therefore, spray atomisation and evaporation rates could be
improved. Thus, an efficient diesel engine performance can be achieved as a
result of controlling injection characteristics, especially when using a
promising additive like butanol or BA blended with D or Bd. Moreover, the experimental results of testing bio-alcohol with diesel showed
that 10% normal-butanol-acetone (n-BA)-90% D blend showed a slight
improvement in brake power (BP). The highest peak in-cylinder pressure was
measured for the iso-butanol-acetone (iso-BA)-D blends and lower carbon
monoxide (CO) emissions than those of the equivalent n-BA-D blend while
nitrogen oxides (NOx) and unburned hydrocarbons (UHC) emission levels of
n-BA-diesel blends were lower than those of the equivalent iso-BA-D blends.
By investigating the effects of n-BA and iso-BA-D blends on engine
performance, the BA fermentation industry could be informed about the type
of butanol that should be produced. Because the different isomers of butanol have different beneficial effects on
engine operation, blending them together as an additive could yield all the
individual benefits of each isomer. Testing a dual blend of iso-butanolnormal-
butanol (iso-B-n-B) blended with D showed that the high dual blend
ratios of 10% and 13% iso-B produced higher peak in-cylinder pressures and
heat release rates (HRR) as well as a substantial reduction in CO emissions.
The higher blend ratios of 10% and 13% n-B produced much lower UHC
emissions. A slight reduction was found in NOx emissions when increasing
either n-B or iso-B, with n-butanol slightly more effective. Therefore, a blend
of n- and iso-butanol could be a promising alternative to a single isomer
additive (iso/n-butanol) to optimise engine performance. Finally, BA as an additive to neat cottonseed biodiesel has been investigated
in relation to spray characteristics and engine performance. The experimental
results of the BA-biodiesel blend revealed that the peak in-cylinder pressure
for 30% BA was comparable to D and higher than that of neat Bd. BP was
slightly improved for 10% BA at an engine speed of 2000 rpm while specific
fuel consumption (SFC) was not significantly higher for any of the BA-Bd
blends because of the smaller heating value of BA. Comparing the effect on
emissions of adding BA to Bd, increasing the amount of BA reduced NOx and
CO compared to neat Bd, but increased UHC. The BA blend was found to be the best additive for D or Bd fuel compared to
ABE or B in related to production cost, blend properties, engine performance
and emissions. Thus, the BA blend is promising as an alternative renewable
environmentally friendly additive, blended with neat D or Bd without diesel
engine modification that could enhance spray characteristics, improve engine
performance and reduce diesel engine emissions. |