Recently, due to the concern on shortage in the supply of energy
source as well as the greenhouse effect of engine exhaust, the use
of renewable fuel, e.g., biodiesel, in the transportation sector is
promoted. However, there are distinctions on both the physical and
chemical properties between biodiesel and fossil diesel. These
deviations in fuel property would result in different combustion
characteristics and affect the performance of exhaust
aftertreatment system, including the catalytic converter and the
diesel particle filter.
The purpose of this study is to investigate the effect of
biodiesel on the performance and the durability of diesel particle
filter. The biofuel adopted in this study was obtained by
transesterification from methanol and spent edible oils, and
fulfills the requirements specified in EN 14214 standard. All the
tests were conducted in a heavy diesel engine (ISUZU 4JJ1E4N). Two
studies were carried out in this paper. In the first study, B5 was
used in a durability test to find out the long term performance of
active DPF running on biodiesel. The durability test followed the
EU ETC procedure for 1000 consecutive hours. The effectiveness test
of DPF was performed every 250 hours. At the end of durability
test, a thorough examination on the performance deterioration was
carried out, including emission conversion efficiency,
deterioration rate, and surface analysis of catalyst.
It was found that after 1000 hours of consecutive running on B5,
the catalytic converter still maintained its conversion efficiency
higher than 90% for both CO and HC during the EU ESC test procedure
with exhaust temperature in the range of 350~460°C. No noticeable
deterioration in CO, THC, and PM conversion efficiency was found.
An examination on the surface of catalyst with SEM and EDS gave the
finding that phosphorous and sulfur contents are lower than 1% by
weight. The active regeneration system works well during the
durability process, and the conversion efficiency on both PM and PN
are higher than 90% in EU ETC test as well as ESC test.
In the second study, different contents of biodiesel (D100, B5,
B20, B40, and B60) were used to find out the effect of biodiesel on
the balance point temperature (BPT) of soot accumulation in DPF as
well as the light-off temperature in DOC. In the balance point
temperature test, the engine speed was set at 2000 rpm. The engine
load was controlled to suppress exhaust temperature lower than
250°C at first to enhance soot accumulation in DPF. Then the engine
load was increased gradually to raise the exhaust temperature until
the accumulated soot ceased increasing, which was monitored with
the differential pressure drop of DPF. It was found that the
balance point temperature for biodiesel is lower than that of
fossil diesel. The decrease in balance point temperature is 13°C
for B20.
In the DOC light-off temperature test, the engine speed was set
at 1200 rpm, and the engine load was increased gradually until
300°C of exhaust temperature was reached. The conversion efficiency
of CO was monitored during the process, and the light-off
temperature was determined as the conversion efficiency reached
80%. It was found that the DOC light-off temperature drops as
biodiesel content increases. The maximum decrease of light-off
temperature is 41°C for B60.