Results and discussion
Experimental results of four different designed orifice plate
geometries with respect to inlet pressure and plate geometry on
methyl ester conversion are described below. In addition,
comparative performance of HC, ultrasonic cavitation and mechanical
stirring, as well as fuel properties are also presented.
6.1. Effect of inlet pressure
The effect of inlet pressure (upstream pressure) over the range
of 1e3 bar at 60 C on the methyl ester conversion derived from
WCO with respect to the reaction time using four different orifice
plate geometries is illustrated in Fig. 2. The results obtained with all
orifice plate geometries show that transesterification reaction rate
of WCO increased with the increase in inlet pressure from 1 to 2 bar,
but there was no significant difference when the operating pressure
was increased further to 3 bar. This could be attributed to the
downstream area of the orifice plate, in which the local area was
filled with a large number of cavities which coalesced and formed a
larger cavity, causing cavitation chocking. A similar result was reported
by Ghayal et al. (2013). In addition, many researchers reported
that up to a certain value of inlet pressure, the reaction rate
decreased, e.g. 4 bar due to degradation (Bagal and Gogate, 2014)
and 3.8 bar due to decomposition reaction (Vichare et al., 2000).
The optimised inlet pressure of 2 bar was chosen for the remaining
experiments. The consumption time for methyl ester conversion of
96.5% which met the minimum requirement of EN 14214
increased significantly with orifice plate 1 for 40 min and orifice
plate 4 for 30 min compared to orifice plate 2 for 15 min and orifice
plate 3 for 20 min at the operating pressure of 2 bar. It was
observed that by applying the inlet pressure of 2 and 3 bar on the
orifice plate 2, the conversion reached 96.5% within 15 min,
whereas 30 min was required when operating at 1 bar (Fig. 3). This
could be attributed to the increase in the inlet pressure causing an
increase in the flow rate and velocity through the orifice plate
(Table 3) which led to an increase in the pressure drop and increase
of liquid pass number. The lower the Cv number, the higher the