Friction test
The injection system of a diesel engine is designed to operate with diesel fuel,
which has a viscosity of 3–8 mPa s. In order to compare the viscosity of CPO
to diesel, a viscosity test was performed with a Brookfield viscometer at various
temperatures, and the results are shown in Fig. 2.
Total friction of an engine consists of the friction between various moving parts
such as piston rings and cylinder, crankshaft and bearings, camshaft and rocker arms
and fuel injection pump assembly, to name a few. Among the engine parts that
contribute to total friction, the injection pump is the only part that comes into contact
with fuel before combustion. So, with all other friction components remaining the
same, the effects of fuel heating on the injection pump can be ascertained by performing
a friction test that allows the fuel to pass through the injection pump and
injector as usual but avoids any combustion taking place. The test was carried out
by motoring the engine with the original injector installed in a way to inject the fuel
outside the combustion chamber. In place of the original injector, a dummy injector
was put in the engine head. Fig. 3 shows the schematic diagram of the modified
friction test, while Fig. 4 shows the photograph of the same set-up.
Before starting the modified friction test, the CPO was heated to liquid form in
its own tank (secondary heating set-up). The set-up was first motored with diesel,
and the diesel was also heated by the primary heating set-up. This was to ensurethat when the fuel was switched to CPO, the fuel lines and fuel filter would be at
a high enough temperature to prevent CPO solidification and subsequent clogging
of the fuel filter. After the engine had reached a steady state, the fuel was switched
to CPO, which was heated to a predefined temperature by the primary heating setup.
Friction was measured with a load cell, and was recorded at various fuel inlet
temperatures, up to 100 °C. After finishing the experiment, the fuel was switched
back to diesel and the engine was left motored until all the CPO had been purged
from the fuel line, injection pump and injector, to prevent clogging by solidified CPO
when the temperature drops below its melting point after the engine was switched off.
The modified friction test was repeated using diesel as a baseline.