The engine was coupled to a direct current (DC)
dynamometer and maintained at a constant speed of 1500 rpm
(±1 rpm) regardless of the engine torque output. The in-cylinder
pressure was measured using a Kistler 6041A water-cooled pressure
transducer with a charge amplifier. Coolant and oil temperatures
were maintained at 85 C and 95 C (±3 C) respectively,
using a proportional integral differential (PID) controller and heat
exchangers. All temperatures were measured with K-type thermocouples.
The compression ratio was modified by adjusting the
number and size of the metal inserts placed beneath the cylinder
head. These acted to adjust the height of the cylinder head in relation
to the piston BDC allowing the compression ratio to be changed.
A 100 litre intake plenum tank (approximately 200 times the
engine’s swept volume) was used to stabilize the intake air flow.