Troels Dyhr Pedersen.indd - Solid Mechanics

would not be increasing the pressure. Additionally it was argued that it would make more sense to compare
HCCI data with DI CI data on the same engine if the setup was identical. The turbocharger did however
increase the absolute pressure up to 1.2 bars at 1800 RPM as the total equivalence ratio was increased with
methanol, which meant that the equivalence ratio for DME became lower than the target.
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Engine ISUZU 4HG1T
No. of cylinders 4
Bore x Stroke 115 mm x 110 mm
Connecting rod length 250 mm
Displacement 4.57 L
Compression ratio 14.5 (19.0 original)
Injection system DME Common rail
Rated power 88 kW @ 3000 RPM
Rated torque 322 Nm @ 1800 RPM
Table 1: Engine specifications
The engine was coupled with a speed regulated motor-generator equipped with a load cell for measuring torque,
which was used for calculating BMEP. The cylinder pressure was measured on all 4 cylinders with piezoelectric
pressure pickups and logged in intervals of 1 CAD.
The geometric compression ratio was reduced from 18 to 14.5 by enlarging the piston bowls. The bowl
geometry was maintained to enable normal DI CI operation.
Changing the engine to HCCI operation required that the electrical connections for the common rail injector
were switched pair wise, due to a limited advance setting in the injector driver software. The injectors were then
set to inject at the beginning of the intake stroke, since this should result in good mixing. The emission values
did not indicate leakage of DME through the exhaust valves when this injection timing was used.
METHANOL INJECTION SYSTEM
Four low pressure gasoline injectors were installed in a custom inlet manifold. The methanol was supplied from
a tank that was pressurized to three Bar. Injector drivers enabled accurate control of the injection duration and
timing. The injection was adjusted to begin at inlet valve opening. Varying the timing showed no significant
change to the heat release or emissions, so it was kept at this position throughout the test.
TEST CONDITIONS
Prior to all tests the engine was heated in normal DI CI operation with DME. After 30 minutes of preheating the
engine was stopped and the injector leads were switched to inject at 360 BTDC for HCCI operation.
The tests were performed at engine speeds of 1000 and 1800 RPM. These two engine speeds used were chosen
since part load operation usually implies running at lower engine speeds. It is however fully possible to operate
with DME HCCI combustion at higher engine speeds, such as 3000 RPM.