Improvement of Engine Performance With Lean Mixture Ignited By Diesel Fuel Injection and Internal Egr 2000-05-0076
The uniform lean methanol-air mixture was provided to the diesel
engine and was ignited by the direct diesel fuel injection. The
internal EGR is added to this ignition method in order to activate
the fuel in the mixture and to increase the mixture temperature.
The test engine was a 4-stroke, single- cylinder direct-injection
diesel engine. The cooling system was forced-air cooling and
displacement volume was about 211 (cm3). The compression ratio
was about 19.9:1.
The experiment was made under constant engine speed of 3000
(r/min). The boost pressure was maintained at 101.3 (kPa). Five
values of mass flow rate of diesel fuel injection were selected
from 0.060 (g/s) to 0.167 (g/s) and five levels of back pressure:
0), 26.7, 53.3, 80.0 and 106.6 (kPa) were selected for the
experiment. The effect of internal EGR is varied by the back
pressure level. It is confirmed that the lean methanol-air mixture
of air-fuel ratio between 130 and 18 could be ignited and burned
when the back pressure of 106.6 (kPa) is applied. The ignition
delay reduces and the maximum combustion pressure increases as the
back pressure increases. Fluctuation of maximum combustion pressure
is gradually decreased as back pressure increases. However, the
brake mean effective pressures decreases as the back pressure
increases because the pumping loss and the reduction of the rate of
specific heat cause the output power reduction. Therefore, the
ignition and combustion characteristics can be improved by applying
the internal EGR, however, the engine performance is deteriorated.
When the back pressure of 106.6 (kPa) is applied, a lot of CO is
emitted, and HC and NOx concentration decrease as back pressure
increases. The stabilization of ignition and combustion caused by
internal EGR makes HC concentration reduce.
