Mode transition between low temperature combustion and
conventional combustion was investigated in a direct injection
diesel engine. Low temperature diesel combustion was realized by
means of high exhaust gas recirculation rate (69~73%) and early
injection timing (-28~ -16 crank angle degree after top dead
center) compared with those (20% exhaust gas recirculation rate and
-8 crank angle degree after top dead center) of conventional
combustion. Tests were carried out at different engine speeds and
injection pressures.
Exhaust gas recirculation rate was changed transiently by
controlling each throttle angle for fresh air and exhaust gas
recirculation to implement mode transition. Various durations for
throttle transition were applied to investigate the effect of speed
change of exhaust gas recirculation rate on the characteristics of
mode transition. Indicated mean effective pressure, intake
pressure, maximum pressure rise rate and real-time unburned
hydrocarbon emissions in the exhaust manifold were analyzed
transiently.
At the early stage (10 - 20 cycles) of mode transition from low
temperature diesel combustion to conventional combustion,
combustion performance became unstable with high fluctuation in
indicated mean effective pressure and rapid increase in maximum
pressure rise rate. In the case of mode transition from
conventional combustion to low temperature diesel combustion,
combustion performance kept stable without substantial change in
indicated mean effective pressure and maximum pressure rise rate.
indicated mean effective pressure kept constant at the early stage,
but decreased gradually to a lower level.
Transient injection strategy, which modulated including
injection timing and injection quantity, cycle to cycle was applied
to reduce fluctuation of indicated mean effective pressure during
mode transition. This process had the result that the range of
fluctuation in indicated mean effective pressure decreased and
maximum pressure rise rate was considerably reduced.