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Extension of Operating Range of a Multi-Cylinder Gasoline HCCI Engine using the Blowdown Supercharging System
Journal Article
2011-01-0896
ISSN: 1946-3936, e-ISSN: 1946-3944
Sector:
Topic:
Citation:
Kuboyama, T., Moriyoshi, Y., Hatamura, K., Takanashi, J. et al., "Extension of Operating Range of a Multi-Cylinder Gasoline HCCI Engine using the Blowdown Supercharging System," SAE Int. J. Engines 4(1):1150-1168, 2011, https://doi.org/10.4271/2011-01-0896.
Language:
English
Abstract:
The objective of this study is to develop a practical technique
to achieve HCCI operation with wide operation range. To attain this
objective, the authors previously proposed the blowdown supercharge
(BDSC) system and demonstrated the potential of the BDSC system to
extend the high load HCCI operational limit. In this study,
experimental works were conducted with focusing on improvement of
combustion stability at low load operation and the reduction in
cylinder to cylinder variation in ignition timing of multi-cylinder
HCCI operation using the BDSC system. The experiments were
conducted using a slightly modified production four-cylinder
gasoline engine with compression ratio of about 12 at constant
engine speed of 1500 rpm. The test fuel used was commercial
gasoline which has RON of 91.
To improve combustion stability at low load operation, the valve
actuation strategy for the BDSC system was newly proposed and
experimentally examined. With the newly proposed valve actuation
strategy, only intake valve lift was varied and EGR and exhaust
valve lifts were fixed with variation in target load. Compared to
the previously proposed valve actuation strategy for the BDSC
system, relatively late EGR valve opening timing with early intake
valve closing timing is applied at low load condition in the
proposed strategy. This provides high in-cylinder temperature and
relatively rich fuel concentration at low load operation while
providing a large amount of diluted mixture at high load operation.
Additionally, effect of coolant water temperature on combustion
stability was experimentally investigated. Coolant water
temperature was varied from 85°C to 105°C. Experimental result
showed that for low load HCCI operation, the valve timing with
early intake valve closing and relatively late EGR valve opening
was effective to increase combustion stability due to increases in
in-cylinder temperature and fuel concentration. With early intake
valve closing and relatively late EGR valve opening, a stable HCCI
operation at net IMEP of 200 kPa was achieved. However, brake
thermal efficiency was slightly deteriorated due to increase in
pumping work utilized to increase in in-cylinder temperature. The
increase in coolant water temperature also improved combustion
stability and extends the low load operational limit due to
increase in in-cylinder temperature. With a cooling water
temperature of 105°C, the low load HCCI with net IMEP of 134 kPa
was attained.
In addition, to reduce the cylinder to cylinder variation in
ignition timing which restricts HCCI operating range with
multi-cylinder operation, the secondary air injection system in
which air is injected into an exhaust port of each cylinder to
control recharged EGR gas temperature using gas fuel injector was
proposed and examined to control ignition timing of each cylinder
independently. As a result, the cylinder to cylinder variation in
ignition timing was successfully reduced and the high load HCCI
operational limit with four-cylinder operation was extended up to
net IMEP of 570 kPa. Compared to conventional SI operation, brake
thermal efficiency was improved by about 15% using the newly
proposed strategy with more than 99% reduction in NOx
emission.