The summary from the report....
The Volkswagen Jetta 2.01 turbodiesel has BSFC of 250 g/
kW-h [17]; a homogeneous gasoline direct-injected sparkignited
engine [21] has BSFC of about 255; the Daimler 3.5L
V6 spray-stratified engine [22] has BSFC of about 247; and a
gasoline spark-ignited engine with increased cooled EGR
(HEDGE)[23] has BSFC of about 245 g/kW-h. The estimated
BSFC for a multi-cylinder GDCI engine is about 210 g/kW-h
or about 16 percent less than the Jetta diesel. This indicates
that, at this important part-load operating condition, GDCI
has good fuel economy potential. Much work is needed to
realize this potential in a practical multi-cylinder engine at
regulated emissions levels.
SUMMARY AND CONCLUSIONS
Preliminary single-cylinder engine tests have been conducted
at 6 bar IMEP and 1500 rpm using RON91 gasoline to
evaluate GDCI injection strategies at low injection pressure.
All tests were conducted using Design of Experiments
methods. Preliminary optimums were determined using
Response Surface Modeling methods and constrained
optimization.
It was found that a triple-injection strategy with optimized
injection timings and quantities produced the best fuel
economy. The triple-injection strategy enabled use of the
lowest injection pressures compared to both single-injection
and double-injection strategies.
For triple-injection GDCI:
1.
A minimum ISFC of 181 g/kW-h was measured. This
corresponds to ITE of 46.2 percent. This was about 8 percent
more efficient than representative tests of a diesel combustion
system running on the same engine. Combustion efficiency
was about 97 percent, which is typical of spark-ignited
engines.
2. ISNOX of 0.7 g/kW-h and FSN of 0.3 were measured at
the minimum ISFC condition with CNL of 85 dBA. A tradeoff
between ISFC and ISNOX was observed. In order to
achieve the preliminary NOx target of 0.2 g/kW-h, a 7.7
percent fuel consumption penalty was required.
3. ISCO2 emissions at the minimum ISFC condition were
542 g/kW-h, or about 14 percent less than the diesel baseline.
4. Hydrocarbon emissions where reasonably low (0.75 g/
kW-h). This may be expected based on preliminary
simulations of the spray and mixing processes. Very little (if
any) fuel penetrated to the piston surfaces or the cool cylinder
wall regions.
5. Carbon monoxide emissions were somewhat elevated and
were attributed to “over-lean” portions of the mixture thatwere also last to burn. More detailed study of CO emissions mechanisms is needed.
Overall, significant progress has been achieved toward
demonstrating the viability of a practical GDCI combustion
system. A developmental GDCI injection system exhibited
good control of mixture stratification. Injection pressure
requirements are much lower than conventional diesel
engines but higher than current gasoline direct injection
(GDI) engines.
BSFC for a multi-cylinder GDCI engine was estimated based
on single-cylinder test results at 6 bar IMEP and 1500 rpm.
On this basis, fuel economy potential appears very good
compared to competitive power trains. Significant
development work is needed to develop a practical GDCI
engine system.
