This paper provides some insight into the future direction for
developing smaller capacity downsized engines, which will be needed
to meet tight CO₂ targets and the world's future powertrain
requirements. This paper focuses on the combustion system
development and combustion analysis results for a downsized
0.43-liter highly turbocharged engine. The inline two-cylinder
engine used in experiments was specifically designed and
constructed to enable 25 bar BMEP. Producing this specific output
is one way forward for future passenger vehicle powertrains,
enabling in excess of 50% swept capacity reduction whilst
maintaining comparable vehicle performance.
Previous experiments and analysis have found that the extent to
which larger engines can be downsized while still maintaining equal
performance is combustion limited. Hence, small engine combustion
is explored over a number of parametric studies, including a range
of manifold absolute pressures up to 270 kPa, engine speeds
exceeding 10,000 rev/min and compression ratios ranging from 9 to
13. Experimental results indicate that small engine combustion
hurdles can be overcome to reliably extend the specific output to
25 bar BMEP. This is believed to be the highest recorded specific
output for a non-intercooled small spark ignition PFI engine
operating on pump gasoline. However, the boosted combustion effects
illustrate that the thermal efficiency is highly dependent on the
combustion efficiency, which deteriorates rapidly if uncontrolled
combustion, specifically knock in the end-gas region is
encountered. However, with this combustion system design strategy,
potential drive cycle fuel consumption improvements in excess of
20% are still achievable.
