Measurements of flow and combustion in a strongly charged spark ignition engine

The spark ignition engine is one of the most widely used power sources for
vehicles. Due to the global warming, the fuel economy is encouraged to contribute
in designing spark ignition engines. Therefore, one promising design is a strongly
boosted downsized spark ignition engine. The present work aims to investigate
combustion from two perspectives, namely, bio-derived fuels performed as additives in a strongly charged engine, and flame propagation at high pressure.
N-butanol and 2,5-dimethylfuran performed as additives in a strongly charged
engine were investigated across a range of spark timings at an engine speed of 750
RPM under stoichiometric conditions. Knock characteristics of those fuels were
studied, and reverse thermodynamic analysis was applied to derive the in-cylinder
charge state and flame speed. The results show that 2,5-dimethylfuran preformed
as additive for current unleaded gasoline and its toluene reference fuel provides
good anti-knock performance in strongly charged engine. N-butanol have great
improvement as an additive on anti-knock performance for toluene reference fuel.
Turbulent flow in the engine was studied by using two dimensional particle
image velocimetry. Meanwhile, the effects of thermal expansion on turbulent flow
which is located in front of the flame was also investigated. Burning velocity
and flame speed of commercial unleaded gasoline and iso-octane under turbulent
intensity of 0.75 m/s and 1.20 m/s were investigated at temperature of 650 K,
pressure of 30 bar. The results suggest that several burning velocity correlations
for predicting turbulent burning velocity not match the experimental outcomes.
Furthermore, the thermal expansion may alter the turbulent intensity which is
located in front of the flame. Flame shape and wrinkles were studied based on the
captured laser tomographic images. The power spectral density of the wrinkles
shows that the flame wrinkling is possibly related to the turbulent energy cascade.
However, due to the limited camera resolutions, the effect of flame instability on
wrinkling spectrum can not be observed clearly.