Abstract
The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV) under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI) engine head at different valve lifts and with a pressure difference of 150 mmH2O across the intake valves. Furthermore, the Proper Orthogonal Decomposition (POD) analytical technique was applied to PIV-measured velocity vector maps to characterize the flow structures at various valve lifts, and hence the different rig tumble values. The results show that at low valve lifts (1 to 5 mm), 48.9 to 46.6% of the flow energy is concentrated in the large (mode 1) eddies with only 8.4 to 11.46% in mode 2 and 7.2 to 7.5 in mode 3. At high valve lifts, it can be clearly seen that some of the energy in the large eddies of mode 1 is transferred to the smaller flow structures of modes 2 and 3. This can be clearly seen at valve lift 10 mm where the values of the flow energy were 40.6%, 17.3%, and 8.0% for modes 1, 2, and 3, respectively.
Highlights
The automotive industry is increasingly motivated by high fuel economy demands and strict pollutant emissions regulations, there is a pressing need for novel combustion systems to meet these demands
The results showed that the strength of tumble motion increased and the cycle to cycle variation (CCV) decreased with the closed tumble flap compared to the open tumble flap
The results demonstrated that there was reasonable agreement between the flow structures measured by Laser Doppler Velocimetry (LDV)
Summary
The automotive industry is increasingly motivated by high fuel economy demands and strict pollutant emissions regulations, there is a pressing need for novel combustion systems to meet these demands. GDI engines potentially offer several considerable advantages relative to port fuel injection (PFI) engines in terms of preventing the fuel wall film in the intake port and reducing the throttling losses (pumping losses) while providing higher thermal efficiency, higher compression ratios, lower fuel consumption, lower CO2 and HC emissions, and higher volumetric efficiency [1,2]. A stratified charge mode (late injection) is utilized at lower engine speeds and loads as the fuel is injected late during the compression stroke. This mode enables engines to burn global very lean mixtures with very high air/fuel ratios, which cannot be achieved using multi point port fuel injection. Exhaust gas recirculation (EGR) is used during this mode to reduce the Energies 2017, 10, 1950; doi:10.3390/en10121950 www.mdpi.com/journal/energies
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