Effects of Enhanced Tumble Ratios on Combustion Performance in SIDI Optical Engine

抄録

It has been proven that intake tumble flow is effective in enhancing the in-cylinder burning rate, but the effect of tumble flow on engine combustion performance and its mechanism is still yet to be systematically studied. To achieve this, the current study first performed CAD design of the tumble deflectors for the intake port, and then conducted CFD simulation to assess the influence of tumble deflectors on in-cylinder tumble ratio (TR) and turbulent kinetics. After this, the tumble deflectors that result in a TR of 0.5, 1.5 and 2.2 were manufactured by 3D printing. Finally firing test of the optical engine installed with different tumble deflectors were carried out. For the experiments, a high speed color camera was used to record crank angle-resolved flame natural luminosity through the quartz window in piston bowl. Along with the flame imaging system, the in-cylinder pressure was monitored simultaneously by a combustion analyzer system (CAS). The blue and yellow flames were captured separately by the color camera. The blue flame is considered to be the chemiluminescence generated by intermediate species such as CH*(430.5nm), and its appearance shows the distribution and development of the flame front. Whereas the yellow part is considered to be the incandescence emitted by soot associated with fuel-rich combustion, hence the position and intensity of yellow flame can be used to evaluate the generation and distribution of soot. Results show that higher TR leads to faster blue flame development and less yellow flame generation, which indicates an increase in flame burning rate and a decrease of the soot formation. This is closely related to the increased turbulence kinetic energy before ignition as was shown in the CFD simulation. Besides, the cycle to cycle variation of flame characteristics are reduced and the IMEP is increased by higher TR.