Characteristics and Cyclic Variation of Spray under the Influence of Swirl Ratio and Flash Boiling in SIDI Engine

Paper #:
  • 2017-01-0831

Published:
  • 2017-03-28
Pages:
8
Abstract:
Cycle-to-cycle variation (CCV) of engine output not only results in fluctuations of the engine torque, but also prohibits the engine from operating at its optimal condition. The CCV of engine can be attributed to multiple root causes such as variation of injection, intake flow and spark discharge, etc. While it is difficult to control the sources of variation, designing a combustion system that is robust to the root causes of variation is a viable approach to suppress the CCV of engine output. Flash boiling spray have been shown in pressurized chamber to be a much more stable spray with smaller penetration length, smaller droplet size, shorter evaporation time and a more homogeneous fuel air mixing. In the meantime, increasing the swirl ratio of the engine intake flow is also proven to be a promising approach to generate air flow that is insensitive to the variation from the complex intake system. Therefore, this paper assesses the influence of flash boiling and swirl ratio on the CCV of spray structure in an optical accessible, single-cylinder spark-ignition direct-injection (SIDI) engine. The experiment was carried out at cold engine conditions (30°C coolant and oil temperature). The fuel temperature was conditioned by water bath at 30 °C, 60 °C and 90 °C corresponding to liquid, transitional flash boiling and flare flash boiling spray, respectively. Crank angle resolved spray images were recorded separately in tumble plane for 50 consecutive cycles using high-speed Mie-scattering technique. CCV of spray structure was evaluated in a quantitative manner using relevance index methods. Results show that with the increase of swirl ratio, the stability of the spray decreases under cold start condition but when flash boiling is introduced stable spray structure can be achieved under both swirl ratios.
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