Experimental study on fuel line pressure fluctuation of biodiesel-DME blends in a common-rail injection system

The fuel line pressure fluctuations at the injector outlet of biodiesel-DME blends in a common-rail injection system are investigated using the wavelet packet transform. The effects of injection condition and dimethyl ether (DME) blending ratio on the pressure fluctuation characteristics are determined. The results show that the pressure fluctuation intensity determines wavelet packet energy distribution in the three sub-signals. The overall pressure fluctuation is reflected by sub-signal Sig1, which is composed of sub-signal Sig2 and Sig3. Sig2 exhibits medium frequency pressure fluctuations, and mainly occurs in the pressure rise stage and the pressure drop stage. Sig3 exhibits high frequency pressure fluctuations, mainly locates in the pressure stabilization stage. The pressure fluctuations at high injection pressure are more significant compared to those at low injection pressure. Biodiesel-DME blends display similar effects of injection pressure. With the increase of injection pressure, the mean energy and the standard deviation of Sig1, Sig 2 and Sig3 increase, especially those of Sig1 and Sig3. When DME is blended in the biodiesel, the pressure fluctuations for biodiesel-DME blends are more significant compared to biodiesel. With the increase of DME blended ratio, the mean energy and the standard deviation of Sig1 and Sig3 gradually increases.