| As an alternative oxygenated fuel,ethanol has important research significance in realizing efficient and clean combustion of diesel engine.However,the miscibility of ethanol and diesel is poor.At present,how to improve the miscibility of ethanol and diesel and to better apply it to diesel engine is one of the hot topics about ethanol fuel research.At the same time,Polyoxymethylene dimethyl ethers(PODE)is a new oxygenated fuel with high cetane number(CN)and high oxygen content,and PODE does not contain C-C bond,so it is a good potential alternative to diesel fuel.In this paper,firstly,the miscibility among PODE,ethanol and diesel was studied,and then the effects of PODE/ethanol/diesel blends and fuel injection control parameters on the combustion and emissions characteristics of a high-pressure common-rail heavy diesel engine were studied.Firstly,the miscibility stability of ethanol/diesel fuel was studied quantitatively at different ambient temperature,different purity of ethanol and PODE as a co-solvent.The results show that PODE can improve the solubility and cetane number of anhydrous ethanol/diesel blends.The solubility of PODE to hydrous ethanol/diesel mixture is greatly affected by ambient temperature.The increase of water content and the decrease of temperature will make PODE/ ethanol/diesel blends less miscible.The test shows that with the increase of PODE and ethanol blending ratio,the weighted brake specific fuel consumption(BSFC)increases significantly,while the weighted equivalent BSFC without the influence of heating value increases slightly,and the weighted HC emissions decrease,while the weighted NOx emissions increase.Blending PODE and ethanol in diesel can reduce the weighted CO emissions,however,as the blending ratio of ethanol increases,the decrease trend of weighted CO emissions get weakened,and DPE15(20% PODE and 5% ethanol in volume)even exhibits increasing trend compared to D100,which is attributed to the increasing CO emissions at cold idle condition.With the increase of PODE and ethanol blending ratio,the weighted soot emissions decrease significantly,and the highest reduction is 86.9% for DPE15 fuel.Then,under different loads and different fuel injection strategies,the combustion and emissions of blending fuel were further studied.The experimental results show that blending ethanol and PODE in diesel can accelerate the combustion rate in late combustion stage and increase the diffusion combustion rate.The brake thermal efficiency(BTE)of the blended fuels is basically the same as that of diesel under medium and small loads.With the increase of load,compared with diesel,HC and soot emissions of blended fuels decrease,while NOx emissions increase.Under different injection timing and injection pressure,CO emissions of blended fuels are basically the same,which is mainly affected by injection timing and injection pressure.With the increase of fuel injection pressure,the growth of NOx emissions of blends compared with D100 increases gradually.The effects of injection timing and injection pressure on soot emissions are smaller than that of D100.The above research shows that PODE can ensure mutual solubility of dieselethanol blend,and the CN of PODE-ethanol-diesel ternary fuel is equivalent to diesel.The combustion and emissions of heavy diesel engine can be improved greatly after burning blends.After burning PODE,the diffusion combustion rate increases,and the soot emissions significantly reduce.Considering BTE and emissions,DPE5(PODE volume fraction 20%,ethanol volume fraction 5%)is the best of the four blended fuels.This study provides reference for the application of ethanol and PODE in diesel engines. |
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