喷孔长度和喷油体温度对乙醇柴油空化及近场喷雾的影响

利用高速摄像机和放大比例的单孔透明喷嘴搭建可视化试验台,研究喷孔长度和喷油体温度对喷孔内乙醇柴油空化流动特性和近场喷雾的影响,试验用喷嘴的孔径均为2 mm,孔长分别为4 mm、6 mm和8 mm,喷油体温度分别控制在303 K、333 K和363 K。试验发现,随着孔内燃油平均流速的增加,各喷孔的空化现象依次经历了无空化、空化初生、空化发展和超空化5个阶段,短喷孔内更易发生空化现象,且在相同的空化阶段短喷孔的孔内燃油平均流速小于长喷孔;此外在相同进出口压差下短喷孔对应的近场喷雾锥角要大于长喷孔喷雾锥角。喷油体温度也会影响喷孔内空化流动特性和近场喷雾形态,喷油体温度越高,空化现象越强烈,空化变化速率越大;当喷孔进出口压差相同时,喷油体温度在303 K、333 K和363 K所对应的近场喷雾锥角依次增大。最大近场喷雾锥角所需的喷射压力随喷油体温度的升高而减小。

Failure in Fuel Injector Nozzles Used in Diesel Engines

This paper aims to conduct a study of the problems associated with the wear of the needles and fuel injection nozzles utilized in diesel engines. The wear found on the needles is mainly associated to impurities in the fuel oil and microcavitation occurred due to high pressure in the phase of the air compression for combustion of the combustible fluid. These pressures associated with the temperature and the fluid velocity results in the occurrence of vaporization, which releases shock waves that cause damage to the affected surface. The impurities solid particles from the fuel oil cause problems inside the nozzles as obstruction of the holes and wear on the needle tip and nozzle seat surface. These failures affect in the atomization of the fuel, since the deterioration of the internal passages of the nozzles interferes in the spray formation and in the end passage of the fluid. For the execution of this study it will be used digital microscopic analysis in specimens that suffered damage, in order to investigate the effects of fuel property, and the temperature conditions and pressure in the formation of the wear on the needles and injector nozzle.