NEW APPROACH TO MITIGATE ICING PHENOMENON IN LIQUID PHASE INJECTION OF LPG FUEL

摘要

The use of various gaseous fuels in automotive engines has been continuously increased in order to meet the enforcing emission regulations as well as to efficiently utilize limited natural resources. Among the numerous gaseous fuel automotive applications, many studies have been conducted on LPG fuelled vehicles, especially for its fuel supply system called a liquid-phase LPG injection system, which pressurizes LPG fuel in liquid phase with fuel pump and injects the liquid-phase fuel through electronically controlled injectors. Since this system allows accurate control of fuel injection and increase in volumetric efficiency, it has advantages in achieving higher engine power and lower emissions compared to the mixer type system typically used in supplying gas-phase fuels. However, despite the several benefits of this liquid phase injection of LPG, it also leads to an unwanted event called icing. This phenomenon occurs when moisture in the air near the injector freezes and becomes frost around the nozzle hole due to immediate extraction of heat from surrounding caused by instant vaporization of the fuel during LPG injection period. As a result, it leads to a difficulty to control air/fuel ratio in engine operation, inducing exacerbation of engine performance and HC emission. One effort to mitigate icing phenomenon is to attach anti-icing injection tip in the end of injector nozzle and design the tip in a way to prevent deposition of frost. However, little work has been done on actual performance measurement and characterization of this anti-icing tip in avoiding ice formation. Therefore, in this study, the effect of engine operation parameters as well as surrounding conditions on icing phenomenon was investigated in a bench test rig with visualization through charge-coupled device (CCD) camera for currently-used anti-icing injection tips. The test results show that considerable ice was deposited on the surface near the nozzle hole of conventional anti-icing tip in low rpm and low load operating conditions with cold start in ambient air condition. This is because acceleration of detachment of deposited ice from the tip surface was induced by increase in injection frequency and fuel injection amount-which represents high load, high rpm, resulting in decrease in frost accumulation. The results of the bench testing also demonstrate that little or no ice was formed in surrounding temperature below a freezing point since the absolute amount of moisture contained in the intake air is too small in such a low temperature.