Study of deposit formation inside diesel injectors nozzles

Abstract

Diesel engines are widely used in heavy duty transportation applications such as in trucks, buses and ships because of their reliability and high torque output. A key diesel technology is the injection system which is constantly improved to produce better spray quality and deeper spray penetration in the combustion chamber by using high injection pressure and improving the design of the nozzle holes. The hole size has been continuously reduced; future diameters less than 100 um are expected. Smaller nozzle holes are vulnerable to deposit formation, which will reduce the flow rate and affect the spray pattern. The objective of this study is to understand the processes that would lead to deposit formation on the injector nozzle surfaces. In specific, a detailed mechanism is proposed after observing engine and injector simulation results. Models for the physical processes and chemical mechanisms responsible for the deposit formation are developed. These models are incorporated into a integrated software package to facilitate calculations of deposit formation rates under different conditions. A benchscale test rig is also constructed to measure the deposit formation of different fuels and detergents. Experiments show that the test procedure can differentiate good detergents from ineffective ones; hence it can be used to pre-screen the detergents and fuels before engine tests. Thus the cost of testing could be reduced substantially. This study is the first to develop a comprehensive quantitative model for injector nozzle deposit formation and a bench scale testing apparatus encompassing the key deposit formation processes of film formation, evaporation and washing.