Experimental Study And Numerical Simulation Of The Spray Process In An Opposed-piston Two-stroke Diesel Engine

With the demand of the reinforcement and lightweight design in diesel engines, opposed-piston two-stroke(OP2S) diesel engine is becoming an increasingly popular research topic at home and abroad due to its dramatical advantages such as high power density, excellent balance performance and high thermal efficiency. In recent years, more and more remarkable achievements that focused on the scavenging process, gas exchange process and in-cylinder process were made in OP2 S engine research and in contrast, little research on spray process in OP2 S engine was carried out. In this paper, the research on the spray process of a folded-crank train OP2 S engine was investigated with a combined method of numerical simulation and experiments. The main research contents are as follows:(1)Several commonly used spray visualization test methods were compared and the schlieren method was selected in the request of the spray visualization experiment. Then a spray visualization test rig that can realize spray impinging inside the chamber was established based on the characteristics of the spray organization in OP2 S. Subsequently, the effect of different injectors’ layout scheme, injection pressure and backpressure on the spatial distribution of spray was analyzed and the spray model in numerical simulation was checked with the results in the spray visualization test.(2)A three-dimensional CFD simulation model was set up based on structure characteristics and working principle of the OP2 S diesel engine and it was calibrated by the spray visualization test and performance test results.(3)After analyzing the macro spray characteristics and micro spray characteristics, a new assessment criteria was improved to evaluate the spray process in OP2 S engines as follow: The ability of spatial development and diffusion of the sprays was evaluated according to the spray penetration and spatial diffusion rate; the atomization rate was evaluated according to the spray SMD and evaporation rate; the mixing quality was evaluated according to the air utilization and equivalence ratio distribution.(4)The influence of the injectors’ arrangement injection pressure and backpressure on the development, breakup, atomization and evaporation of the sprays was studied respectively and the spray organization strategy in OP2 S engine was determined according to the research results as well as the engine structure. Subsequently, the impact of different spray angles on the spray development, atomization and mixing between the air and the spray was studied and an optimum angle was chose to obtain both good mixing quality and burning quality.(5)With the consideration of the in-cylinder gas motion in OP2 S engine is form by the asymmetric inlet chamber and the tangential angle, CFD numerical simulation was applied to study the tangential angle’s effect on the spray development, atomization and mixture formation and 20° was finally selected as the optimal tangential angle to achieve excellent engine performance.This paper studies the spray process inside the OP2 S cylinder based on the above research and it is supposed to provide supports to the design of fuel injection system in the folded crank train OP2 S diesel engine.