Numerical Study on High-Load Performance of a Two-Stage Boosted Poppet-Valved Two-stroke Diesel Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">Two-stroke cycle is one of the most effective methods to increase the torque and power output of a four-stroke engine due to the doubled firing frequency compared to four-stroke cycle at the same engine speed. As the two-stroke cycle lacks separate intake and exhaust strokes, the positive pressure difference between intake and exhaust ports is required to drive fresh charge into the cylinder, and is affected by intake port structures due to the different amounts of short-circuited fresh charge during scavenging process. To evaluate the effects of intake port structures on the high-load performance of a boosted poppet-valved two-stroke diesel engine, one-dimensional gas dynamic model and three-dimensional computational fluid dynamics model were established and used to predict the high-load performance of the boosted two-stroke diesel engine with top-entry intake ports, inclined side-entry intake ports, and side-entry intake ports, respectively. The results show that the engine with inclined side-entry intake ports has a much higher scavenging quality coefficient than the engine with other intake port structures. The maximum brake power of the 4.1 L four-cylinder two-stroke diesel engine equipped with a two-stage serial boosting system with a turbocharger and a downstream supercharger can reach 1.4 times that of a 5.1 L four-cylinder four-stroke diesel engine in the cases of top-entry and inclined side-entry intake ports, while that of the two-stroke engine with side-entry intake ports can only reach 1.2 times that of the four-stroke engine due to more power consumed by the supercharger resulted by large amount of short-circuited fresh charge. When the brake power of two-stroke engine is equal to 1.2 times that of the four-stroke engine, the intake pressure and mass flow rate of fresh charge are obviously decreased about 37.3% and 39.3% when intake port structure is changed from side-entry intake ports to inclined side-entry intake ports.</div></div>