In 2010, researchers from the Beijing Institute of Technology proposed a new combustion system for diesel engines: the Double Swirl Combustion System (DSCS) (Li et al. 2010). Within the DSCS, the Double Swirl (DS) chamber is one of the most noticeable factors in the new system.
The configuration of DS chamber is made up of two dishes: the smaller dish is in the center of the chamber which forms the inner chamber, and the larger one forms the outer chamber. The cone face (Line o–3 in the diagram below) from the nozzle orifices to circular ridge forms a theoretical interface between the outer and inner chambers. A truncated cone is in the middle of the inner chamber.
Double swirl combustion chamber. Li et al. (2010)
The team hypothesized that the fuel spray collides with the circular ridge, splits into two parts, and then forms double swirls, which makes the core of the single spray meet the air directly.
As a result, the fuel is distributed more evenly than that in an ordinary type of chamber, and the air in the chamber—especially the air in the inner part of chamber—can be fully utilized, and the fuel-air mixing can be improved. The DSCS in a diesel engine can make significant efficiency improvements and emission reductions.
Now, researchers from the Beijing Institute of Technology have investigated the effects of DSCS combustion chamber diameter on performance under various conditions. They report their results in a paper in the journal Fuel.
DSCSs with diameters of 83, 91, and 98 mm (DSCS83, DSCS91, and DSCS98) were designed and tested in a single-cylinder diesel engine at the maximum torque speed of 1800 rpm under various loads and various excess air coefficients (φ).
Experiments showed that DSCS83 outperformed the other DSCSs, with a 2.1–4.9% decrease in brake specific fuel consumption (BSFC), 12.4–23.1% reduction in soot, and a shortening of the combustion period by 1.6–3.6 °CA.
Simulation results using AVL-Fire indicated that the wall-flow-guiding effects and in-cylinder air motion including air entrainment and reversed squish improved as the combustion chamber diameter decreased, which contributed to fast fuel–air mixing in the outer chamber and the clearance, high indicated power and low soot generation.
However, when the combustion chamber further decreased from 83 to 76 mm, the unutilized air in the inner chamber and the clearance reduced the performance.
An analysis of the uniformity index of the equivalence ratio in different parts of DSCS found that DSCS83 had a 1.2–4.8% improvement in the whole-chamber uniformity index at 60 °CA ATDC at 32% load condition.
These results could be an essential reference in the optimization and application of DSCSs in diesel engines.—Kang et al.
Xiangrong Li, Zuoyu Sun, Wei Du & Rong Wei (2010) ”Research and Development of Double Swirl Combustion System for a DI Diesel Engine,“ Combustion Science and Technology, 182:8, 1029-1049, doi: 10.1080/00102200903544271
Yuning Kang, Xiangrong Li, Hongji Shen, Yanlin Chen, Dong Liu, Jiang Chang (2022) “Effects of combustion chamber diameter on the performance and fuel–air mixing of a double swirl combustion system in a diesel engine,” Fuel, Volume 324, Part A doi: 10.1016/j.fuel.2022.124392