A Comprehensive Numerical Analysis of the Scavenging Process in a Uniflow Two-Stroke Diesel Engine for General Aviation

Abstract

The scavenging process of two-stroke engines plays a fundamental role in cylinder flow patterns and in the overall engine performance. In this work, 3D CFD simulations of the scavenging in a uniflow, two-stroke, compression ignition engine for general aviation, named GF56, have been performed by using a 3D finite-volume FANS equations solver with k-ϵ closure. The GF56 engine consists of six cylinders, separated into two quasi-symmetric banks. Both the right and the left banks, together with the corresponding cylinders, are carefully analyzed. Charging and trapping efficiencies are computed as a function of the delivery ratio for different mass flow rates entering into the plenum, and the influence of the exhaust pressure and of the cylinder’s location in the bank are analyzed. The results show that the fresh air trapped during the scavenging process is quite similar for each cylinder of the right bank and it is about 92% of the in-cylinder mass. The cylinder’s location in the bank by itself slightly affects the scavenging performance, whereas the pressure profile at the outlet section has a major role. The design of the intake ports is fundamental for establishing the in-cylinder flow field and a new ports configuration is proposed to enhance the swirl ratio and, consequently, the scavenging performance with high delivery ratios.

Numerical optimization of supercharging and combustion on a two-stroke compression ignition aircraft engine

“…The methodology and the results will not be discussed here, since they are comprehensively described in another paper. 17 However, the analysis shows that the patterns of the scavenging process are quite independent on the gasdynamic conditions across the cylinder, and on the position of the cylinder within the air-chest.…”

“…The proposed 2S engine adopts a Uniflow scavenging system, with two exhaust poppet valves on the cylinder head, and a set of inlet ports along the cylinder liner. The details of the scavenging system design, supported by 3D-CFD simulations, are comprehensively described in Faruoli et al 17 while the general concepts can be found. 18–20…”

“…The methodology and the results will not be discussed here, since they are comprehensively described in another paper. 17…”

“…The details of the scavenging system design, supported by 3D-CFD simulations, are comprehensively described in Faruoli et al 17 while the general concepts can be found. [18][19][20] The combustion system -made up of an axisymmetric piston bowl, and a Common Rail injector installed in a position almost coincident with the cylinder axis -is identical to a 4S engine.…”

“…The current version is the outcome of a long design process supported not only by CFD simulations, but also by a comprehensive experimental campaign on physical prototypes. Since many design concepts have been already discussed in previous publications, 1,[15][16][17] only the fundamental aspects will be summarized in following.…”