The dynamic process, acting on the exhaust flow, plays an important role in multi-cylinder turbocharged two-stroke diesel engines design.
In this type of engine, with ports opened and closed by the piston motion, the pressure pulses coming from the discharge of cylinders produce pressure waves in the exhaust manifold. There are combinations of design parameters and operating conditions in which we can take advantage of such pressure waves in order to minimize bypass flow (air flown directly from intake to exhaust ports) and increase the air mass trapped in cylinder.
The aim of this work is to find which are the above mentioned combinations. In order to solve this question, it is essential to study in a detailed way, pipe's geometry and the effect produced by pressure waves created during the aperture of exhaust ports.
The optimization is obtained both in fluid and structural aspects. The former is done because of the importance of the flow field in the scavenging process and impact on engine performance. The latter is due to thermal-structural stresses present in pipes and flanges.
A numerical code has been developed in order to calculate pressure variations in the pipes. This code is also used to calculate the boundary conditions present in both entrance and exit of intake and exhaust ports. Boundary conditions are used for simulation of scavenging process in the cylinder with Kiva-3 code.
The thermal-structural study was carried out using the method of finite elements. Convection heat transfer coefficients are evaluated from Malchow, Sorenson and Buckius correlation. The geometry has been modelled in a parametric way, so variations of lengths, thickness and diameters of the pipes can be analyzed very easily.
The results of the models were checked with experimental results. Adequate correlation values have been obtained with errors smaller than 4%.