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Calibration of internal combustion engines at different altitudes, above or below sea level, is important to improve engine performance and to reduce fuel consumption and emissions in these conditions. In this work, a flow test rig that reproduces altitude pressure variation is presented. The system stands out by its altitude range, compactness, portability and easy control. It is based on the use of turbomachinery to provide the target pressure to the engine intake and exhaust lines. The core of the system is composed of a variable geometry turbine (VGT) with a waste-gate (WG) and a mechanical compressor. Given a set of turbomachinery systems, the operation pressure and the air mass flow are controlled by the speed of the mechanical compressor and the VGT and WG position. A simple modification in the installation setup makes possible to change the operating mode from vacuum to overpressure. So that simulating altitude increase or decrease with the same flow test rig components.

A theoretical-experimental study is presented in the paper, whose objective is to propose a method that allows determining the average efficiency of the radial turbines, usually employed in the internal combustion engines, under real operating conditions. Due to the unsteady behaviour of the exhaust gasses flow, the efficiency information obtained from steady flow tests cannot be considered when the turbine is connected to an internal combustion engine. The efficiency differences between steady and unsteady flow patterns, can be obtained by testing the turbine, connected to the engine, under real pulsating flow conditions. For the correct turbine workflow characterisation, a wave action model has been used, together with information obtained from engine tests. The engine test cell includes a specific measuring device for this purpose. The results obtained have been compared with those provided by the turbine manufacturer.

The purpose of this paper is to describe a methodology based on experimental and theoretical studies for the modeling of typical exhaust systems used in two-stroke small engines. The steady and dynamic behaviors of these systems have been measured in a flow test rig and in an impulse test rig, respectively. Information obtained from these experiments is used in two ways: to find a suitable geometric model to be used in a finite-difference scheme code, and to provide a mean pressure and a frequency domain reflecting boundary, in the frame of a hybrid method. A complete 50cc engine was modeled and comparisons between predicted and measured instantaneous pressure at the exhaust port show a fair agreement, the results of the hybrid approach being more accurate.