Concepção de um sistema de combustão baseado na autoignição controlada do etanol em um motor monocilíndrico de pesquisa

Abstract

Changes are inevitable, but not always positive. Perspectives of revolution in the automobile industry, towards electric propulsion systems, demand technical-scientific knowledge and responsibility for proposing truly effective solutions to reduce the carbon footprint. This thesis presents a development route for future internal combustion engines, by conceiving a combustion system based on ethanol's controlled autoignition (CAI) in a single-cylinder research engine. Specifically, the objective is to reach the limits of fuel conversion efficiency through the advanced combustion mode HCCI, involving innovative strategies by combining the ethanol auto-ignition with the use of combustion pre-chambers. The methodology reports the experimental procedures that enabled the successful transition between SI-HCCI combustion modes, describes the laboratory infrastructure available for the tests, and explains the mathematical data analysis. The results show success during engine operation in the advanced combustion mode. CAI has been achieved in the face of a lambda factor at least twice of that obtained in SI, by heating the intake air to temperatures above 240°C, provided by two electrical resistances. Minimal reductions of 14% in specific fuel consumption have been reported, as well as a decrease of about 80% in combustion duration, and lower CO2 and NOX emissions, the latter reaching quite negligible rates. The supercharged HCCI achieved an air/fuel ratio above the measurement capability of the lambda probe (λ = 8.10). The use of combustion pre-chambers proved effective in reducing dependence on the external heat source, enabling extrapolation of operating points to higher loads, at which 61.91% and 43.04% have been achieved for thermal and ethanol conversion efficiencies, respectively. By refuting the indication of a single or best solution for future propulsion systems, this thesis encourages the development of engines and biofuels as a fundamental path to the sustainability of Brazilian mobility.