Estudo experimental do desempenho de um sistema de ignição com pré-câmara por jatos turbulentos em um motor monocilíndrico de pesquisa operando com etanol

Abstract

The use of fossil fuels as energy sources contributes for the emission of greenhouse gases on atmosphere, such as carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC) e nitrogen oxides (NOX). These gases impact on climate and environment has motivated the implementation of agreements and regulations that seek to reduce these emissions. Many of these legislations are aimed at the automotive sector, which is responsible for a sizable proportion of it. The studies performed in this context point to renewable fuels, such as ethanol, as a great potential solution to reduce emissions and improve efficiencies in internal combustion engines. Another potential technology is the pre-chamber ignition system. This technology uses a separated volume where the combustion is initiated and partially burned gaseous jets are introduced in the main chamber with high kinetic, thermal, and chemical energy, reducing ignition delay and combustion duration. Four passive pre-chamber geometries were designed with two intern volume values and two different orifice configurations. These geometries were produced with two different materials, stainless steel I304 and a copper, chrome, and zirconium alloy CuCr1Zr, totaling eight produced pre-chambers. These prechambers were installed on a 14:1 compression ratio single cylinder research engine operating with ethanol and tested for five different operational conditions. Engine dead volume variation due to the assembly of the prechambers was compensated, allowing a closer compression ratio in all tested conditions. Results show reduction of up to 75% in NOX emissions and a reduction of up to 62% on HC emissions, In addition to an improvement of up to 2% in fuel conversion efficiency. Furthermore, reductions of up to 15% on combustion duration were obtained on 19 of the 20 conditions tested, which improves the knock resistance of the engine. As a result, future improvements on fuel conversion efficiency can be achieved increasing the compression ratio. Results indicate that optimal prechamber geometry depends on engines operational condition.