| Resumo : |
Due to the rapid expansion of the transportation sector and the widespread use of fossil fuels, environmental concerns have been growing. The exponential increase in harmful emissions has led to agreements aimed at achieving more stringent sustainability standards, thereby increasing the global demand for renewable, zero- carbon energy sources. In this context, hydrogen (H2) emerges as a promising alternative fuel because of its high energy density and zero-carbon combustion. However, using H2 as a fuel in internal combustion engines (ICEs) presents technological challenges.These challenges include increased (NOx) emissions resulting from high combustion temperatures and the low volumetric energy density of H2. One approach to overcoming these limitations is using H2 as an additive in renewable fuels, such as ethanol, which is widely produced in the US, Brazil, and India. Ethanol has several advantages. It has a high octane rating and low (CO2) emissions when compared over its entire life cycle, making it an excellent alternative for SI engines. However, although ethanol is a renewable fuel, it emits aldehydes that are harmful to health. The addition of H2 has the potential to extend the flammability limit, increase thermal efficiency, and reduce harmful emissions. An experimental study was conducted on a spark-ignition engine with optical access, featuring direct lateral injection of ethanol and port injection of H2. The investigation of hydrogen-enriched ethanol combustion was carried out through thermodynamic analysis, flame morphology imaging, and finally, exhaust emission measurements. Tests were performed under conditions ranging from near stoichiometric to lean mixtures, by progressively increasing the ? up to the flammability limit of ethanol. Then, H2 was then injected for enrichment. The results indicate that ethanol combustion became unstable at ? values above 1.6, with significant increases in COVimep, in addition to a decrease in indicated efficiency. In contrast, H2 enrichment effectively restored combustion (COVimep <5%), increased flame propagation speed, and improved heat release. Regarding emissions, the addition of H2 reduced CO and UHCs, and aldehydes under lean conditions, as well as NOx emissions. Overall, the study confirms that H2 enrichment is an effective strategy for expanding the poor operating limits of ethanol while maintaining efficiency and reducing emissions. These results lend to support the strategy of dual fuel injection as a technically feasible and sustainable alternative for future spark ignition engine technologies. |