Abstract
Keywords: hydrogen, alternative fuel, lean mixture, qualitative adjustment, spontaneous ignition, engines testing
Among alternative fuels, hydrogen due to its properties can be considered a fuel for the future. It’s not a fossil fuel and in burning processes don’t produce CO2 emission, providing this way the reducing of greenhouse gaseous emission, an important aspects according to Kyoto Protocol which was accepted by many countries. With its unlimited production resources, capability of store and transportation, hydrogen represents a vector of energy.
The researches regarding SI engines fuelled with hydrogen have been developed on two main directions:
- hydrogen addition in the gasoline-air mixtures;
- total substitution of gasoline by hydrogen.
Regarding the addition of hydrogen in the gasoline – air mixtures, the researches were focused on low addition ratios (10 to 20 %) in order to increase the efficiency of the combustion process. Due to the wide flammability limits, hydrogen expands the range of lean mixtures that can be burned in the engine without affecting the stability of engine operation. In this way, the polluting emissions are decreasing due to the replacement of carbon by hydrogen molecules. Due to the high burning rate of hydrogen, the efficiency of the combustion process is increased especially in the areas in the cylinder were the air – gasoline mixture is not flammable. For lean mixtures, the thermal efficiency is increased due to the increase of the global ratio of specific heat, decreasing the dissociation processes and the heat transferred to the cooling system. This fuelling solution can be considered as a step to the integral hydrogen fuelling process which will offer a clearly advantage in polluting emission decreasing.
If we don’t take in consideration the carbon oxide fractions and the hydrocarbons provided by oil burning, at the fuelling with hydrogen, the only pollutant substance present into exhaust burning gases is NOx. Because of the higher combustion temperature the NOx emission level is higher for =1…2 comparative to gasoline fuelled engine, but decrease a lot for leaner mixture values, >2. NOx emission neutralization methods can be applied at the operating regimes with high NOx emission levels.
The paper presents the results of the theoretical and experimental research’s carried on the spark ignition engine. Are presented the influence of the mixture quality on burning process, on polluting and energetically engine performance at the fuelling with hydrogen using direct injection method.