Conventional fossil fuel for combustion system, such as gasoline and petroleum have long been recognized as powerful energy source, however these have a number of problems related to emissions and energy security. The use of hydrogen blends with natural gas is a viable alternative to pure fossil fuels. Because of the expected reduction of the total pollutant emissions and increase of efficiency. Enhancement of chemical reaction with hydrogen addition is regarded as the increase of H, O and OH radical mole fraction in the flame. Also in SI engines will move the lean limit to leaner mixture, increasing the combustion speed and temperature. Results show that the hydrogen has a catalyzing effect in the ignition of hydrocarbons with only a few percent addition of hydrogen by volume and by adding it to the pure natural gas (CNG) this difference in spark advance of the engine may be reduced, as a result of the higher flame speed of hydrogen. In this paper, we can present the most advances and development made on internal combustion engines which operate with mixture of hydrogen/CNG, doing more emphasis in the combustion process, ignition energy and injection systems. Also the nozzle geometry has an important influence on injection process and combustion development and shows that degree of conicity can be evaluated for each nozzle by the K- Factor.

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