Hydrogen Combustion in I.C Engines

Abstract

The use of hydrogen as a fuel for the internal combustion engine represents an alternative to solve both of the greatest problems related to the use of classic fuels: the limitation of the fossil fuels consumption and the environment pollution. We first describe hydrogen-engine fundamentals by examining the engine-specific properties of hydrogen and topics that are discussed include abnormal combustion (backfire, pre-ignition and knock),emissions of NOx and load control strategies (power output versus NOx tradeoff). Finally, we consider comprehensive overview of the design features of a dedicated hydrogen S.I., Direct-Injection hydrogen fueled internal combustion engine. I. Introduction: At the moment the estimation of the number of motor vehicles is about 800 million. To replace them in a relatively short time by fuel cells is impossible. There are several reasons for converting the gasoline, diesel or natural gas engines to hydrogen fuelled internal combustion engines. ICEs are proven technology, are simple and well-known and the adaptations can be made with a low cost. During the transition period bi-fuel solutions are possible (to run the engine either on gasoline or pure hydrogen). For larger engines (buses, trucks) mixtures of natural gas with hydrogen (about 20%) are easy to exploit. During this transition period, experience can be gained with the production, storage and infrastructure of hydrogen. Currently the hydrogen production is the cheapest through the steam reforming of methane. But CO2 emissions can not be avoided. Renewable energy, e.g. solar power, hydroelectric, tidal, … can give ―CO2-free‖ electricity to electrolyze water to hydrogen. The downside is that these electricity costs are mostly expensive. Interesting is also the application of peak shaving of wind turbine power. Other possibilities are solar thermal, biomass, bacterial… The unique combustion characteristics of hydrogen that allow clean and efficient operation at low engine loads present difficulties at high engine loads. Here, the low ignition energies of hydrogen-air mixtures cause frequent unscheduled combustion events, and high combustion temperatures of mixtures closer to the stoichiometric composition lead to increased NOx production. Both effects, in practical application, limit the power densities of H2ICEs. The recent research thrust and progress on this front is the development of advanced hydrogen engines with improved power densities and reduced NOx emissions at high engine loads.