An Overview on Pollutant Emissions of Internal Combustion Engines

The necessity of pollution reduction of the pollutant emission levels and of the greenhouse gases appears todays as an important demand from the UE regulations for many industry and activities sectors. The transportation sector is also under more sever rules which impose the limitation of the pollutant and GHG emissions levels, emitted by auto motives internal combustion engines. The European Commission aims to reduce CO2 emissions issued by transportations by 37.5% till 2030. The pollutant emissions produced by the internal combustion engine mainly have two important sources, such as the combustion of fuel in the engine cylinders and, respectively, the emissions of fuel vapors at the level of the fuel system, in the case of the use of liquid fuels. In a stoichiometric combustion process, the majority of combustion products are non-toxic substances such as CO2, nitrogen and water vapor, but under certain conditions, when operating with rich or lean mixtures, harmful products such as CO, unburned hydrocarbons, nitrogen oxides, smoke, soot, material particles as PM (Particulate Matter). The problem with these chemical substances is that may affect the clinic heath of humans that lives in the large urban areas. Therefore, employing alternative fuels emerges as a viable solution, enabling fossil fuels replacement and pollutant emissions concentration reduction. The use of hydrogen as alternative fuel may represents an efficient instrument to decrease the pollutant emissions level. The use of small hydrogen quantities are injected into a diesel engine inlet, decrease the smoke opacity with 35.7% and the smoke number with 6.6%, the unburned HC emission level with 32.3%, the NOx emission level with 2.8%, the CO2 emission level with 4.5%. The use of hydrogen as alternative fuel for spark ignition engine assure the reduction of the NOx emission level with a maximum of 90% at λ = 3 comparative to stoichiometric conditions. The HC, CO and CO2 emission level were decreased till zero at hydrogen use and lean mixture operation.