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General
- Hydrocarbons are a group comprising hundreds of organic compounds, to which carbon, hydrogen, nitrogen, oxygen and sulphur may be bound
- Given the complex nature of hydrocarbon emissions, it is difficult to define the risks they pose to human health
- Hydrocarbon emissions are generally divided into two categories: total hydrocarbons (THC) and non-methane hydrocarbons (NMHC)
- Another term used is volatile organic compounds (VOC), which is generally understood to mean all hydrocarbons from which either methane or both the methane and ethane have been removed.
Environmental impacts
- THC are influencing the formation of ozone and smog in the lower atmosphere in densely populated urban environments
- Some hydrocarbons are considered to be carcinogenic
- Of the hydrocarbons that fall within the category of greenhouse gases, methane in particular is strongly influencing the climate warming.
Formation in engines
- THC and VOC emissions form in the combustion chamber as a result of the local absence of combustion air, as well as low combustion temperatures and the evaporation of lubricating oil from the combustion chamber towards the end of firing period
- In diesel engines, THC and NMHC emission levels are low compared to other emission sources due to the efficient combustion process and high excess air quantities
- Hydrocarbon emissions when burning heavy fuel oil are generally at a lower level compared to the use of light fuel oil as evaporation is lower
- In gas engines, THC emissions are relatively high due to premixing and the relatively low combustion temperatures in these engines.
Feasible emissions reduction technology
- Diesel engine: no commercial technology is available when using heavy or light fuel oils
- Gas engine:
o Oxidation catalyst for NMHC and VOC emissions
o No commercial technology currently available for THC.
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