About emissions of particulates and smoke

Environmental impacts

• Apart from the visual nuisance caused by smoke, particles are regarded as being harmful to human health
• Small size particles are considered to reach the lungs. Some of the particles arising from the combustion process belong to this category
• Larger particles are considered to be less of a health hazard as they are efficiently captured in the airway before reaching the lungs
• Since small particles are easily air-borne, their detrimental effects on health are often visible far from their source.

Formation in engines

• Particles form in the combustion space as a result of locally low quantities of excess air. Some of the particles do not have time to burn completely but pass out into the atmosphere in the exhaust gases. The amount of particles in the exhaust depends on the amount of hydrocarbons in the fuel and lubricating oil and on the amount of sulphur and ash in the fuel. The amount of absorbed and condensed matter (particulates) strongly depends on the cooling conditions i.e. temperature, cooling rate and residence time in the engine combustion chamber and also in the exhaust pipe and in the measurement dvice itself. A big part of the particulates is formed in the measurement device outside the engine 
• When using heavy fuel oil, typically more than 50% of particles in the exhaust come from the ash and sulphur components in the fuel
• When using light fuel oil, most of the particles consist of carbon or hydrocarbons and only a small proportion comes from the ash and sulphur components in the fuel
• Particles smaller than about 0.4 µm are considered to be invisible. A proportion of the particles produced by an engine fall below this size
• Gas engines have very low levels of particle emissions.
  Reduction methods in engines
• In diesel engines, raising the fuel injection pressure as this improves fuel droplet formation and combustion efficiency
• Raising the temperature of the intake air
• Optimizing the geometry of the combustion space, the compression ratio, and the fuel injection pattern
• Many measures taken to reduce particle emissions also tend to increase NO_x emissions.

Feasible emissions reduction technology

• Of the commercial technologies available today, only the electrostatic precipitator is suitable for diesel engine power plants but its investment costs are high. Sometimes, in conjunction with desulphurization equipment, bag filters are used to reduce particle emissions.
• No feasible partibulate after-cleaning method exists for marine engines