For the past 60 years, diesel engines have been the propulsor of choice for large merchant vessels. In addition to their reliability and durability, low and high speed diesel engines have the significant advantage of low fuel consumption relative to the power produced. Compared to other methods of propulsion, low-speed diesel engines have the additional advantage of being able to burn low-quality, and therefore lower cost, residual fuels with relative ease.
This, combined with the overall efficiency of waterborne transport, has enabled low-speed diesel powered vessels to offer consumers a low cost and efficient method of moving goods and materials. However, recent years have seen an increase in concern regarding the effect that commercial shipping is having on the environment and one of the issues that has received the most attention is the effect that airborne emissions from marine vessels are having on the environment. Similar to other technologies that rely on combustion engines for power, the primary exhaust constituents of concern that are generated by ships’ engines include CO2, NOX, SOX, and particulate matter. However, relative to other combustion technologies, the emissions from low-speed diesel engines of the type that would typically be used for ship propulsion are characterized by increased levels in the emission of both the oxides of sulfur and nitrogen (SOX and NOX). Of the two, SOx is relatively easy to control by reducing the sulfur content of the fuel that is being burned. The reduction of NOx emissions, on the other hand, is much more problematic because the formation of NOx is a function of high local temperature within the combustion chamber.
Nitrogen oxide emissions
Vehicle emissions control is the study and practice of reducing the motor vehicle emissions -emissions produced by motor vehicles, especially internal combustion engines.
Emissions of many air pollutants have been shown to have variety of negative effects on public health and the natural environment. Emissions that are principal pollutants of concern include:
Hydrocarbons – A class of burned or partially burned fuel, hydrocarbons are toxins. Hydrocarbons are a major contributor to smog, which can be a major problem in urban areas.
Nitrogen oxides (NOx) – Generated when nitrogen in the air reacts with oxygen at the high temperature and pressure inside the engine. NOx is a precursor to smog and acid rain.