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The Influence of Injection Timing over Nitrogen Oxides Formation in Marine Diesel Engines
Juan Moreno Gutierrez, Ismael Rodriguez Maestre, Tarik Chafik, Cristina V. Duran Grados, and Palomarocio Cubillas

The atmospheric emissions (i.e. atmospheric contaminants, greenhouse effect gases and many other substances which damage the ozone layer), produced by ships navigating through-out the maritime zones of the European Union, are registering worrying levels. These emissions spread inland. If we just take into account NOx emissions, which could be present for as long as three days, they could reach between 400 and 1,200 km inland. (1) Recent studies suggest that NOx emissions from marine diesel engines represent about 17% of the total NOx emissions produced by fossil fuel combustion. Effective techniques in reducing or eliminating these emissions can be divided into three main categories, depending on the stage they are applied in the combustion process. These categories include: pre-combustion, combustion and post-combustion emissions control techniques.

In this article we are presenting a practical method to control the combustion conditions through NOx measurements in medium speed marine diesel engines on ships. In medium speed vessels the control methods usually focus on the reading of exhaust emissions temperatures and, in some cases, the state of the combustion pressures. We have taken many measurements of NOx emissions in some marine diesel engines of 600 kW on board and we have detected combustion anomalies. The timing difference between cam and pump drive was enough to produce NOx concentrations higher than 20% of the main emissions.

Annex VI of MARPOL 73/78 & the NOx Code came into force on 18th May 2005 for marine engines. It set a NOx limit and periodical checks. These only affect engines >130 kW installed on ships built after 1st January 2000 or that underwent a major conversation after that date. The existing ones are not affected by this annex. (There are 25,000 ships over 25 years old still on service.) Most marine engine builders are trying to reach the above mentioned limits. However, it is obvious that the modifications already per-formed on new engines cannot be applied to the existing ones. Nevertheless we can obtain valuable data on the combustion and engine efficiency as shown in this article.

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