Study of Correction Factors on NOx Emission from Medium Speed Diesel Engine
Hiromi KONDOH*, Takahide KAWANO**, Kazuhiko MASUDA** and Yutaka INUI*
ABSTRACT
This paper describes the influences of variation factors in respect to NOx emissions from medium speed diesel engine operated under constant speed. The level of NOx emission is liable to be influenced by moisture and temperature of air, and ignitability of fuel etc.
In order to confirm the possible influences of absolute humidity, ambient temperature and intercooled air temperature, the authors attempted to modify the yearlong measured result of NOx from two cogeneration engines. As a result, the influence of each correction factor was quantified and it was clarified that absolute humidity most greatly influences the level of NOx.
Furthermore, to clarify the influence of absolute humidity and intercooled air temperature on NOx emission, combustion test by using the single cylinder engine was executed. As a result, it was clarified that the NOx changes remarkably by the change in absolute humidity compared with the change in intercooler air temperature.
On 26 September 1997, the Conference of Parties to the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 relating thereto (MARPOL 73/78), adopted, by Conference resolution 2, the Technical Code on Control of Emission of Nitrogen Oxides from Marine Diesel Engines [1]. Under the provisions of Annex VI_ Regulations for the Prevention of Air Pollution from Ships, of MARPOL 73/78, and subsequent to the entry into force of Annex VI, each marine diesel engine to which regulation 13 of that annex applies, must comply with the provisions of this Code. The NOx Technical Code specifies inspections and tests to be performed to implement regulations on NOx emissions. In the procedure for obtaining a NOx emission value, the NOx Technical Code describes the correction of NOx-concentration measurements according to ambient temperature, absolute humidity and so on obtained at the time of measurement, as NOx concentration varies depending on these factors.
Regarding the NOx-concentration correction formula specified in the NOx Technical Code, the authors conducted long-term research using two types of power-generating medium-speed diesel engines, which may be used as ship's engines as well as in cogeneration applications. One engine's cylinders were 280 mm in bore diameter and the other's were 220 mm. Furthermore, the authors conducted a combustion test by using the single cylinder engine according to the test cycle type D2 (E2) specified in the NOx Technical Code. A single-cylinder engine that had the same specifications as those of an engine with a cylinder 200 mm in bore diameter, which was developed to meet the IMO's NOx regulations, was used. Using samples collected from the emissions of these engines, analysis was conducted to determine factors that might be influencing NOx concentration, which showed seasonal fluctuation.
