2. ACTUAL MEASUREMENTS OF EMISSION FROM DIESEL ENGINES IN OPERATION
To begin with, in 1991, Kibankyo Committee has collected the actual values of emissions for various types of diesel engine from existing literature, and also measured emissions during operation on a 11,500 GT domestic car ferry equipped with two 14,400 PS four-stroke engines, and a 170,000 GT ocean-going bulk carrier equipped with an 18,400 PS two-stroke engine. All these engines are of the newest types.
Fig.1 shows some examples of the measured data. SOx values are around 500 ppm, and becomes higher as the engine load increases. NOx emission takes lower values both at lower and higher load range, and it takes maximum values at middle load range. This pattern is almost the same for both the two-and four-stroke engine, but the maximum values are different. For the two-stroke engine, NOx concentration takes up to 2,200 ppm (13% O2 equivalent), but for the four-stroke engine it takes lower value as 1,950 ppm. It can be seen that the values taken at sea running condition are larger, in general, compared with the values taken at shop test, but the differences are not so much. It is considered to be due to the differences between the measuring conditions, especially for the absolute humidity. For the two-stroke engine, change-over tests from diesel oil to heavy oil and vice versa have been carried out, but the differences are not so significant.
In 1998, the MAP Committee of MESJ could gather NOx data for 207 diesel engines from the committee member companies, of which 2-stroke engines were 108 units from 3 companies and 4-stroke engines were 99 units from 2 companies. 2-stroke engines were all main engines and 4-stroke engines were mainly for generators. Almost all of the data were obtained at the shop trial testing, but some data were taken at the sea trial. The fuel oil for shop testing was bunker A, and for sea trial was bunker C. The data obtained at full load are compared with the proposed limit line of IMO's NOx Technical Code as shown in Fig.2 [2]. The emission levels of the newer engines are going to become lower than the proposed limit. The NOx emission data at full load are also plotted against the engine power in Fig.3. All the data are well correlated with a single line for a wide range of engine output. The data at part load show increase slightly from the values at full load.
Fig.1. Examples of Emission Measurement on Ships in Service (Kibankyo Committee)
Fig.2. NOx Emissions vs. Engine Speed
Fig.3. Correlation of NOx Emission at Full Load
