Technical Papers
NOx Emission Characteristics of Large Bore 2 Stroke Diesel Engines in Area of Layout Diagram*
Youichi Nakamura, Tetsuo Tokuoka, Yoshishige Sakai, Nobuyuki Nakayama
The marine large bore 2 stroke diesel engines have their own layout diagram defined by a certain range of mean effective pressure pme and of engine speed n. Customers can select voluntarily any combination of power and speed within this layout diagram as the MCR point of their engines. In relation to the exhaust emission regulation by IMO, it is very important and urgent subject to clarify the NOx emission characteristics of the engines in the layout diagram.
In this paper, the behavior of the maximum average gas temperature in cylinder Tmax in the layout diagram was analyzed and also the many NOx emission data on the shop trials were investigated. Consequently, the following facts have been clarified.
The NOx emission values on the E3 mode in the IMO Technical Code coincide relatively well with those at 100% load. Therefore the evaluation and analysis of the NOx emission characteristics can be executed by means of NOx emission values at 100% load.
The values of the degree of explosion pmax/pc correlates closely with Tmax, and also Tmax correlates closely with the NOx emission values. One of the cause of the relatively large dispersion of the NOx emission values is the scattering of the pmax/pc on the shop trials.
In case of the pme derating in the layout diagram, if the slope ps/pme against pme/pme0 is set as approx. -0.11, that is to say, the value of ps/pme is made to increase gradually along with the decrease of pme/pme0 by the adequate turbocharger matching, then the value of Tmax can be kept almost constant, subsequently the value of NOx is kept also almost constant.
1. Introduction
As well known, the marine large bore 2 stroke diesel engines have their own layout diagram defined by a certain range of mean effective pressure pme and of engine speed n. Customers can select voluntarily any combination of power and speed within this layout diagram as the MCR point of their engines.
On the other hand, the Conference of Parties to MARPOL 73/78 was held in September 1997 and the Protocol of 1997 to amend MARPOL 73/78 to add new Annex VI on Regulation on the Prevention of Air Pollution from Ships was adopted. When this Annex VI will come into force, the regulation is applied retroactively to the engines installed in the ships built after December 31, 1999. Also, the Annex VI has the “engine group” concept where only the parent engine in the group is required to take the certification test together with NOx measurement test then the other engines belong to this group are certified without NOx measurement test.
In relation to these, it is very important and urgent subject to clarify the NOx emission characteristics on the layout diagram, in other words, to evaluate the change of NOx value of the engine when the MCR point is altered in the layout diagram.
In this paper, the behavior of the maximum average gas temperature in cylinder Tmax in the layout diagram was analyzed and also the many NOx emission data on the shop trials were investigated. The results are as follows.
2. Test engine particulars and data analyzing method
2.1 Test engine particulars and data number
Table 1 shows the test engine particulars and data number. Here, the engines are classified into three groups (I to III) according to the level of pme and the value of the stroke bore ratio S/D in group I differs from that in group II and III. Each group includes the data with different cylinder diameter. with different cylinder number, with different revolution ratio, n/n0 and with different mean effective pressure ratio pme/pme0 on the basis of the max. MCR point, but the engines in each group are designed strictly similarly. The total data number is 87.
* Translated from Journal of MESJ Vol. 34, No. 4 (Manuscript received Oct. 28, 1998)
** Kawasaki Heavy Industries, Ltd. (Chuou-ku, Kobe City)
