Technical Papers
Characteristics of Particulate Emission from Marine Diesel engines*
-Comparison between High Speed Four-stroke Engine and Low Speed Two-stroke Engine-
Tatsuro Tsukamoto**, Tomohiro Miyoshi***, Kenji Ohe**, Hiroshi Okada**
In this paper, experimental investigation was conducted with two marine diesel engines, such as high speed four-stroke engine and low speed two-stroke engine, to know the present condition and characteristics of particulate emission. Particulate matter collected on a sampling filter by dilution tunnel system was divided into SOF and ISF by Soxhlet extraction method. The results show that SOF concentration decreases and ISF increases as engine load becomes larger for the four-stroke engine. On the other hand, an increase in engine load promotes both SOF and ISF emission for the two-stroke engine. An analysis of SOF by gas chromatography suggests that cylinder lubrication has a significant effect on SOF concentration in the exhaust gas of the two-stroke engine.
1. Introduction
With the increase of the concerns for the global environmental protection, the further reduction of particulates, NOx, and SOx exhausted from internal combustion engines has become a social problem. Also, for marine diesel engines, the emission of NOx and SOx is scheduled to be regulated by the International Marine Organization (IMO).1) Further, particulates is thought to become a subject of the regulation in the future. Most of particulates exhausted from diesel engines can be divided into soluble and insoluble organic fractions (SOF and ISF). Harmful components such as polynuclear aromatic hydrocarbon (PAH), etc. are mainly contained in SOF, so that the reduction of SOF has become an important problem.
So far, the concentration of particulates exhausted from marine diesel engines has been measured by a smoke meter or a direct sampling method standardized by JIS Z 8808 that catches particulates by filtering the exhaust gas with its high temperature. However, because these methods cannot measure total particulates containing SOF, ISO (International Organization for Standardization) proposes that, for all reciprocating internal combustion engines, such particulates should be measured by a dilution method that catches particulates by filtering the exhaust gas diluted with a large quantity of air.2)
* Translated from Journal of MESJ Vol.33, No.4 (Manuscript received Oct. 24, 1997) Lectured May 15, 1996
** Tokyo University of Mercantile Marine (Koutou-ku, Tokyo)
** Daihatsu Diesel Manufacturing Co., Ltd. (Chuou-ku, Osaka City) February 1999
In this paper, the concentration of exhausted particulates was measured by the dilution method for both high speed four-stroke and low speed two-stroke marine diesel engines, with their engine load changed respectively. Also SOF in the collected particulates were extracted by a Soxlet extractor and analyzed for the components by gas chromatography to study their characteristics.
2. Experimental Apparatus and Methods
A three-cylinder four-stroke trunk-piston type diesel engine and a three-cylinder two-stroke cross-head type diesel engine were used as the test engines. The specifications are shown in Tables 1 and 2 for both engines respectively. Diesel oil was used for the fuel. Its characteristics are shown in Table 3. For the four-stroke engine, the concentration of exhaust particulates was measured with the engine load changed both in propeller load and generator load operations. In the propeller load operation, the engine output was varied proportionally to the third power of engine speed, and in the generator load operation, the torque was varied at a constant engine speed of 1,200 rpm. For the two-stroke engine, the engine load was changed in the propeller load operation.
The particulate concentration was measured by the partial flow dilution method using a small sized dilution tunnel (70mm inner diameter, 1400mm length). The dilution rate was determined by the ratio of NOx concentrations before and after the dilution. The NOx concentration was measured by a chemiluminescence type NOx meter.
The filter was weighed before and after filtration of particulates, after the filter was placed for eight hours in the room kept at constant temperature and humidity (297 ±2K,45±5%).
