Measurement and Analysis of Particulate Matter (PM) from Marine Diesel Engines
Yasuharu NAKAJIMA, Yoshio TAKASUGI, Masaaki KIKUCHI, Magoshiro KUWABARA, Sumito NISHIO, Eiko ISHIMURA, Jie ZHANG and Kazumi NISHIKAWA
The emission characteristics and chemical aspects of particulate matter (PM) from four-stroke marine Diesel engines were investigated. PM showed higher emission rate at lowcr engine loads and dccreased with an increase in engine load to be minimized at 75% engine load. SOF/PM ratio was also lowered with an increase in engine load while the content of soot and sulphate in PM increased with engine load. Moreover, GC and GC-MS analysis showed that SOF contained not only paraffins but also aromatics and heterocyclic compounds. In addition, the effect of the fuel ignition timing on PM emission characteristics was investigated with timing-variable fuel injection system. PM was minimized at 8 degrees after TDC while the fuel ignition timing was varied from 0 to 10 degrees after TDC. Furthermore, the optimization of the fuel ignition timing corresponding to engine load provided the significant reduction of PM emission rate compared with the fixed timing.
Key Words: Marine Diesel Engine, Particulate Matter (PM), Soluble Organic Fraction (SOF), Emission Characteristics, Chemical Aspects, Fuel Ignition Timing
The emission of particulate matter (PM) from Diesel engines is expected to have significant effects on human health and global environment. For the former problem, it has been argued that soot, a main component of PM, could cause the diseases of the respiratory organs. In addition, it has been reported that Diesel PM might contain carcinogens such as Benzo[a]pyrene and its derivatives. On the other hand, for the latter problem, PM suspended in the atmosphere is expected to raise the reflectance of the atmosphere to affect the global climate change. Moreover, not only its chemical aspects but also its distribution of particle size characterize these features. That is, various factors of engine, fuel, lubricants and other events on engine operation are concerned with its properties and formation processes.  Thus, PM emission characteristics and chemical aspects are required to develop the reduction methods as well as to evaluate these effects. However, although PM in automotive emission has been investigated widely, that from marine Diesel engines has not been studied thoroughly yet.
Then, we have investigated PM emission characteristics from four-stroke marine Diesel engines and reported that the emission characteristics are affected by fuel injection system as well as fuel quality.  This paper describes the basic emission characteristics and chemical aspects of PM. In addition, the effect of the fuel ignition timing on PM emission characteristics was also studied by the experiments with timing-variable fuel injection system.
2. EXPERIMENTAL PROCEDURE
2.1 Measurement of PM Emission Characteristics
In this study, a four-stroke medium-speed marine Diesel engine was operated with marine Diesel oil (MDO) and marine fuel oil (MFO) along propeller performance and generator performance (fixed-speed) curves. The principal particulars of the engine, fuel properties and engine operating conditions are shown in Tables 1, 2 and 3. PM was sampled on Teflon coated filters with double dilution tunnel system (Firmtech: MIT-1000) by partial dilution method (PDM) according to the technical code 8178 of International Organization of Standardization (ISO). The schematic diagram of the double dilution tunnel system is shown in Fig.1. PM was weighed after conditioning at 298K and relative humidity of 50% in a conditioning chamber for 24 hours.
In addition, fuel injection system was changed from cam-drive type to computer-controlled hydraulic drive type so that the fuel ignition timing could be varied easily to investigate the effect of the timing on PM emission characteristics. The hydraulic drive fuel injection system consists of control unit, hydradie generator and cylinder unit with electronic valves. Presettled Bosch pumps were also used with the new injection. The schematic diagram of the hydraulic drive system is shown in Fig.2. 
The fuel ignition timing was defined as the angle where dp/dθ＞1000 MPa/degree (p: cylinder pressure, θ: crank angle). The cylinder pressure was measured with a Diesel engine analyzer (YSK Systems: NHX-2). The opening timing of the electronic valve in each cylinder was adjusted to obtain the desired ignition timing.
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