Takasaki Koji

Visual Study about Combustion Characteristics of Heavy Fuel in Diesel Engines

Bunker fuel oil, which mainly consists of residue from crude oil refining process, is commonly used for stationary and marine diesel engines. In spite decreasing quality of bunker fuel oil during the last years, higher combustion efficiency and lower emission must be achieved. Up to today, ignition quality was the only criterion for combustion characteristics of such fuels. Therefore, contrary to gas oil, formation of the fuel spray and combustion process are not examined in detail yet. These are clarified in this paper, based on results from engine trials and visualisation of fuel spray combustion. Further, methods to improve combustion are discussed.

Exhaust Emissions from Marine Diesel Engines Using Residual Fuel

Recently the air pollution caused by marine diesel has become a more serious problem. For such engines heavy fuel, e. g. bunker fuel oil, is usually used. High residual portion and long ignition delay are the main disadvantage of heavy fuel. Their effects are especially severe at low load, which is the running condition of ships near the seashore where the pollution is a more serious problem.In this study the emission from a relatively high speed marine diesel engine using heavy fuel is examined. Because the effects caused by heavy fuel can be observed more clearly on a high speed diesel engine, such one was used for the experiments instead of a low speed engine.The experiments show clearly that heavy fuel causes higher smoke density than gas oil. The higher smoke density is caused by direct impingement of the unevaporated residual portion onto the piston.On the other hand the effect of heavy fuel on NOx emission can not be explained simply, because it is influenced by two counteracting effects : the higher pre-mixed combustion rate, which increases NOx formation, and the later ignition timing, which decreases it.

An Experimental Study on the Fuel Spray Distribution and Combustion in a Direct-Injection Typed Diesel Engine

流入スワ-ル強度可変機構を設けた単流掃気形二サイクルディーゼル機関を使用した実験から、燃焼に最適なスワ-ルの強さは、噴射ノズルの噴口数だけでなく、噴霧の衝突条件や燃焼室形状、また燃焼性状によっても変化することがあきらかとなった。またビストンに設けた皿を深くすることによって、噴口数が少ない場合の排煙濃度を改善でき、皿の形状を変えることによって、さらに燃焼改善をはかる自由度があることも確かめられた。