Marine Log - May 2008 - (Page 26)

DIESEL TECHNOLOGY ICE CLASS TANKERS Fuel consumption being friendly to the global environment. To attain further CO2 reductions, additional studies are required to increase the thermal efficiency of the engine itself and to recover the energy lost in the exhaust gas and the waste heat in the exhaust gas and cooling water. Since MHI also manufactures exhaust turbochargers, the company is working on developing a hybrid turbocharger. Nox emissions TIME TO SLOW DOWN? The classic response of shipowners to high fuel prices has long been “slow steaming.” Since less fuel consumption means lower CO 2 emissions, any thoughts of a “carbon levy” will persuade operators to re-examine service speeds very carefully. Of course, in a world in which carbon is taxed, there’s no point in slowing service speed if that creates a need for additional ships (and thus additional emissions). However, another way to move the same cargo volumes more slowly and fuel efficiently is in ever bigger ships (a trend that favors large twostroke crosshead engines). A recent paper by Mikael C. Jensen, Senior Manager of Large-bore Design at MAN Diesel A/S, Copenhagen, notes that reducing the speed of a modern, large post-panamax container vessel reduces the power requirement substantially. Reducing ship speed by, for example, 4 knots, reduces the power requirement by some 50%. This means that a ship whose main engine has been chosen with sufficient power to handle high speeds, must also be able to operate at low loads for long periods. Comparison of the trade-off relationship between fuel consumption rate and NOx emissions indicates that an electrically controlled engine is superior to a conventional cam engine The key to reducing CO 2 emissions from ships is to burn less fuel—and that is the real advantage of the diesel engine. One reason for this is quite simply that they are piston engines. In a recent issue of its Technical Review dealing with “Global Warming Countermeasures,” a paper from Japan’s Mitsubishi Heavy Industries makes the point that “a piston engine is inherently advantageous in its working principles and characteristics. In a piston engine, a sequence of strokes, including compression, combustion, and expansion, takes place repeatedly within one cylinder, making up a high-temperature pressure cycle. The maximum temperature constraints of the working media inside the cylinder are not very severe due to the unsteady cyclic combustion. A piston engine has another advantage in that its thermal losses can be reduced because of the slow gas flow, leading to higher thermal efficiencies.” The MHI paper (by Tatsuo Takaishi, Akira Numata, Ryouji Nakano and Katsuhiko Sakaguchi) argues that, large, low-speed, two-stroke marine diesel engines will be important in reducing CO2 emissions from shipping because of their efficiency. The paper says that, from the beginning, these engines have had a high level thermal efficiency of over 50% (lower calorific value criteria), which is higher than in other engines and turbines. This high thermal efficiency is obtained because of the large cylinder diameter, long stroke, high air excess ratio, and low revolution speed. “These factors are assumed to contribute to the reduction of various losses and the realization of a cycle that is thermodynamically close to ideal. From the viewpoint of combustion, a slow gas flow 26 MARINE LOG MAY 2008 inside the cylinder is achieved as static compression and expansion are enabled in the piston engine. Therefore, although the working media reach high temperatures and pressures, the heat loss can be reduced. The temporal constraints of unsteady combustion in low speed, twostroke diesel engines are not as severe as in small, high-speed diesel engines. Because of this, the gas flow speed inside the cylinder can be reduced, which is advantageous from the perspective of reducing the heat loss and increasing the thermal efficiency.” ENTER THE ERA OF ELECTRONIC CONTROLS MHI’s latest developments in the large, low-speed marine diesel engine sector parallels developments by European designers by introducing new electronic control technology. In MHI’s UEC Eco-Engine, the conventional mechanically controlled systems, including the fuel injection, exhaust value, starting, and cylinder lubrication systems, are electronically controlled so that the operation timing and fuel injection rate can be freely changed according to the engine load, ambient conditions, and fuel properties. As a result, the trade-off relationship between the NOx emissions and fuel consumption rate can be greatly improved. In comparison with conventional cams, this engine reduces NOx emissions by 10 to 15 % when the NOx priority mode is selected and the fuel oil consumption is kept constant, and improves the fuel oil consumption by 1 to 2% when the fuel oil consumption priority mode is selected and the NOx emissions are kept constant. Thus, MHI can provide marine diesel engines that satisfy the economic efficiency required by customers while Relative propulsion power needed for a large container vessel shown as a function of ship speed www.marinelog.com http://www.marinelog.com

Table of Contents Feed for the Digital Edition of Marine Log - May 2008

Marine Log - May 2008 Contents Editorial Second Thoughts Update Inside Washington Europe Plots Its Tech Strategy SDNV Container Ship Update Diesels Can Burn Anything: Even Clean Fuel Boost for Small Shipyards Gateway to the Caribbean Room to Grow Show Review Tech News Newsmakers Contracts Events Website Directory ML Buyer's Guide ML Marketplace Maritime Salvage Letters

Marine Log - May 2008

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