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Numerical Simulation of Methane Slip in Dual Fuel Marine Engines
Jaehyun Han(한재현),Michael Vincent Jensen,Kar Mun Pang,Jens Honore Walther,Jesper Schramm,Choongsik Bae(배충식) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
The methane slip is the problematic issue for the engines using natural gas(NG). Because methane is more powerful greenhouse gas (GHG) than CO₂, understanding of the methane slip during gas exchange process of the engines is essential. In this study, the influence of the gas pipe geometry and the valve timings on the methane slip was investigated. MAN L28/32DF engine was modeled to simulate the gas exchange process of the four stroke NG-diesel dual fuel engines. The mesh size of the model was decided based on the sensitivity study on the peak pressure of the cylinder and the fuel mass estimations. The simulations with various gas pipe geometries were conducted. It seemed that the effect of the change in injection direction is more dominant than the change in the gas hole configuration. The favorable injection direction for minimum amount of methane slip was discovered as the direction which helps developing the flow of methane far from the exhaust ports. The effects of various valve tuning settings were also simulated. The advancement of the exhaust valve closing was more efficient than the retardation of the intake valve opening. A little retardation of the intake valve opening even resulted in the increase of the amount of methane slip.
Modeling Services Liberalization: The Case of Tanzania
( Thomas F. Rutherford ),( David G. Tarr ),( Jesper Jensen ) 세종대학교 경제통합연구소 (구 세종대학교 국제경제연구소) 2010 Journal of Economic Integration Vol.25 No.4
Despite economic theory and empirical literature that have shown that wide availability of business services contributes significantly to productivity gains and growth, economic modelers have been slow to meaningfully incorporate services into their models. This paper employs a 52-sector, small, open-economy computable general equilibrium model of the Tanzanian economy to assess the impact of the liberalization of regulatory barriers against foreign and domestic business service providers in Tanzania. The model incorporates foreign direct investment in services, and productivity effects in both goods and services markets endogenously through a Dixit-Stiglitz framework. The paper summarizes and builds on the surveys and policy notes of the regulatory regimes in business services in Tanzania, and estimates the ad valorem equivalent of barriers to foreign direct investment. The paper estimates significant gains to Tanzania from services reforms, especially in banking, maritime and road transportation. Decomposition exercises reveal that the largest gains will derive from liberalization of non-discriminatory regulatory barriers.