# Environmental and Economic Aspects of a Containership Engine Performance in Off-Design Conditions
## 3 Methodology
### Engine Simulation Model  
The 1D/0D simulation model of a six-cylinder two-stroke marine diesel engine is made in AVL Boost(tm), as shown in Figure 5. The model consists of a turbocharger (TC1), intake air cooler (CO1), intake plenums (PL1 and VP), cylinders (C1-C6), and exhaust pipes. \begin{table}
\begin{tabular}{l c} \hline
**Engine Name** & **Wartsila Sulzer RTA-96C** \\ \hline Type & two-stroke diesel, turbocharged, liquid cooling \\ Scavenging type & unidirectional with exhaust valve \\ Fuel & MDF—marine diesel fuel (LHV = 42.7 MJ/kg) \\ Cylinder bore & 960 mm \\ Piston stroke & 2500 mm \\ Maximum engine speed & 120 rpm \\ Maximum BMEP * & 19.6 bar \\ Maximum brake power * & 5490 kW per cylinder \\ BSFC at max. constant rating (at R1 operating point) * & 171 g/kWh \\ (ISO 3046-1) [33] & \\ Cylinder arrangement and numbers (this study) & inline; 6; 7 and 8 cylinders \\ \hline \end{tabular}  
* ISO standard reference conditions: total barometric pressure 1.0 bar, suction air temperature 25 \({}^{\circ}\)C, charge air cooling–water temperature 25 \({}^{\circ}\)C, relative humidity 60%.  
\end{table} 
Table 3: Specification of two-stroke marine diesel engine data and performance [32]. The intake system boundary (SB1) defines the intake boundary condition of pressure and temperature set to 0.98 bar and 25 \({}^{\circ}\)C, respectively. On the other hand, the exhaust boundary condition (SB2) of pressure is set to 0.98 bar, while the temperature is set to 225 \({}^{\circ}\)C. Such specification of boundary conditions represents the reduced engine intake and exhaust system without detailed modeling of filters, plenums, aftertreatment systems, etc. A simplified model of the turbocharger is used in which the turbocharger discharge coefficient is calculated to satisfy the desired pressure ratio at the compressor. At the engine speed of 102 rpm and BMEP of 19.6 bar (R1 operating point), the calculated boost pressure is equal to 3.7 bar. The excess air ratio is set to 1.6 at maximum loads and it increases as the engine load decreases. The combustion process is described using a two-zone Vibe function. A two-zone combustion model formulation means that in-cylinder mass during the combustion process consists of burned and unburned zones, creating better conditions for pollutant calculation, especially NO\({}_{X}\). The start of combustion is set to 5\({}^{\circ}\) crank angles after the Top Dead Center (TDC) at maximum engine speed according to manufacturer data regarding fuel injection timing [32]. The shape parameter and combustion duration of the Vibe function are set to 0.6 and 35\({}^{\circ}\) crank angles, respectively. The combustion model parameters are selected because the engine has 3 diesel fuel injectors per cylinder that intensify in-cylinder swirling, mixture formation, and hence the combustion burning rate is increased. The in-cylinder heat transfer is calculated using the well-known Woschni correlation, while the maximum temperature of the piston top surface is set to 380 \({}^{\circ}\)C as measured by the manufacturer [32]. The cylinder head temperature is set to 370 \({}^{\circ}\)C, while the cylinder liner temperature at TDC is equal to 285 \({}^{\circ}\)C and it decreases to BDC (bottom dead center) to 240 \({}^{\circ}\)C.  
NO\({}_{X}\) emissions are calculated considering six reactions that are based on the Zeldovich mechanism. More detail about reaction rates (\(r_{1}-r_{6}\)) and coefficients (\(k_{0,1}-k_{0,6}\)) using the Arrhenius-type form can be found in [34]. The soot emission is considered by calculating the soot formation and oxidation mechanism [35].