# Economic Feasibility of Retrofitting an Ageing Ship to Improve the Environmental Footprint
## 2 Retrofitting the Propulsion System
### Engine Modifications  
The ship is equipped with one four-stroke medium-speed, non-reversible type diesel engine with a gas turbine set for supercharging, intended to operate on heavy fuel oil of viscosity 380 CST at 50 \({}^{\circ}\)C. The cylinder jackets and covers are cooled with fresh water, and LO cools the pistons.  
Analysing the possibilities of retrofitting the ship's power plant, it was found that the model of the ship's main engine--MAK-Caterpillar 6M43C is very suitable for retrofitting into a dual-fuel engine, namely using the new modification of the MAK-Caterpillar 6M46 DF, which is essentially the same size as the 6M43C.  
The 6M43C has the same footprint as the new M46 DF engine. This makes conversion of the existing M43C engines possible and easy to achieve such a conversion holding on to significant components, such as the engine block, crankshaft, air cooler and turbocharger.  
These are the remaining parts and the rest are to be renewed for M46 DF components. The primary drive is increasing the cylinder bore from 430 mm to 460 mm. Therefore, the following parts will be renewed: cylinder liners, cooling water jackets, pistons, cylinder heads, gas fuel line and engine electronics. Additionally, the following equipment is introduced: big end bearing temperature monitoring, leading bearing temperature monitoring and timing sensors to the camshaft gear wheel and flywheel.  
Next to the engine itself, many components must be placed near and next to the engine to make it possible to run the engine on gas. These are:  
* The Gas Valve Unit (GVU) controls the pressure of the gaseous fuel towards the engine and ensures safe operation with double block and bleed valves and ventilation possibilities.
* The Ignition Fuel Module (IFM) unit ensures enough filtered fuel oil is delivered to the pilot fuel injection system. The pilot fuel injection system ignites the gaseous fuel.
* Vacuum pump unit. The fuel gas line on the engine and between the GVU outlet and the engine is double walled. This unit creates pressure in the double wall barrier to monitoring any leakage. The extracted air is monitored for gas leakage content and blown off outside.
* Exhaust ventilation module services in the event of an emergency engine shutdown in gas mode. The exhaust pipe after the turbocharger is to be flushed to prevent the accumulation of an explosive mixture in the exhaust pipe.
* Slow turn the device is mounted on the cylinder heads due to the engine's construction, no indicator or over-pressure valves. To detect water on the piston, a slow turn device is mounted to slowly turn the engine before starting.  
Additionally, the ship is to be equipped with gas storage tanks, the master gas valve on deck and transfer pumps suitable for LNG, safety devices according to the IGF Code, such as ex-safety zones, double wall gas piping throughout enclosed spaces and inert gas production, storage and deployment equipment.  
The comparison of the dimensions of both engines is presented in Table 2, which shows that they are practically the same.  
The dual-fuel engine has additional equipment, such as a ventilation module, pre-ignition module, GVU gas supply module, glycol-GU module, BS bunker station, engine slow rotation module, etc. Summing up the weight of the additional equipment, the dual-combustion engine will be heavier by about 4 tonnes, which will not affect the engine's characteristics.