COST EFFICIENCY OF OPTIMIZING AUTOMATIC TEMPERATURE CONTROL PARAMETERS IN A DIESEL ENGINE COOLING SYSTEM ON A CRUISING VESSEL – A CASE STUDY

With the enforcement of international regulations aimed at reducing environmental pollution, various measures and procedures have been proposed to reduce fuel consumption and increase energy effi ciency of ships. Cruising ships that are commonly visiting some of most sensitive and protected sea areas are of particularly interest. This case study outlines measure that can be applied tocruising vessels without installing new or modifi cations of existing systems and will require somewhat increased attention of chief engineer during voyage. Modern medium speed marine diesel engines, out of the total energy contained in the fuel, utilize slightly less than half while the rest is a thermal loss.Therefore, ships are equipped with waste heat recovery systems utilizing the excessive heat of diesel engine exhaust gases and cooling water. The fi ndings in this paper shows that correct selection of parameters in automated control of cooling water temperature results with a signifi cant improvement of diesel engine thermal effi ciency, reduced fuel consumption and improved costs effi ciency. The results are applicable for all similar marine or industrial power systems as well.


INTRODUCTION
Amendments to the MARPOL 73/78 Annex 6 [1] impose new requirements primarily focused on reduction of harmful emissions from ships and increasing their energy effi ciency. The Ship Energy Effi ciency Management Plan (SEEMP), International Energy Effi ciency Certificate (IEEC) and the Energy Effi ciency Design Index (EEDI) are required for new ships. The SEEMP contains a set of measures aimed to improve energy effi ciency. The plan also enables a non-mandatory Energy Effi ciency Operational Indicator (EEOI) as a possibility for companies to manage whole fl eet. EEDI is a technical measure used to promote energy-effi cient and environmentally-friendly power plants onboard vessels. EEDI is not required for existing engines. Relevant publication [2] that is addressingenergy efficiency of the ships recognize many possibilities but most commonly such as: voyage optimization, energy consumption management, hull propulsion and plant maintenance, structural alteration or the use of alternative fuels [3]. This paper shows that signifi cant savings in fuel costs can only be achieved by optimizing of automatic temperature control parameters in the diesel engine cooling system. The calculations and results presented here are based on the real data gathered on board cruise ship built in 'Voyager' class and they are applicable for entire class, but not limited to that class exclusively.

General characteristic of the ship
The ship was built in the "Kvaerner Masa" shipyard (Turku, Finland) in the "Voyager" class. With a length overall of 311 m, a beam of 38.6 m at the waterline (48 m max), draft of 8.6 m and 139,570 BT today is among the largest passenger vessels in the world. The concept of a "fully integrated electrical system" was applied to the ship. The six diesel generators (6 × Wärtsilä 12V46; 6 × 12,600 kW) producing high-voltage electricity (11 kV) that is being distributed to consumers. It is used primarily for propulsion engines, bow and stern thrusters, and through 11 kV / 440 V transformers for power supply of engine room and other ship requirements (in ex.hoteling). The ship diesel electric propulsion includes two ABB azipods, one fi xipod and four bow thrusters. Maximum passenger capacity is 3.807 and crew of 1.213. Maximum speed 24 knots. The ship has built-in waste heat recovery system utilizing the excessive heat from diesel generator water cooling and charged air from turbo-chargers (scavenging air) and it is consisting of: • sanitary hot water heating system • fresh water generator heating system • air-conditioning water heating system. Use of waste heat of cooling water of diesel engine improves thermal effi ciency and reduces fuel consumption.

Waste heat recovery system
Modern large cruise ships have large energy needs to be used for various technological processes on board. Table 1 shows typical values, depending on the operational conditions, i.e.: 1. maximum consumption -all diesel generators at 100 % load 2. winter time in port -one diesel generator at 80 % load 3. winter time at sea -four diesel generators at 80 % load 4. summer time in port -one diesel generator at 80 % load 5. summer time at sea -four diesel generators at 80 % load 6. summer time at sea, cruising speed of 16 knotsthree diesel generators at 72 % load. It is almost commonly known that modern marine four stroke diesel engines transform in to mechanical work only about 45-48% of total energy contained in the fuel while the rest of 52-55% is heat loss (exhaust gases, scavenging air cooling, cylinders cooling, lubrication oil cooling, cooling and radiation in the engine room). In order to prevent such loss waste heat recovery systems (WHRS) are widely in use in modern vessels. In that manner the heat of exhaust gases is recovering in exhaust gas boilers to produce the steam for different purposes onboard. On this particular type of passenger ship the heat produced from scavenging air and from high temperature (HT) cooling system are recovering for: • Distillated water production (evaporator)   [3] • Heating of sanitary hot water • Heating of air conditioning system (AC re-heating). HT water cooling system on board particular vessel is used for cooling of cylinder liner, cylinder heads, turbo chargers (TC), scavenging air cooler (1 st stage) and then to heating of evaporator, sanitary hot water andAC re-heater). Finally, the water is returning to engine or mixed with low temperature (LT) cooling system depending on outlet temperature after waste heat recovery. LT cooling water system is used for cooling of generators, scavenging air (2 nd stage), lub-oil cooling and cooling of HT water system over mixing valve.
Although some heat is recovering in that systems it can be seen that automatic temperature control parameters in the diesel engine cooling system might be optimized to increase energy effi ciency and fuel economy.

Methodology
The cooling system of each of the six Wärtsilä 12V46 diesel engines consists of the following components ( Fig. 1): Red line -HT water cooling system Violet line -preheating Blue line -LT water cooling system Light blue line -connections to expansion tank Figure 1: Diesel engine fresh water cooling system (Source: authors -adopted from [4], [5]) 1. expansion tank 2. automatic three-way valve for regulation of LT water temperature 1 3. fresh water (FW) cooler 4. air vent tank 5. LT water circulation pump for scavenging air and lubricating oil cooling (attached to the engine) 6. automatic three-way valve for regulation of LT water temperature 2 7. LT scavenging air cooler (2 nd stage) 8. lubricating oil cooler 9. LT water circulation pump for generator cooling (driven by electromotor) 10. LT generator cooler 11. automatic three-way valve for regulation of HT water temperature 1 12. automatic three-way valve for regulation of WHRS 13. HT water circulation pump (attached to the engine) 14. HT scavenging air cooler (1 st stage) 15. automatic three-way valve for regulation of HT water temperature 2 16. evaporator (1 st stage of WHRS) hot water heating (2 nd stage of WHRS). The thermal effi ciency of the diesel engine cooling system is (Fig. 1): where: -mass fl ow through waste recovery system -mass fl ow through engine cooling system c W -specifi c heat capacity of cooling water Δt WHR -temperature difference WHR system Δt ECW -temperature difference HT/LT cooling system Due to equal mass fl ow ( = ) the relevant formula is: Useful power (P) or thermal heat recovered (THR): Where P HT is power from engine HT cooling system (jacket water and charge air HT circuit). The waste heat in the HT cooling water can be used for fresh water production, central heating, fuel tank heating etc. The heat available from HT cooling water is affected by engine load and ambient conditions. Recoverable heat is reduced by circulation to the expansion tank, radiation from piping and leakages in temperature control valves. Data provided by the manufacturer for heat bal- Figure 2: Diesel engine HT fresh water cooling system (Source: authors -adopted from [4], [5])

Temperatures recorded on board:
Temperature before cylinders t 1 72°C   ance at 100% load for diesel engine 12V46F taken from [6], and recalculated for engine load at operational condition -6 (three diesel generators at 72 % load). P H -power required for water production, hot water heating (sanitary) and air conditioning (re-heating) in operational condition -6 are taken from Table 1.

Optimization
It is common practice on board that there is no any in-tention of the engine crew to optimize waste heat recovery system of scavenging air cooling or HT/LT fresh water cooling. With correct selection of parameters ("set points") in automated control of automatic three-way valve (11,12 and 15), (Fig. 2) it is possible to optimize the system. Improvement in the thermal effi ciency and reduced fuel consumption might be achieved through temperature adjustment as shown in the following tables ( Table 2, 3 and 4).

Temperatures recorded on board:
Temperature before cylinders t 1 75°C

RESULTS AND DISCUSSION
The settings of the control parameters in the automatic temperature control system before and after optimization as well as both thermal effi ciencies are shown in Table 5.
Although it is theoretically possible to adjust parameters in such way that there will be no heat loss at all (if Δt WHR = Δt ECW ) it is obvious that such recovery cannot be achieved in practice. Due to that reason, the parameters are to be selected on highest possible level allowed by manufacturer with maximum savings.
The difference obtained in reused power is: The recovered heat as useful power can be presented through savings in daily cruising fuel consumption (FCd) when running one of engines with specifi c fuel consumption (SFOC) of 200 g/kWh as: Considering global average bunker price [7] for Intermedial Fuel Oil 380 (IFO 380) that is 463.50 USD/t daily savings on cruising will be 7282 USD (or approximately 2.6 mil USD/year) which is quite signifi cant for any company.

CONCLUSION
Taking into consideration development of environmental legislation as well as capital and operational expenses for ship owners to comply with it is obvious thatenergy effi ciency of the ship becomes more important. Traditionally, the Chief Engineer on board will keep the settings of the automatic temperature control system of the diesel generator HT/LT water cooling system at the same values (or as close as possible to the minimum deviation) as it was set during the trial run or at the values transmitted during the "Chief Engineers' handover protocol". This papershows that signifi cant savings might be achieved through optimization of parameters in automatic temperature control of diesel engines HT/LT cooling water system. Different settings are resulting with different thermal effi ciencies. Consequently, recovered heat reduce fuel consumption and increases energy and costs effi ciency. However, it is to be noted that before attempting of any parameter adjustment, the mechanical and physical condition of all elements included into system (engine, coolers, pumps, regulation valves, …) must be carefully examined as well as operational condition in sailing area. Further research will be focused on cruising speed optimization respecting diesel electric propulsion.