Development of Electric Propulsion Vessels with Contra ... - J-Stage

Development of Electric Propulsion Vessels with Contra-Rotating Propeller

Development of Electric Propulsion Vessels Development of Electric Propulsion Vessels with Contra-Rotating Propeller ＊ with Contra-Rotating Propeller ＊ Yasuhiko Inukai ** Yasuhiko Inukai ＊＊

ABSTRACT

electric propulsion vessel is not widespread.

IHI Marine United Inc. (IHIMU) has developed an environmental-friendly and economically efficient diesel-electric propulsion system with CRP designated as “IHIMU-CRP Electric Propulsion System (IHIMU-CEPS)”. Several vessels with the IHIMU-CEPS have already been delivered and their significant fuel savings have been verified in sea trials. This paper presents an outline of the IHIMU-CEPS and its inherent hydrodynamic performance especially those which are manifested through the self-propulsion factors of the CRP system. 1. INTRODUCTION

To overcome this problem, IHI Marine United Inc. (IHIMU) has combined a diesel-electric propulsion system with CRP and developed an environmental-friendly and economically efficient system as “IHIMUCRP Electric Propulsion System (IHIMU-CEPS)”. Several vessels with the IHIMU-CEPS have been already delivered and their excellent performances were verified on the sea trials. In this paper, outline of the IHIMU-CEPS is presented first and its inherent hydrodynamic performance is discussed based on the model test and sea trial data especially focusing on its large benefit in effective wake, which is one of the self-propulsion factors.

Today, social demands for energy saving and greenhouse gases (GHG) reduction is increasing more than ever. To meet such demands, application of contra-rotating propeller (CRP) will be encountered as one of the solutions. CRP is well known as an efficient energy saving device, which can recover rotational energy loss of forward propeller by aft propeller. Several ocean going vessels equipped with CRP, such as bulk carriers and very large crude carriers, have already been in service successfully and a high energy-saving effect was respectively reported1),2),3). As a whole, CRP can improve the efficiency of the vessel around 10% compared with conventional propeller (CP). Meanwhile, an electric propulsion system is also focused as one of the solutions4) for the aforementioned demands. Japanese government has recommended for ship owners to build the environmental-friendly diesel-electric propulsion vessels called “Super Eco Ship (SES)” since 2005 for Japanese coastal shipping. However, while electric propulsion has many advantages as described later, its fuel efficiency is generally worse than the conventional diesel engine due to the energy conversion loss, which arises in the electric components. And it is one of the reasons why the * **

Received February 16, 2011 IHI Marine United Inc., Tokyo, Japan

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2. IHIMU ELECTRIC PROPULSION SYSTEM (IHIMU CEPS)5) 2.1 Outline of The IHIMU-CEPS Diesel engine direct-driven propulsion system (Figure 2) is a typical and popular system for conventional vessels. The drive power is supplied by a large-size and low-speed main diesel engine directly to propeller shaft. And diesel

－1－日本マリンエンジニアリング学会誌第 00 巻第 00 号 (2005) ― 26 ― 日本マリンエンジニアリング学会誌　第46巻　第３号（2011）

Development ElectricPropulsion Propulsion Vessels Vessels with Propeller Development of of Electric withContra-Rotating Contra-Rotating Propeller

generators are separately equipped for electric equipment such as auxiliary machineries and cargo handling gears. On the other hand, in the electric propulsion system (Figure 3), propellers are connected to electric propulsion motors instead of main diesel engine. The diesel generators driven by small-size and medium-speed generator engines are designed to cover all electrical demands for electric propulsion motors and any other electric equipment in a vessel.

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However, the electric propulsion system has disadvantage for fuel efficiency as previously mentioned. The energy conversion losses is said to reach about 15% as a whole. Therefore, the key point for the application of this system to merchant vessels is to develop energy-saving technology to recover this energy loss. This is the reason why we apply CRP for the IHIMUCEPS. 2.2 Features of The CRP System An arrangement of the electric motor-driven CRP system is shown in Figure 4. The power from twin propulsion motors positioned side-by-side is transmitted to the aft and fore propellers respectively via inner and outer propeller shafts, which are able to rotate independently to each other. The system ensures redundancy in order to secure continuous navigation by use of one propulsion shaft system when malfunctioning occurs on the other shaft. 3. PROPULSION PERFORMANCE OF A VESSEL WITH CRP

This system has several advantages compared with the conventional diesel main engine as follows. - Design flexibility for aft hull forms generally increases because propulsion motors need less space than diesel main engine. - Efficient power management is possible because all necessary electric power is supplied only by diesel generators. - Diesel generator makes noise, vibration and emission of NOx suppressed at a low level. - It has high redundancy because it consists of multi diesel generators and motors. - It is easy to control power, shaft revolution speed and torque with wider range.

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CRP has a long history since John Ericsson’s patent was exhibited in the early 19th century. In a long history, many researchers have made great efforts to clarify the hydrodynamic performance of CRP and revealed that the open water efficiency is much better than CP by experimental and theoretical approach6),7) ( See Figure 5 ). Their efforts greatly contributed to the reduction of fuel consumption for a vessel with CRP. And it is known that not only open water efficiency but also interaction between propeller, hull and rudder, which is so called self-propulsion factors, are changed. Some papers reported effective wake factors for a vessel with CRP were considerably improved from that of CP2),7),8). However, detailed investigation on the self-propulsion factors, especially on the effective wake factor for a vessel with CRP is not yet appeared in the past. It is important to clarify the physical characteristics of this



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factor in order to do the optimum design of CRP successfully. In this section, an example of self-propulsion test results for vessel with CP and CRP are presented first. Next, we applied the momentum theory to clarify the physical meaning of this large wake gain.

out. Propeller shaft revolutions were adjusted to generate the same thrust under the equal advanced speed in open water condition.

3.1 Self-Propulsion Factors Figure 6 shows self-propulsion test results for a model of 2,500m3 chemical tanker with the IHIMU-CEPS delivered in 2008. Model tests were carried out for the same hull shape with CRP and CP respectively for comparison purpose. The diameter of CP was chosen to be the same as the fore propeller of CRP. A number of self-propulsion tests were carried out for other vessels under the SES projects, and the differences between self-propulsion factors of CRP and CP indicated similar tendency, which could be summarized as follows, Effective wake factor (1-we) 1-we of CRP gets better by 10% or more compared with CP. The cause for this difference is closely discussed in the following subsection. Thrust deduction factor (1-t) 1-t of CRP is a few percentages inferior to CP. This phenomena can be explained due to a resistance increase of the rudder by a lack of propeller rotational velocity, which has already been clarified from both experimental and theoretical approaches7),9). Relative rotative efficiency(η R) No apparent change was observed on the factor of η R when CRP and CP are applied respectively. From the overall test results, it is found that the hull efficiency for a vessel with CRP is improved thanks to a large amount of wake gain. 3.2 Effective Wake Gain with CRP8) Both experimental and theoretical investigations were carried out to clarify the physical characteristics of 1-we when CRP is equipped. As for theoretical approach, concept of flow tube diameter based on momentum theory was applied in this study. To confirm the validity of this approach for CRP, flow measurements and self-propulsion tests with different propeller load were carried out. 3.2.1 Flow Measurement in Front of Propeller Flow field in front of propeller was measured at 3 different planes forward from CP and fore propeller of CRP. Calculations based on the infinite theory7) was also carried Journal of the JIME

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Figure 7 shows axial velocity distribution of CRP and CP by measurement and calculation. Further, Figure 8 shows the calculated streamlines through the tip of CP and fore propeller of CRP. From these figures, it was found that flow velocity in front of CRP is lower and the induced velocity



field is smaller than those of CP even if they generate the same thrust.

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where Dp’=flow tube diameter; Dp=propeller diameter (in case of CRP, diameter of fore propeller) ; T=thrust; ρ=water density; A=propeller disk area; V=propeller advance speed; wn=nominal wake fraction and rb=propeller boss radius. Based on the forerunner’s work, we also estimated Dp’ of CRP by applying formula (1). Table 1 shows the comparison of CT and Dp’ between CP and each propeller of CRP. CT of aft and fore propellers is smaller than that of CP because two propellers share total thrust. Particularly, CT of aft propeller is rather smaller than that of fore propeller because it works in an accelerated flow behind fore propeller. Therefore, it can be said that Dp’ of CRP is governed mainly by CT of fore propeller and always smaller than that of CP.

3.2.2 Concept of Flow Tube Diameter It is well known that the induced velocity varies with thrust loading factor (CT). Nagamatsu et al and Adachi expressed the 1-we as a function of CT from the viewpoint of flow contraction effect of propeller10), 11). Especially Nagamatsu introduced a concept of flow tube diameter (Dp’), as shown in Figure 8, by formula (1) derived from momentum theory. And it was found that 1-we had a clear correlation with nominal wake factor (1-wn) which is an integrated value within a disk area of Dp’ 10).

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Subsequently, we compared the relationship between 1- we and 1-wn, which is integrated within disk area of Dp and Dp’ by using formula (3), for our accumulated tank test data. Accordingly, it is found that 1-wn (Dp’) shows clear relationship with 1-we compared with that 1-wn (Dp) as shown in Figure 9. This implies the flow field in front of propeller would cause the difference of 1-we between CRP and CP.



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3.2.3 Self-Propulsion Tests with Different Propeller Load Self-propulsion tests with varying CT of fore propeller of CRP were carried out to clarify the relationship between CT of fore propeller and 1-we. In order to change CT of fore propeller, propeller revolution ratio between aft and fore propeller (Na/ Nf) was adjusted. Figure 10 shows the relationship between 1-we, 1-wn (Dp’) and power ratio of fore propeller to the total power (Pf/ P). It is found that both 1-we and 1-wn of CRP reached to that of CP as Pf/P increased up to 1.0. This indicates 1-we of CRP is strongly influenced by fore propeller load.

very important to consider the interaction between hull and propeller at the design stage. 4. ACTUAL VESSEL’S PERFORMANCE We have made efforts to optimize hull form and interaction between hull and propeller under favor of design flexibility in aft body as stated in 2.1. Designs for several kinds of vessels have been completed and their performances were verified on the sea trials. Table 2 shows the principal particulars of the delivered vessels with CRP. The large-size oceangoing vessels with diesel engine driven are also shown as a reference. During the sea trials, advantage in wake gain appeared in model tests was confirmed by load varying test utilizing the specific characteristics of electric propulsion system. This section presents the actual vessel’s performance confirmed by sea trial.

From the above, it can be concluded that the reason why 1-we of CRP is superior to CP is strongly connected to the fact that the CT of fore propeller of CRP is smaller than CP. Although the design of CRP has been mainly aimed for improvement of open water efficiency until now, it is also

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4.1 Confirmation of Wake Gain by Sea Trial8) As mentioned in the section 2, vessels with the IHIMU-CEPS are easy to change propeller revolution of each aft and fore propeller independently. We carried out speed tests with varying Pf/P like aforementioned model tests for two vessels (Ship A; 1,230m3 chemical tanker and Ship B; 2,200m3 oil product tanker) in order to confirm wake gain for full-scaled vessels with CRP. Propeller revolutions of aft and fore propeller were varied to achieve Pf/P=0.5, 0.7, 0.9, 0.95 by keeping the same total power. In addition, we also carried out a test of aft propeller freely rotated.

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test results, it was found that 1-we is increased as Pf/P increased and reached to the value in case of only fore propeller condition (aft propeller freely rotated). Compared with the normal operating condition at around Pf/P=50%, effective wake was strongly changed by the amount of 7-11%. From the above, theoretical approach described in the section 3.2 was proven to be correct also from sea trial. 4.2 Superiority of The Vessels with The IHIMU-CEPS5) Through the sea trials, the following superiorities of the vessels with the IHIMU-CEPS were verified. 1) Large fuel savings have been achieved by application of CRP and hull form improvement. Figure 13 shows the comparison of the fuel oil consumption between 1,230m3 type chemical tanker with the IHIMU-CEPS and the same sized existing vessel. The fuel oil consumption has been reduced by about 20% compared with the existing vessel. Accordingly, emissions of CO2 and SOx are reduced by about 20%. 2) Emission of NOx has been reduced by about 40%. 3) Vibration and noise in the whole working space have decreased much less than half as shown in Figure 14. 4) The maneuvering performance at low speed has excellently improved due to availability of higher torque driven by the electric motors.

Figure 12 shows the relationship between Pf/P and 1-we derived from sea trial analysis results. Similar to the model

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49-53 5) H.Yamada, H.Miyabe and A.Saeki: Development of DieselElectric Propulsion System For Japanese Coastal Vessels, International Symposium on Marine Engineering, 2009 6) H. Morgan: The Design of Counterrotating Propellers Using Lerbs’ Theory, Transactions of Society of Naval Architects & Marine Engineers, Vol. 68, 1960 7) N. Sasaki: Study on Contrarotating Propellers, Doctor thesis, Kyushu University, Japan, 1990 8)Y. Inukai, F. Ochi: A Study on the Characteristics of SelfPropulsioni Factors for a Ship Equipped with Contra-Rotating Propeller, The first International Symposium on Marine Propulsors, 2009, pp.112-116 9) Y. Ukon, Y. Kurobe, Y. Kawakami, T. Yanagihara, H. Kadoi and T. Kudu: On the Design of Contrarotating Propeller,

5. CONCLUSION

Transactions of the West Japan Society of Naval Architect, 75, 1988, pp. 52-64

IHIMU-CRP Electric Propulsion System (IHIMU-CEPS) was applied to the Japanese coastal vessel market and attained a large amount of fuel oil reduction and GHG emission.

10) T. Nagamatsu and T. Sasajima: Effect of Propeller Suction on

From hydrodynamics point of view, it was clarified that wake gain contributes greatly to fuel savings of a vessel with CRP through the detailed investigation including the sea trial tests.

Based on the Propeller Load Varying Test Concept), Journal of

Wake, Journal of the Society of Naval Architect of Japan, 137, 1975, pp. 58-63 11) H. Adachi, and M. Hinatsu; On Effective Wake (Consideration Kansai Society of Naval Architect, 191, 1983, pp.41-50

The above technology is going to expand its coverage to any type of vessels aiming for environmental protection. Effort will be continued on the optimization of hull-CRP interaction and the development of new concept propulsion system using fuel cell and any other new technologies in the future. REFERENCES 1) S. Nakamura, T. Ohta, K.Yonekura, T.Sasajima and K.Sake:World’s First Contrarotating Propeller System Successfully Fitted to a Merchant Ship, the 11th International Marine Propulsion Conference & Exhibition, 1989, pp.1-14 2) R. Fujino, S. Nishiyama, Y. Sakamoto, S. Ishida and M. Oshima: Development of Contra Rotating Propeller System for JUNO a 37,000DWT Class Bulk-Carrier, Transactions of Society of Naval Architects & Marine Engineers, 198, 1990, pp.77-52 3) Y. Sakamoto, R. Fujino, K. Katsumata and T. Narita: Okinoshima Maru,258 000DWT Contra-Rotating Propeller Tanker, IHI Engineering Review, Vol. 22(4), 1994 4) T. Furuta, M. Watanabe, T. Nakai and H. Miyabe: Development of Electric Propulsion Chemical Tanker with Contra-Rotating Propeller(CRP), IHI Engineering Review, Vol. 40(2), 2007, pp. Journal of the JIME

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