Fuel-Saving Potential of Different Bulk Carriers using Air Lubrication Systems

1 Fuel-Saving Potential of Different Bulk Carriers using Air Lubrication Systems Shibo Zhao 1,* Kayvan Pazouki 1 and Rosemary Norman 1 1 Newcastle University, Newcastle upon Tyne, UK Abstract. Due to the impact of global warming, there is an increasing motivation to improve the energy efficiency of propulsion systems or use new technologies to reduce ship energy consumption. Air lubrication systems (ALS) have been proposed as a promising energy-saving technology that can effectively reduce fuel consumption and greenhouse gas emissions of ships. However, the current evaluation indicators for ALS to reduce ship energy consumption mainly use power saving rate or drag reduction rate, which cannot intuitively reflect the fuel saving effect of the entire ship. At the same time, the fuel saving effect of ALS on different ship types may also be different. This paper employs the Holtrop method to estimate ship resistance and extends the drag reduction rate obtained from experimental calculations to full-scale with the application of an air lubrication system. The main engine output power is determined based on the force equilibrium principle in steady sailing, while also considering variations in diesel generator load from the air lubrication system. A regression analysis is conducted to establish the relationship between fuel consumption and the load on both the main engine and diesel generators. Furthermore, a gray-box ship fuel consumption model incorporating air lubrication technology is developed using MATLAB/Simulink for simulation. By applying air lubrication technology to six different types of bulk carrier - Small, Handysize, Handymax, Panamax, Capesize and VLBC - the fuel saving effects of different ship types when using ALS are compared. The results show that VLBC bulk carriers achieve the highest fuel savings at higher speeds, while smaller ship types exhibit more significant drag reduction effects. Notably, small bulk carriers can achieve a fuel saving rate of up to 16.3% at a speed of 14 knots. Keywords: Air Lubrication System, Modelling, Simulation, Bulk carriers. 1 Introduction Due to the impacts of global warming and air pollution, various regulations and standards to limit the emission of greenhouse gases and air-quality pollutants have been formulated and implemented [1]. As restrictions on carbon emissions from ships become increasingly stringent, the shipping industry is actively adopting new technologies to comply with the regulatory requirements [2]. The air lubrication system (ALS) is an energy saving device that reduces the frictional resistance of the hull by forming a layer of microbubbles at the bottom of the hull, thereby reducing the power demand of the main engine (ME) and fuel consumption [3]. ALS demonstrates multiple comparative advantages over other energy saving devices. First, its operational performance is only minimally affected by environmental conditions, which gives it broader applicability compared to climate-dependent technologies such as wind-assisted propulsion. Second, the system requires the installation of air injection devices only along the bottom of the hull. This arrangement does not interfere with deck operations or reduce cargo hold capacity, thus minimising negative impacts on the vessel’s operational efficiency. Third, the overall system weight is relatively low. In contrast to large-scale energy-saving equipment such as sails or waste heat recovery systems, ALS imposes limited additional weight on the vessel. This helps avoid increased fuel consumption that may result from higher deadweight. In addition to reducing greenhouse gas emissions, hull air lubrication can also help mitigate underwater noise by minimizing vibrations, engine noise, and the accumulation of marine organisms [4]. Due to these technical advantages, ALS has attracted more and more attention from the shipping industry and researchers. Kodama et al. conducted experiments using model ships, confirming that bubbles reduced both the total resistance acting on the model and the local friction acting on the ship's bottom [5]. Park et al. conducted an experiment on an oil tanker model, achieving a drag reduction of 18.1% by selecting the optimal air injection * Correspondence to: [email protected] 16th International Symposium on Practical Design of Ships and Other Floating Structures PRADS 2025 Ann Arbor, MI, USA, October 19th – 23rd 2025 2 configuration and the distribution ratio between two injectors [6]. Kim et al. built an ALS energy-saving model, which showed a potential net power savings rate of 3-24% for the global fleet [7]. Although research on air lubrication system has been relatively extensive, current studies primarily use indicators for the potential for an ALS to reduce ship energy consumption mainly use power saving rate or drag reduction rate. However, these metrics do not intuitively reflect the fuel saving effect of the whole ship. At the same time, the fuel saving effect of an ALS may also vary for different ship types. Therefore, to gain a more comprehensive understanding of the application prospects of ALS, this study compares and analyses the fuel saving effect of various types of bulk carrier. This will allow shipping companies to better evaluate the application value of air lubrication systems for different bulk carriers, thereby effectively reducing fuel consumption and improving the economic benefits of overall operations. The rest of this paper is organised as follows: The materials and modelling method will be introduced in Section 2. The simulation results of fuel saving using air lubrication systems on different ships are analysed in Section 3. Section 4 presents the conclusions, summarising the fuel saving potential of using ALS on six different bulk carriers. 2 Materials and methods 2.1 Ship Specifications Six different types of bulk carrier are used as reference ships in this study - Small, Handysize, Handymax, Panamax, Capesize and VLBC. The dimensions, size and ME Maximum Continuous Rating (MCR) Power parameters of the reference ships are shown in Table 1. Table 1. Main parameters of the target ship Classes Dimensions (L×B×D, m) Size (DWT) ME MCR Power (kW) Small 115×15.26 ×11.5 14500 1×5500 Handysize 170×26.3 ×10 33500 1×8250 Handymax 190×32.26 ×11.5 53000 1×10500 Panamax 225×32.3 ×13.1 71000 1×11500 Capesize 285×45 ×18 172000 1×18000 VLBC 300×50 ×18.73 205000 1×20900 The electrical power requirements of different types of bulk carrier using air lubrication systems, Pg, can be calculated using Eq. (1). 𝑃 𝑔 = 𝑃 𝑆 + 𝑃 A,L (1) where PA,L is the electrical power requirement of the air jet pump when using air lubrication technology and PS is the power requirement of the bulk carrier when sailing at sea, as shown in Table 2 [8]. Table 2. Bulk carrier power requirements Vessel Power demand (kW) Type Size (dwt) Berth Anchor Man. Sea 0-9999 110 180 500 190 10000-34999 110 180 500 190 35000-59999 150 250 680 260 60000-99999 240 400 1100 410 100000-199999 240 400 1100 410 Bulk carrier 200000-+ 240 400 1100 410 3 2.2 Ship Resistance In this paper, the resistance mainly considers the hydrostatic resistance. The hydrostatic resistance refers to the resistance generated by the water on the hull when the ship is sailing in calm water. According to the Holtrop resistance estimation method, the ship's calm water resistance can be expressed as Eq. (2) [9]. 𝑅 𝑡 = 𝑅 𝑓 (1 + 𝑘 1 ) + 𝑅 app + 𝑅 𝑤 + 𝑅 𝑏 + 𝑅 tr + 𝑅 𝑎 (2) where Rt is the total hydrostatic resistance, Rf is the frictional resistance, k1 the viscous resistance factor from different ship types, Rapp is the appendage resistance, Rw is the wave-making resistance, Rb is the bulbus bow resistance, Rtr is the transom resistance and Ra is the model correlation resistance. (1) Frictional resistance Frictional resistance is the resistance due to the friction of the water flow against the surface of the hull. This part of resistance usually accounts for a larger proportion of the total resistance. The frictional resistance can be expressed as Eq. (3) [9]. 𝑅 𝑓 = 1 2 𝐶 𝑓 𝜌𝑆 𝑉 2 𝑠 (3) where Cf is the coefficient of frictional resistance, ρ is the density of seawater, S is the wetted area, and Vs is the ship speed through water. According to the calculation guidelines recommended by ITTC in 1957 [9], Cf can be calculated by the Eq. (4). 𝐶 𝑓 = 0.075 ( 𝑙𝑜𝑔 10 𝑅 𝑒 ― 2 ) 2 (4) where Re is the Reynolds number, which can be obtained by Eq. (5). 𝑅 𝑒 = 𝑉 𝑠 𝐿 wl 𝜈 (5) where v is the dynamic viscosity of water and Lwl is waterline length. (2) Appendage resistance Appendage resistance refers to the resistance or drag caused by the presence of the parts or appendages of a ship that extend into the water, such as the bilge keels, rudder, propeller, or any other protruding parts. The formula used here for calculating the appendage resistance is given by Eq. (6) [9]. 𝑅 app = 0.5𝜌 𝑉 𝑠 2 𝑆 app (1 + 𝑘 2 ) eq 𝐶 𝑓 (6) where Sapp is wetted surface area of a ship's appendages, 1+k2 is the shape factor of ship appendages. (3) Wave-making resistance Wave-making resistance is the resistance produced by waves generated when a ship moves in water. It is the most important component of resistance at higher speeds, and wave resistance is proportional to the square of the ship's speed and the amount of water displaced by the hull. The formula used here for calculating Rw is [9]: 𝑅 𝑤 = 𝐶 1 𝐶 2 𝐶 5 𝛥𝜌 𝑒 { 𝑚 1 𝐹 𝑟 ― 0.9 + 𝑚 2 𝑐𝑜𝑠 ( 𝜆𝐹 𝑟 ― 2 ) } (7) where 𝛥 is the displacement volume of a ship, in m3, C1, C2, C5, m1, m2 and λ are all coefficients, which are determined by relevant calculation formulas. The formula for the Froude number Fr is as shown in Eq. (8) 𝐹𝑟 = 𝑉 𝑠 𝑔 𝐿 wl (8) 4 where g is the gravitational acceleration, taken as 9.8 m/s2. (4) Bulbus bow resistance Bulbous bow resistance is a term used in ship hydrodynamics to describe the additional resistance or drag created by the bulbous bow on the front of a ship. The bulbous bow is a protrusion or bulb-like shape that extends from the hull of the ship below the waterline. It can be calculated by the following Eq. (9) [9]. 𝑅 𝑏 = 0.11 𝑒 ( ― 3 𝑃 ℎ ― 2 ) 𝐹 𝑟 3 𝑖 𝐴 1.5 BT 𝜌𝑔 (1 + 𝐹 𝑟 2 𝑖 ) (9) where Ph is related to the water immersion depth of the bow, Fri is the Froude number based on the water immersion, ABT is the transverse sectional area of the ship. Since the bulbous bow resistance accounts for a small amount of the total hydrostatic resistance, usually less than one ten-thousandth, the bulbous bow resistance is not considered in the modelling in this paper. (5) Transom resistance Ship transom resistance refers to the resistance or drag created by the flat or slightly curved stern of a ship, which is known as the transom. Rtr can be calculated by the following Eq. (10) [9]. 𝑅 tr = 0.5𝜌 𝑉 𝑠 2 𝐴 𝑇 𝐶 6 (10) where AT is the midship sectional area of the immersed stern, AT=0.051AM=0.051BdCM, CM is the midship section coefficient, C6 is related to the Froude number of the immersed stern, when Frd＜5, C6=0.2(1-0.2Frd), when Frd≥5, C6=0. Frd is the Froude number of immersion. (6) model correlation resistance Ship model correlation resistance refers to the process of comparing the measured resistance of a ship model in a towing tank to the predicted resistance of a full-scale ship. The aim of this process is to validate the accuracy of the ship model and the reliability of the methods used to predict the performance of the full-scale ship. The formula for Ra is [9]: 𝑅 𝑎 = 0.5𝜌 𝑉 𝑠 2 𝑆 𝐶 𝐴 (11) where CA is the correlation allowance coefficient. 2.3 Air lubrication System An ALS uses gas injectors installed at the bottom of the ship to release compressed air, forming a layer of micro-bubbles as a blanket under the hull, thereby lowering frictional resistance. Its main principle is to reduce frictional resistance by reducing direct contact area with the water, that is, by releasing bubbles and covering part of the bottom surface of the hull to reduce the wetted surface area. Due to the complexity of bubble flow, this paper calculates the drag reduction rate by combining the drag reduction effects under different air flow rates (Fig. 1) by Zhao et al. [10]. Based on three different drag reduction zones—microbubble drag reduction, air lubrication layer, and the zone between them—the drag reduction rates are interpolated for different Froude numbers and air injection rates. This approach integrates theory with data to model the air injection drag reduction technology using a gray-box model. 5 Figure 1. The drag reduction efficiency in the experiments at different air flow rates (adapted from [10]) As can be seen from Fig. 1, to better ensure the fluid dynamics similarity between the experiment and the fullscale ship, and to make the analysis of drag reduction efficiency at different air flow rates more scientific and scalable, different Froude numbers are given in the figure to analyse the drag reduction efficiency under different air flow rates. When the Froude number is the same, the full-scale ship speed can be calculated from the model ship speed using Eq. (8). The drag reduction rate ηR using ALS is defined as Eq (12). 𝜂 𝑅 = 𝑅 0 ― 𝑅 𝑅 0 × 100% (12) The required power for air injection is estimated as the power required to compress a given amount of air through a multidirectional process at standard atmospheric pressure [3]. 𝑃 con = 𝑚 𝐴𝑖𝑟 𝜂 𝑐 𝜌 𝑔,𝑎 ⋅ 𝑝 1 ⋅ 𝑛 (𝑛 ― 1) ( [ 𝑝 2 𝑝 1 ] (𝑛 ― 1)/𝑛 ― 1 ) (13) where mAir is the mass flow rate of the injected air, the multiple index n is replaced by the air specific heat ratio k=1.40, ρg,a is the initial density of the compressed air, ηc is the compressor efficiency, p1 is the initial pressure, assumed to be 1atm, p2 is the pressure the gas needs to be compressed to, which can be calculated by using Eq. (14) [3]. 𝑝 2 = 𝑝 1 + 𝜌 𝑠 ⋅ 𝑔 ⋅ 𝑇 + 𝛥𝑝 (14) where ρS is the density of seawater. Since the air injection rate in Fig. 1 is based on an experimental ship model, it needs to be converted into the air injection rate of the actual size ship, which can be obtained through Eqs. (15) and (16) [3]. 𝑡 AL = 𝑄 Air 𝑉 Inflow ⋅ 𝐵 Air (15) 𝑡 AL = 𝑄 Air 𝑉 𝑠 ⋅ 𝐵 Unit (16) where QAir is the volume flow rate of injected air, and BUnit is the width of the injected air unit. 0 2 4 6 8 10 Q (m3/h) -10 -5 0 5 10 15 20 η(%) Fr=0.08 Fr=0.10 Fr=0.12 Fr=0.16 Fr=0.20 6 2.4 Ship fuel Consumption For ships equipped with ALS, a layer of microbubbles is formed under the hull to reduce the resistance encountered during sailing, thereby reducing the propulsion power required from the main engine. When the ship is sailing at a steady speed, the propeller thrust balances the hull resistance, and this relationship can be described by Eqs. (17) and (18). 𝑅 𝐴 = 𝑅 𝑡 ⋅ (100% ― 𝜂 𝑅 ) = 𝑇 𝐸 (17) 𝑃 𝐸 = 𝑇 𝐸 ⋅ 𝑉 𝑆 = 𝑅 ⋅ (100% ― 𝜂 𝑅 ) ⋅ 𝑉 𝑆 (18) where RA is the total resistance using ALS, TE is the effective thrust of the propeller and PE is the effective power of propeller. Due to losses associated with the propeller, the power delivered to the propeller PD must be greater than the effective power of propeller PE. The ratio of the effective power to the delivered power is called the quasi propulsive coefficient ηD, which is usually between 0.55 and 0.65 [11]. Therefore, the power transfer relationships are illustrated by Eqs. (19) and (20). 𝑃 𝐷 = 𝑃 𝐸 / 𝜂 𝐷 (19) 𝑃 𝐵 = 𝑃 𝐷 /( 𝜂 𝐺 ⋅ 𝜂 𝑆 ) (20) where PB is the main engine power output, ηG is the gearbox efficiency, ηS is the shaft transmission efficiency. According to the research by Deng et al., the propulsion efficiency loss using the air lubrication system is less than 1%, indicating that the impact of bubbles on the propeller may be minimal [12]. Based on this finding, and in the interest of model simplicity, this study neglects the variation in propulsion efficiency caused by bubbles. The fuel oil consumption of the main engine can be determined using Specific Fuel Oil Consumption (SFOC) of the main engine and Eqs. (21) and (22). 𝑞 𝑚 = 𝑃 𝐵 ⋅ 𝑔 𝑚 (21) 𝐹 𝐶 𝑚 = 𝑞 m × 𝑡 (22) where q m is the hourly fuel consumption of the ship, g m is the SFOC of the main engine, FCm is the total fuel consumption of the ME, t is the runtime of the engine (in hours). The fuel consumption of the diesel generator (D/G) can be determined using the quadratic regression polynomial of the fuel consumption of the diesel generator set at different loads and Eq. (23). 𝐹 𝐶 𝑔 = 𝑛 ∑ 𝑖 = 1 𝑞 g, i ( 𝑃 𝑔 ) × 𝑡 i (14) where FCg is the total fuel consumption of the D/Gs, qg is the consumption rate (kg/h), i is the number of D/Gs in operation. Overall, the total energy consumption of the ship is given by the sum of the ME fuel consumption and the fuel consumption of the D/Gs, as shown in Eq. (24). 𝐹𝐶 = 𝐹 𝐶 𝑚 + 𝐹 𝐶 𝑔 (14) where FC is the total fuel consumption of the ship. 2.5 Power distribution strategy The electrical distribution system model using the ALS is shown in Fig. 2. 7 Figure 2. Power distribution system model using ALS It can be seen from the figure that three D/Gs are used to power the ALS and other electrical loads on the ship. Due to the small difference in fuel consumption of D/Gs with different installed powers when using air lubrication technology, it is assumed that all six types of bulk carriers are equipped with three 500kW D/Gs, and the D/G fuel consumption using ALS is calculated. In the study by Yiğit et al. [13], quadratic regression polynomials were used for fuel consumption under different loads of 500 kW D/Gs. Their findings showed that operating the generator at 90% capacity, instead of 40%, results in lower fuel consumption and reduced fuel costs. Based on this, the loadsharing limit for the generator is set to 90% [13]. The load sharing practice between three different generators can be seen in Fig. 3. Figure 3. Load sharing practice between generators 3 Results and discussion A ship fuel consumption model for the ship equipped with ALS was developed, and the electrical load after adopting ALS was allocated according to the developed diesel generator power allocation strategy. To compare the impact of different speeds on the fuel efficiency of the ship equipped with ALS, the fuel consumption and fuel savings rates for different types of bulk carriers were calculated at different ship speeds with an air injection rate of 10 m3/h, as shown in Fig. 4 and Table 3. 8 (A) Small (B) Handysize (C) Handymax (D) Panamax (E) Capesize (F) VLBC Figure 4. Comparison of fuel consumption and fuel saving for different ship types and different speeds Table 3. Main parameters of the target ship Classes Fuel saving amount (kg/h) Fuel saving rate (%) Small 128.1 15.9 Handysize 144.2 13.8 Handymax 181.9 13.3 Panamax 190.7 12.3 Capesize 309.0 10.6 VLBC 335.5 10.1 As can be seen from Fig. 4, as the speed increases, the fuel saving efficiency of the six types of bulk carriers rises. This is because as the ship speed increases, the bubbles formed by the air injection are more easily evenly distributed on the bottom of the ship, forming a stable and continuous bubble layer. This not only effectively reduces the frictional resistance between the hull and the water but also significantly enhances the drag reduction performance of the air lubrication system, leading to greater fuel savings. At a maximum design speed of 14 knots, the fuel saving rate varies from 10.1% for the VLBC to 15.9% for the Small sized bulk carrier when using ALS. The VLBC has the highest hourly fuel consumption so, although it has the lowest fuel saving rate at the selected speed, it still saves the most fuel. To compare the impact of different air injection rates on the fuel efficiency of the ship equipped with ALS, the fuel consumption and fuel savings rates for different types of bulk carriers were calculated at different air injection rates with a ship speed of 14 kn, as shown in Fig. 5. As can be seen from Fig. 5, varying the air injection rate from 6 to 10m3/h has little effect on the fuel consumption of each ship type, as this range falls within the air lubrication layer zone. At this stage, a continuous and stable bubble layer has already formed beneath the hull, effectively minimising hull–water contact. Further increases in air injection do not significantly reduce the contact area, resulting in a saturated drag reduction effect and a fuel saving rate that no longer improves appreciably. Additionally, Handysize, Handymax, Panamax, Capesize, and VLBC bulk carriers have the best fuel saving effect when the air injection rate is 10 m3/h. Continuing to increase the air injection rate has limited impact on fuel saving but will increase the D/G load and fuel consumption, resulting in an increase in total fuel consumption. However, the Small bulk carrier reached its optimal drag reduction rate with an air injection rate of 6 m3/h. 0 5 10 15 20 Fuel Saving Rate (%) 10 11 12 13 14 Ship Speed (kn) 200 300 400 500 600 700 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 10 11 12 13 14 Ship Speed (kn) 0 200 400 600 800 1000 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 10 11 12 13 14 Ship Speed (kn) 200 400 600 800 1000 1200 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 10 11 12 13 14 Ship Speed (kn) 200 400 600 800 1000 1200 1400 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 10 11 12 13 14 Ship Speed (kn) 0 500 1000 1500 2000 2500 3000 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 10 11 12 13 14 Ship Speed (kn) 500 1000 1500 2000 2500 3000 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 9 (A) Small (B) Handysize (C) Handymax (D) Panamax (E) Capesize (F) VLBC Figure 5. Comparison of fuel consumption and fuel saving for different ship types and different air injection rate 4 Conclusion The fuel consumption models of six different types of bulk carrier, including small, Handysize, Handymax, Panamax, Capesize carriers and VLBC, when using ALS were developed. The simulation results show that a higher speed may achieve a more significant drag reduction effect. The highest fuel saving rate is for small bulk carriers at 14 kn, with a fuel saving rate of up to 16.3%. The maximum fuel saving capacity is for the VLBC at 14 kn, which is 335.5kg/h. In the air layer drag reduction area of the ship, when the drag reduction rate increases to a certain extent, continuing to increase the air injection rate has little positive effect on fuel saving, and may lead to an increase in total fuel consumption due to the increase in D/G fuel consumption. The future research should focus on optimising the air injection rate for different ship types and operating conditions to achieve a balance between drag reduction and total fuel consumption. Additionally, it is also recommended to explore the long-term operational performance and economic feasibility of ALS under varied sea states and voyage profiles. Acknowledgments Author SZ was supported by grant 202206950022 from the China Scholarship Council. References [1] L.P. Perera and B. Mo. Emission control based energy efficiency measures in ship operations. Applied Ocean Research, 60: 29-46, 2016. [2] V.J. Jimenez, H. Kim and Z.H. Munim. A review of ship energy efficiency research and directions towards emission reduction in the maritime industry. Journal of Cleaner Production, 366: 132888, 2022. [3] J. Jang, S.H. Choi, S.M. Ahn, B. Kim and J.S. Seo. Experimental investigation of frictional resistance reduction with air layer on the hull bottom of a ship. International Journal of Naval Architecture and Ocean Engineering, 6(2): 363-379, 2014. [4] Safety4Sea. Air Lubrication: How Blowing Bubbles under Ships Can Reduce Emissions, Greece, 2023. https://safety4sea.com/cm-how-blowing-bubbles-under-ships-can-reduceemissions/?utm_medium=DNV%20-%20Maritime&utm_campaign=MARANDE%2CBAMaritime&utm_source=linkedin&utm_content=90d3105014b744b7b4fde5c8672526285011444&utm_term=social&fbclid=IwAR1DLxJyO2IinhsRqoTAPcvh_OmCrKLWmRWnxhCAhYOK61TQuKkVg2hzPQ [accessed 24 July 2025]. 0 5 10 15 20 Fuel Saving Rate (%) 6 7 8 9 10 Air injection rate (m3/h) 0 200 400 600 800 1000 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 6 7 8 9 10 Air injection rate (m3/h) 0 200 400 600 800 1000 1200 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 6 7 8 9 10 Air injection rate (m3/h) 0 500 1000 1500 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 6 7 8 9 10 Air injection rate (m3/h) 0 200 400 600 800 1000 1200 1400 1600 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 6 7 8 9 10 Air injection rate (m3/h) 0 500 1000 1500 2000 2500 3000 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate 0 5 10 15 20 Fuel Saving Rate (%) 6 7 8 9 10 Air injection rate (m3/h) 0 500 1000 1500 2000 2500 3000 3500 Fuel Consumption (kg) Fuel Consumption Fuel Saving Rate