During the last decade, a number of developmental projects have been initiated both in civil as well as military aviation, for Powered Hang Gliders for aerial spraying of pesticides, Small Aircraft, Pilot-less Target Aircrafts and Unmanned Aerial Vehicles. The requirements for all these applications are similar in that the power to weight ratio should be high, specific fuel consumption (sfc) should be low, noise and vibration levels must be low, thermal efficiency must be reasonably higher and maintenance and serviceability should be acceptable. A prominent contender that can meet all the above requirements is the Wankel engine. In recent years, they are found increasingly in roles where their compact size and quiet running is important, notably in Unmanned Aerial Vehicles (UAVs).13; At present, the National Aerospace Laboratories is involved in the indigenous development of Wankel engines to support the nationx2019;s UAVs program. A 55 hp single rotor, liquid cooled, Wankel engine was designed, developed and the 1st Proto type (PT1) was successfully tested. This paper describes the developmental work carried out on the Wankel engine and the performance validation of the engine

Isaac, JJ

Kumar, K Satish

Mithran, AJS

Murthy, YVS

Pillai, KM

Sinha, UK

Varadarajan, MN

William Grips, VK

English

NAL-IR

   DESIGN AND DEVELOPMENT OF AN INDIGENOUS 55 HP  WANKEL ENGINE  K.Monickavasagom Pillai, A.J. Steve Mithran, V.K. William Grips, K. Satish Kumar, Umesh Kumar Sinha, M.N. Varadarajan, J.J. Isaac and Y.V.S.Murthy1 National Aerospace Laboratories, Bangalore, India, kmpillai@css.nal.res.in (Council of Scientific & Industrial Research, India) 1Aeronautical Development Establishment, Bangalore.   ABSTRACT: During the last decade, a number of developmental projects have been initiated both in civil as well as military aviation, for Powered Hang Gliders for aerial spraying of pesticides, Small Aircraft, Pilot-less Target Aircrafts and Unmanned Aerial Vehicles. The requirements for all these applications are similar in that the power to weight ratio should be high, specific fuel consumption (sfc) should be low, noise and vibration levels must be low, thermal efficiency must be reasonably higher and maintenance and serviceability should be acceptable. A prominent contender that can meet all the above requirements is the Wankel engine. In recent years, they are found increasingly in roles where their compact size and quiet running is important, notably in Unmanned Aerial Vehicles (UAVs).   At present, the National Aerospace Laboratories is involved in the indigenous development of Wankel engines to support the nation’s UAVs program. A 55 hp single rotor, liquid cooled, Wankel engine was designed, developed and the 1st Proto type (PT1) was successfully tested. This paper describes the developmental work carried out on the Wankel engine and the performance validation of the engine.   1. INTRODUCTION     Aerospace propulsion demands a power plant with the minimum weight possible without sacrificing on torque and power. Out of the various possible options, the Wankel engine has been actively considered for powering light aircraft and UAVs. This is because of its salient features like high power to weight ratio, good anti knock properties and smaller size when compared to a piston engine of the same class. NAL has acquired the necessary expertise in design and development of rotary combustion engine over many years due to the developmental work carried out on an air-cooled 35hp Wankel engine. Due to the expertise gained over the years, NAL was entrusted with the design and development of a 55hp liquid cooled Wankel engine for a UAV application.   2. INDIGENOUS ENGINE DESIGN 2.1 Design Methodology     The brief specifications of the indigenous 55hp Wankel engine is given in Table 1. The first step in any engine design is sizing the engine i.e. deriving the basic parameters of the engine.  Table 1 Brief specifications of the proposed 55 hp engine Type Single rotor Wankel engine Cycle Otto cycle Power 55 hp (41 kW) @ 8000 rpm at ISA-sea level (without exhaust muffler) Compression ratio 9.2 Housing Cooling Water-Glycol mixture Rotor cooling Air Lubrication Total loss forced lubrication system Ignition CDI system Carburettor Diaphragm type Specific fuel consumption 335 to 365 g/ kWh (0.55 to 0.60 lb/ hp h Engine weight 35.6 kg Proceedings of the International Conference on Aerospace Science and Technology                                                                          26 - 28 June 2008, Bangaloire, India The following three step design methodology has been followed for the present 55 hp Wankel engine development. i.From  first principles      The thermodynamic cycle analysis and design of the engine components have been derived from first principles. ii.Knowledge base available Since NAL had gained expertise in developing a 35hp air cooled engine, the knowledge base was utilised for the present development. iii.Reference to the proven engines A survey was made to analyse proven designs of rotary combustion engines close to the required power output range and with modifications of the geometry and/or other parameters in order to obtain the required power output and performance.   2.2 Basic Parameters     The basic parameters[1] of a rotary combustion engine design are displacement, eccentricity, rotor radius, rotor radius and chamber width. These parameters were calculated [5,6] to meet the power output of the 55 hp engine and are given in Table 2. Table 2   Summary of geometric parameters of the 55 hp engine Sl No. Parameter  1. Eccentricity (e) 11.6 mm 2. R/e 6.12 3. Rotor radius (R) 71 mm 4. Trochoid profile shift (a) 0.5 mm 5. Chamber width (w) 75.2 mm 6. Displacement (Vs) 324 cm3 7. Recess volume 15.82 cm3  2.3 Thermodynamic Cycle Analysis     After arriving at the above basic parameters to make sure that above parameters could develop the required power and to also design the cooling system, a detailed thermodynamic cycle analysis of the engine was carried out using the Wankel engine cycle analysis program exclusively developed for analysing the Wankel engines[4]. This confirmed that the selected parameters could produce the specified power.[5,6]    2.4 Major Components of the Wankel engine     The major components of the Wankel engine are shown in the exploded view (fig 1). A detailed design and analyse of all the major components were made.  Fig. 1 Exploded view of the 55 hp indigenous Wankel engine Proceedings of the International Conference on Aerospace Science and Technology                                                                          26 - 28 June 2008, Bangaloire, India 3. ASSEMBLY AND TESTING     The core engine has the following sub-assemblies: Drive side housing assembly, trochoid housing assembly, eccentric shaft assembly, rotor assembly, non-drive side housing assembly, water pump assembly, fan assembly. All the components for the PT1 engine were indigenously manufactured to accomplish the above sub-assemblies. The complete engine assembly was made at the Rotary Engines and Ceramics Application Laboratory (RECAL) in the Propulsion Division. After satisfactory motoring trials of PT1 on the motoring rig, the engine was shifted to the dynamometer test bed. Components like carburettor, ignition system, radiator and lube oil pump were provided by the Aeronautical Development Establishment (ADE), Bangalore since they were not in the scope of NAL for the present development program. After precise alignment of dynamometer shaft with the engine shaft, the performance tests were conducted.  4. EXPERIMENTAL SET UP The following line diagram (fig 2) shows the experimental set up for the performance test and the various parameters to be measured during the testing. 6 7 129 1011853 4 2 1 1 1. Torque display  2. Speed display  3. Dynamometer   4. Engine   5. Radiator   6. Fuel flow sensor   7. Fuel pump   8. Fuel tank   9. Engine exhaust temperature 10. Coolant out temp sensor   11. Coolant in temp sensor   12. Rotor cooling air out temperature sensor.  Fig.  2  Schematic of the experimental set up  Figure 3 shows the engine mounted on the dynamometer test rig before the performance test.                              Fig.  3   PT Engine mounting on the dynamometer bed  The dynamometer specifications are given below: Make: SAJ, Pune, Capacity: 80 kW, Type: Eddy current The dynamometer is equipped with a non-contact type speed pick up to measure the speed and the load cell to measure the engine torque. Through the dynamometer control system the load acting on the engine could be varied. The cooling water inlet and outlet temperature and the rotor cooling air temperature were Proceedings of the International Conference on Aerospace Science and Technology                                                                          26 - 28 June 2008, Bangaloire, India measured by RTD (Pt 1000) sensors. The engine exhaust gas temperature and intake air temperature were measured by thermocouples.  The fuel flow rate was measured by a volume flow meter.  100LL AVGAS was used as fuel for the testing. The dynamometer and all the instruments were calibrated before testing PT1engine.  5. RESULTS AND DISCUSSIONS     The dynamometer test results are given in the table 3. Since the engine was tested at Bangalore conditions, the brake power output from the engine was corrected to sea level condition as per the Indian Standard 10000[2] Test conditions: Ambient pressure = 910 mbar, Ambient temperature = 26 oC, Relative humidity = 48.5%  Inlet air temperature = 50 oC  Table 3   Dynamometer performance test results of the 55 hp indigenous PT1 Wankel engine Corrected parameters at ISA conditions  Sl No. Speed Torque EGT Fuel flow Brake Power sfc Brake Power sfc   RPM N m o C Lit /h kW hp kg/ kW h kW hp kg/ kW h 1 4500 32.0 630 10.53 15.08 20.24 0.50 19.72 26.44 0.47 2 5000 33.4 656 11.33 17.49 23.47 0.46 22.87 30.67 0.44 3 6000 35.5 727 14.43 22.31 29.94 0.46 29.17 39.11 0.44 4 6500 36.5 772 16.04 24.84 33.35 0.46 32.49 43.57 0.44 5 7000 37.0 798 16.82 27.12 36.41 0.44 35.47 47.56 0.42 6 7500 36.6 827 17.81 28.75 38.58 0.44 37.59 50.41 0.42 7 8000 36.0 856 18.06 30.16 40.48 0.43 39.44 52.89 0.41 8 8101 35.8 870 18.32 30.37 40.77 0.43 39.72 53.26 0.41  Figure 4 shows the variation of brake power and sfc with speed at the Wide Open Throttle (WOT) condition. 0.650.700.750.800.850.900.951.001.051.101.151.201.250510152025303540455055600 1000 2000 3000 4000 5000 6000 7000 8000 9000Brake Power in hpSpeed in RPMbhp sfc Fig.  4   Variation of power with engine speed at Wide Open Throttle (WOT) condition  Proceedings of the International Conference on Aerospace Science and Technology                                                                          26 - 28 June 2008, Bangaloire, India The above results clearly show that the brake power output of the indigenous PT1 engine is around 53 hp, which is very close to the initial specified power. The specific fuel consumption (sfc) was 0.41 kg/kWh (0.68 lb/bhp h) at 8000 rpm, which is higher than the specified values and this will be addressed in the next proto types. The PT1 engine ran very smoothly throughout the entire operating speed range.   Fig.  5   PT Engine mounting on the thrust cradle  6. CONCLUSION      This is the first step in the indigenous Wankel engine development for UAV application. The indigenous PT1 Wankel engine has been tested extensively on the dynamometer test bed. The engine produced 53.3 hp at ISA condition. The performance test results were quite encouraging, since at the first attempt itself the engine produced close to the designed power. The thrust cradle measurements (Fig 5) which were done after the dynamometer tests also showed that the engine consistently produced the required thrust with the propeller of the intended UAV.   ACKNOWLEDGEMENTS The authors wish to acknowledge the following divisions of NAL and DRDO laboratories i. Propulsion Systems Division, Aeronautical Development Establishment, Bangalore. ii. Engines Division, Vehicle Research and Development Establishment, Ahmed Nagar.            iii. Failure Analysis & Accident Investigation Group, Material Science Division, NAL, Bangalore. iv. Special Purpose Machine Shop, Propulsion Division, National Aerospace Laboratories, Bangalore. v. Regional Centre for Military Airworthiness (Engines), Bangalore. vi. Chief Resident Inspector (Engines), Bangalore. vii. RECAL Project Team, Propulsion Division, National Aerospace Laboratories, Bangalore.  REFERENCES [1]    Ansdale RF. The Wankel RC Engine Design and Performance. Iliffe Books Ltd, London, 1968. [2]    Indian standard IS: 10000, Methods of Testes for Internal Combustion Engines.1980 (2006). [3]  John .B. Heywood. Internal Combustion Engine Fundamentals, McGraw-Hill International Editions, 1988. [4]   Monickavasagom Pillai K, Sivasankaram K and Pai BR. Thermodynamic Analysis of Wankel Engine, Paper   No. B5.4., Proceedings of the Sixth National Conference on Air Breathing Engines and Aerospace Propulsion, Bangalore, 2003. [5] Monickavasagom Pillai K, Satish Kumar K and Pai BR. Preliminary Design Report on Development of Technologies for Rotary Engine Systems, Project Document PR 0413, National Aerospace Laboratories, Bangalore, 2004. [6] Monickavasagom Pillai K, Steve Mithran A.J, Satish Kumar K, Manjunath K Hiremani, Srinivas K, Roshan Antony and Rajesh M. Development of Technologies for Rotary Engine Systems – A Detailed Design Report (Revised), Project Document PR 0505, National Aerospace Laboratories, Bangalore, 2005. [7]    Yamamoto K. Rotary Engine, Mazda, 1981.  Proceedings of the International Conference on Aerospace Science and Technology                                                                          26 - 28 June 2008, Bangaloire, India 

Design and development of an indigenous 55 HP wankel engine

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Design and development of an indigenous 55 HP wankel engine

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