Structural design of a two-stroke diesel engine

Transcription

1 Structural design of a two-stroke diesel engine Henrik Andersson, MAN Diesel, Copenhagen, Denmark Abstract Design of a large two-stroke ship diesel engine differs in one fundamental point from design of smaller engines: The prototype engine is sold. This together with the fact that an engine failure can be life threatening at sea means that smaller design change increments are usually taken. On the other hand, loading is very well defined as the engine usually runs at maximum load, 100%. By comparing strain gauge measurements on existing engines with simulations, the complete simulation chain is tested. This includes the meshed geometry, material data, structural and thermal load application, post processing routines and experimental methods. Today, the difference between the measured and calculated strain history over an engine revolution is so small that again larger design increments can be allowed. The new engine series, ME-B, includes a few large design increments. One of the most striking is the now welded main bearing support. The paper at hand describes the simulation process, its objective, what tools are being used, some of the design philosophy and some results. The design objective is to make the main bearing support as cheap as possible while still maintaining a high degree of reliability. The results show that the most severely loaded parts experience the same load as before, however it is now made of a rolled plate as compared to cast steel. As for all welded designs, the loading on the welds need to be carefully simulated. Here, it is shown how the HyperWorks suite fits into the environment where UG, in-house codes for loading, Abaqus and FE-safe are also present. A second example that will be shown is the thrust bearing design that includes elasto-hydro-dynamic oil film calculations and some HyperStudy optimisation. [LDD1/HRA] MAN Diesel A/S 2007/08/31 1 Structural design of a two-stroke diesel engine Presented by Henrik Andersson, Ph.D. New Design Department, Research & Development MAN Diesel A/S EHTC, October 2007, BERLIN [LDD1/HRA] MAN Diesel A/S 2007/08/31 2 1

2 MAN Diesel Group Locations in Europe Employees worldwide: 6,400 Great Britain MAN Diesel Ltd. Service Frederikshavn Copenhagen Denmark MAN Diesel A/S Service, two- and four-stroke engines, propellers Holeby Stockport Colchester Rostock Hamburg France MAN Diesel SA Service, four-stroke engines Villepinte/Paris Saint-Nazaire Jouet Augsburg Velká Bìteš Czech Republic PBS Turbo s.r.o. Turbocharger Status: 12/05 Germany MAN Diesel SE Service, four-stroke engines, turbocharger (GMC/PDP) [LDD1/HRA] MAN Diesel A/S 2007/08/31 3 Introduction: The Product Large Two-Stroke Diesel Engines 10K98MC-C and 6S35MC Two-stroke Crosshead Turbo charged Low speed, RPM Bore from 35 cm to 108 cm Stroke up to 3.45 m Up to 14 cylinders Engines range from to BHP Up to 2800 tonnes Continuous demand for cost reduction Reliability is crucial [LDD1/HRA] MAN Diesel A/S 2007/08/31 4 2

3 Market Shares Worldwide Marine Diesel Engines Diesel Engines Low-speed diesel engines for ships ordered in 2006 (Jan.-Sept.) 87% Medium-speed diesel engines Orders June 2005 to May % 77% 4% MAN Diesel Wärtsila Mitsubishi 9% 66% MAN Diesel Competitors (Wärtsila, Cat/MaK) Source:: Lloyd`s Register Fairplay Ltd. Source: Diesel and Gas Turbine, Prop. and aux. engines > 0.5 MW (GK/MM) [LDD1/HRA] MAN Diesel A/S 2007/08/31 5 Introduction Overview of the two-stroke crosshead cycle Main bearing design today Shell Cap [LDD1/HRA] MAN Diesel A/S 2007/08/31 6 3

4 Introduction Stress / strain amplitude as calculated Main bearing #6. Standard gauges fore side (aft cyl 5) strain x 1e6 (-) Angle wrt cyl 1 TDC (deg) BEA501 BEA502 BEA503 BEA504 BMA501 BMA502 BMA503 BMA504 BEA502 56±112 BEA ±101 BEA504-94±154 BMA ±147 BMA502 81±101 BMA ±100 BMA504-87±145 [LDD1/HRA] MAN Diesel A/S 2007/08/31 7 Problem definition Work flow Main dimensions of the engine is decided This incudes cylinder distance, stroke, bore and Pmax A 3D sketch of the bed plate, including the main bearing is made The crankshaft is more or less designed Loading for the main bearings are calculated as a function of crankshaft angle Our work begins... Objective: The new design should among other things: Be possible to manufacture both from a rolled plate and a casting Include as simple welding as possible Provide sufficient safety against fatigue failure [LDD1/HRA] MAN Diesel A/S 2007/08/31 8 4

5 Analysis Stress analysis of the main structure Gas forces Cam shaft loads Guide shoe forces Random forces from vibration Axial vibration loads Main bearing loads In this case the load is applied as 36 load steps from 5 to 355 degrees after cylinder 1 TDC by use of an in-house program. [LDD1/HRA] MAN Diesel A/S 2007/08/31 9 Analysis Stress analysis of the main bearing Shell elements Solid elements [LDD1/HRA] MAN Diesel A/S 2007/08/

6 Analysis Example of shapes Width of the main bearing For the main bearing there are a few shapes that are possible to alter, e.g. the width and height of the thick plate. Height of the main bearing [LDD1/HRA] MAN Diesel A/S 2007/08/31 11 Analysis Weld analysis of the main bearing The welds are analysed by several different methods. In this case: 1.Finding the stress amplitude by use of FE-safe 2.Finding the two dominating crankshaft angles and then do a simple subtraction => this equals max principle and the stress range. This gives an overview of the stress direction. Parallell or perpendicular? 3.Doing a hot spot extrapolation and using FAT 100 with a safety factor 1.5. [LDD1/HRA] MAN Diesel A/S 2007/08/

7 Results 25 mm thick plate 45 deg slope 170 mm thick plate R40 rounding 10 mm nose [LDD1/HRA] MAN Diesel A/S 2007/08/31 13 Analysis Thrust bearing 1. The structure is divided into two components - the crankshaft with the thrust collar UG / HyperMesh - the structure with the bearing segments 2. Shapes are generated HyperMesh 3. Optimisation criteria are set Shapes are applied 4. The stiffness matrices are being extracted by use of *SUBSTRUCTURE GENERATE *SUBSTRUCTURE MATRIX OUTPUT HyperStudy Abaqus 5. Elasto hydro dynamic calculation In-house code of the oil film using the mean thrust Output: Oil film thickness, Oil film pressure 6. The solution is mapped back to the structure models In-house code 7. A structural calculation of the stress and displacement Abaqus 8. New shapes are found and point 4 is repeated. HyperStudy [LDD1/HRA] MAN Diesel A/S 2007/08/

8 Analysis Thrust bearing parts Aft thrust segments attached to bedplate Crankshaft [LDD1/HRA] MAN Diesel A/S 2007/08/31 15 Analysis Example of thrust bearing shapes Flange thickness Groove slope When varying collar radius the segment radius and thus MB support need to follow the shapes. [LDD1/HRA] MAN Diesel A/S 2007/08/

9 Analysis EHD calculated pressure on segments The top two segments carry > 40 % of the total load [LDD1/HRA] MAN Diesel A/S 2007/08/31 17 Thrust bearing- Structural stresses EHD pressures mapped onto mesh Bedplate Thrust collar Crankshaft (attached to the propeller) Thrust bearing of cast design These are the mean stresses, the varying stress is function of the mean stress depending upon ship speed, number of cylinders, propeller, etc. [LDD1/HRA] MAN Diesel A/S 2007/08/

10 Discussion and Conclusion Structural design: The main bearing presented will be tested on the first 6S40ME-B engine that will be running on the testbed in November The thrust bearing will run on sea trial in early Strain gauge verification will be extensive on the test bed. Over 100 strain gauges have been specified. No strain gauge verification of the thrust bearing is planned. Software and program environment: The software environment is well functioning It is possible to write in-house codes for special purposes like load application and EHD calculation [LDD1/HRA] MAN Diesel A/S 2007/08/31 19 Coffee break [LDD1/HRA] MAN Diesel A/S 2007/08/