SIMULATION OF AUTOMOTIVE ENGINE IN LOTUS SIMULATION TOOLS Ing. Branislav Duleba, PhD. Technical University of Kosice Faculty of mechanical engineering Institute of Technologies and Management Masiarska 74, 040 01 Kosice e-mail: branislav.duleba@tuke.sk Abstract The use of engine simulation tools is an essential tool to the performance engine parts developing process. This simulation and design can drastically reduce time and costs. In this article LES (Lotus engine simulation V5) was used to simulate Subaru EJ20 engine stock and modified. After simulation, real engine was built with selected components and the performance characteristics of engine were measured and compared with outputs of simulation. Key words: engine simulation, LES, Lotus Engine Simulation, EJ20 engine Lotus Vehicle Simulation can be used to specify the torque curve and gearbox specification required to produce a given vehicle performance. Having established a target engine torque curve Lotus Engine Simulation can be used to define the bore / stroke ratio, valve sizes, cam profiles, and intake and exhaust manifold geometry which enable the powertrain unit to meet the performance target. With this first phase of the engine simulation complete the resulting basic engine dimensions, cam period, valve lifts and cylinder gas pressure loading can be fed into the appropriate software for initial component sizing. A starting point for camshaft profile definition is obtained using Lotus Concept Valve Train. This data can be used to set up a valve train sub-system template for use in ADAMS/Engine Valve Train where a full valve train system model can be constructed. INTRODUCTION Computer simulation is now an inextricable component of many automotive engineering projects. At the start of the development of a new engine extensive optimization is performed using performance simulation and base-engine analysis software which directly drives the prototype design function. Various commercial packages have been developed and are available to solve engineering problems related to design and optimization of internal combustion engines (ICEs). There are four primary engine simulation commercial packages used in the automotive industry today: Ricardo Wave (RW), Lotus Engine Simulation (LESoft), AVL fire, and GT-Power. The commercially availability of the analysis codes constituting Lotus Engineering Software have arisen from the successful use of these programs on many powertrain and vehicle projects at Lotus over the past 15 years. These packages are similar in purpose and functionality. They require detailed input parameters to simulate the engine operation in an integrated manner rather than using different subsystems. The Lotus Engine Simulation program is capable of modelling the combustion and gas flow processes, computing the indicated and brake parameters while considering the influence of the heat transfer and the friction phenomena. Lotus Engine Simulation program represents a powerful tool for optimization of engine dynamic parameters and processes. Fig. 1 Inter-relation of Lotus and ADAMS powertrain analysis codes Next pages presents the model building process and simulation of Subaru EJ20 engine (turbocharged 2.0litre Impreza engine), which will be compared to stock parameters. As follows, few chosen parameters will be changed for values of aftermarket racing parts. After simulation, engine was built with use of these components and tested on dynamometer. THE MODEL BUILDING PROCESS AND SIMULATION For simulation, the solver reads a model from a main input file which contains all data required for a simulation (the model network, initial conditions for the flow field and all control data for the run). The solver produces an output file when run. The output file contains information, important in understanding the input, run-time processing and output of a model (time step output, engine 48
summary, fuel burn progress summary, engine geometry, operating conditions, engine cylinder heat transfer, performance). A general flow diagram for the development of a model is shown in Figure 2. Fig. 2 Development of engine model The basic engine data include engine geometry (bore, stroke, connector rod length, compression ratio), engine inertia (mass and inertia of various components), cylinder and valve event phasing. Initial conditions such as exhaust temperatures, intake temperatures, and wall temperatures need to be input as reasonable values. The motion of the piston is calculated based on the data specified for bore, stroke, and connecting rod length. The clearance volume is calculated based on the compression ratio. Once the basic inputs are defined, the advanced inputs need to be defined. These inputs are port flow coefficients, valve lift per crankshaft rotation, combustion and heat transfer modeling (types of models to be used for representing the combustion and heat transfer processes and the surface areas and temperatures of various components within the cylinder, phasing of cylinder firing with respect to TDC). Some intuition is used to determine the parameters due to the large difference in engine operating speed and difference in engine type. To define the operation of the cylinder head, the valve lift per incremental camshaft rotation is defined. The results of valve lift versus incremental camshaft rotation are related to crankshaft rotation based on published valve opening points with reference to crankshaft position. Flow versus valve lift is defined. The input is in the form of flow coefficients or discharge coefficients taken from the empirical data. Fig. 3 LES Combustion chamber tool 49
Tab.1 Main values of stock EJ20 engine Power/RPM 220HP/600 Stroke 75mm Torque 260Nm/6000 Compression ratio 8.0:1 Displacement 1994cc Turbocharger MHI TD05 Bore 92mm TCH pressure 0,8 bar Firs part of model built was to define combustion chamber, what was done in Lotus Combustion Chamber tool Fig.3. After that, type of engine was defined, in our case Boxer engine. After that, more than 300 parameters were defined, like length and type of intake pipes, diameter of throttle body, type and complete map of supercharger, shape and diameters of exhaust, heat transfer model, scavenging model, material types to friction analysis tool and other Whole simulation was set to calculate only the values at 7 exact RPMs (1000-7000, step by 1000). Whole simulation took about 9 hours (3,5GHz X4, 4Gb ddr3). Simulation showed, that maximum power of model engine was 158kW (211,8Hp). Compared to the value specified by the manufacturer, this represents a deviation 8,2Hp, representing a deviation of less than 4% of the difference, which can be considered negligible. This showed that the motor model can be used for further analysis. SIMULATION OF MODIFIED EJ20 ENGINE Next step in model simulation was to build modified engine model. Over 90 parameters were changed compression ratio, thickness of head gasket, diameter of exhaust and intake valves, diameter and type of intake and exhaust, type of turbocharger and its map, complete camshaft profile and valve lift and another. Fig.5 displays the modified camshaft characteristics (related to Brian Crower BC0601). Movement of complete valve train was simulated in Valvetrain tool and is showed on Fig. 6. Fig.5 Camshaft characteristics Fig. 4 Simulation model of EJ20 engine 50
Fig.6 LES Valve train simulation tool Simulation estimated the resulting performance of modified engine with selected components to 345HP (257 kilowatts) and torque of 416Nm. (Fig. 7, Fig. 8). This value corresponds best to the intended use of the vehicle. As the highest speed was chosen value of 7200 rev / min. In practice, the engine can be used in the short term and over that limit. Progress of power and torque is at such a high power output per liter of engine very favorable. Program recorded only 7 points, which were subsequently connected by the graph, the real power curve and torque will therefore have a somewhat different shape. REALIZATION OF ENGINE MODIFICATIONS Objective of the build was engine suitable for everyday use, but the occasional also for competition purposes. Progress of power and torque in this case was as important as its maximum value. Target values were more than 300HP and 400Nm. Simulation showed that these values will be probably exceeded. Only mechanical modification and complete built was realized, complete engine management system was tuned at Red Sun Service, Budapest. Power measurements were performed on roller test MAHA - IW2 that allows performance measurement and tuning the car with four-wheel drive. The original engine block has been replaced by a stronger block from the Japanese version of the Subaru Impreza STI Ra, which is dimensionally identical, but due to a smaller holes for coolant can withstand higher internal pressures. Main internals of engine were replaced: forged pistons Mahle SUB287642I12 for bore 92,5mm and forged Manley 14024-4 con rods, which can handle the power improvement. Crankshaft was left stock, only polished. Head gasket Cometic and head studs ARP can also handle up to 600+Hp. Biggest differences can be found in cylinder head assemblyhead was ported and polished, oversized +1 forged valves were installed, camshafts were replaced by Brian Crower BC0601 (10,16mm lift, 272 ), titanium retainers and dual valve springs were installed. Fig.7 Estimated progress of power and torque Fig. 9 Complete engine short block assembly Fig. 8 Simulated performance characteristics of moddified model Main difference was in selected turbocharger original TD05 was replaced by ballbearing Garrett GT2871R. Subsequently, the whole intake and exhaust tract had to be modified (Tomei stainless steel manifold, exhaust pipe diameter change from 45mm to 63,5mm). As injectors the low-impedance RC555 were installed. As seen on Fig.10, the resulting power output from this engine was 327Hp and 410 Nm, what is gain of 112Hp and 105Nm. 51
Fig. 10 The resulting graph of power and torque CONCLUSION The paper has shown how Lotus Engineering Software can be used as an integral part of the powertrain design and development process. Lotus Vehicle Simulation can be used to set engine performance targets required to achieve a stipulated vehicle performance envelope. The quality of engine simulation results is directly related to the effort exerted in assembling the data which comprises the model. Thorough preparation of information describing the engine and its operating conditions is essential to achieving reliable predictions. In this paper, the simulation of stock EJ20 Subaru engine was presented. Model with stock components produced 158kW, what is only 6 less than the original engine. Modified model produced 345HP (257 kilowatts) and torque of 416Nm. On the basis of these results, the complete engine was build. The resulting power output from this engine was 327Hp and 410 Nm, what is gain of 112Hp and 105Nm compared to stock engine and difference only 18Hp compared to modified model. References [1] Pearson, R.J., Bassett, M.D., Fleming, N.P. Rodemann, T.: Lotus Engineering Software An Approach to Model-Based Design, The 2002 North American ADAMS Conference in Scottsdale, Arizona, 2002 [2] Winterbone, D.E., Pearson, R.J.: Theory of engine manifold design: Wave action methods for IC engines. Professional Engineering Publications Ltd, London, 2000. ISBN 1 86058 209 5. [3] Chan, K.Y, Ordys, A., Volkov, K., Duran, O.: Comparison of Engine Simulation Software for Development of Control System, Modelling and Simulation in Engineering, vol. 2013, Article ID 401643, 2013. doi:10.1155/2013/401643 [4] http://performancetrends.com This article was created by implementation of the grant project VEGA 1/0824/12. 52