Numerical Investigation of Diesel Engine Characteristics During Control System Development Aleksandr Aleksandrovich Kudryavtsev, Aleksandr Gavriilovich Kuznetsov Sergey Viktorovich Kharitonov and Dmitriy Sergeevich Vornychev LLC TransSensor, 24, st. Geroev-Panfilovtsev, Moscow 125480, Russian Federation. Abstract The goal of this work is to perform numerical investigation of static characteristics and transitional processes of diesel engine at the early stage of control system development in order to obtain initial values for system settings. The subject of this study is modern turbocharged diesel engine with Common Rail fuel equipment for locomotive and marine applications. The method of locomotive characteristic obtaining is provided considering diesel engine operation on minimal specific fuel consumption. Model of diesel engine as a part of locomotive or marine power plant was developed; it allows describing static and dynamic operation modes. Transitional processes of diesel engine due to rotating speed setting change were simulated using developed model. According to the study results, initial settings were obtained for control system: coefficients for proportional-integral regulatory law and degree of air feeding correction on air pressure. Keywords: Diesel engine, control system, static characteristics transitional processes. PROBLEM FORMULATION FOR THE STUDY There is a stage during diesel engine control system development when initial settings of the system should be obtained by means of numerical investigation and hardware-in-loop simulation. It is expedient to obtain values for system settings according to engine operating modes optimization. Fuel economy in steady modes and quality indicators of transitional processes could be criteria for optimization. The form of mathematical model of diesel engine is crucial to numerical investigation. This model should be dynamic and should describe both steady and transitional processes. Convergence of calculations to real engine characteristics relies on features of model configuration. During dynamical engine model design, it is expendable to use the following criteria: model accuracy, development time and model complexity. In dynamical models turbocharged diesel engine is described as complex of interrelated parts: cylinders, turbocharger, intake and exhaust manifolds, fuel equipment and other devices. Each of listed parts is described as a mathematical model in the form of differential and algebraical equations. Equations of mechanical, heat energy and gases mass balances are used for dynamical processes description in elements of turbocharged engine [1-5]. Values of torques and flow rates in dynamical balance equations could be determined on each cycle of diesel engine operation by the means of working process theory using software [6-8]. Such approach features high accuracy but demands significant calculation time. It disallows real-time model performance that is needed for HiL-simulation. Linear model on the base of transfer functions offers the simplest form and minimal calculation time, however such models do not provide required calculation accuracy. Thereby it is necessary to develop integral type models, based on generalized efficiency indicators of working flow without detailed consideration of engine cycles. The main purpose is to find compromise combination of theoretical and empirical approaches for dynamical processes real-time calculation with required accuracy. Reference data acquiring takes significant part in mathematical model development. One of the issues is that engine characteristics which cannot be acquired during static tests are needed for dynamical engine modes description. Special test procedures of engines with dynamical modes imitation are rarely performed due to high costs and other complications. Another issue appears if model designer has no ability to get enough information on engine parts when new engine is at development stage and its characteristics are undefined yet. Mentioned obstacles can be overcome by the method of reference data reconstruction using diesel engine simulation software [9]. SUBJECT OF STUDY AND ITS STATICAL CHARACTERISTIC The simulation subject is 6-cylinder 20/28 turbocharged diesel engine with Common Rail fuel equipment system. ABB turbocharger type A135-H is planned to be used as turbocharger unit. Engine is designed for locomotive, marine and generator applications. Task is set to develop engine control system using numerical investigation to obtain initial settings values. Because engine is at the development stage, its characteristics are not known yet in full. Data reconstruction approach was used to obtain reference data as they required. Values of diesel engine parameters were obtained using Diesel-RK software [6]. Characteristic of the studied engine in coordinates rotating speed n e effective torque M is represented on Figure 1 with curves of constant specific effective fuel consumption g c = 200; 210; 220 g/(kwt*hour). 11560
Figure 1. Characteristic of diesel engine ANALYSIS ON ENGINE OPERATION MODES WITH MINIMAL FUEL CONSUMPTION Let s consider operation features of diesel engine as a part of locomotive power plant. Locomotive power plant is a hybrid device in which energy from diesel engine is transferred to locomotive wheels through electrical transmission. Hybrid power plants have greater flexibility in operating modes due to absence of mechanical connection between engine shaft and wheels. Diesel engine and traction motors can work in different operating modes of rotating speed and torque. Diesel engine operating performance in locomotive power plants in steady modes is described by locomotive characteristic on which engine power corresponds to chosen position of regulation lever (controller). Required power rises as position number increases. Control methods of hybrid power plants with diesel engine as power source control are more diverse comparing to power plants with mechanical transmissions. Locomotive characteristic can be shaped using control system to achieve minimal fuel consumption. Locomotive characteristic for engine performance with best fuel economy must match the curve of minimal effective fuel consumption on the field of engine operating modes. The following method of obtaining such curve is proposed. General characteristic of diesel engine in coordinates rotating speed n e effective torque M is used as reference data along with curve of minimal fuel consumption g e = const (see Fig. 1). Also, curves of constant power N = const are used which have hyperbolic shape in this coordinate system. Fig.1 represented hyperboles of constant values of power N = 1000; 700; 400 kwt. For each power value, a point is defined corresponding to minimal value of specific effective fuel consumption g emin. As it can be seen from Figure 1, engine could provide the same power N by different combinations of rotating speed n e and torque M. Curve of minimal fuel consumption passes through all points corresponding to minimal fuel consumption for each value of power. Hybrid power plant control system specific to locomotives allows engine operation with minimal fuel consumption for different settings of demanded power. To implement this, dependency of rotating speed on demanded power n 0(N) must be obtained. Curve n 0(N) corresponds to the curve of minimal specific fuel consumption g emin on general engine characteristic. Dependency of optimal rotating speed n 0 in the aspect of fuel economy on demanded power N is shown in Figure 2 by the rebuilding of g emin curve. Control system program should be able to vary engine shaft rotating speed on demanded power change according to operator controller positions. 11561
Figure 2. The dependence of the rotation speed of the power DYNAMIC MATHEMATICAL MODEL OF DIESEL ENGINE AND COMPUTER IMPLEMENTATION FOR TRANSITIONAL PROCESSES CALCULATIONS Mathematical model was obtained for studied engine simulation and implemented using MATLAB/Simulink software [10]. Appearance of diesel engine dynamical model implementation with rotating speed regulator is shown on Figure 3. Main parts of model are: cylinder group with crankshaft, turbocharger, intake and exhaust manifolds. Figure 3. Computer implementation of diesel engine mode 11562
The following differential equations are used to describe variation of engine parameters in time. Variation of rotating speed n of crankshaft is described by dynamic balance of torques on engine shaft: dω e dt = 1 I e (M i M loss M load ), where I e moment of inertia of engine shaft with considering moment of inertia of consumer shaft; M i indicated engine torque, M loss torque of internal energy losses; M load torque of energy consumer (engine load). To describe rotating speed variation of turbocharger n t the following equation is used: dω t dt = 1 I t (M t M c ), where I t moment of inertia of turbocharger; M t turbine torque; M c compressor torque. Considering ideal gas law, variation of air pressure in intake manifold p c is described by dynamic balance of air masses passing through intake manifold and consuming by engine: dp c = R at a (G dt V c G e ), in where V in volume of intake manifold; R a gas constant of air; T a air temperature in intake manifold; G c air flow rate through compressor; G d air flow rate through engine. Equation of exhaust gases pressure variation in exhaust manifold p g is obtained in a similar way: dp g dt = R gt g V out (G e + G f G t ) where V out exhaust manifold volume; R g gas constant of exhaust gases; T g exhaust gases temperature in exhaust manifold; G f fuel flow rate; G t gas flow rate through turbine. Parameters on the right sides of differential equations are determined by functional dependencies between working process parameters [1]. For rotating speed of engine shaft stabilization in computer model, PI (proportional-integral) regulator is used it is marked as Controller on Figure 3. Regulating effect h on fuel injection system is formed according to PI regulation law considering rotating speed deviation E from given value: h k E k Edt, p where k p and k i are coefficients of PI regulation law. Numerical investigation of transitional processes of studied diesel engine was performed using developed computer model to obtain initial settings for control system. Requirements to dynamic indicators of control system depend on engine application. Locomotive and marine applications were reviewed in current investigation. i t 0 Typical locomotive power plant contain diesel engine and electrical transmission, current rectifier and traction motors connected to wheels through gearboxes. Model of electrical transmission was connected to model of diesel engine to assist simulation. Due to work focus on diesel engine parameters, generator and traction motors models were simplified. As outcoming parameters of generator model the following parameters were chosen: torque on generator shaft and voltage in motors supply circuit. Incoming parameters are rotating speed of diesel engine shaft, voltage setpoint and current in motors supply circuit. PI regulator is used in generator model to stabilize generated voltage. Model of electromotors is implemented in separate module. Two stabilizers are used in supply circuit the same way as in generator. Incoming parameters of motor model are load torque of locomotive wheels and current in supply circuit next to current rectifier. Electrical processes in electromotor winding are described in separate module. To describe inertial properties of windings in electrical motors models, first-order transfer functions were used taking into account restrictions of electrical parameters. Mechanical inertia of generator rotor was included in summary inertia moment of diesel-generator installation. Locomotive was considered as wheeled installation of given mass with torque applied to wheels. Inertia of locomotive was taken into account in inertia moment of electromotors. Determination of time constants values for different parts of power plant shows that electrical inertia of electrical motors is about two orders of magnitude smaller than mechanical inertia of their rotors. Thus, considering electrical inertia weakly affect transitional processes calculation. Mechanical inertia of components significantly less than inertia of locomotive itself, but it should be considered because of its role in energy transformation process in power plant. In marine power plant, the diesel engine drives ship propeller via gearbox. In computer model, inertia moment of gearbox and propeller was added to inertia moment of engine shaft and load torque was determined using propeller characteristic. During transitional processes calculation for control system of the studied diesel engine, initial values were adjusted for settings that determine dynamic properties of engine as a part of locomotive or marine power plant. These settings include coefficients of PI regulation law. Most typical transitional processes for locomotive applications consider regulation process when rotating speed setpoint is changed. Maximal deviation of the rotating speed and process time were used as transitional processes quality indicators. As a result of calculations, the following values of regulator coefficients were accepted: k p = 0.1, k i = 0.1. Transitional process of engine rotating speed variation using accepted coefficient values represented in Figure 4. The dashed line shows setpoint change, the solid line shows rotating speed variation. 11563
Figure 4. Transitional process Also, quality of transitional processes depends on matching operating modes of fuel equipment and air feeding on dynamical modes. Regulator quickly rises fuel injection quantity with increase of rotating speed setpoint, while air feeding rises slowly due to turbocharger inertia. The simplest method of matching fuel and air flow rates is to correct fuel flow according to boosted air pressure while limiting maximal value of fuel consumption. With increase of boosted air pressure, fuel flow rate also should be increased. Condition of fuel consumption limiting is provision of minimal excess air ratio α min. Correction of fuel flow rate on boosted air pressure leads to deceleration of transitional processes. The more minimal excess air ratio, the better engine operation performance in dynamic mode, but the worse transitional process quality in time. Transitional process simulation using developed model allows estimating effect of permissible minimal excess air ratio on transitional process quality. Transitional processes of rotating speed and boosted air pressure variation in time due to rotating speed setpoint change considering marine diesel application are represented in Figures 5-6. Excess air ratio was limited to α min=1.3 (Figure 5) and α min = 1.5 (Figure 6). Also, another control system settings could be adjusted using transitional processes calculation with developed model. Figure 5. Transitional process 11564
REFERENCES Figure 6. Transitional process CONCLUSION It is expedient to determine initial diesel engine control system settings on early stage of control system development by the means of numerical investigation of static characteristics and transitional processes. In hybrid power plants with diesel engine and electrical transmissions under locomotive operating conditions it is possible to organize engine operation using characteristic of minimal effective specific fuel consumption. Such characteristic could be obtained using the proposed method. Computer model of diesel engine as a part of power plant was developed. It describes both static and dynamic operation modes of engine and contains differential equations of rotating speed, air and exhaust gases pressures variation in time, equations obtained using engine working process theory, and relations between engine parameters. Initial values of control system settings were obtained during transitional process simulation. Considered settings determine the quality of regulation processes and include PI regulation law coefficients, degree of air correction on boosted air pressure etc. [1] Kuznetsov, S. Kharitonov, & D. Vornychev, A mathematical model of a diesel engine for simulation modelling of the control system. Global Journal Of Pure And Applied Mathematics, vol. 12, no. 1, pp. 213-228, 2016. [2] Berber, Mathematical Model for Fuel Flow Performance of Diesel Engine. International Journal Of Automotive Engineering And Technologies, vol. 5, no. 1, pp. 17, 2016. [3] K. Yum, & E. Pedersen, Architecture of model libraries for modelling turbocharged diesel engines. Mathematical And Computer Modelling Of Dynamical Systems, vol. 22, no. 6, pp. 584-612, 2016. [4] D. Yu, A. Hamad, J. Gomm, & M. Sangha, Dynamic fault detection and isolation for automotive engine air path by independent neural network model. International Journal Of Engine Research, vol. 15, no. 1, pp. 87-100, 2012. [5] O. Keita, T. Hedhli, & J. Bessrour, Model for dynamic behavior of the crankshaft of an air cooled diesel engine subjected to severe functioning. International Journal Of Automotive Technology, vol. 15, no. 5, pp. 823-833, 2014. [6] V. Zenkin, & A. Kuleshov, Shaping of inlet ports of a diesel for conditions of high pressure charging and high pressure differentials between a collector and a cylinder. Science And Education Of The Bauman MSTU, vol. 13, no. 10, pp. 43-84, 2013. [7] GT-POWER Engine Simulation Software Gamma Technologies. 2016. Retrieved 19 November 2016, from https://www.gtisoft.com/gt-suiteapplications/propulsion-systems/gt-power-enginesimulation-software/ [8] AVL FIRE. 2016. Retrieved 19 November 2016, from https://www.avl.com/fire2 [9] Kuznetsov, A. Kuleshov, & S. Kharitonov, An initial data reconstruction method for developing mathematical models of diesel engines. Machine building, vol. 5, 49 54, 2014. [10] Simulink - Simulation and Model-Based Design. 2016. Retrieved 19 November 2016, from https://www.mathworks.com/products/simulink ACKNOWLEDGMENT The presented results were obtained during research on the development of control systems and adaptation of sensors and actuators of fuel equipment with perspective technical parameters with the financial support of the Ministry of Education and Science of the Russian Federation in the form of subsidies from the federal budget (code of the lot RFMEFI57915X0095). 11565