In cylinder combustion model of diesel engines

Diesel engines are commonly used in various industries such as automotive, aviation and marine for years, because of their high torque and low fuel consumption. However; in comparison with gasoline engines, diesel engines have some disadvantages in terms of emission. For diesel engines, the basic exhaust gases are particulate matter(PM), nitrogen oxide(NOx), hydrocarbons(HC) and carbonmonoxide(CO). Especially, NOx and PM emissions which are quite harmful for human health and environment are much more in diesel engines compared with gasoline engines. Nitrogen oxides accumulate on atmosphere and lead to acid rains. Besides, it is known that particulate matter is quite detrimental for human health and it causes some diseases such as asthma and lung cancer. Due to the negative effects on human health and nature, increasing of precautions against to emission release day by day and restrictions imposed regarding emission regulations resolved a serious problem to diesel emissions. Although the expectations of drivers for high torque and low fuel consumption, decreasing on emission limitations each passing day become an optimization problem to diesel engine control. On the purpose of meeting these requirements and restrictions, the number of sensor, actuator and component used for diesel engine increased considerably compared to the first years of diesel engines. Depending on growing of the number of sensor and actuator, electronic control became inevitable for diesel engines. In the last years, in comparison with mechanical improvements on diesel engines, developments in electronic control are much more. As a result of the increasing of the number of actuators, the number of control variables in diesel engines rose as well and so model-based control methods has become more important. At the present time, there are lots of calibration parameters containing in hundreds maps and curves inside of diesel engine control units. Each of these maps and curves are calibrated seperately for every vehicle and this operation takes too much time. On the other hand, since some of the calibration processes is made on engine dynamometer, the cost of these operations are high. Besides, using of map-based models prevents that various control methods can be applied on diesel engine. Developing technology and depending on this, improvements in sensor and actuator technologies make possible to be applied different control algorithms on diesel engine control as well. The main systems used for diesel engine control are fuel and air systems. In diesel engines, turbocharger, EGR valve and throttle valve are used for air control. Throttle valve are not used on most of diesel engines, however; some of diesel engines include it. It has important role for controlling of air quantity in cylinder. Moreover, turbocharger is most widely used actuator for air control in diesel engines. On the other hand, EGR valve is commonly used in diesel engine control. The oxygen ratio in cylinder is adjusted by using EGR valve. Injectors which are used for fuel injection control on diesel engines are an actuator. Injected fuel mass, injection time, the number of injection and injection pressure are controlled by using injectors. Recently, the piezo injectors are appropriate for multiple injection. By the help of these injectors, it is possible to make 10-12 injections during one engine cycle. In diesel engine control, some parameters which belong to air and fuel injection systems are optimized, so it is purposed that desired torque and emission level are satisfied. In the scope of this study, mainly in cylinder combustion which has the most important effect on fuel consumption, performance and emission requirements for diesel engines was modelled dynamically on Matlab/Simulink environment. Basically, this study consists of five chapter. In the first chapter, an introduction was made for thesis. And, it was mentioned about the purpose of thesis. Then, the studies regarding diesel engine modelling methods in literature was explained and the hypothesis was clarified. In the second chapter, some general informations, which contains the history of internal combustion engines, the working principle of diesel engines, main performance parameters and definitions for diesel engine, modelling methods was given. In the third chapter, the subsystems which form complete combustion model expressed one by one. Also, the equations used in these subsystems was showed. The combustion model includes ten main subsystems. These subsystems: • Kinematic model, • Charge exchange model, • Mass balance model, • Fuel injection model, • Heat release model, • Enthalphy of mass flow model, • Air-fuel ratio model, • Heat losses model, • Volumetric work model, • Calculation of state variables model. The euler method was used for kinematic model and pin-offset effect was took into consideration. For heat release model, double wiebe approach was utilized. Hohenberg method was used for heat losses model. As modelling methods, zero-dimensional modelling technique, which is based substantially on physical equations and includes also empirical equations, was used instead of map-based modelling methods used on today's diesel engine control units. Through the creation of models, the balance between model complexness and simpleness is crucial. If the model is very simple, the simulation results diverge from real test results. On the other hand, when the complex structure is used in modelling, the simulation takes too much time and it will not suitable for real-time simulations. Zero dimensional modelling method is quite suitable for diesel engine control and real time applications. For validation of combustion model developed on Matlab/Simulink envrionment, a one cylinder diesel engine model was created and run on GT-Suite environment. The simulation results obtained GT-Suite simulation were utilized for combustion model validation on Matlab/Simulink side. In the fourth chapter, the simulation results was demonstrated. The simulation results of the model created Matlab/Simulink environment was compared with GT-Suite simulation results. Also, the results was evaluated. In the last chapter, the results of this studies was explained and it was made some suggestions for the next studies about this topic.