Tomaž Katrašnik

A New Criterion to Determine the Start of Combustion in Diesel Engines

A new criterion for the determination of the start of combustion (SOC) from the diesel engine in-cylinder pressure diagram was developed. It is defined as the maximum of the third-order derivative of the cylinder pressure with respect to the crank angle. This criterion declares SOC more precisely than other previously published criteria based on pressure diagnostics. This fact was proven analytically and was discernable from the analysis of the experimental data. Besides its accuracy it is also robust enough to allow automatic evaluation of the SOC during processing of the pressure data for a large number of cycles. By applying the first law of thermodynamics analysis to the engine cylinder it was discovered that the third-order derivative of the in-cylinder pressure with respect to the crank angle is the most suitable criterion for determination of the SOC from the in-cylinder pressure diagram. Subsequently, the criterion was validated through experimental data analysis of the in-cylinder pressure diagrams for various engine speeds and loads. In order to evaluate the rate of heat release (ROHR), which formed the base for the experimental validation, in-cylinder pressure diagrams were processed with a computer code based on the first law of thermodynamics. The cylinder pressure was measured with an advanced piezoelectric sensor at the resolution 0.1 deg CA. Top dead center was determined with the capacitive top dead center sensor. Due to the analytic foundation of the developed method and its validation through highly accurate experimental data it can be concluded that new criterion is credible for the determination of the SOC.

Improvement of the dynamic characteristic of an automotive engine by a turbocharger assisted by an electric motor

Turbocharging and subsequent charge cooling of the working medium usually causes increase of the mean effective pressure in an automotive diesel engine. Poor performance during the engine load increase is attributed to the nature of energy exchange between the engine and the turbocharger. Filling of the intake and exhaust manifolds, as well as consequent increase of the pressure and acceleration of the rotating components of the turbocharger require a certain period of time. Dynamic performance of the turbocharger can be substantially improved by means of an electric motor attached directly to the turbo shaft. A new concept of asynchronous electric motor with a very thin rotor was applied to support the turbocharger during the transient operation of the engine. The experimental work of matching an electrically assisted turbocharger to an engine is rather expensive; it was therefore decided to determine general characteristic of the electric motor separately through experiments, whereas transient response of the turbocharged and intercooled diesel engine was simulated by a zero-dimensional filling and emptying computer simulation method. A lot of experimentally obtained data and empirical formulae for the compressor, gas turbine, flow coefficients of the engine valves, intercooler, high-pressure fuel pump with the pneumatic control device (LDA), combustion parameters, etc., were applied to overcome deficiency introduced by the zero-dimensional simulation model. As the result a reliable and accurate program compatible with the experimental results in steady and transient engine operation was developed and is presented in the work. Faster transient response, i.e., better load acceptance of the engine was obtained by applying an adequate electric motor to assist the turbocharger; three versions of electric motors with different torque to mass moment of inertia ratios and different operating regimes were introduced in the simulation program to investigate their influence on the transient behavior of the engine.

An Analysis of Turbocharged Diesel Engine Dynamic Response Improvement by Electric Assisting Systems

It is well known that turbocharged diesel engines suffer from an inadequate response to sudden load increase, this being a consequence of the nature of the energy exchange between the engine and the turbocharger. The dynamic response of turbocharged diesel engines could be improved by electric assisting systems, either by direct energy supply with an integrated starter-generator-booster (ISG) mounted on the engine flywheel, or indirect energy supply with an electrically assisted turbocharger. A previously verified zero dimensional computer simulation method was used for the analysis of both types of electrical assistance. The credibility of the data presented is further assured by the experimentally determined characteristics of the electric motors used as input parameters of the simulation. The paper offers an analysis of the interaction between a turbocharged diesel engine operating under various load conditions and electric assisting systems, as well as the requirements for supporting electric motors suitable for the improvement of an engine’ s dynamic response. It is evident that an electrically assisted turbocharger outperforms an integrated starter-generator-booster for vehicle application, however ISG is the preferred solution when instant power increase is demanded.

Assessment of engine thermal management through advanced system engineering modeling

Abstract A physically based approach to model vehicle dynamics, transient engine performance and engine thermal management system is presented. This approach enables modeling dynamic processes in the individual components and is the dynamic interaction of all relevant domains. The modeling framework is based on a common innovative solver, where all processes are solved using tailored numerical techniques suited to account for characteristic time scales of individual domains. This approach enables achieving very short computational times of the overall model. The paper focuses on the integration of cooling and lubrication models into the framework of a vehicle dynamics simulation including transient engine performance demonstrated on a modern passenger car featuring split cooling functionality. A validated model with a mechanically driven coolant pump provides the base for analyzing the impact of introducing an electrically driven coolant pump. Analyses are performed for two drive cycles featuring significantly different velocity profiles to reveal their influences on the operational principles of the powertrain components and their interaction. The results show for both drive cycles fuel saving due to the application of the electric water pump is relatively small and amounts between 0.75% and 1.1%. However, it is important to address that application of the electric coolant pump results in higher turbine outlet temperatures and thus in faster catalyst heat-up. Detailed analyses of the interaction between vehicle dynamics, transient engine performance and engine thermal management system provide insight into the underlying mechanisms. This is made possible by the application of physically based system level model.

Methods for improving transient response of diesel engines – influences of different electrically assisted turbocharging topologies

The paper presents a comprehensive study on engine performance improvement attributable to application of different electrically assisted turbocharger topologies. Performance of a baseline turbocharged high-speed direct-injection (HSDI) diesel engine is compared to the performance of an engine utilizing an electrically assisted turbocharger, an engine utilizing a turbocharger with an additional electrically driven compressor, and an engine utilizing an electrically split turbocharger. Analyses are performed based on a validated physically based engine and vehicle model comprising detailed models of all vehicle components, thus ensuring adequacy of results. Analyses are performed for various driving conditions, including tip-in in the fixed gears and the new European drive cycle (NEDC). Results reveal that electrically assisted turbocharger topologies improve transient response of the engine and thus driveability of the vehicle. Additionally, over a limited period of time, electrically assisted turbocharger topologies are able to improve steady-state torque output of the engine with retained fuelling, which is made possible by the availability of energy in electric storage devices. It was also revealed that the utilization of electrically split turbocharger enables considerable reduction in fuel consumption when driven according to urban drive cycles.

Designing the microturbine engine for waste-derived fuels

Presented paper deals with adaptation procedure of a microturbine (MGT) for exploitation of refuse derived fuels (RDF). RDF often possess significantly different properties than conventional fuels and usually require at least some adaptations of internal combustion systems to obtain full functionality. With the methodology, developed in the paper it is possible to evaluate the extent of required adaptations by performing a thorough analysis of fuel combustion properties in a dedicated experimental rig suitable for testing of wide-variety of waste and biomass derived fuels. In the first part key turbine components are analyzed followed by cause and effect analysis of interaction between different fuel properties and design parameters of the components. The data are then used to build a dedicated test system where two fuels with diametric physical and chemical properties are tested - liquefied biomass waste (LW) and waste tire pyrolysis oil (TPO). The analysis suggests that exploitation of LW requires higher complexity of target MGT system as stable combustion can be achieved only with regenerative thermodynamic cycle, high fuel preheat temperatures and optimized fuel injection nozzle. Contrary, TPO requires less complex MGT design and sufficient operational stability is achieved already with simple cycle MGT and conventional fuel system. The presented approach of testing can significantly reduce the extent and cost of required adaptations of commercial system as pre-selection procedure of suitable MGT is done in developed test system. The obtained data can at the same time serve as an input for fine-tuning the processes for RDF production.

Impedance spectroscopy characterisation of automotive NMC/graphite Li-ion cells aged with realistic PHEV load profile

The ageing behaviour of Li-ion cells in automotive applications is known to be strongly non-linear with respect to operating conditions. In addition, it has a profound impact on performance, cost and reliability of the target vehicle. The work presented in this paper concerns automotive type NMC/graphite Li-ion battery cells aged under realistic and accelerated conditions, analyzed using electrochemical impedance spectroscopy and with the implementation of an electric equivalent circuit model. Two cycle life tests were performed at +22°C and +45°C surrounding temperature, with reference performance tests performed at ±0°C, +22°C and +45°C. The duty cycle applied is derived from speed samples of real-world city driving characteristics for electric passenger cars with fast charging at 2C-rate. Results show that despite a significant decrease in capacity, a decrease in charge transfer resistance can be observed during the first stages of aging which may be correlated to an increased double layer capacitance. Also, an increase in peak power at low temperatures is observed.

Tailored Cylinder Models for System Level Engine Modelling

Abstract The model of the cylinder block represents the most challenging part of the engine model when establishing appropriate balance between the level of detail of the model and its computational speed. Furthermore its coupling to the gas path model significantly influences the performance of the overall engine model. The paper addresses various couplings of the 0D gas path models and the surrogate and the crank angle resolved cylinder block models. In addition two innovative coupling approaches are presented and discussed: 1. coupling of the mean value gas path model and the crank angle resolved cylinder model and 2. time domain decoupled interaction between the filling and emptying gas path model and the crank angle resolved cylinder model. In the paper physical background of the models is presented along with their characteristics and computational performances in terms of RT factors.

Modelling of the twin-entry turbocharger turbine

Abstract An original physical model to calculate the fluid dynamics and energy conversion in twin-entry turbocharger turbines for internal combustion engines is presented. The model is to be used as the boundary condition for one-dimensional wave action techniques and is also capable of considering variable gas properties and composition. The model is based on a simple variable-area approach; however, it is capable of adequately modelling complex flows that occur in multi-cylinder turbocharged engines. This is confirmed through the good agreement between calculated and measured turbine and engine parameters.

Innovative approach to air management strategy for turbocharged diesel aircraft engines

Theoretical study on performance optimization of a turbocharged diesel aircraft engine is presented in this article. It is based on a verified engine thermodynamics and fluid dynamics simulation model. An efficient air management strategy for increasing power-to-engine displacement ratios of a turbocharged diesel aircraft engines is introduced and analysed. Air management strategies generally applied to turbocharged spark ignition aircraft engines do not enable to take full advantage of potentials given by turbocharging diesel aircraft engines. A conceptually different air management strategy, where turbochargers waste-gate is fully closed up to the critical altitude, was therefore proposed and investigated in this article. Proposed air management strategy assures increased safety of engine operation through very simple and reliable engine controlling. Guidelines for selecting adequate air management components are also given in this article.