Potential Of Water Injection For Gasoline Engines By Means Of A 3d Cfd Virtual Test Bench

Water injection is one of the most promising technologies to improve the engine combustion efficiency, by mitigating knock occurrences and controlling exhaust gas temperature before turbine. As result, the engine can operate at stoichiometric conditions over the whole engine map, even during the more power-demanding RDE cycles. Antonino Vacca presents a methodology to study and optimize the effect of water injection for gasoline engines by investigating different engine layouts and injection strategies through the set-up of a 3D-CFD virtual test bench. He investigates indirect and direct water injection strategies to increase the engine knock limit and to reduce exhaust gas temperature for several operating points.

Marvin Sascha Wahl presents the possibilities for optimising diesel engine combustion. In the advanced process of partially premixed diesel combustion, nitrogen oxide and soot emissions can be minimised at the same time. A new feature is the possibility of applying this strategy up to 2000 revolutions and 10 bar indicated mean pressure. In this work, various effective parameters are also compared and correlated with each other. A final comparison with conventional diesel combustion shows the advantages and disadvantages and evaluates them.

This book deals with the simulative prediction of efficiency and CO2-emissions of future powertrain systems for the year 2040. For this purpose, a suitable simulation environment is first created. This is followed by a technology extrapolation of all relevant powertrain systems, for example: combustion engines, electric drives, fuel cells as well as all relevant additional components. These components are then used to build 57 vehicle variants for the simulation. Finally, extensive simulations of the vehicle variants are carried out, evaluated and compared. Comprehensive tables of results are available for all simulated vehicle variants. The evaluations are of interest to anyone concerned with energy consumption and CO2-emissions of future vehicles.

Downsizing of modern gasoline engines with direct injection is a key concept for achieving future CO22 emission targets. However, high power densities and optimum efficiency are limited by an uncontrolled autoignition of the unburned air-fuel mixture, the so-called spark knock phenomena. By a combination of three-dimensional Computational Fluid Dynamics (3D-CFD) and experiments incorporating optical diagnostics, this work presents an integral approach for predicting combustion and autoignition in Spark Ignition (SI) engines. The turbulent premixed combustion and flame front propagation in 3D-CFD is modeled with the G-equation combustion model, i.e. a laminar flamelet approach, in combination with the level set method. Autoignition in the unburned gas zone is modeled with the Shell model based on reduced chemical reactions using optimized reaction rate coefficients for different octane numbers (ON) as well as engine relevant pressures, temperatures and EGR rates. The basic functionality and sensitivities of improved sub-models, e.g. laminar flame speed, are proven in simplified test cases followed by adequate engine test cases. It is shown that the G-equation combustion model performs well even on unstructured grids with polyhedral cells and coarse grid resolution. The validation of the knock model with respect to temporal and spatial knock onset is done with fiber optical spark plug measurements and statistical evaluation of individual knocking cycles with a frequency based pressure analysis. The results show a good correlation with the Shell autoignition relevant species in the simulation. The combined model approach with G-equation and Shell autoignition in an active formulation enables a realistic representation of thin flame fronts and hence the thermodynamic conditions prior to knocking by taking into account the ignition chemistry in unburned gas, temperature fluctuations and self-acceleration effects due to pre-reactions. By the modeling approach and simulation methodology presented in this work the overall predictive capability for the virtual development of future knockproof SI engines is improved.

It is generally accepted that the worldwide change of the climate is caused by the manmade emissions of the greenhouse gas CO2. For this reason the development of new technologies for propulsion aims at the reduction of the CO2-emissions. Using hydrogen as an energy carrier offers the possibility to produce the fuel for vehicles from renewable energy sources, thus avoiding the emission of CO2 completely. The on-board storage of liquid hydrogen at very low(cryogenic) temperatures offers currently the best basis to achieve acceptable cruising ranges of hydrogen vehicles. The consistent utilisation of the cold hydrogen using cryogenic mixture formation offers unique opportunities for the optimisation of a combustion engine with regard to power and efficiency. To fully exploit the potential of this promising mixture formation strategy, the usage of modern simulation techniques is necessary. In the course of this thesis, 1D and 3D computational fluid dynamic simulation tools were brought to a serviceable state ready for the optimisation of a hydrogen engine with cryogenic mixture formation. The simulation of the mixing and the combustion with novel models, adapted for hydrogen engine simulations, was verified by comparison to engine test bench results and optical experiments. Careful model and mesh studies have been performed. The ability of a Turbulent Flame Speed Closure (TFC) combustion model to predict the combustion process for a large part of the engine operating map could be demonstrated. This is a significant progress compared to results achieved until now regarding hydrogen engine simulations. A crucial point of the cryogenic mixture formation is the formation of frost inside the intake port due to the low mixture temperature. For the simulation of this phenomenon, a novel approach to compute frost formation in combination with a 3D CFD simulation has been developed. The validity of the model could be demonstrated on the basis of experimental results reported in literature and by comparison to preexisting cryogenic hydrogen injection experiments. The innovative simulation tool could be applied developing suggestions how to avoid the undesired formation of frost. A simple but robust solution for the frosting issue was elaborated, whose functionality could be demonstrated during engine operation at the test bench, which is regarded as an essential step towards the realisation of a hydrogen engine with cryogenic mixture formation. The presented thesis was conducted at BMW Group Research and Technology in the course of the European funded project HyICE – Optimisation of a Hydrogen Powered Internal Combustion Engine.

Computational Optimization of Internal Combustion Engines presents the state of the art of computational models and optimization methods for internal combustion engine development using multi-dimensional computational fluid dynamics (CFD) tools and genetic algorithms. Strategies to reduce computational cost and mesh dependency are discussed, as well as regression analysis methods. Several case studies are presented in a section devoted to applications, including assessments of: spark-ignition engines, dual-fuel engines, heavy duty and light duty diesel engines. Through regression analysis, optimization results are used to explain complex interactions between engine design parameters, such as nozzle design, injection timing, swirl, exhaust gas recirculation, bore size, and piston bowl shape. Computational Optimization of Internal Combustion Engines demonstrates that the current multi-dimensional CFD tools are mature enough for practical development of internal combustion engines. It is written for researchers and designers in mechanical engineering and the automotive industry.

Phenomenology of Diesel Combustion and Modeling Diesel is the most efficient combustion engine today and it plays an important role in transport of goods and passengers on land and on high seas. The emissions must be controlled as stipulated by the society without sacrificing the legendary fuel economy of the diesel engines. These important drivers caused innovations in diesel engineering like re-entrant combustion chambers in the piston, lower swirl support and high pressure injection, in turn reducing the ignition delay and hence the nitric oxides. The limits on emissions are being continually reduced. The- fore, the required accuracy of the models to predict the emissions and efficiency of the engines is high. The phenomenological combustion models based on physical and chemical description of the processes in the engine are practical to describe diesel engine combustion and to carry out parametric studies. This is because the injection process, which can be relatively well predicted, has the dominant effect on mixture formation and subsequent course of combustion. The need for improving these models by incorporating new developments in engine designs is explained in Chapter 2. With “model based control programs” used in the Electronic Control Units of the engines, phenomenological models are assuming more importance now because the detailed CFD based models are too slow to be handled by the Electronic Control Units. Experimental work is necessary to develop the basic understanding of the pr- esses.

The international marine shipping industry is responsible for the transport of around 90% of the total world trade. Low-speed two-stroke diesel engines usually propel the largest trading ships. This engine type choice is mainly motivated by its high fuel efficiency and the capacity to burn cheap low-quality fuels. To reduce the marine freight impact on the environment, the International Maritime Organization (IMO) has introduced stricter limits on the engine pollutant emissions. One of these new restrictions, named Tier III, sets the maximum NOx emissions permitted. New emission reduction technologies have to be developed to fulfill the Tier III limits on two-stroke engines since adjusting the engine combustion alone is not sufficient. There are several promising technologies to achieve the required NOx reductions, Exhaust Gas Recirculation (EGR) is one of them. For automotive applications, EGR is a mature technology, and many of the research findings can be used directly in marine applications. However, there are some differences in marine two-stroke engines, which require further development to apply and control EGR. The number of available engines for testing EGR controllers on ships and test beds is low due to the recent introduction of EGR. Hence, engine simulation models are a good alternative for developing controllers, and many different engine loading scenarios can be simulated without the high costs of running real engine tests. The primary focus of this thesis is the development and validation of models for two-stroke marine engines with EGR. The modeling follows a Mean Value Engine Model (MVEM) approach, which has a low computational complexity and permits faster than real-time simulations suitable for controller testing. A parameterization process that deals with the low measurement data availability, compared to the available data on automotive engines, is also investigated and described. As a result, the proposed model is parameterized to two different two-stroke engines showing a good agreement with the measurements in both stationary and dynamic conditions. Several engine components have been developed. One of these is a new analytic in-cylinder pressure model that captures the influence of the injection and exhaust valve timings without increasing the simulation time. A new compressor model that can extrapolate to low speeds and pressure ratios in a physically sound way is also described. This compressor model is a requirement to be able to simulate low engine loads. Moreover, a novel parameterization algorithm is shown to handle well the model nonlinearities and to obtain a good model agreement with a large number of tested compressor maps. Furthermore, the engine model is complemented with dynamic models for ship and propeller to be able to simulate transient sailing scenarios, where good EGR controller performance is crucial. The model is used to identify the low load area as the most challenging for the controller performance, due to the slower engine air path dynamics. Further low load simulations indicate that sensor bias can be problematic and lead to an undesired black smoke formation, while errors in the parameters of the controller flow estimators are not as critical. This result is valuable because for a newly built engine a proper sensor setup is more straightforward to verify than to get the right parameters for the flow estimators.