Severin Jonathan Hänggi

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Hänggi

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Severin Jonathan

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0000-0001-8250-4189

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Publications 1 - 10 of 15

Zünd- und Brennverfahren für mager betriebene Pkw-Erdgasmotoren
Soltic, Patrik; Hilfiker, Thomas; Hänggi, Severin Jonathan; et al. (2017)
Currently, passenger car CNG engines are based on boosted petrol engines. Such engines have typically restrictions, e.g. combustion peak pressures, which prevent from exploiting the potential of methane based fuels. Additionally, the use of cost-efficient three-way-catalysis limits the engine operation to λ=1. Here, we present the efficiency potential and the raw emission characteristics for passenger car CNG engines without sticking to combustion peak pressure and λ limitations. Lean combustion reduces the knocking tendency but, because of the higher pressure levels, increases the ignition energy demand. Therefore, different ignition systems (spark plug, prechamber, diesel pilot) have been used and compared.
Experimental comparison of efficiency and emission levels of four-cylinder lean-burn passenger car-sized CNG engines with different ignition concepts
Soltic, Patrik; Hilfiker, Thomas; Hutter, Richard; et al. (2019)
Combustion Engines
Today’s passenger car CNG engines are based on petrol engines which typically have restrictions preventing the exploitation of the full potential of methane based fuels, especially if they have to be operated also on petrol as a second fuel. Additionally, the use of threeway-catalysis limits the engine operation to λ = 1. Here, we present the efficiency potential and the raw emission characteristics for a dedicated four cylinder passenger car CNG engine without sticking to the usual combustion peak pressure and λ limitations. Lean combustion reduces the knocking tendency but, because of the higher pressure levels, increases the ignition energy demand. Therefore, different ignition systems (spark plug, prechamber, Diesel pilot) have been used.
Optimal Control for Direct-Injection Compression-Ignition Engines
Hänggi, Severin Jonathan (2023)
Reducing carbon dioxide and pollutant emissions has been the main objective of research on internal combustion engines and will keep playing an essential role in the years ahead. Developments towards these objectives have led to a continuous increase in the complexity of engine systems, pushing traditionally applied control concepts to their limits. However, the computing power of embedded processors has significantly increased as well, enabling more powerful control methods to be executed in real-time. This thesis presents two novel control algorithms, designed to reduce the calibration effort and to increase the control performance of direct-injection compression-ignition engines. They are based on economic nonlinear model predictive control methods, which allow to systematically and intuitively create algorithms to tackle complex control problems. The first algorithm presented is designed for controlling the air path of a diesel engine. It is formulated as a general control framework applicable to various engines of different size and air path layout. Its core consists of grey-box models of individual air path components, which are suited for algorithmic differentiation and gradient-based optimization. These can be arranged to represent prediction models for a variety of complex air paths and can be identified with a low amount of measurement data. Based on these models, a two-layer nonlinear model-predictive control structure enables the tracking of arbitrary air path reference signals and allows the introduction of economic control objectives. Using rapid control prototyping hardware, the general applicability and the effectiveness of this approach are experimentally evaluated on two laboratory engines. For a turbocharged light-duty diesel engine with dual-loop exhaust gas recirculation, the proposed control structure is applied to track intake manifold gas pressure and oxygen concentration while simultaneously minimizing engine pumping losses. The tracking performance and the pumping losses achieved are compared to those obtained with alternative control strategies. For a turbocharged heavy-duty engine with highpressure exhaust gas recirculation, the same control structure is parameterized to track the intake manifold gas pressure and oxygen concentration. The tracking performance achieved is compared to that obtained with an existing reference controller. The second algorithm presented in this thesis is designed to control the fuel combustion using multiple injections. It is formulated as a nonlinear program with an economic cost, which determines the number of injections as well as their duration and timing to achieve a desired engine load with the lowest amount of fuel possible. Further performance criteria, such as the engine noise or the exhaust gas enthalpy available for aftertreatment system heat-up strategies are considered as well. A continuously differentiable grey-box model of the in-cylinder process is used for prediction. It is based on physical first principles and calculates the in-cylinder pressure curve and further performance criteria as a function of the injector actuation, the rail pressure, the engine speed, and the gas conditions and composition in the intake manifold. Within a simulation study, the optimal solutions found by the nonlinear program as well as the performance of different solver methods are evaluated.
Data-based modeling for the crank angle resolved CI combustion process
Schilliger, Jan; Keller, Nils; Hänggi, Severin Jonathan; et al. (2020)
Data Analysis for Direct Numerical Simulations of Turbulent Combustion
For new combustion control concepts such as Combustion Rate Shaping, a crank angle resolved model of the compression ignition (CI) combustion process is necessary. The complex CI combustion process involving fuel injection, turbulent flow, and chemical reactions has to be reproduced. However, to be suitable for control, it has to be computationally efficient at the same time. To allow for learning-based control, themodel should be able to adapt to the current measurement data. This paper proposes two algorithms that model the CI combustion dynamics by learning a crank angle resolved model from past heat release rate (HRR) measurement data. They are characterized by short learning and evaluation times, low calibration effort, and high adaptability. Both approaches approximate the total HRR as the linear superposition of the HRRs of individual fuel packages. The first algorithm approximates the HRR of a single fuel package as a Vibe function and identifies the parameters by solving a nonlinear program having the squared difference between themeasured HRR and the superposition as cost. The second algorithm approximates the individual packages’ HRRs as Gaussian distributions and estimates the parameters by solving a nonlinear program with the Kullback-Leibler divergence between the measurement and the superposition as cost function using the expectation-maximization algorithm. Both algorithms are validated using test bench measurement data. © Springer Nature Switzerland AG 2020.
Control Barrier Functions for Cyber-Physical Systems and Applications to NMPC
Schilliger, Jan; Lew, Thomas; Richards, Spencer M.; et al. (2021)
IEEE Robotics and Automation Letters
Tractable safety-ensuring algorithms for cyber-physical systems are important in critical applications. Approaches based on Control Barrier Functions assume continuous enforcement, which is not possible in an online fashion. This letter presents two tractable algorithms to ensure forward invariance of discrete-time controlled cyber-physical systems. Both approaches are based on Control Barrier Functions to provide strict mathematical safety guarantees. The first algorithm exploits Lipschitz continuity and formulates the safety condition as a robust program which is subsequently relaxed to a set of affine conditions. The second algorithm is inspired by tube-NMPC and uses an affine Control Barrier Function formulation in conjunction with an auxiliary controller to guarantee safety of the system. We combine an approximate NMPC controller with the second algorithm to guarantee strict safety despite approximated constraints and show its effectiveness experimentally on a mini-Segway.
A method to quantify the advantages of a variable valve train for CI engines
Moretto, Giordano; Hänggi, Severin Jonathan; Omanovic, Andyn; et al. (2024)
International Journal of Engine Research
Today’s CI engines are subject to strict regulations of pollutant emissions and ambitious fuel consumption targets. Therefore, the interaction between the engine and the exhaust aftertreatment system (ATS) has become increasingly important. Numerous studies have shown that a variable valve train (VVT) improves the interaction between engine and ATS. However, most of these studies either quantify the advantage on a specific engine or only present complex CFD models, such that the results are not easily transferable to different engines. Thus, engine manufacturers cannot directly use these results to assess the advantage of various VVT strategies for their engines. In this paper, we propose a cycle-discrete cylinder model based on first principles which allows to simulate various VVT strategies. In contrast to present methods based on CFD, the proposed cylinder model can be realized with the equations presented. Furthermore, the model is identified with measurement data of an engine without a VVT. A separate engine, which is retrofitted with a fully VVT, is used to validate the proposed modeling approach. Using the identified model in combination with a mean-value model of the air path, we are able to simulate the effects of early intake valve closing, early exhaust valve opening, and cylinder deactivation for a complete CI engine that has no VVT installed. The model is then used to highlight the advantage of a VVT for two scenarios at part-load operation. At cold start, where the temperature of the ATS must be increased quickly, variable valve timing achieves higher enthalpy flows to the ATS while also lowering engine-out NOx emissions when compared to a standard engine strategy. If the ATS is at the operating temperature, cylinder deactivation achieves significantly higher enthalpy flows which prevents the ATS from cooling down. In addition, cylinder deactivation also lowers fuel consumption and engine-out NOx emissions.
Control-oriented analysis of a lean-burn light-duty natural gas research engine with scavenged pre-chamber ignition
Hänggi, Severin Jonathan; Hilfiker, Thomas; Soltic, Patrik; et al. (2019)
Combustion Engines
Natural gas is well-suited as a fuel in the transport sector. Due to its excellent combustion characteristics, engines operating with compressed natural gas (CNG) reach high efficiency, especially if operated at lean conditions. However, CNG engine research mainly focusses on stoichiometric conditions in order to use a three-way catalytic converter for the exhaust gas after treatment system. With the objective to explore the potential of CNG engines operated at lean conditions, a turbo-charged CNG engine with high compression ratio is developed and optimized for lean operation. In order to increase the ignition energy, the CNG engine is equipped with scavenged pre-chambers. A specific control structure is developed, which allows to operate the engine at a pre-defined (lean) air-to-fuel ratio. Further functionalities such as the combustion placement control and algorithms to estimate the conditions inside of the prechamber are implemented. The first part of this paper describes this engine control structure, which is specifically developed for the lean-burn CNG engine. In the second part, the effects of pre-chamber scavenging on engine performance criteria such as the combustion stability, engine efficiency or engine emissions are analyzed. With the objective to use pre-chamber scavenging to improve engine performance, a scavenging feedback control strategy is proposed. In order to control the ignition delay, this strategy adapts the amount of CNG injected into the prechamber with a linear controller or an extremum seeking algorithm depending on the air-to-fuel ratio of the main chamber.
Efficient light-duty engine using turbulent jet ignition of lean methane mixtures
Soltic, Patrik; Hilfiker, Thomas; Hänggi, Severin Jonathan (2021)
International Journal of Engine Research
Diesel engines use diffusion-controlled combustion of a high-reactivity fuel and offer high efficiencies because they combine lean combustion with a high compression ratio. For low-reactivity fuels such as gasoline or natural gas, premixed combustion is used, which leads to lower efficiency levels as usually stoichiometric combustion is combined with lower compression ratios. Trying to apply diesel-like process parameters to low-reactivity fuels inevitably leads to problems with classical spark ignition systems as they are not able to establish robust flame propagation for such hard-to-ignite conditions. One possibility to enable fast combustion for diluted mixtures at high pressure levels is to establish ignition in a prechamber and ignite the charge of the main combustion chamber using the turbulent jets exiting the prechamber. In this study, the experimental results of a prechamber-equipped four-cylinder natural gas engine with 2 L displacement are discussed in detail. In the majority of the engine map, auxiliary fueling is used in the prechamber and a global air–fuel equivalence ratio λ is set to 1.7. At full load, a λ of 1.5 is applied without auxiliary prechamber fueling. The experiments show that such a setup is able to achieve brake efficiency levels of above 45% while maintaining peak brake mean effective pressure levels above 20 bar. At high load conditions, cylinder pressure levels at ignition timing achieve more than 80 bar and cylinder peak pressures of around 180 bars occur. The technology proved to enable robust and very fast combustion at comparably low NOx levels. A remaining challenge for the on-road use of such a technology is the reduction of the methane emissions at lean conditions.
Combustion Rate Shaping for Cycle-to-cycle Control
Moretto, Giordano; Hänggi, Severin Jonathan; Albin, Thivaharan; et al. (2019)
Thinking the Future - Zukunft denken ~ SCC - Symposium for Combustion Control
We propose a combustion control method for multiple injections in Diesel engines using the heat release rate derived from the cylinder pressure trace as feedback signal. Assuming that each injection contributes to an observable combustion, we present an algorithm that assigns the peak location of the heat release rate to each injection. The peak location is controlled using an offline identified ignition delay model. A feedback controller ensures constant load using a predefined fuel mass split between all injections. The fuel mass of each injection is feedforward controlled using an injector map. Reference tracking and disturbance rejection of the combined control are tested with up to three injections.
Optimal combustion calibration for direct-injection compression-ignition engines using multiple injections
Moretto, Giordano; Hänggi, Severin Jonathan; Onder, Christopher (2023)
International Journal of Engine Research
Multiple injections are widely used for direct-injection compression-ignition engines to mainly increase efficiency, lower pollutant emissions, and increase exhaust enthalpy. However, with each additional injection the degrees of freedom increase, which makes finding an optimal injection input by design of experiments a time-consuming task. In this paper, we present a model-based calibration method that determines the number of injections for a predefined set of requirements. First, we derive a zero-dimensional crank-angle-resolved cylinder process model based on first principles. The model includes a fuel injector and requires a low calibration effort. Second, we use this model in an optimal control problem that minimizes the fuel consumption subject to several constraints such as load, maximal pressure, maximal pressure gradient, engine-out temperature, and the limitations of the fuel injector. The optimal injector inputs are used as feedforward control signals on a real engine to validate the simulative results. In general, the experimental results are in good agreement with those obtained in simulations. Finally, we compare our approach to a state-of-the-art method known as pressure reference tracking which consists of two separate steps: the creation of an optimal pressure reference and the tracking by a discrete injector. We show that our method, which combines these two steps in a single optimization problem, results in an increase in indicated efficiency compared to the solution obtained by pressure reference tracking.

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Severin Jonathan Hänggi

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