Frank Willems

Ammonia sensor for closed-loop SCR control

Selective Catalytic Reduction (SCR) is the dominant solution for meeting future NOx reduction regulations for heavy-duty diesel powertrains. SCR systems benefit from closed-loop control if an appropriate exhaust gas sensor were available. An ammonia sensor has recently been developed for use as a feedback element in closed-loop control of urea dosing in a diesel SCR aftertreatment system. Closed-loop control of SCR dosing enables the SCR system to be robust against disturbances and to meet conformity of production (COP) and in-use compliance norms.

Modeling for surge control of centrifugal compressors: comparison with experiment

A dynamic model based on the thermo- and fluid-mechanic processes taking place in a centrifugal compressor is validated. The background for this is the need for an energy based model including the rotational speed as a state in order to perform energy based active surge control. The response of the model is compared with experimental results from the Energy Technology Laboratory at Eindhoven University of Technology. Both the calculated compressor characteristic and transient responses for set point changes and in-surge response were compared to experiment with good results.

Modeling of Surge in Free-Spool Centrifugal Compressors: Experimental Validation

The derivation of a compressor characteristic, and the experimental validation of a dynamic model for a variable speed centrifugal compressor using this characteristic, are presented. The dynamic compressor model of Fink et al. is used, and a variable speed compressor characteristic is derived by the use of energy transfer and loss analysis. It is demonstrated that taking into account the losses due to friction, incidence, mixing, and blade loading results in compressor characteristics that closely match the measured characteristics. The simulated response of the dynamic model was found to be in excellent agreement with the experimental results, both for set point changes using fuel flow and blow off and for surge oscillations. Analysis of the power spectrum of the in-surge rotational speed and pressure oscillations reveal that the simulated nonlinear oscillations match experimental values up to the third harmonic, both with respect to frequency and amplitude.

Cost and Fuel Efficient SCR-only Solution for Post-2010 HD Emission Standards

A promising SCR-only solution is presented to meet post-2010 NOx emission targets for heavy duty applications. The proposed concept is based on an engine from a EURO IV SCR application, which is considered optimal with respect to fuel economy and costs. The addition of advanced SCR after treatment comprising a standard and a close-coupled SCR catalyst offers a feasible emission solution, especially suited for EURO VI. In this paper, results of a simulation study are presented. This study concentrates on optimizing SCR deNOx performance. Simulation results of cold start FTP and WHTC test cycles are presented to demonstrate the potential of the close-coupled SCR concept. Comparison with measured engine out emissions of an EGR engine shows that a close-coupled SCR catalyst potentially has NOx reduction performance as good as EGR. Practical issues regarding the use of an SCR catalyst in closecoupled position will be addressed, as well as engine and exhaust layout. For comparison, the requirements of a US 2010/EURO VI compliant high EGR engine are discussed: base engine design, heat rejection, fuel injection equipment, turbo charging and fuel economy. From this study, it is concluded that the SCR-only approach leads to a less expensive engine design with better fuel economy and lower PM emissions.

Heat exchanger modeling and identification for control of Waste Heat Recovery systems in diesel engines

To meet future CO2 emission targets, Waste Heat Recovery systems have recently attracted much attention for automotive applications, especially for long haul trucks. This paper focuses on the development of a dynamic counter-flow heat exchanger model for control purposes. The model captures the dynamic phenomena of two-phase fluid flow using the mass and energy balance equations. While most of the studies use chemical libraries to retrieve the working fluid properties, in this model mathematical equations are derived. Compared to other evaporator models, the proposed model is validated on data from a complete engine platform. Experiments are done on a state-of-the-art Euro-VI heavy-duty diesel engine, which is equipped with a Waste Heat Recovery system. For transient conditions over a wide range of operating points, simulation results show good agreement in comparison with experimental data. This makes the model suitable for real-time simulations, diagnostics and control algorithm designs.

Integrated Powertrain Control to meet future CO 2 and Euro-6 emissions targets for a diesel hybrid with SCR-deNO x system

A new concept is introduced to optimize the performance of the entire powertrain: Integrated Powertrain Control (IPC). In this concept, the synergy between engine, driveline and aftertreatment system is exploited by integrated energy and emission management. As a result, fuel efficiency and drivability can be optimized simultaneously within the boundaries set by emission legislation. This is essential to meet both future CO2 targets and ultra low emission limits. As a first step towards IPC, the potential of the proposed approach is demonstrated for a series hybrid diesel passenger car. The studied powertrain is based on a VW 1.2l TDI engine, which is equipped with a urea-based SCR-deNOx aftertreatment system. For three different energy management strategies, chassis dynamometer results are presented over a European NEDC test cycle. Additional simulations demonstrate the potential of integrated energy and emission management, especially during low temperature conditions. Projections show that 130 g/km CO2 and Euro-6 NOx emission targets can be simultaneously met for the studied C-segment vehicle.

Towards control-oriented modeling of natural gas-diesel RCCI combustion

For natural gas (NG)-diesel RCCI, a multi-zonal, detailed chemistry modeling approach is presented. This dual fuel combustion process requires further understanding of the ignition and combustion processes to maximize thermal efficiency and minimize (partially) unburned fuel emissions. The introduction of two fuels with different physical and chemical properties makes the combustion process complicated and challenging to model. In this study, a multi-zone approach is applied to NG-diesel RCCI combustion in a heavy-duty engine. Auto-ignition chemistry is believed to be the key process in RCCI. Starting from a multi-zone model that can describe auto-ignition dominated processes, such as HCCI and PCCI, this model is adapted by including reaction mechanisms for natural gas and NOx and by improving the incylinder pressure prediction. The model is validated using NG-diesel RCCI measurements that are performed on a 6 cylinder heavy-duty engine. For three different engine operating points, it is operated at various diesel injection timings and NG-diesel blend ratios. The validation is focused on variables that are relevant for engine control, such as CA50, peak cylinder pressure, and engine-out NOx emissions. The validation shows that the multi-zone method with detailed chemistry reproduces the correct trends for important control parameters. From this validated model, real-time, map-based RCCI models are derived, which are considered to be an important step towards model-based NG-diesel RCCI control development.

Automated model fit tool for SCR control and OBD development

Reaching EUROVI Heavy Duty emission limits will result in more testing time for developing control and OBD algorithms than to reach EUROV emissions. It is likely that these algorithms have to be adapted for a WHTC (World Heavy Duty Transient Cycle) for EUROVI. This cycle when started cold can only be performed a limited times a day on the engine testbench, because of the cooling down time. The development time and cost increases to reach EUROVI emission levels. Accurate simulation tools can reduce the time and costs by reducing the amount of tests required on the testbench. In order to use simulation tools to develop pre calibrations, the models must be fitted and validated. This paper will focus on the fit process of an SCR (Selective Catalytic Reduction) model. A unique test procedure has been developed to characterize an SCR catalyst using an engine testbench in ±2 days. This data is used in an automatic SCR fit tool to obtain the model parameters in a few days. The result is a model that predicts the NO, NO 2 and NH 3 SCR out concentration accurately. The fitted SCR model can predict tailpipe NO x emissions for a wide range of test cycles within 10 % (see Table 5). The validated model is used to develop and calibrate SCR control and OBD algorithms.

Positive feedback stabilization of compressor surge

Stable operation of axial and centrifugal compressors is limited towards low mass flows due to the onset of surge. The stable operating region can be enlarged by active control. In this study, we use a control valve which is nominally closed and only opens to stabilize the system around the desired operating point. Hence, only non-negative control values are allowed which complicates the controller design considerably. A novel positive feedback controller is proposed with clear design parameters to obtain a desirable closed loop behavior. The technique has successfully been applied to a compression system model. For arbitrarily large control valve capacities, the system can be stabilized in the entire operating region. Simulations show that the surge point mass flow can be reduced up to 15% for the relatively small control valve to be implemented on the actual installation. Using this efficient control strategy, the stabilized operating point is reached with zero control valve mass flow.

Integrated Energy & Emission Management for Heavy-Duty Diesel Engines with Waste Heat Recovery System

Abstract This study presents an integrated energy and emission management strategy for an Euro-VI diesel engine with Waste Heat Recovery (WHR) system. This Integrated Powertrain Control (IPC) strategy optimizes the CO 2 -NO x trade-off by minimizing the operational costs associated with fuel and AdBlue consumption. The main contribution of this work is that the effect of tailpipe emissions and WHR dynamics are included in the control design. In a simulation study, the potential of this strategy is demonstrated over a World Harmonized Transient Cycle. These results are compared with a baseline engine control strategy. This study shows that slow WHR dynamics strongly affect the engine performance: neglecting these dynamics in the control design leads to unacceptable high tailpipe NO x emissions. By applying the IPC strategy, an additional 2.8% CO 2 reduction is achieved within the NO x emission limit compared to the baseline strategy.