Search Results

Pneumatic hybridization of internal combustion engines may prove to be a viable and cost-efficient alternative to electric hybridization. This paper evaluates the effects of pneumatic hybridization of various engine concepts using the criteria of fuel efficiency, driveability, emissions, and cost efficiency. The most promising engine concept is found to be the pneumatic hybridization combined with downsizing and supercharging spark-ignited engines. With this concept, a fuel consumption reduction of over 30% compared to a standard engine with the same rated power can be achieved. The poor driveability usually associated with heavily downsized and supercharged engines is completely overcome by injecting additional air during transients. The most important design issues for this new concept are discussed and several possible solutions are presented. Following these considerations, the first fully functional hybrid pneumatic engine was realized.

The selection and configuration of sensors can strongly influence the closed-loop dynamics of a system. Therefore a methodology for finding the best sensor placement is a valuable tool. This paper deals with this problem by formulating an optimization problem and applies the new method on an SI engine. The best sensor configuration is one that minimizes the overall system costs, yet still meets the system constraints. Before solving the optimization problem, the system is modeled, different sensor configurations are defined, the appropriate controller and the feedback term are developed, and the locations and size of the various errors present in the model are determined. Then, the objective function and the system constraints are defined and the optimization problem is solved considering the worst-case combination of modeling errors, which is computed using genetic algorithms. The objective function is defined as the sum of the sensor costs and of a penalty term.

In practical applications of ammonia SCR aftertreatment systems using urea as the reductant storage compound, one major difficulty is the often constrained packaging envelope. As a consequence, complete mixing of the urea solution into the exhaust gas stream as well as uniform flow and reductant distribution profiles across the catalyst inlet face are difficult to achieve. This paper discusses a modeling approach, where a combination of 3D CFD and a lumped parameter SCR model enables the prediction of system performance, even with non-uniform exhaust flow and ammonia distribution profiles. From the urea injection nozzle to SCR catalyst exit, each step in the modeling process is described and validated individually. Finally the modeling approach was applied to a design study where the performance of a range of urea-exhaust gas mixing sections was evaluated.

Instantaneous in-cylinder pressure, a key variable in the improvement of engine performance and reduction of emissions, is not likely to be measured directly in production type engines in the near future. As a countermeasure, a pressure estimation method based on physical first principles for the estimation of the instantaneous in-cylinder pressure of an SI engine using measured crankshaft angular velocity is presented here. The approach consists of (a) mapping the model parameters at nominal operating conditions and (b) adapting the model parameters to current operating conditions using the instantaneous crankshaft angular velocity. The model reflects all essential effects on in-cylinder pressure, while the simulation time was reduced to 6 milliseconds per cycle on a standard PC. This makes it possible to estimate a cylinder-averaged pressure for each cycle up to an engine speed of more than 6000 rpm. The estimated in-cylinder pressure is available with a delay of one engine cycle.

Basic knowledge about the reaction kinetics of the selective catalytic reduction (SCR) as well as measurement data from a dynamometer are used for the design of a physical mean-value model of an SCR catalytic converter system. The converter system consists of an injection device for urea solution and a coated metallic honeycomb-type converter. It is mounted in the tailpipe of a mobile, heavy-duty diesel engine. The core of the catalytic converter model is a series of identical SCR cells describing the thermal and chemical behavior of the SCR catalytic converter. It may be used to design dynamic, model-based feedforward controllers for the injection of reducing agent. Measurements on the dynamometer show that these controllers significantly improve the performance of the SCR system.

In this paper a novel IC engine load-control device is described which actively throttles the intake air and thereby produces electric power. The main component is a small axial turbine that replaces the conventional throttle. This turbine is connected with an electric generator and an appropriate electric load control system. This paper describes the complete system including the turbine, the control system, and the necessary auxiliary parts. A prototype of the proposed system has been realized. The paper shows the results in electric power generation obtained with this prototype in steady-state driving conditions and in standard test cycles. Moreover, extrapolations of the expected benefits in other engine-vehicle combinations are computed using mathematical models of the main parts of the system.

Very stringent limits for exhaust gas emissions as well as high claims for onboard diagnosis (OBD) of the three-way catalytic converter (TWC) demand a sophisticated control and observer strategy which can both further reduce the exhaust gas emissions and also estimate the relevant parameters allowing to monitor the decreasing performance of the TWC over its lifetime. The most crucial parameter and state, respectively, are widely believed to be the oxygen storage capacity (OSC) and the relative oxygen level (ROL) of the TWC. The TWC's performance decreases with a diminishing OSC. Therefore, an accurate estimation of the OSC can be used for OBD. Keeping the ROL at an optimal level by means of control enhances the TWC's performance significantly, even during transients of the air/fuel ratio imposed by the driver. In order to monitor both the ROL and the OSC, an observer has been derived from a complex TWC model.

The goal of the Clean Engine Vehicle project (CEV) was the conversion of a gasoline engine to dedicated natural gas operation in order to achieve a significant reduction in CO2 emissions. The targeted reduction was 30% compared with a gasoline vehicle with similar performance. Along with the reduction in emissions, the second major requirement of the project, however, was compliance of the results with Euro-4 and SULEV emission limits. The project entailed modifications to the engine and the pre-existing model-based engine control system, the introduction of an enhanced catalytic converter and downsizing and turbocharging of the engine. As required by the initiators of the project, all components used were commonly available, some of them just being optimized or modified for natural gas operation.

In modern spark-ignited engines the accurate estimation of the amount of fuel to be injected is an important issue, in particular if a specific air-to-fuel ratio is required. The knowledge of the events occurring between the intake duct (injectors) and the exhaust duct (λ-sensor) is thus very important. Among all the systems that play a role, the best studied are the wall-wetting dynamics. Nowadays, the wall-wetting effects are compensated on the basis of simple linear models that are tuned with the help of a large number of measurements. These models are quite effective but they cannot be used universally.Their extrapolation for a non-measured operating point can lead to unsatisfactory results. Other problems arise at operating points where direct measurements are difficult, e.g., at cold start. Complex models already exist, but usually they require a lot of work in the parameterization phase.

An advanced controller for a urea SCR (Selective Catalytic Reduction) catalytic converter system for a mobile heavy-duty diesel engine is presented. The after-treatment system is composed of the injecting device for urea solution and a single SCR catalytic converter. The control strategy consists of three parts: A primary feedforward controller, a surface coverage observer, and a feedback controller. A nitrogen oxide (NOx) gas sensor with non-negligible cross-sensitivity to ammonia (NH3) is used for a good feedback control performance. The control strategy is validated with ESC and ETC cycles: While the average NH3 slip is kept below 10 ppm, the emission of NOx is reduced by 82%.

The burned gas remaining in the cylinder after the exhaust stroke of an SI engine, i.e. the residual gas fraction, has a significant influence on both the torque production and the composition of the exhaust gas. This work investigates the behavior of the residual gas fraction over the entire operating range of the engine. A combined discrete-continuous linear model is identified, which describes the dynamic effects of the gas composition from when the gases enter the cylinder up to the measurement with a specific sensor. In this investigation, that sensor is a fast NO measurement device. The system is modelled by three elements in series: the in-cylinder mixing, the transport delay, and the exhaust mixing. The resulting model contains three elements in series connection: the in cylinder mixing, the transport delay, and the exhaust gas mixing. The model is able to calculate the fuel mass entering the cylinder during a fuel injection transient.

Compressed Natural Gas (CNG) engines have become a promising alternative to classical IC engines because of low pollutant and carbon dioxide emissions. This paper will first briefly summarize these advantages and then concentrate on the modeling and the control of CNG engines. In the modeling part, it will be shown which effects are similar to those observed in gasoline SI engines and what new sub-models are necessary. In the control part, the problem of sudden A/F ratio changes (for instance during the regeneration of NOx trap catalysts) will be considered. In order to avoid excessive NOx engine-out emission in these transients it is important to switch from lean to rich conditions within very few combustion cycles while keeping the engine torque constant (for comfort reasons). The paper presents a model of the most important phenomena associated with those transients and a feedforward control that meets the mentioned requirements.

Conventionally, in automotive applications cooling pumps have been directly mechanically driven. This paper presents the significant improvements possible with their substitution by electrical cooling pumps A model of the thermal behaviour of the engine and of the cooling circuit has been developed. Two different configurations of the cooling system have been considered, the conventional one and one with an electrical cooling pump and an electrical operated bypass valve instead of the thermostat. Result of the modeling is a fourth order system with additional delays. The coolant mass flow through the pump and the bypass valve position are inputs. A control for the electrical pump and the electrical valve is developed, which influences the cooling fluid temperature and the engine temperature, with the aim of reducing the fuel consumption and mechanical wear during cold start and part load operating conditions.

The wall-wetting dynamics represent a very important subsystem of the air/fuel path of an SI engine. The precise feedforward control of the air/fuel ratio requires a valid model of the wall-wetting dynamics over the whole operating region of the engine. A global wall-wetting model has been developed for a production SPFI gasoline engine. This model is capable of describing the wall-wetting dynamics not only in a fixed operating point, but also for radical changes of the operating point. Its structure specifically allows for model-based compensator design and on-line parameter identification. Earlier, related publications discussed linear model structures. Those models described the dynamics around a fixed operating point only. This paper shows how one global model for the whole operating range can be constructed from a linear model and its parameter range.