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Variable compression engines are a mean to meet the demand on lower fuel consumptions. A high compression ratio results in high engine efficiency, but also increases the knock tendency. On conventional engines with fixed compression ratio, knock is avoided by retarding the ignition angle. The variable compression engine offers an extra dimension in knock control, since both ignition angle and compression ratio can be adjusted. A vital question is thus what combination of compression ratio and ignition angle should be used to achieve maximum engine efficiency. Fuel optimal control of a variable compression engine is studied and it is shown that a crucial component is the model for the engine torque. A model for the produced work that captures the important effects of ignition and compression ratio is proposed and investigated. The main task for the model is to be a mean for determining the fuel optimal control signals, for each requested engine torque and speed.

The objective is to investigate models of the specific heat ratio for the single-zone heat release model, and find a model accurate enough to introduce a modeling error less than or in the order of the cylinder pressure measurement noise, while keeping the computational complexity at a minimum. Based on assumptions of frozen mixture for the unburned mixture and chemical equilibrium for the burned mixture, the specific heat ratio is calculated using a full equilibrium program for an unburned and a burned air-fuel mixture, and compared to already existing and newly proposed approximative models of γ. A two-zone mean temperature model, Matekunas pressure ratio management and the Vibe function are used to parameterize the mass fraction burned. The mass fraction burned is used to interpolate the specific heats for the unburned and burned mixture, and then form the specific heat ratio, which renders a small enough modeling error in γ.

Observers for air mass flow to the cylinder is studied on a turbocharged SI-engine with wastegate. A position change of the wastegate influences the residual gas mass and causes the volumetric efficiency to change, which produces a transient in the air mass flow to the cylinder. Two standard methods of estimating air-to-cylinder are investigated. A new nonlinear air-to-cylinder observer is suggested with two states: one for intake manifold pressure and one for the offset in in-cylinder air mass compared to expected through the volumetric efficiency. The observers are validated on intake manifold pressure data from a turbocharged spark ignited production engine with wastegate.

Throttles and wastegates are devices used in modern engines for accurate control of the gas flows. It is beneficial, for the control implementation, to have compact and accurate models that describe the flow behavior. The compressible isentropic restriction is a frequently used model, it is simple and reasonable accurate but it has some issues. One special issue is that it predicts that the choking occurs at too high pressure ratios, for example the isentropic model predicts choking at a pressure ratio of 0.52, while experimental data can have choking at 0.4 or even lower. In this work, experimental data is acquired from throttles tested both in a flow bench and mounted as main throttle on a turbocharged gasoline engine. To analyze the flow behavior several flow characterizations are performed at different throttle openings.

A program package, that calculates chemical equilibrium and thermodynamic properties of reactants and products of a combustion reaction between fuel and air, has been developed and validated. The package consists of the following four parts: 1) A program for calculating chemical equilibrium. 2) A database that contains thermochemical information about the molecules, which comes from the GRI-Mech tables. 3) A GUI that allows the user to easily select fuels, fuel/air ratio for the reaction, and combustion products. 4) A set of functions designed to access the thermochemical database and the chemical equilibrium programs. Results are validated against both the NASA equilibrium program (Gordon and McBride, 1994) and the program developed by Olikara and Borman (1975). It is shown that the new method gives results identical to those well recognized Fortran programs.

The work extends a methodology, for searching for optimal heat release profiles, by adding complex constraints on states. To find the optimum heat release profile a methodology, that uses available theory and methods, was developed that enables the use of state of the art optimal control software to find the optimum combustion trace for a model. The methodology is here extended to include constraints and the method is then applied to study how sensitive the solution is to different effects such as heat transfer, crevice flow, maximum rate of pressure rise, maximum pressure, knock and NO generation. The Gatowski single zone model is extended to a pseudo two zone model, to get an unburned zone that is used to describe the knocking and a burned zone for NO generation. A modification of the extended Zeldovich mechanism that makes it continuously differentiable, is used for NO generation.

Three methods for estimating the compression from measured cylinder pressure traces are described and evaluated for both motored and fired cycles against simulated and measured cylinder pressure. The first two rely upon a model of polytropic compression, and it is shown that they give a good estimate of the compression ratio for simulated cycles for low compression ratios. For high compression ratios, these simple models lack the information about heat transfer. The third method includes a standard heat transfer and crevice effect model, together with a heat release model and is able to estimate the compression ratio more accurately.

The combustion process has a high impact on the engine efficiency, and in the search for efficient engines it is of interest to study the combustion. Optimization and optimal control theory is used to compute the most efficient combustion profiles for single zone model with heat transfer and crevice effects. A model is first developed and tuned to experimental data, the model is a modification of the well known Gatowski et al.-model [1]. This model is selected since it gives a very good description of the in-cylinder pressure, and thus the produced work, and achieves this with a low computational complexity. This enables an efficient search method that can maximize the work to be developed. First, smooth combustion profiles are studied where the combustion is modeled using the Vibe function, and parametric optimization is used to search for the optimal profile.

Variable cam timing engines pose new questions for engine control system designers. The cam timing directly influences cylinder air charge and residual mass fraction. Three models that predict residual mass fraction are investigated for a turbocharged dual independent Variable Cam Timing (VCT) engine. The three models (Fox et. al. 1993, Ponti et. al. 2002, and Mladek et. al. 2000) that all have real time capabilities are evaluated and validated against data from a crank angle based reference model. None of these models have previously been validated to cover this engine type. It is shown that all three models can be extended to dual independent VCT engines and that they also give a good description of the residual gas fraction. However, it is shown that the two most advanced models, based on a thermodynamic energy balance, are very sensitive to the model inputs and proper care must therefore be taken when these models are used.

Mean value cylinder air charge (CAC) estimation models for control and diagnosis are investigated on turbocharged SI-engines. Two topics are studied; Firstly CAC changes due to fuel enrichment and secondly CAC sensitivity to exhaust manifold pressure changes. The objective is to find a CAC model suitable for control and diagnosis. Measurements show that CAC models based on volumetric efficiency gives up to 10% error during fuel enrichment. The error is caused by the cooling effect that the fuel has as it evaporates and thus increases the charge density. To better describe the CAC during fuel enrichment a simple one parameter model is proposed which reduces the CAC estimation error on experimental data from 10% to 3%. With active wastegate control, the pressure changes in the exhaust manifold influences the CAC. The magnitude of this influence is investigated using sensitivity analysis on an exhaust manifold pressure dependent CAC-model.

It is important to determine the phasing of a measured cylinder pressure trace and crank angle with high accuracy. The reason is that erroneous determination of the position of TDC is a major error source when calculating properties such as heat release etc. A common way to determine the TDC position is to study motored cycles. Heat transfer makes the task more complicated, since it shifts the position of the maximum pressure away from TDC. In this paper a new method for determining the TDC position is proposed that does not require any additional sensors other than a cylinder pressure sensor and an incremental encoder. The idea is to find a point that the cylinder pressure from a motored cycle is symmetric around, since the volume is close to symmetric on either side of TDC. The new method and four published methods are tested and evaluated. Cylinder pressure data used for comparison are from simulations of a SAAB Variable Compression engine.

Today’s need for fuel efficient vehicles, together with increasing engine component complexity, makes optimal control a valuable tool in the process of finding the most fuel efficient control strategies. To efficiently calculate the solution to optimal control problems a gradient based optimization technique is desirable, making continuously differentiable models preferable. Many existing control-oriented Diesel engine models do not fully posses this property, often due to signal saturations or discrete conditions. This paper offers a continuously differentiable, mean value engine model, of a heavy-duty diesel engine equipped with VGT and EGR, suitable for optimal control purposes. The model is developed from an existing, validated, engine model, but adapted to be continuously differentiable and therefore tailored for usage in an optimal control environment. The changes due to the conversion are quantified and presented.

Cylinder air-charge is one of the most important parts of the torque control in a gasoline engine, due to the necessity to keep a stoichiometric air-fuel ratio, for the three-way catalyst to work efficiently. Throttle and phasing of the camshafts are actuators that have a big effect on the cylinder air-charge, this results in a cross-coupling between the actuators. One approach to handle the cross-coupling that occurs with multiple actuators is to use model predictive control (MPC), that handles the cross-coupling through the use of models and optimization. Models that support computation of gradients and hessians are desirable for use in MPC. To support the model design experimental data of cylinder pressure, from an inline four-cylinder engine with dual independent cam phasing, supported by gas exchange simulation, the effects from variable valve timing on the cylinder air-charge are investigated during the valve overlap period.

A method for determining turbocharger performance on installations in an engine test bench is developed and investigated. The focus is on the mapping of compressor performance but some attention is also given to the turbine mapping. An analysis of the limits that an engine installation imposes on the reachable points in the compressor map is performed, in particular it shows what corrected flows and pressure ratios can be reached and what these limitations depend on. To be able to span over a larger region of the corrected flow a throttle before the compressor is suggested and this is also verified in the test bench. Turbocharger mapping is a time consuming process and there is a need for a systematic process that can be executed automatically. An engine and test cell control structure that can be used to automate and monitor the measurements by controlling the system to the desired operating points is also proposed.

The aim of this paper is to compile the state of the art of engine control and develop scenarios for improvements in a number of applications of engine control where the pace of technology change is at its most marked. The first application is control of downsized engines with enhancement of combustion using direct injection, variable valve actuation and turbo charging. The second application is electrification of the powertrain with its impact on engine control. Various architectures are explored such as micro, mild, full hybrid and range extenders. The third application is exhaust gas after-treatment, with a focus on the trade-off between engine and after-treatment control. The fourth application is implementation of powertrain control systems, hardware, software, methods, and tools. The paper summarizes several examples where the performance depends on the availability of control systems for automotive applications.

The combustion stability of a direct injected spark ignited engine depends on the injection timing and it is desirable to have controller that minimizes the combustion variability. A novel approach for determining combustion stability in stratified mode is presented that rely on the ionization current and enables closed loop control of the injection timing. The co-efficient of variation for IMEP is used as a measure of combustion stability and a connection between maximum torque and low combustion variability is pointed out. The coefficient of variation of the ion current integral is well correlated with the coefficient of variation for IMEP. Furthermore, it is shown how the integral of the ion current together with COV(ion integral) can be used to determine the combustion stability and to distinguish high combustion stability from misfire.

Exhaust temperatures are important for turbine and catalyst performance. A set of exhaust temperature models suitable for turbo matching as well as design and analysis of engine control systems are developed and investigated. The models are lumped parameter heat transfer models, that fall within the category of mean value engine models. The model is developed for describing exit temperatures from the exhaust manifold and temperature drops in pipe sections in the exhaust system. The components used to model the exhaust temperature are: engine out temperature, temperature drop in a straight pipe, and a set of heat transfer modes. The model is validated using data from three different engines. It is shown that, for a spark ignited engine operating at MBT and stoichiometric conditions, it is sufficient to model the engine out temperature as a linear function of mass flow. Recommendations for tuning the model are also given.

Three methods for compression ratio estimation based on cylinder pressure traces are developed and evaluated for both motored and fired cycles. Two methods rely upon models of polytropic compression and expansion for the cylinder pressure. It is shown that they give a good estimate of the compression ratio, although the estimates are biased. A method based on a variable projection algorithm with a logarithmic norm of the cylinder pressure, which uses interpolation of polytropic models of the expansion and compression asymptotes, is recommended when computational time is an important issue. For motored cycles it yields the smallest bias and confidence intervals for these two methods. For firing cycles a user-specified weighting factor is needed during the combustion phase, which pays off in a smaller estimation bias but also a higher variance. The third method includes heat transfer, crevice effects, and a commonly used heat release model for firing cycles.

Exhaust aftertreatment systems are essential components in modern powertrains, needed to reach the low legislated levels of NOx and soot emissions. A well designed diesel engine exhaust aftertreatment system can have NOx conversion rates above 95%. However, to achieve high conversion the aftertreatment system must be warm. Because of this, large parts of the total NOx emissions come from cold starts where the engine has been turned off long enough for the aftertreatment system to cool down and loose its capacity to reduce NOx. It is therefore important to understand how the aftertreatment cools down when the engine in turned off. Experimental data for a catalyst cool-down process is presented and analyzed. The analysis shows that it is important to capture the spatial distribution of temperatures both in axial and radial directions. The data and analysis are used to design a catalyst thermal model that can be used for model based catalyst temperature monitoring and control.

Spark ignited engines require accurate control of both air and fuel, and one important component in this system is the throttle servo. A non-linear throttle model is built and used for control design. It is shown that the non-linear model-based controller improves the performance compared to a conventional gain scheduled PI controller. Furthermore a method for estimating the load torque that the air flow produces on the throttle shaft is presented.