<p>The aim is to share experience gained when simulating (and doing measurements on) the turbocharged SI-engine as well as describing the limits of current state of the technology. In addition an overview of current boosting systems is provided.</p><p>The target readers of this text are engineers employed in the engine industry as well as academia who will get in contact, or is experienced, with 1D engine performance simulation and/or boosting systems. Therefore the text requires general knowledge about engines.</p><p>The papers included in the thesis are, in reverse chronological order:</p><p>[8] SAE 2005-XX-XXX Calculation accuracy of pulsating flow through the turbine of SI-engine turbochargers - Part 2 Measurements, simulation correlations and conclusions Westin & Ångström</p><p>To be submitted to the 2005 SAE Powertrain and Fluid Systems Conference in San Antonio</p><p>[7] SAE 2005-01-2113 Optimization of Turbocharged Engines’ Transient Response with Application on a Formula SAE / Student engine Westin & Ångström</p><p>Approved for publication at the 2005 SAE Spring Fuels and Lubricants Meeting in Rio de Janeiro</p><p>[6] SAE 2005-01-0222 Calculation accuracy of pulsating flow through the turbine of SI-engine turbochargers - Part 1 Calculations for choice of turbines with different flow characteristics Westin & Ångström</p><p>Published at the 2005 SAE World Congress in Detroit April 11-14, 2005</p><p>[5] SAE 2004-01-0996 Heat Losses from the Turbine of a Turbocharged SI-Engine – Measurements and Simulation Westin, Rosenqvist & Ångström</p><p>Presented at the 2004 SAE World Congress in Detroit March 8-11, 2004</p><p>[4] SAE 2003-01-3124 Simulation of a turbocharged SI-engine with two software and comparison with measured data Westin & Ångström</p><p>Presented at the 2003 SAE Powertrain and Fluid Systems Conference in Pittsburgh</p><p>[3] SIA C06 Correlation between engine simulations and measured data - experiences gained with 1D-simulations of turbocharged SI-engines Westin, Elmqvist & Ångström</p><p>Presented at the SIA International Congress SIMULATION, as essential tool for risk management in industrial product development in Poissy, Paris September 17-18 2003</p><p>[2] IMechE C602/029/2002 A method of investigating the on-engine turbine efficiency combining experiments and modelling Westin & Ångström</p><p>Presented at the 7th International Conference on Turbochargers and Turbocharging in London 14-15 May, 2002</p><p>[1] SAE 2000-01-2840 The Influence of Residual Gases on Knock in Turbocharged SI-Engines Westin, Grandin & Ångström</p><p>Presented at the SAE International Fall Fuels and Lubricants Meeting in Baltimore October 16-19, 2000</p><p>The first step in the investigation about the simulation accuracy was to model the engine as accurately as possible and to correlate it against as accurate measurements as possible. That work is covered in the chapters 3 and 5 and in paper no. 3 in the list above. The scientific contribution here is to isolate the main inaccuracy to the simulation of turbine efficiency.</p><p>In order to have anything to compare the simulated turbine efficiency against, a method was developed that enables calculation of the CA-resolved on-engine turbine efficiency from measured data, with a little support from a few simulated properties. That work was published in papers 2 and 8 and is the main scope of chapter 6 in the thesis. The scientific contributions here are several:</p><p>· The application on a running SI-engine is a first</p><p>· It was proven that CA-resolution is absolutely necessary in order to have a physically and mathematically valid expression for the turbine efficiency. A new definition of the time-varying efficiency is developed.</p><p>· It tests an approach to cover possible mass accumulation in the turbine housing</p><p>· It reveals that the common method for incorporating bearing losses, a constant mechanical efficiency, is too crude.</p><p>The next step was to investigate if different commercial codes differ in the results, even though they use equal theoretical foundation. That work is presented in chapter 4, which corresponds to paper 4. This work has given useful input to the industry in the process of choosing simulation tools.</p><p>The next theory to test was if heat losses were a major reason for the simulation accuracy. The scientific contribution in this part of the work was a model for the heat transport within the turbocharger that was developed, calibrated and incorporated in the simulations. It was concluded that heat losses only contributed to a minor part of the inaccuracy, but that is was a major reason for a common simulation error of the turbine outlet temperature, which is very important when trying to simulate catalyst light off. This work was published in paper 5 and is covered in chapter 7.</p><p>Chapter 8, and papers 6 and 8, covers the last investigation of this work. It is a broad study where the impact of design changes of both manifold at turbines on both simulation accuracy as well as engine performance. The scientific contribution here is that the common theory that the simulation inaccuracy is proportional to the pulsation amplitude of the flow is non-valid. It was shown that the reaction was of minor importance for the efficiency of the turbine in the pulsating engine environment. Furthermore it presents a method to calculate internal flow properties in the turbine, by use of a steady-flow design software in a quasi-steady procedure. Of more direct use for the industry is important information of how to design the manifolds as well as it sheds more light on how the turbine works under unsteady flow, for instance that the throat area is the single most important property of the turbine and that the system has a far larger sensitivity to this parameter than to any other design parameters of the turbine. Furthermore it was proven that the variation among individual turbines is of minor importance, and that the simulation error was of similar magnitude for different turbine manufacturers.</p><p>Paper 7, and chapter 9, cover a simulation exercise where the transient performance of turbocharged engines is optimised with help from factorials. It sorts out the relative importance of several design parameters of turbocharged engines and gives the industry important information of where to put the majority of the work in order to maximize the efficiency in the optimisation process.</p><p>Overall, the work presented in this thesis has established a method for calibration of models to measured data in a sequence that makes the process efficient and accurate. It has been shown that use of controllers in this process can save time and effort tenfold or more.</p><p>When designing turbocharged engines the residual gas is a very important factor. It affects both knock sensitivity and the volumetric efficiency. The flow in the cylinder is in its nature of more dimensions than one and is therefore not physically modelled in 1D codes. It is modelled through models of perfect mixing or perfect displacement, or at a certain mix between them. Before the actual project started, the amount of residual gases in an engine was measured and it’s influence on knock was established and quantified. This was the scope of paper 1. This information has been useful when interpreting the model results throughout the entire work.</p>

A spark ignition engine was retrofitted to operate on biogas fuel. Biogas was synthetically generated through the mixing of various pure gases. The air-fuel ratio was accurately controlled using a closed feedback system consisting of flow controllers and a wide range oxygen sensor. A natural gas catalytic converter was implemented with the use of biogas fuel. To achieve full NOx and CO reduction the engine was required to run at a slightly rich equivalence ratio. Methane emissions posed to be the hardest to reduce across the catalyst. The biogas fuel composition had no effect on the catalyst performance. The catalyst performance was only affected by exhaust temperature and equivalence ratio. The catalyst requires tight A/F ratio control for optimal performance. A Catalytic converter can be used to reach low emissions but requires the knowledge of the biogas fuel composition.

A spark ignition engine was retrofitted to operate on biogas fuel. Biogas was synthetically generated through the mixing of various pure gases. The air-fuel ratio was accurately controlled using a closed feedback system consisting of flow controllers and a wide range oxygen sensor. A natural gas catalytic converter was implemented with the use of biogas fuel. To achieve full NOx and CO reduction the engine was required to run at a slightly rich equivalence ratio. Methane emissions posed to be the hardest to reduce across the catalyst. The biogas fuel composition had no effect on the catalyst performance. The catalyst performance was only affected by exhaust temperature and equivalence ratio. The catalyst requires tight A/F ratio control for optimal performance. A Catalytic converter can be used to reach low emissions but requires the knowledge of the biogas fuel composition.

<p>Emission from cars today is one of the biggest environmental issues, hence stringent government standards have been introduced to decrease emission. Car companies do not only have to satisfy government standards, but also meet consumer demands on increased fuel economy and good drivablility. This report will introduce controllers designed to control the air/fuel ratio in an SI engine. The engine model used is simplified. The engine components modelled include the inlet manifold, fuel dynamics, combustion and exhaust sensor. </p><p>Nonlinearities and delays are inherent in the engine dynamics and as such a Smith Predictor is utilised as the basis for controller structure to compensate for the delays. Here the Smith Predictor is combined with feedforwarding of the mass air charge, which is estimated from both the inlet and combustion models. Therefore different ways of merging the estimates are also explored. </p><p>A real engine was not accesible, thus simulators were implemented using data sets provided by General Motors. Model errors were introduced to test the controllers performance. The proposed methods should be tested on a real engine to ensure that this isa viable approach, as the simulations show it maybe promising to use in practice.</p>

<p>Ion current sensing, where information about the combustion process in an SI-engine is gained by applying a voltage over the spark gap, is currently used to detect and avoid knock and misfire. Several researchers have pointed out that information on peak pressure location and air/fuel ratio can be gained from the ion current and have suggested several ways to estimate these parameters.</p><p>Here a simplified Bayesian approach was taken to construct a lowpass-like filter or estimator that makes use of prior information to improve estimates in crucial areas. The algorithm is computationally light and could, if successful, improve estimates enough for production use.</p><p>The filter was implemented in several variants and evaluated in a number of simulated cases. It was found that the proposed filter requires a number of trade-offs between variance, bias, tracking speed and accuracy that are difficult to balance. For satisfactory estimates and trade-off balance the prior information must be more accurate than was available.</p><p>It was also found that similar a task, constructing a general Bayesian estimator, has already been tackled in the area of particle filtering and that there are promising and unexplored possibilities there. However, particle filters require computational power that will not be available to production engines for some years. </p> / <p>Vid jonströmsmätning utvinns information om förbränningsprocessen i en bensinmotor genom att en spänning läggs över gnistgapet och den resulterande strömmen mäts. Jonströmsmätning används idag för knack- och feltändningsdetektion. Flera forskare har påpekat att det finns än mer information i jonströmmen, bl.a. om bränsleblandningen och cylindertrycket och har även föreslagit metoder för att utvinna och använda den informationen för skattning av dessa parametrar.</p><p>Här presenteras en förenklad Bayesisk metod i form av en lågpassfilter-liknande skattare som använder förkunskap till att förbättra estimat på relevanta områden. Algoritmen är beräkningsmässigt lätt och kan, om den är framgångsrik, leverera skattningar av förbränningsparametrar som är tillräckligt bra för att användas för sluten styrning av en bensinmotor.</p><p>Skattaren, eller filtret, implementerades i flera varianter och utvärderades i ett antal simulerade fall. Resultaten visade på att flera svåra avvägningar måste göras mellan förbättring i varians, avvikelse och följning eftersom förbättring i den ena ledde till försämring i de andra. För att göra dessa avvägningar och få goda skattningar krävs bättre förhandskunskap och mätdata än vad som var tillgängligt.</p><p>Bayesisk skattning är ett stort befintligt område inom statistik och signalbehandling och den mest generella skattaren är partikelfiltret som har många intressanta tillämpningar och möjligheter. De har hittills inte använts inom skattning av förbränningsparametrar och har således go potential för framtida utveckling. De är dock beräkningsmässigt tunga och kräver beräkningsresurser utöver vad som är tillgängliga i ett motorstyrsystem idag.</p>

<p>This masters thesis investigates the possibility to estimate the ethanol content in the fuel using ion currents. Flexible fuel cars can be run on gasoline-ethanol blends with an ethanol content from0 to 85 percentage. It is important for the engine control system to have information about the fuel. In todays cars the measurements of the fuel blend are done by a sensor. If it is possible to do this with ion currents this can be used to detect if the sensor is broken, and then estimate the ethanol content until the sensor gets fixed. The benefit</p><p>of using ion currents is that the signal is measured directly from the spark plug and therefore no extra hardware is needed. To be able to see how the ethanol ratio affects the ion currents, the dependencies of the operating point have been investigated. This has been done by a literature review and by measurements in a Saab 9-3. Engine speed, load, ignition timing, lambda and spark plugs effects on the ion currents are especially studied. A black box model for the ion currents dependence on operating point is developed. This model describes the engine speed, load and ignition timing dependencies well, but it can not be used to estimate the ethanol ratio.</p>

The aim is to share experience gained when simulating (and doing measurements on) the turbocharged SI-engine as well as describing the limits of current state of the technology. In addition an overview of current boosting systems is provided. The target readers of this text are engineers employed in the engine industry as well as academia who will get in contact, or is experienced, with 1D engine performance simulation and/or boosting systems. Therefore the text requires general knowledge about engines. The papers included in the thesis are, in reverse chronological order: [8] SAE 2005-XX-XXX Calculation accuracy of pulsating flow through the turbine of SI-engine turbochargers - Part 2 Measurements, simulation correlations and conclusions Westin &amp; Ångström To be submitted to the 2005 SAE Powertrain and Fluid Systems Conference in San Antonio [7] SAE 2005-01-2113 Optimization of Turbocharged Engines’ Transient Response with Application on a Formula SAE / Student engine Westin &amp; Ångström Approved for publication at the 2005 SAE Spring Fuels and Lubricants Meeting in Rio de Janeiro [6] SAE 2005-01-0222 Calculation accuracy of pulsating flow through the turbine of SI-engine turbochargers - Part 1 Calculations for choice of turbines with different flow characteristics Westin &amp; Ångström Published at the 2005 SAE World Congress in Detroit April 11-14, 2005 [5] SAE 2004-01-0996 Heat Losses from the Turbine of a Turbocharged SI-Engine – Measurements and Simulation Westin, Rosenqvist &amp; Ångström Presented at the 2004 SAE World Congress in Detroit March 8-11, 2004 [4] SAE 2003-01-3124 Simulation of a turbocharged SI-engine with two software and comparison with measured data Westin &amp; Ångström Presented at the 2003 SAE Powertrain and Fluid Systems Conference in Pittsburgh [3] SIA C06 Correlation between engine simulations and measured data - experiences gained with 1D-simulations of turbocharged SI-engines Westin, Elmqvist &amp; Ångström Presented at the SIA International Congress SIMULATION, as essential tool for risk management in industrial product development in Poissy, Paris September 17-18 2003 [2] IMechE C602/029/2002 A method of investigating the on-engine turbine efficiency combining experiments and modelling Westin &amp; Ångström Presented at the 7th International Conference on Turbochargers and Turbocharging in London 14-15 May, 2002 [1] SAE 2000-01-2840 The Influence of Residual Gases on Knock in Turbocharged SI-Engines Westin, Grandin &amp; Ångström Presented at the SAE International Fall Fuels and Lubricants Meeting in Baltimore October 16-19, 2000 The first step in the investigation about the simulation accuracy was to model the engine as accurately as possible and to correlate it against as accurate measurements as possible. That work is covered in the chapters 3 and 5 and in paper no. 3 in the list above. The scientific contribution here is to isolate the main inaccuracy to the simulation of turbine efficiency. In order to have anything to compare the simulated turbine efficiency against, a method was developed that enables calculation of the CA-resolved on-engine turbine efficiency from measured data, with a little support from a few simulated properties. That work was published in papers 2 and 8 and is the main scope of chapter 6 in the thesis. The scientific contributions here are several: · The application on a running SI-engine is a first · It was proven that CA-resolution is absolutely necessary in order to have a physically and mathematically valid expression for the turbine efficiency. A new definition of the time-varying efficiency is developed. · It tests an approach to cover possible mass accumulation in the turbine housing · It reveals that the common method for incorporating bearing losses, a constant mechanical efficiency, is too crude. The next step was to investigate if different commercial codes differ in the results, even though they use equal theoretical foundation. That work is presented in chapter 4, which corresponds to paper 4. This work has given useful input to the industry in the process of choosing simulation tools. The next theory to test was if heat losses were a major reason for the simulation accuracy. The scientific contribution in this part of the work was a model for the heat transport within the turbocharger that was developed, calibrated and incorporated in the simulations. It was concluded that heat losses only contributed to a minor part of the inaccuracy, but that is was a major reason for a common simulation error of the turbine outlet temperature, which is very important when trying to simulate catalyst light off. This work was published in paper 5 and is covered in chapter 7. Chapter 8, and papers 6 and 8, covers the last investigation of this work. It is a broad study where the impact of design changes of both manifold at turbines on both simulation accuracy as well as engine performance. The scientific contribution here is that the common theory that the simulation inaccuracy is proportional to the pulsation amplitude of the flow is non-valid. It was shown that the reaction was of minor importance for the efficiency of the turbine in the pulsating engine environment. Furthermore it presents a method to calculate internal flow properties in the turbine, by use of a steady-flow design software in a quasi-steady procedure. Of more direct use for the industry is important information of how to design the manifolds as well as it sheds more light on how the turbine works under unsteady flow, for instance that the throat area is the single most important property of the turbine and that the system has a far larger sensitivity to this parameter than to any other design parameters of the turbine. Furthermore it was proven that the variation among individual turbines is of minor importance, and that the simulation error was of similar magnitude for different turbine manufacturers. Paper 7, and chapter 9, cover a simulation exercise where the transient performance of turbocharged engines is optimised with help from factorials. It sorts out the relative importance of several design parameters of turbocharged engines and gives the industry important information of where to put the majority of the work in order to maximize the efficiency in the optimisation process. Overall, the work presented in this thesis has established a method for calibration of models to measured data in a sequence that makes the process efficient and accurate. It has been shown that use of controllers in this process can save time and effort tenfold or more. When designing turbocharged engines the residual gas is a very important factor. It affects both knock sensitivity and the volumetric efficiency. The flow in the cylinder is in its nature of more dimensions than one and is therefore not physically modelled in 1D codes. It is modelled through models of perfect mixing or perfect displacement, or at a certain mix between them. Before the actual project started, the amount of residual gases in an engine was measured and it’s influence on knock was established and quantified. This was the scope of paper 1. This information has been useful when interpreting the model results throughout the entire work.

The effects on heat transfer of piston crown surface finish and use of a metal based thermal barrier coating (TBC) on the piston crown were studied in an SI engine. Measured engine parameters such as power, fuel consumption, emissions and cylinder pressure were used to identify the effects of the coating and its surface finish. Two piston coatings were tested: a baseline copper coating and a metal TBC. Reducing surface roughness of both coatings increased in-cylinder temperature and pressure as a result of reduced heat transfer through the piston crown. These increases resulted in small improvements in both power and fuel consumption, while also having measurable effect on emissions. Oxides of nitrogen emissions were increased while total hydrocarbon emissions were decreased. Improvements attributed to the TBC were found to be small, but statistically significant. At an equivalent surface finish, the TBC performed better than the baseline copper finish.

The effects on heat transfer of piston crown surface finish and use of a metal based thermal barrier coating (TBC) on the piston crown were studied in an SI engine. Measured engine parameters such as power, fuel consumption, emissions and cylinder pressure were used to identify the effects of the coating and its surface finish. Two piston coatings were tested: a baseline copper coating and a metal TBC. Reducing surface roughness of both coatings increased in-cylinder temperature and pressure as a result of reduced heat transfer through the piston crown. These increases resulted in small improvements in both power and fuel consumption, while also having measurable effect on emissions. Oxides of nitrogen emissions were increased while total hydrocarbon emissions were decreased. Improvements attributed to the TBC were found to be small, but statistically significant. At an equivalent surface finish, the TBC performed better than the baseline copper finish.

This masters thesis investigates the possibility to estimate the ethanol content in the fuel using ion currents. Flexible fuel cars can be run on gasoline-ethanol blends with an ethanol content from0 to 85 percentage. It is important for the engine control system to have information about the fuel. In todays cars the measurements of the fuel blend are done by a sensor. If it is possible to do this with ion currents this can be used to detect if the sensor is broken, and then estimate the ethanol content until the sensor gets fixed. The benefit of using ion currents is that the signal is measured directly from the spark plug and therefore no extra hardware is needed. To be able to see how the ethanol ratio affects the ion currents, the dependencies of the operating point have been investigated. This has been done by a literature review and by measurements in a Saab 9-3. Engine speed, load, ignition timing, lambda and spark plugs effects on the ion currents are especially studied. A black box model for the ion currents dependence on operating point is developed. This model describes the engine speed, load and ignition timing dependencies well, but it can not be used to estimate the ethanol ratio.