The experiments detailed in this thesis give necessary preliminary information for analyzing the theoretical potential of direct exhaust pulse energy harvesting through expander devices. A detailed review of pertinent literature determined that there has been little specific focus on directly converting exhaust pulse energy into useful power. Crank position resolved exhaust pressure was measured as engine load and speed were varied to quantify their influences. Potential theoretical improvements average a 15.6% increase in overall fuel conversion efficiencies while indicated power can potentially be increased by an average of 14.3% for the operating conditions tested. A potential increase of up to 20% in indicated specific fuel consumption was shown. With increasing regulations on combustion engine efficiencies, emissions, and fuel requirements, the ability to reduce waste energy through improving existing waste energy recovery (WER) technologies and proposing novel WER strategies that maximize WER have the potential to be extremely valuable.

In the European Union the legislation governing fleet CO2 emissions is already in place with a fleet average limit of 130g/km currently being imposed on all vehicle manufacturers. With the target for this legislation falling to 95g/km by 2020 and hefty fines for noncompliance automotive engineers are working a pace to develop new technologies that lower the CO2 emissions and hence fuel consumption of new to market vehicles. As average new vehicle CO2 emissions continue to decline the task of measuring these emissions with high precision becomes increasingly challenging. With the introduction of real world emissions legislation planned for 2017 there is a development driven need to precisely assess the vehicle CO2 emissions on chassis dynamometers over a wide operating range. Furthermore since all type approval and certification testing is completed on chassis dynamometers, any new technology must be proven against these test techniques. Typical technology improvements nowadays require repeatability limits which were unprecedented 5-10 years ago and the challenge now is how to deliver this level of precision. Detailed studies are conducted into the four key areas that cause significant noise to the CO2 emissions results from chassis dynamometer tests. These are the vehicle electrical system, driver behaviour, procedural factors and the chassis dynamometer itself. In each of these areas, the existing contribution of imprecision is quantified, methods are proposed then demonstrated for improving the precision and the improved case is quantified. It was found that the electrical system can be controlled by charging the vehicle battery, not using auxiliary devices and installing current measurement devices on the vehicle. Simply charging the vehicle battery prior to each test was found to cause a change to the CO2 emissions of 2.2% at 95% confidence. Whilst auxiliary devices were found to cause changes to the CO2 emissions of up to 43% for even a relatively basic vehicle. The driver behaviour can be controlled by firstly removing the tolerances from the driver’s aid which it was found improved the precision of the CO2 emissions by 43.5% and secondly by recording the throttle pedal movements to enable the validation of test results. Procedural factors, such as tyre pressures can be easily controlled by resisting the temptation to over check and by installing pressure sensing equipment. Using a modern chassis dynamometer with low parasitic losses will make the job of controlling the dynamometer easier, but all dynamometers can be controlled by following the industry standard quality assurance procedures and implementing statistical process control tools to check the key results. The implementation of statistical process control alone improved the precision of unloaded dynamometer coastdown checks by reducing the coefficient of variation from 6.6 to 4.0%. Using the dynamometer to accelerate the vehicle before coastdown checks was found to approximately halve the variability in coastdown times. It was also demonstrated that verification of the dynamometer inertia simulation and response time are both critically important, as the industry standard coastdown test is insufficient, in isolation, to validate the loading on a vehicle. Six sigma and statistical process control techniques have shown that for complex multiple input single output systems, such as chassis dynamometer fuel economy tests, it is insufficient to improve only one input to the system to achieve a change to the output. As a result, suggested improvements in each noise factor often have to be validated against an input metric rather than the output CO2 emissions. Despite this, the overall level of precision of the CO2 emissions and fuel consumption seen at the start of the research, measured by the coefficient of variation of approximately 2.6%, has been improved by over six times through the simultaneous implementation of the findings from this research with the demonstration of coefficient of variation as low as 0.4%. Through this research three major contributions have been made to the state of the art. Firstly, from the work on driver behaviour an extension is proposed to the Society of Automotive Engineers J2951 drive quality metric standard to include the a newly developed Cumulative Absolute Speed Error metric and to suggest that metrics are reviewed across the duration of a test to identify differences in driving behaviours during a test that do not cause a change to the end of test result. Secondly, the need to instrument the vehicle and test cell to record variability in the key noise factors has been demonstrated. Thirdly, a universal method has been developed and published from this research, to use response modelling techniques for the validation of test repeatability and the correction of CO2 emissions. The impact of these contributions is that the precision of chassis dynamometer emissions tests can be improved by a factor of 6.5 and this is of critical importance as the new real world driving and world light-duty harmonised emissions legislation comes into force over the next two to five years. This legislation will require an unprecedented level of precision for the effective testing of full vehicle system interactions over a larger operating range but within a controlled laboratory environment. If this level of precision is not met then opportunities to reduce vehicle fuel consumption through technology that only has a small improvement on fuel consumption, which is likely given the large advances that have be achieved over the last few decades, will be missed.

In the last decades, the focus of internal combustion engine development has moved towards more efficient and less pollutant engines. In a Diesel engine, approximately 30-40% of the energy provided by combustion is lost through the exhaust gases. The exhaust gases are hot and therefore rich of energy. Some of this energy can be recovered by recycling the exhaust gases into turbocharger. However, the energy losses in the exhaust port are highly undesired and the mechanisms driving the total pressure losses in the exhaust manifold not fully understood. Moreover, the efficiency of the turbine is highly dependent on the upstream flow conditions. Thus, a numerical study of the flow in the exhaust port geometry of a Scania heavy-duty Diesel engine is carried out mainly by using the Large Eddy Simulation (LES) approach. The purpose is to characterize the flow in the exhaust port, analyze and identify the sources of the total pressure losses. Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation results are included for comparison purposes. The calculations are performed with fixed valve and stationary boundary conditions for which experimental data are available. The simulations include a verification study of the solver using different grid resolutions and different valve lift states. The calculated numerical data are compared to existent measured pressure loss data. The results show that even global parameters like total pressure losses are predicted better by LES than by URANS. The complex three-dimensional flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means. The near valve region is a major source of losses. Due to the presence of the valve, an annular, jet-like flow structure is formed where the high-velocity flow follows the valve stem into the port. Flow separation occurs immediately downstream of the valve seat on the walls of the port and also on the surface of the valve body. Strong longitudinal, non-stationary secondary flow structures (i.e. in the plane normal to the main flow direction) are observed in the exhaust manifold. Such structures can degrade the efficiency of a possible turbine of a turbocharger located downstream on the exhaust manifold. The effect of the valve and piston motion has also been studied by the Large Eddy Simulation (LES) approach. Within the exhaust process, the valves open while the piston continues moving in the combustion chamber. This process is often analyzed modeling the piston and valves at fixed locations, but conserving the total mass flow. Using advanced methods, this process can be simulated numerically in a more accurate manner. Based on LES data, the discharge coefficients are calculated following the strict definition. The results show that the discharge coefficient can be overestimated (about 20 %) when using simplified experiments, e. g. flow bench. Simple cases using fixed positions for valve and piston are contrasted with cases which consider the motion of piston and/or valves. The overall flow characteristics are compared within the cases. The comparison shows it is impossible to rebuild the dynamic flow field with the simplification with fixed valves. It is better to employ LES to simulate the dynamic flow and associated losses with valve and piston motion. / <p>QC 20131204</p>

In the past decades, stricter legislation has been imposed to improve fuel economy and to reduce tail-end emissions of automotive vehicles worldwide. One of the important and effective technologies adopted by the automobile manufacturers to fulfill legislation requirements is the turbocharger technology. As unavoidable large temperature gradients exists in an automotive turbocharger, heat transfer is prominent. However, the effects of heat loss on the turbocharger turbine performance is unclear, i.e. there is no consensus about its effects among researchers. Therefore, the objective of the licentiate thesis is to investigate the effects of heat transfer on an automotive turbocharger radial turbine performance. Furthermore, the thesis also aims to quantify the heat transfer related losses in a turbocharger turbine. Both gas stand (continuous flow) and engine-like (pulsating flow) conditions are considered. By using Detached Eddy Simulation (DES), the flow field of the targeted turbocharger turbine is computed under adiabatic and non-adiabatic conditions. Energy balance and exergy concept are then applied to the simulations data to study the effects of heat loss on performance and to quantify the heat transfer related losses. The main findings of the licentiate thesis are 1) Pressure ratio drop in turbine is less sensitive to heat loss as compared with turbine power. Hence there is a risk of making wrong conclusions about the heat transfer effects on the turbine performance by just comparing the measured pressure ratio under adiabatic and non-adiabatic scenarios; 2) It is possible to quantify heat transfer related losses in a turbocharger turbine. This quantification allows understanding on how well the turbine system utilizes the available energy, and assisting identification of the system component that is sensitive to heat transfer; 3) Heat loss has insignificant effect on turbine power under the investigated engine-like pulsating flow condition; and 4) Even under unavoidable non-adiabatic conditions, much of the exergy discharged out to the environment and more effort could be done to recover the wasted exergy as useful turbine work in the current turbine system. The outcomes of the licentiate thesis naturally lead to the main focus of future work, i.e. exploring different exhaust valve strategies to minimize losses and to optimize flow exergy extraction as useful turbine work for better exhaust gas exergy utilization. / Under de senaste decennierna har allt strängare lagstiftning införts för att förbättra bränsleekonomin och minska avgasutsläppen från motorfordon världen över. En av de viktigaste och mest effektiva tekniker som införts av biltillverkarna för att kunna uppfylla lagkraven är turboladdartekniken. Eftersom stora temperaturgradienter existerar i en fordonsturboladdare, spelar värmeöverföring en framträdande roll. Emellertid är effekterna av värmeförluster på turboturbinprestanda oklar, dvs det finns ingen konsensus bland forskare om dess effekter. Syftet med denna licentiatavhandling är därför att undersöka effekterna av värmeöverföring på prestanda för radialturbinen i en fordonsturboladdare. Vidare syftar avhandlingen till att kvantifiera värmeöverföringsrelaterade förluster i en turboladdares turbin. Både fall med kontinuerligt gas flöde och motorliknande, pulserande flöde beaktas. Strömningsfältet i den utvalda turboladdarens turbin beräknas med en metod kallad Detached Eddy Simulation (DES) under adiabatiska och icke adiabatiska förhållanden. Energi- och exergibalanser för simuleringsresultaten analyseras sedan för att studera effekterna av värmeförluster på prestanda och kvantifiera värmeöverföringsrelaterade förluster. De viktigaste resultaten av licentiatuppsatsen är 1) Tryckförhållandet över turbinen är mindre känsligt för värmeförluster jämfört med turbineffekten. Därmed finns det en risk för att felaktiga slutsatser dras beträffande effekterna av värmeöverföring på turbinprestanda genom att enbart jämföra det uppmätta tryckförhållandet under adiabatiska och icke adiabatiska förhållanden; 2) Det är möjligt att kvantifiera värmeöverföringsrelaterade förluster i en turboladdares turbin. Denna kvantifiering ger förståelse för hur väl turbinsystemet utnyttjar den tillgängliga energin, och bistår med identifiering av systemkomponenter som är känsliga för värmeöverföring; 3) Värmeförluster har en obetydlig inverkan på turbineffekten för det undersökta motorliknande, pulserande flödesförhållandet; och 4) Under oundvikliga, icke-adiabatiska förhållanden, släpps även en stor del av exergin ut till omgivningen och det finns utrymme för förbättringar gällande exergiutnyttjandet i det aktuella turbinsystemet. Baserat på resultaten av licentiatavhandlingen kommer det fortsatta arbetet att fokusera på att utforska olika avgasventilstrategier för att minimera förluster och optimera omvandling av flödesexergi till användbart turbinarbete för bättre avgasexergiutnyttjande. / <p>QC 20161213</p> / KTH CCGEx HOTSIDE project

The aim ofthe study was to provideinformation and experience gained with fine wire thermocouples (TCs)or resistance wire thermometers (RWTs) temperature signals to estimate the timeresolved heat transfercoefficient. Constant current method was assumed in the study and medium used in this study was air. Here the heat balance equation has been described, different Nucorrelations and further discusses potential hurdles and difficulties one may encounter while calculating heat transfer coefficient. As asolution, the use of an appropriate heatbalance equation and lowpass filter was suggested as this provides a more accurate fitting. The investigation was carried out for Reynolds number (Re) 103 to 107 and Prandlt number (Pr) 0.734. The impact of the Re and Pr on the Nusselts number (Nu) around a cylinder was represented and all the results were compared with GT-POWER engine simulation software. / Syftet med studien var att tillhandahålla information och erfarenhet från fina trådtermoelement (TC) eller motståndstrådstermometrar (RWT) temperatursignaler för att uppskatta den tidsupplösta värmeöverföringskoefficienten. Metoden med konstant flöde antogs i studien och mediet som användes i denna studie var luft. Här har värmebalansekvationen beskrivits, olika Nu-korrelationer och diskuterat ytterligare potentiella hinder och svårigheter man kan stöta på vid beräkning av värmeöverföringskoefficienten. Som en lösning föreslogs användning av en lämplig värmebalansekvation och lågpassfilter eftersom detta ger en mer exaktpassform. Undersökningen genomfördes för Reynoldsnummer (Re) 103 till 107 och Prandlt nummer (Pr) 0,734. Effekten av Re och Pr på Nusselts-numret (Nu) runt en cylinder representerades och alla resultat jämfördes med GT-POWER-motorns simuleringsprogram.