Rocket combustors and other high-performance chemical propulsion systems are prone to combustion instability. Recent simulations of rocket combustors using detailed chemical kinetics show that the constant pressure assumption used in classical treatments may be suspect due to high rates of heat release. This study is a exploration on the effects of these extraordinary rates of heat addition on the local pressure field, and interactions between the heat release and an acoustic field. <br> <br>The full problem is decomposed into simpler unit problems focused on the particular interactions of physical phenomena involved in combustion instability. The overall strategy consists of analyzing fundamental problems with simplified scenarios and then build up the complexity by adding more phenomena to the analysis. Seven unit problems are proposed in this study. <br> <br>The first unit problem consists of the pressure response to an unsteady heat release source in an unconfined one-dimensional domain. An analytical model based on the acoustic wave equation with planar symmetry and an unsteady heat source is derived and then compared against results from highly-resolved numerical simulations. Two different heat release profiles, one a Gaussian spatial distribution with a step temporal profile, and the other a Gaussian spatial distribution with a Gaussian temporal distribution, are used to model the heat source. The analytical solutions predict two different regimes in the pressure response depending on the Helmholtz number, which is defined as the ratio of the acoustic time over the duration of the heat release pulse. A critical Helmholtz number is found to dictate the pressure response regime. For compact cases, in the subcritical regime, the amplitude of the pressure pulse remains constant in space. For noncompact cases, above the critical Helmholtz number, the pressure pulse reaches a maximum at the center of the heat source, and then decays in space converging to a lower far field amplitude. At the limits of very small and very large Helmholtz numbers, the heat release response tends to be a constant pressure process and a constant volume process, respectively. The parameters of the study are chosen to be representative of the extreme conditions in a rocket combustor. The analytical models for both heat source profiles closely match the simulations with a slight overprediction. The differences observed in the analytical solutions are due to neglecting mean flow property variations and the absence of loss mechanisms. The numerical simulations also reveal the presence of nonlinear effects such as weak shocks that cannot be captured by the linear acoustic wave equation. <br> <br>The second unit problem extends the analysis of the pressure response of an unsteady heat release source to an unconfined three-dimensional domain. An analytical model based on the spherical acoustic wave equation with an unsteady heat source is derived and then compared against results from highly-resolved three-dimensional numerical simulations. Two different heat release profiles, a three-dimensional Gaussian spherical distribution with either a step or a Gaussian temporal distribution, are used to model the heat source. Two different regimes in the pressure response depending on the Helmholtz number are found. This analysis also reveals that whereas for the one-dimensional case the pressure amplitude is constant over the distance, for the three-dimensional case it decays with the radial distance from the heat source. In addition, although for moderate heat release values the analytical solution is able to capture the dynamics of the fluid response, for large heat release values the nonlinear effects deviate the highly-resolved numerical solution from the analytical model. <br> <br>The third unit problem studies the pressure response of a fluctuating unsteady heat release source to an unconfined one-dimensional domain. An analytical model based on the acoustic wave equation with planar symmetry and an unsteady heat source is derived and then compared against results from highly-resolved numerical simulations. Two different heat release profiles, a flat spatial distribution with sinusoidal temporal profile and a Gaussian spatial distribution and sinusoidal temporal profile, are used to model the heat source. For both cases, the acoustically compact and noncompact regimes depending on the Helmholtz number are analyzed. While in the compact regime the amplitude of the pressure is constant over the distance, in the noncompact regime the amplitude of the pressure fluctuation is larger within the heat source area of application, and once outside the heat source decays to a far field pressure value. In addition, the analytical model does not capture the nonlinear effects present in the highly-resolved numerical simulations for large rates of heat release such as the ones present in rocket combustors.<br> <br>Finally, the last four unit problems focus on the interaction between unsteady heat release and the longitudinal acoustic modes of a combustor. The goal is to assess and quantify how pressure fluctuations due to unsteady heat release amplify a longitudinal acoustic mode. To investigate the nonlinear effects and the limitations based on the acoustic wave equation, the analytical models are compared against highly-resolved numerical simulations. The fourth unit problem consists of the pressure response to a moving rigid surface that generates a forced sinusoidal velocity fluctuation in a one-dimensional open-ended cavity. The fifth unit problem combines an analytical solution from the velocity harmonic fluctuation with an unsteady heat pulse with Gaussian spatial and temporal distribution developed in the first unit problem. The choice of an open-ended cavity simplifies the analysis and serves as a stepping stone to the sixth unit problem, which also includes the pressure reflections provoked by the acoustic boundaries of the duct. This sixth unit problem describes the establishment of a 1L acoustic longitudinal mode inside a closed duct using the harmonic velocity fluctuations from the fourth unit problem. A wall on the left end of the duct is only moved for one cycle at the 1L mode frequency to establish a 1L mode in the initially quiescent fluid. The last unit problem combines the analytical solution of the 1L mode acoustic field developed in the sixth unit problem with an unsteady heat pulse with Gaussian spatial and temporal distribution, and also accounts for pressure reflections. The derivation of the present analytical models includes the identification of relevant length and time scales that are condensed into the Helmholtz number, the phase shift between the longitudinal fluctuating pressure field and the heat source, and ratio of the fluctuating periods. The analytical solution is able to capture with an acceptable degree of accuracy the pressure trace of the numerical solution during the fist few cycles of the 1L mode, but it quickly deviates very significantly from the numerical solution due to wave steepening and the formation of weak shocks. Therefore, models based on the acoustic wave equation can provide a good understanding of the combustion instability behavior, but not accurately predict the evolution of the pressure fluctuations as the nonlinear effects play a major role in the combustion dynamics of liquid rocket engines.

The present thesis deals with the fundamental aspects of turbulent mixingand non-premixed combustion in wall-jet flows. Direct numerical simulations(DNS) of compressible turbulent flows are performed in a wall-jet configura-tion, which has a close resemblance to many industrial combustion applica-tions. The triple ”turbulence-chemistry-wall” interactions are also present inthis flow set-up. These interactions have been addressed by first focusing onturbulent flow effects on the isothermal reaction, including the near-wall issues.Then, by adding heat-release to the simulations, it has been concentrated onheat-release effects on various phenomena that occur in the reacting turbulentwall-jet flow. In the computational domain, fuel and oxidizer enter separatelyin a non-premixed manner and the flow is fully turbulent and subsonic in allsimulations. In the first phase of this study, the case of a turbulent wall-jetincluding an isothermal reaction without heat release is addressed in order toisolate the near-wall effects and the mixing characteristics of the flow and thekey statistics for combustion are studied in the absence of thermal effects. Adeeper insight into three-dimensional mixing and reaction characteristics in aturbulent wall-jet has been gained through investigation of the probability den-sity functions, higher order moments of velocities and reacting scalars and thescalar dissipation rates of different species. In the second phase, DNS of turbu-lent reacting wall-jets including heat release is performed, where a single-stepglobal exothermic reaction with an Arrhenius-type reaction rate is considered.The main target was to identify the heat-release effects on different mixingscales of turbulent wall-jet flow. The scalar dissipation rates, time scale ratios,two-point correlations, one and two-dimensional premultiplied spectra are usedto illustrate the heat release induced modifications. It is observed that heatrelease effects delay the transition process in the chemically reacting cases andenlarge the fluctuation intensities of density and pressure, but have a dampingeffect on all velocity fluctuation intensities. Finer small mixing scales were ob-served in the isothermal simulations and larger vortical structures formed afteradding significant amounts of heat-release. Simulations with different Damk ̈h-  oler numbers, but comparable temperature-rise are performed and the expectedbehavior, a thinner flame with increasing Damk ̈hler number, is observed. Finally, some heat transfer related quantities are examined. The wall heat fluxand the corresponding Nusselt numbers are addressed. The near-wall reactioneffects on the skin friction coefficient are studied and further the reaction char-acteristics are investigated throughout the domain. / QC 20110908

Closed-loop combustion control is an on-going field of research for improving reducing engine emissions and increasing efficiency. Cylinder pressure is a key parameter to monitor for combustion feedback. Measuring pressure with a transducer is an option, although being able to estimate the pressure based on the crank angle measurement instead would be beneficial in terms of costs. A virtual crank angle based pressure sensor was therefore developed within this thesis. It was studied how the in-cylinder pressure trace for a full closed cycle could be modelled from a pressure trace from a rigid crankshaft model, the angular velocity measurement and heat release modelling. The pressure trace from the crankshaft model was subjected to a singularity at TDC and torsional oscillations, it was therefore of interest to study whether the singularity could be avoided by modelling the heat release. Further on, the indicated work and total heat released during combustion were estimated from the angular velocity measurements as they are important parameters for determining the heat release trace.   It was found that the indicated work could be approximated by comparing the kinetic power trace, obtained from the measured angular velocity, with the piston power trace, estimated using isentropic pressure curves for the compression and expansion within the cylinder. Accurate results were obtained for operating points at 800 rpm while large deviations were seen for higher speeds as a consequence of larger torsional effect on the angular velocity trace; on the form of perturbed oscillations. The results could be improved from local averaging of the kinetic power trace at the occasions of deceleration, although it could be concluded that only the low speed operating were still accurate enough.   The kinetic power trace was attempted to be corrected for torsional power using angular displacement estimations of the crankshaft nodes from a dynamic crankshaft model. Even though the model seemed to capture the torsional behaviour at parts of the cycle, the oscillations could not be completely removed and it was determined that the final work estimate could not be improved from the torsional power estimate. The torsion was further studied regarding frequency and amplitude of the oscillations within the angular velocity and acceleration trace. No clear relations between the torsional behaviour and operating speed and load could be concluded. Further, since inversion of the dynamic crankshaft model for pressure estimation resulted in an improper solution since before, the model was iterated instead. The pressure trace could thereby be derived accounting for torsion, however the trace still contained oscillations which highlights the challenge of estimating the torsion accurately. The torsion is a complex phenomenon to describe and further development of a model for estimating the torsion with high accuracy for all operating points would improve the virtual pressure sensor significantly.   The heat release was, as a first step, modelled as isochoric and isobaric. These models gave information of the limits of SOC by comparing the indicated work from the resulting pressure trace with the work estimate from the angular velocity measurement. Further, one Wiebe function was parametrised such that the resulting pressure derivative during late combustion was adapted to the trace from the crankshaft model in a least-square sense. This allowed for better adaption as the partial pressure trace was subjected to torsional oscillations. The fitted Wiebe function described the diffusive combustion well but missed out the shape of the premixed combustion. Lastly, a double Wiebe function parametrisation was done where the diffusive combustion function was fitted to the late combustion data and the premixed combustion function was adapted such that the resulting indicated work matched the estimated work. To receive more accurate results, the premixed SOC and duration had to be approximated beforehand from the kinetic power trace. The virtual pressure sensor and most of the sub models were most accurate for low speed operating points. It was concluded that the reason is most probably the torsional effect on the input data to all sub models. It was shown that the crankshaft model can be complemented with heat release estimations which improved the final pressure trace and removed the singularity present around TDC. / Förbränningsåterkoppling är ett aktuellt forskningsområde inom utvecklingsarbetet för att minska utsläpp och öka verkningsgraden hos förbränningsmotorer. Cylindertryck är en viktig parameter att mäta . Ett alternativ är att använda en tryckgivare men det skulle vara mer kostnadseffektivt att kunna uppskatta trycket baserat på vevvinkeln som redan idag mäts i motorer. Därav utvecklades en virtuell sensor för uppskattning av cylindertrycket genom detta examensarbete. Studien har berört hur tryck spår, bitvis noggranna för kompressionen och expansionen, från en stel vevaxelmodell kan kompletteras med modeller för värmeavgivningen från förbränningen för att erhålla ett fullt tryck spår. För att kunna bygga och utveckla modellerna utvecklades en metod för att bestämma det indikerade arbetet baserat på den uppmätta varvtalssignalen som beror mycket på hur förbränningen skett och är därmed en viktig parameter vid modellerande av värmeavgivningen.   Det indikerade arbetet kunde uppskattas genom att jämföra den kinetiska effekten med den effekt som kolvarna totalt bidrog med. Det upptäcktes att offseten mellan kurvorna motsvarade effekten av förlusterna och lasten som därmed kunde bestämmas vid de punkter där momentet från cylindrarna var i jämvikt. Den kinetiska effekten beräknades från varvtalssignalen medan effekten från kolvarna uppskattades genom att använda isentropiska tryckkurvor för kompressionen och expansionen, innan och efter förbränningen respektive. Relativt noggranna resultat erhölls för arbetspunkterna med ett varvtal på 800 rpm medan större avvikelser inträdde vid högre varvtal. Anledningen till detta var att torsionssvängningar influerade varvtalssignalen mer vid högre varvtal. Resultaten kunde förbättras genom lokal medelvärdesbildning av den kinetiska effekten vid de decelerationer som sker efter förbränningen i respektive cylinder. II   Torsionens inverkan på vevaxelns dynamik uppskattades genom att använda estimeringar av förvridningen av vevaxeln från en dynamisk vevaxelmodell. Uppskattningen tycktes vara tillräckligt noggrann inom vissa intervall men det var inte möjligt att avlägsna torsionssvängningarna i kinetiska effektspåret för hela cykeln. Uppskattningen av indikerat arbete kunde därför inte förbättras genom denna torsionsuppskattning. Torsionen var vidare studerad i form av frekvens och amplitud av svängningarna inom varvtalssignalen. Inga tydliga samband kunde säkerställas mellan svängningarna och arbetspunkternas varvtal och last. Detta tyder på att torsionen är för komplex att förutse. Vidare, då invertering av den dynamiska vevaxelmodellen tidigare visat sig ge en oriktig lösning kunde modellen istället itereras för att bestämma tryck spåret likt tidigare gjort för den stela vevaxelmodellen. Torsionssvängningarna influerade dock fortfarande det resulterande tryck spåret. Det finns stor potential att förbättra den virtuella sensorn om torsionen kan uppskattas noggrant för alla arbetspunkter.   Värmeavgivningen från förbränning var först modellerad som isochorisk och isobarisk i två respektive modeller. Dessa modeller gav information om gränsvärdena för tändningen genom att finna den tändning för modellerna som resulterade i samma arbete som det tidigare estimerade indikerade arbetet. Därefter anpassades en Wiebe funktion så att den resulterande tryckderivatan minsta-kvadrat anpassades till tryckderivatan från vevaxelmodellen under den sena förbränningen där vevaxelmodellen var mest noggrann. Wiebe funktion gav en bra anpassning till den senare diffusiva förbränningen men var inte tillräcklig för att beskriva den förblandade förbränningen. Slutligen anpassades två Wiebe funktioner där den diffusiva förbränningen anpassades likt för singel Wiebe-funktions anpassningen medan den förblandade förbränningen anpassades så att det resulterande arbetet stämde med det uppskattade indikerade arbetet. För att få bättre resultat bestämdes den förblandade förbränningens start och duration från uppskattningen av den kinetiska effekten innan anpassningen.   Den virtuella trycksensorn och de flesta av dess delmodeller var mest noggranna för arbetspunkterna vid låga varvtal. Slutsatsen var att det var främst på grund av torsionssvängningarnas påverkan på insignalerna till delmodellerna som noggrannheten föll för de högra varvtalen. Genom denna studie visades det att deltrycksspåret från vevaxelmodellen kunde kompletteras med en modell för värmeavgivningen för att slutligen få en bättre uppskattning av hela tryck spåret där singulariteten vid TDC kunde undvikas.

Closed-loop combustion control is an on-going field of research for improving reducing engine emissions and increasing efficiency. Cylinder pressure is a key parameter to monitor for combustion feedback. Measuring pressure with a transducer is an option, although being able to estimate the pressure based on the crank angle measurement instead would be beneficial in terms of costs. A virtual crank angle based pressure sensor was therefore developed within this thesis. It was studied how the in-cylinder pressure trace for a full closed cycle could be modelled from a pressure trace from a rigid crankshaft model, the angular velocity measurement and heat release modelling. The pressure trace from the crankshaft model was subjected to a singularity at TDC and torsional oscillations, it was therefore of interest to study whether the singularity could be avoided by modelling the heat release. Further on, the indicated work and total heat released during combustion were estimated from the angular velocity measurements as they are important parameters for determining the heat release trace. It was found that the indicated work could be approximated by comparing the kinetic power trace, obtained from the measured angular velocity, with the piston power trace, estimated using isentropic pressure curves for the compression and expansion within the cylinder. Accurate results were obtained for operating points at 800 rpm while large deviations were seen for higher speeds as a consequence of larger torsional effect on the angular velocity trace; on the form of perturbed oscillations. The results could be improved from local averaging of the kinetic power trace at the occasions of deceleration, although it could be concluded that only the low speed operating were still accurate enough. The kinetic power trace was attempted to be corrected for torsional power using angular displacement estimations of the crankshaft nodes from a dynamic crankshaft model. Even though the model seemed to capture the torsional behaviour at parts of the cycle, the oscillations could not be completely removed and it was determined that the final work estimate could not be improved from the torsional power estimate. The torsion was further studied regarding frequency and amplitude of the oscillations within the angular velocity and acceleration trace. No clear relations between the torsional behaviour and operating speed and load could be concluded. Further, since inversion of the dynamic crankshaft model for pressure estimation resulted in an improper solution since before, the model was iterated instead. The pressure trace could thereby be derived accounting for torsion, however the trace still contained oscillations which highlights the challenge of estimating the torsion accurately. The torsion is a complex phenomenon to describe and further development of a model for estimating the torsion with high accuracy for all operating points would improve the virtual pressure sensor significantly. The heat release was, as a first step, modelled as isochoric and isobaric. These models gave information of the limits of SOC by comparing the indicated work from the resulting pressure trace with the work estimate from the angular velocity measurement. Further, one Wiebe function was parametrised such that the resulting pressure derivative during late combustion was adapted to the trace from the crankshaft model in a least-square sense. This allowed for better adaption as the partial pressure trace was subjected to torsional oscillations. The fitted Wiebe function described the diffusive combustion well but missed out the shape of the premixed combustion. Lastly, a double Wiebe function parametrisation was done where the diffusive combustion function was fitted to the late combustion data and the premixed combustion function was adapted such that the resulting indicated work matched the estimated work. To receive more accurate results, the premixed SOC and duration had to be approximated beforehand from the kinetic power trace. The virtual pressure sensor and most of the sub models were most accurate for low speed operating points. It was concluded that the reason is most probably the torsional effect on the input data to all sub models. It was shown that the crankshaft model can be complemented with heat release estimations which improved the final pressure trace and removed the singularity present around TDC. / Förbränningsåterkoppling är ett aktuellt forskningsområde inom utvecklingsarbetet för att minska utsläpp och öka verkningsgraden hos förbränningsmotorer. Cylindertryck är en viktig parameter att mäta . Ett alternativ är att använda en tryckgivare men det skulle vara mer kostnadseffektivt att kunna uppskatta trycket baserat på vevvinkeln som redan idag mäts i motorer. Därav utvecklades en virtuell sensor för uppskattning av cylindertrycket genom detta examensarbete. Studien har berört hur tryck spår, bitvis noggranna för kompressionen och expansionen, från en stel vevaxelmodell kan kompletteras med modeller för värmeavgivningen från förbränningen för att erhålla ett fullt tryck spår. För att kunna bygga och utveckla modellerna utvecklades en metod för att bestämma det indikerade arbetet baserat på den uppmätta varvtalssignalen som beror mycket på hur förbränningen skett och är därmed en viktig parameter vid modellerande av värmeavgivningen. Det indikerade arbetet kunde uppskattas genom att jämföra den kinetiska effekten med den effekt som kolvarna totalt bidrog med. Det upptäcktes att offseten mellan kurvorna motsvarade effekten av förlusterna och lasten som därmed kunde bestämmas vid de punkter där momentet från cylindrarna var i jämvikt. Den kinetiska effekten beräknades från varvtalssignalen medan effekten från kolvarna uppskattades genom att använda isentropiska tryckkurvor för kompressionen och expansionen, innan och efter förbränningen respektive. Relativt noggranna resultat erhölls för arbetspunkterna med ett varvtal på 800 rpm medan större avvikelser inträdde vid högre varvtal. Anledningen till detta var att torsionssvängningar influerade varvtalssignalen mer vid högre varvtal. Resultaten kunde förbättras genom lokal medelvärdesbildning av den kinetiska effekten vid de decelerationer som sker efter förbränningen i respektive cylinder. Torsionens inverkan på vevaxelns dynamik uppskattades genom att använda estimeringar av förvridningen av vevaxeln från en dynamisk vevaxelmodell. Uppskattningen tycktes vara tillräckligt noggrann inom vissa intervall men det var inte möjligt att avlägsna torsionssvängningarna i kinetiska effektspåret för hela cykeln. Uppskattningen av indikerat arbete kunde därför inte förbättras genom denna torsionsuppskattning. Torsionen var vidare studerad i form av frekvens och amplitud av svängningarna inom varvtalssignalen. Inga tydliga samband kunde säkerställas mellan svängningarna och arbetspunkternas varvtal och last. Detta tyder på att torsionen är för komplex att förutse. Vidare, då invertering av den dynamiska vevaxelmodellen tidigare visat sig ge en oriktig lösning kunde modellen istället itereras för att bestämma tryck spåret likt tidigare gjort för den stela vevaxelmodellen. Torsionssvängningarna influerade dock fortfarande det resulterande tryck spåret. Det finns stor potential att förbättra den virtuella sensorn om torsionen kan uppskattas noggrant för alla arbetspunkter. Värmeavgivningen från förbränning var först modellerad som isochorisk och isobarisk i två respektive modeller. Dessa modeller gav information om gränsvärdena för tändningen genom att finna den tändning för modellerna som resulterade i samma arbete som det tidigare estimerade indikerade arbetet. Därefter anpassades en Wiebe funktion så att den resulterande tryckderivatan minsta-kvadrat anpassades till tryckderivatan från vevaxelmodellen under den sena förbränningen där vevaxelmodellen var mest noggrann. Wiebe funktion gav en bra anpassning till den senare diffusiva förbränningen men var inte tillräcklig för att beskriva den förblandade förbränningen. Slutligen anpassades två Wiebe funktioner där den diffusiva förbränningen anpassades likt för singel Wiebe-funktions anpassningen medan den förblandade förbränningen anpassades så att det resulterande arbetet stämde med det uppskattade indikerade arbetet. För att få bättre resultat bestämdes den förblandade förbränningens start och duration från uppskattningen av den kinetiska effekten innan anpassningen. Den virtuella trycksensorn och de flesta av dess delmodeller var mest noggranna för arbetspunkterna vid låga varvtal. Slutsatsen var att det var främst på grund av torsionssvängningarnas påverkan på insignalerna till delmodellerna som noggrannheten föll för de högra varvtalen. Genom denna studie visades det att deltrycksspåret från vevaxelmodellen kunde kompletteras med en modell för värmeavgivningen för att slutligen få en bättre uppskattning av hela tryck spåret där singulariteten vid TDC kunde undvikas.

Controlled Auto Ignition (CAI) combustion is a new combustion principle in internal combustion engines which has in recent years attracted increased attention. In CAI combustion, which combines features of spark ignition (SI) and compression ignition (CI) principles, air/fuel mixture is premixed, as in SI combustion and auto-ignited by piston compression as in CI combustion. Ignition is provided in multiple points, and thus the charge gives a simultaneous energy release. This results in uniform and simultaneous auto-ignition and chemical reaction throughout the whole charge without flame propagation. CAI combustion is controlled by the chemical kinetics of air/fuel mixture with no influence of turbulence. The CAI engine offers benefits in comparison to spark ignited and compression ignited engines in higher efficiency due to elimination of throttling losses at part and idle loads. There is a possibility to use high compression ratios since it is not knock limited, and in significant lower NOx emission (≈90%) and particle matter emission (≈50%), due to much lower combustion temperature and elimination of fuel rich zones. However, there are several disadvantages of the CAI engine that limits its practical application, such as high level of hydrocarbon and carbon monoxide emissions, high peak pressures, high rates of heat release, reduced power per displacement and difficulties in starting and controlling the engine. Controlling the operation over a wide range of loads and speeds is probably the major difficulty facing CAI engines. Controlling is actually two-components as it consists of auto-ignition phasing and controlling the rates of heat release. As CAI combustion is controlled by chemical kinetics of air/fuel mixture, the auto-ignition timing and heat release rate are determined by the charge properties such as temperature, composition and pressure. Therefore, changes in engine operational parameters or in types of fuel, results in changing of the charge properties. Hence, the auto-ignition timing and the rate of heat release. The Thesis investigates a controlled auto-ignition (CAI) combustion in internal combustion engines suitable for transport applications. The CAI engine environment is simulated by using a single-zone, homogeneous reactor model with a time variable volume according to the slider-crank relationship. The model uses detailed chemical kinetics and distributed heat transfer losses according to Woschini's correlation [1]. The fundamentals of chemical kinetics, and their relationship with combustion related problems are presented. The phenomenology and principles of auto-ignition process itself and its characteristics in CAI combustion are explained. The simulation model for representing CAI engine environment is established and calibrated with respect to the experimental data. The influences of fuel composition on the auto-ignition timing and the rate of heat release in a CAI engine are investigated. The effects of engine parameters on CAI combustion in different engine concepts fuelled with various fuels are analysed. The effects of internal gas recirculation (IEGR) in controlling the auto-ignition timing and the heat release rate in a CAI engine fuelled with different fuels are investigated. The effects of variable valve timings strategy on gas exchange process in CAI engine fuelled with commercial gasoline (95RON) are analysed.

No description available.

This thesis examines the development and validation of Canadian Land Surface Scheme (CLASS) for various wetland landscapes individually, along with an evaluation of modelled results over a heterogeneous surface with airborne observations. A further statistical analysis of the effects of land surface classification procedures over the study area and their influence on modelled results is performed. CLASS is tested over individual wetland types: bog, fen and marsh in a stand-alone (non-GCM coupled) mode. Atmospheric conditions are provided for the eight site locations from tower measured data, while each surface is parameterized within the model from site specific measurements. Resulting model turbulent and radiative flux output is then statistically evaluated against observed tower data. Findings show that while CLASS models vascular dominated wetland areas (fen and marsh) quite well, non-vascular wetlands (bogs) are poorly represented, even with improved soil descriptions. At times when the water table is close to the surface, evaporation is greatly overestimated, whereas lowered water tables generate a vastly underestimated latent heat flux. Because CLASS does not include a moisture transfer scheme applicable for non-vascular vegetation, the description of this vegetation type as either a vascular plant or bare soil appears inappropriate. / CLASS was then tuned for a specific bog location found in the Hudson Bay Lowland (HBL) during the Northern Wetlands Study (NOWES). With bog surfaces better described within the model, testing of CLASS over a highly heterogeneous 169 km2 HBL region is then undertaken. The model is first modified for lake and pond surfaces and then separate runs for bog, fen, lake and tree/shrub categories is undertaken. Using a GIS, the test region under which airborne flux measurements are available is divided into 104 grid cells and proportions of each surface type are calculated within each cell. Findings indicate that although the modelled grid average radiation and flux values are reasonably well reproduced (4% error for net radiation, 10% for latent heat flux and 30% for sensible heat flux), spatial agreement between modelled and observed grid cells is disappointing. (Abstract shortened by UMI.)

The landscape of the boreal forest in north-central Canada is characterised by mosaics of broad-leaved deciduous trees (aspen, Populus; birch, Betula), evergreen conifers (black spruce, Picea mariana; jack pine, Pinus banksiana; and larch, Larix), fens and lakes. The forest has been cited as the possible location of a global carbon sink, and its likely response in the event of global climate change remains unclear. To improve our current understanding of the links between the boreal forest ecosystem and the lower atmosphere, the Boreal Ecosystem-Atmosphere Study (BOREAS) was executed in a series of field experiments in 1994 and 1996. This thesis documents the efforts made to characterise and map temporal and spatial distributions of the fluxes of heat, water vapour and CO2 over two 16 km x 16 km heterogeneous sites at the BOREAS study sites. / Most of the data in this thesis were obtained from the airborne observations by the Canadian Twin Otter Aircraft, operated by the Institute for Aerospace Research of the Canadian National Research Council, at the BOREAS Northern Study Area (NSA), and Southern Study Area (SSA). The research aircraft was flown at a fixed altitude of about 30 m agl. The data acquired in 1994 were primarily used to develop an objective deterending scheme in eddy-correlation flux estimates, that took into consideration the physical nature of turbulent transport during convective daytime conditions, and to map the spatial distribution of sensible heat, latent heat and CO2 fluxes over three intensive field campaigns. Maps of spatial patterns of the surface characteristics, such as the surface temperature excess over air temperature (Ts-T a) and Greenness index (GI), were also constructed. The mapping procedure involved generation of an array of grid points by block averaging the parameter of interests along the flight lines, spaced 2 km apart, over 2 km windows, with 1 km overlap between adjacent windows. The (Ts-Ta) maps showed, not surprisingly, that surface temperatures were relatively cooler over the mature forests than over the disturbed, regenerating and burn areas. However, they also showed a decoupling between sensible heat flux and T s-Ta not seen in less complex terrain. By contrast, close correspondence was observed between maps of CO2 flux and greenness, suggesting that the potential to infer CO2 exchange from remote sensing observations of the surface is higher than that for energy exchange. (Abstract shortened by UMI.)

No description available.

An understanding of compartment fire behaviour is important for fire protection engineers. For design purposes, whether to use a prescriptive code or performance based design, life safety and property protection issues are required to be assessed. The use of design fires in computer modelling is the general method to determine fire safety. However these computer models are generally limited to the input of one design fire, with consideration of the complex interaction between fuel packages and the compartment environment being simplified. Of particular interest is the Heat Release Rate, HRR, as this is the commonly prescribed design parameter for fire modelling. If the HRR is not accurate then it can be subsequently argued that the design scenario may be flawed. Therefore the selection of the most appropriate fire design scenario is critical, and an increased level of understanding of compartment behaviour is an invaluable aid to fire engineering assumptions. This thesis details an experimental study to enhance the understanding of the impact and interaction that the size and location of pool fires within an enclosure have upon the compartment fire behaviour. Thirty four experiments were conducted in a reduced scale compartment (½ height) with dimensions of 3.6m long by 2.4m wide by 1.2m high using five typical ventilation geometries (fully open, soffit, door, window and small window). Heptane pool fires were used, located in permutations of three evenly distributed locations within the compartment (rear, centre and front) as well as larger equivalent area pans located only in the centre. This thesis describes the experimental development, setup and results of the experimental study. To assist in the classification of compartment fire behaviour during the experiments, a ‘phi’ meter was developed to measure the time dependent equivalence ratio. The phi meter was developed and configured to measure O₂, CO₂ and CO. The background development, calibration, and experimental results are reported. A review of compartment fire modelling using Fire Dynamics Simulator, has also been completed and the results discussed. The results of this experimental study were found to have significant implications for Fire Safety Engineering in that the size of the fire is not as significant as the location of the fire. The effect of a fire near the vent opening was found to have a significant impact on compartment fire behaviour with the vent located fuel source increasing the total compartment heat release rate by a factor of 1.7 to that of a centrally placed pool fire of the same total fuel area. The assumption that a fire located in the centre of the room provides for the highest heat release rate is not valid for post-flashover compartment fires. The phi meter was found to provide good agreement with the equivalence ratio calculated from total compartment mass loss rates, and the results of FDS modelling indicate that the use of the model in its current form can not be applied to complex pool fire geometries.