Historically, the traditional planning process has not given much attention to the road safety evaluation of development plans. To make an informed, defensible, and proactive choice between alternative plans and their safety implications, it is necessary to have a procedure for estimating and evaluating safety performance. A procedure is required for examining the influence of the urban network development on road safety, and in particular, determining the effects of the many variables that affect safety in urban planning. Safety planning models can provide a decision-support tool that facilitates the assessment of the safety implications of alternative network plans. The first objective of this research study is to develop safety planning models that are consistent with the regional models commonly used for urban transportation planning. Geographically weighted Poisson regression (GWPR), full-Bayesian semiparametric additive (FBSA), and traditional generalized linear modelling (GLM) techniques are used to develop the models. The study evaluates how well each model is able to handle spatial variations in the relationship between collision explanatory variables and the number of collisions in a zone. The evaluation uses measures of goodness of fit (GOF) and finds that the GWPR and FBSA models perform much better than the conventional GLM approach. There is little difference between the GOF values for the FBSA and GWPR models. The second objective of this research study is to examine the temporal transferability of the safety planning models and alternative updating methods. The updating procedures examine the Bayesian approach and application of calibration factors. The results show that the models are not temporally transferable in a strict statistical sense. However, relative measures of transferability indicate that the transferred models yield useful information in the application context. The results also show that the updated safety planning models using the Bayesian approach predict the number of collisions better than the calibration factor procedure.

Historically, the traditional planning process has not given much attention to the road safety evaluation of development plans. To make an informed, defensible, and proactive choice between alternative plans and their safety implications, it is necessary to have a procedure for estimating and evaluating safety performance. A procedure is required for examining the influence of the urban network development on road safety, and in particular, determining the effects of the many variables that affect safety in urban planning. Safety planning models can provide a decision-support tool that facilitates the assessment of the safety implications of alternative network plans. The first objective of this research study is to develop safety planning models that are consistent with the regional models commonly used for urban transportation planning. Geographically weighted Poisson regression (GWPR), full-Bayesian semiparametric additive (FBSA), and traditional generalized linear modelling (GLM) techniques are used to develop the models. The study evaluates how well each model is able to handle spatial variations in the relationship between collision explanatory variables and the number of collisions in a zone. The evaluation uses measures of goodness of fit (GOF) and finds that the GWPR and FBSA models perform much better than the conventional GLM approach. There is little difference between the GOF values for the FBSA and GWPR models. The second objective of this research study is to examine the temporal transferability of the safety planning models and alternative updating methods. The updating procedures examine the Bayesian approach and application of calibration factors. The results show that the models are not temporally transferable in a strict statistical sense. However, relative measures of transferability indicate that the transferred models yield useful information in the application context. The results also show that the updated safety planning models using the Bayesian approach predict the number of collisions better than the calibration factor procedure.

The homogeneous charge compression ignition (HCCI) concept has been acknowledged as a potential combustion concept for engines, due to low NOx and soot emissions and high efficiency, especially at part-load. Early direct-injection (DI) during the compression stroke is an option when Diesel fuel is used in HCCI. This implies that the risk for wall impingement increases, due to the decreasing in-cylinder density. The fuel sprays has to be well dispersed in order to avoid wall impingement. Specially designed impinging nozzles providing a collision of the Diesel sprays in the vicinity of the orifice exits have experimentally been verified to yield well dispersed sprays and the desired benefits of HCCI under various conditions. The purpose of this work is to use Computational Fluid Dynamics (CFD) as a tool to simulate and evaluate non-impinging and impinging nozzles with respect to mixture formation in direct-injected HCCI. Three different nozzles are considered: one non-impinging and two impinging nozzles with 30 and 60 degree collision angle respectively. Lagrangian CFD simulations of impinging sprays using the traditional collision model of O’Rourke is not sufficient in order obtain the correct spray properties of impinging sprays. This work proposes an enhanced collision model, which is an extension of the O’Rourke model with respect to collision frequency, post collisional velocities and collision induced break-up. The enhanced model is referred to as the EORIS model (Enhanced O’Rourke model for Impinging Sprays). The initial drop size distribution at orifice and break-up time constant of the standard Wave model is calibrated and calculated wall impingement (piston and liner) is compared with combustion efficiency, smoke, HC and CO emissions as a function of injection timing. A set of model parameters were selected for further evaluation. These model parameters and the EORIS collision model were applied to non-impinging and impinging nozzles under low- and high load conditions. The EORIS model and the selected model parameters are able to predict wall impingement in agreement with experimental measurements of combustion efficiency and smoke emissions under low- and high load conditions for the investigated nozzles. A benefit is that one set of model parameters can be used to predict mixture formation, and there is no need for additional model calibration when, for instance, the injection timing or nozzle geometry is changed. In general, experiments and simulations indicate that impinging nozzles are recommended for early injection timing in the compression stroke. This is due to the shorter penetration which leads to a reduced risk for wall impingement. The non-impinging nozzles are, however, beneficial for later injection timing in the compression stroke. During these injection conditions the impinging nozzles have a more stratified charge and under some conditions poor mixture quality is achieved. / HCCI-konceptet (Homogeneous Charge Compression Ignition) är en tänkbar förbränningsprincip för att uppnå låga NOx och sotemissioner, speciellt under låglast förhållanden. Då Diesel används som bränsle är tidig direktinsprutning under kompressionsslaget en tänkbar strategi för att åstadkomma gynnsamma HCCI-förhållanden. Den tidiga direktinsprutningen medför däremot att risken för väggvätning ökar, på grund av den minskade densiteten i cylindern. Detta ställer krav på bränslesprejen som måste vara väl fördelad i cylindern för att undvika väggvätning. Specialkonstruerade spridarspetsar som skapar kollision av sprejerna nära hålmynningen, så kallade kolliderande sprejer, har experimentellt påvisats vara fördelaktiga för HCCI förbränning, tack vare kortare sprejpenetration och voluminös sprej. Syftet med detta arbete är att använda CFD (Computational FluidDynamics) som ett verktyg för att simulera och evaluera ickekolliderande och kolliderande sprejer med avseende på blandningsbildning under direktinsprutade HCCI förhållanden. Tre olika spridarspetsar har undersökts: en icke-kolliderande och två kolliderande med kollisionsvinkel 30 och 60 grader. CFD-simuleringar av kolliderande sprejer med Lagrangiansk modelleringsteknik och O’Rourkes traditionella kollisionsmodell har visat sig vara otillräcklig för att uppnå korrekta sprejegenskaper. Den här avhandlingen presenterar en förbättrad kollisionsmodell baserad på O’Rourkes ursprungliga kollisionsmodell med avseende på kollisionsfrekvens, dropphastighet efter kollision och kollisionsviinducerad break-up. Den förbättrade modellen kallas EORIS (Enhanced O’Rourke model for Impinging Sprays). Den initiala droppfördelningen vid spridarspetsens hålmynning och Wave-modellens tidskonstant för break-up har kalibrerats och beräknad väggvätning (kolv och foder) har jämförts med förbränningsverkningsgrad, rök, HC och CO-emissioner som funktion av insprutningstidpunkt. De valda modellparametrarna och EORIS-modellen tillämpades för att evaluera blandningsbildningen på kolliderande och icke-kolliderande spridarspetsar under låg- och höglast-förhållanden. EORIS-modellen och de utvalda modellparametrarna kan predikteraväggvätning i överensstämmelse med uppmätt förbränningsverkningsgrad och rökemissioner under låglast- och höglastförhållanden för de undersökta spridarspetsarna. En fördel är att de utvalda modellparametrarna kan prediktera blandningsbildningen och det finns inget behov att justera modellparametrarna då t.ex. insprutningstidpunkten eller spridarspetsgeometrin ändras. Generellt påvisar såväl experiment som simuleringar att de kolliderande sprejerna är lämpliga för tidig direktinsprutning underkompressionsslaget. Det är på grund av kort sprejpenetration som reducerar risken för väggvätning. De icke-kolliderande sprejerna är dock lämpliga för sen direktinsprutning under kompressionsslaget. Under dessa förhållanden har de kolliderande sprejerna en mer stratifierad blandning och under vissa förhållanden uppnås då en ofördelaktig blandningskvalitet. / QC 20100819