Steven Rogak

Professor

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Doctoral Student Supervision (Jan 2008 - Nov 2019)
Impact of humidity, temperature, and particulate fouling on membrane-based energy exchangers (2018)

Membrane-based energy recovery ventilators (ERVs) improve building energy efficiency by transporting heat and moisture between incoming and outgoing air streams. Although long-term studies are not available due to the recent implementation of this technology, there are preliminary indications that moisture transport might degrade with the extended operation, possibly as the result of exposure to air pollution or other environmental stresses. The scope of this dissertation is to quantify the influence of environmental factors on the permeation properties of current-generation composite membranes and the overall performance of ERV exchanger cores.First, the impact of particulate fouling was investigated via accelerated membrane- and core-level fouling experiments. The core-level experiments showed minimal impact on the effectiveness of ERV cores from coarse dust loadings. However, membrane-level examination with aerosol nanoparticles indicated that moisture transport through membranes was especially impaired when particles were hygroscopic or contained liquids. These results suggest that the optimal protection by filters and the orientation of the membrane would depend on the nature of the indoor and outdoor aerosols.Second, the effects of relative humidity and temperature on the transport of water vapor and CO₂ (as a surrogate for indoor air pollutants) was evaluated through a systematic study of some standard polymers suitable for ERV use. It was shown that the permeability and selectivity of membranes could vary up to an order of magnitude depending on the membrane material, the temperature and relative humidity on both feed and permeate sides of the membrane, as well as orientation in asymmetric composite membranes. A theoretical model for predicting permeability of composite membranes, based on a limited number of kinetic water vapor sorption tests of the selective coating polymer, was successfully developed and validated for a commercial membrane. This model was then coupled with a heat and mass transfer model of cross-flow ERV exchanger cores to interpret the membrane-level variations regarding ERV exchanger core performance. A study of the effects of outdoor air parameters showed that the effectiveness of ERV exchangers could increase or decrease significantly with outdoor air relative humidity, while outdoor air temperature had only a minimal influence on effectiveness parameters.

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Characterization of primary particle size variation and its influence on measurable properties of aerosol soot (2017)

Accurate measurement of the properties, emission rates, and environmental impacts (i.e. climate forcing) of aggregated aerosols depend on precise measurement of their morphology (i.e. primary particle diameter, dp, and its polydispersity).For decades soot has been modeled as fractal-like aggregates of nearly equiaxed spherules. However, examination of the soot particles collected from different combustion environments shows that the larger aggregates contain larger primary particles and the variation in dp is much smaller within individual aggregates than between aggregates.In addition to this size dependency, measurements of optical properties of mass-classified soot particles revealed that the mass-specific absorption cross section of soot also depends on particle mass. This along with the correlations observed between dp and aggregate size, suggest that these aggregates are formed in relatively homogeneous microscopic regions; after which particles with different formation, growth, and oxidation histories are mixed. This suggests that there is a need for accurate estimation of primary particle size distribution and refinement of assumptions commonly used in the conventional simulations and interpretation of the measurements.Morphology characterization of the agglomerates is commonly performed by labor-intensive manual analysis of the images produced by transmission electron microscopy. A new method has been developed for automatic determination of dp based on the variation of the 2-D pair correlation function. Results obtained from this method approximately deviate ~4% from the manual method. Application of this method is not limited to the soot particles and it can be applied to any type of the agglomerates. As an alternative approach, indirect in situ mass-mobility method proposed for the estimation of dp in zirconia particles has been tested and calibrated for soot particles. It was found that with some calibration, this method can provide results with useful accuracy.Polydispersity of the primary particles has also been neglected in the previous investigations of the hydrodynamic properties of clusters. It was shown that the mobility-equivalent diameter and the overall size of the agglomerates not only depend on dp but also increase substantially with its polydispersity. New correlations were developed for the free-molecular and continuum mobility diameters using stochastic projection and Stokesian Dynamics methods, respectively.

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Effect of injection strategies on particulate matter emissions from HPDI natural-gas engine (2016)

Internal combustion engines produce emissions of NOx and particulate matter (PM). Westport Innovations Inc. has developed the pilot-ignited high-pressure direct-injection (HPDI) natural gas (NG) engine system. To ignite the natural gas, HPDI uses a small diesel pilot injection (~5% of total fuel energy), which is normally injected before the NG. Although HPDI engines produce less PM than diesel engines, further reductions of engine-out PM emissions are desired in order to meet future regulations. The goal of this project is to reduce PM from HPDI engines and study the drawbacks of the injection strategies in terms of engine performance or other emissions. This thesis proposes mechanisms for two injection strategies useful in PM reduction: Late Post Injection (LPI) and Slightly Premixed Combustion (SPC). Tests on LPI and SPC were performed in the UBC Single Cylinder Research Engine (SCRE). In LPI, a second natural gas injection (10-25% of total fuel mass) is injected into the cylinder later in the cycle. In SPC, more premixing of NG is achieved by injecting NG before the diesel injection and engine operating parameters are adjusted to minimize the effect on other emissions. Both of the injection strategies show significant PM reduction (over 75% on the SCRE) with small effects on other emissions and engine performance. Westport’s computational fluid dynamics package, “GOLD”, was used to help to understand the mechanisms of the new injection strategies. The PM reductions from LPI and SPC were captured by GOLD.A phenomenological model (Transient Slice Model, TSM) has been developed in this study to provide better insight into the PM reduction process, using the Hiroyasu model with a transport equation for soot. TSM results show good agreement in the prediction of pressure trace and heat release rates in most cases. Engine-out PM trends with changing engine parameters are well-captured in the TSM for exhaust gas recirculation (EGR), equivalence ratio (EQR), load and natural gas (NG) flow. TSM cannot predict the effect of NG injection pressure. For the new injection strategies, TSM can predict the PM trends for LPI, relative gas-diesel timing and the SPC injection strategy.

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Air filtration : predicting and improving indoor air quality and energy performance (2015)

Air filtration is used to reduce particle concentrations in the indoor environment to provide improved occupant health due to reduced exposure. Increased focus on occupant health in emerging design standards is leading to the installation of higher efficiency filtration systems. These systems generally have higher resistance to flow and therefore impose a greater energy penalty. Previous air filter models have used simplified assumptions with regards to the dynamics of filter operation, which have limited the potential to determine energy efficiency or optimization approaches to system design and operation. This dissertation focuses on developing an improved air filter model to investigate the potential for system modifications to reduce energy consumption and improve indoor air quality (IAQ) within commercial buildings.A new air filter performance model was developed using generalizable results from ASHRAE Standard 52.2-2012 and validated against laboratory and real-world experiments. The results showed better agreement with laboratory tests than with real operation. The filter model was combined with existing indoor particle dynamics and epidemiological models to determine the impacts of changes to system operation through monetization of operation costs and health benefits. Laboratory experiments were performed to evaluate the role that particle properties and relative humidity play in determining the filter performance changes with the aim of better understanding the reasons for discrepancies in operation between laboratory and field filter tests.Operation can now be optimized by accounting for dynamic characteristics of filter performance. Benefits of improved filtration efficiency were found to outweigh added costs. Adopting specific indoor particle concentration limits is recommended to replace existing specifications relying on filter efficiency. System designs can then be optimized to account for local particle concentration and energy costs. A number of system design changes have been highlighted that allow for simultaneous reduction in operation cost and indoor particle concentrations. Relative humidity has been identified as a critical parameter in filter performance and standardized tests should be modified to account for variability in relative humidity and particle characteristics typical of real operation to allow for improvements to future model predictions. Supplementary materials: http://hdl.handle.net/2429/54056

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Dispersion of expiratory droplets in a model single patient hospital recovery room with stratified ventilation (2013)

No abstract available.

Morphology and optical properties of coated aggregates (2013)

Soot particles are often internally mixed with non-absorbing organic which enhances light scattering and absorption, but the magnitude of this enhancement is highly uncertain. A better characterization of optical properties of coated soot is critical for interpreting optical soot measurements. Simulations using numerically generated aggregates were performed to assess the impact of coatings on the optical properties. A cluster-cluster aggregation algorithm was used to produce aggregates (Df = 1.78 and 2.1) containing 15–600 primary particles with dp = 30 nm. The optical properties were calculated using the discrete-dipole approximation (DDA). For uncoated aggregates, their optical properties were compared with the Rayleigh-Debye-Gans. It was found that the aggregates with similar fractal dimension and prefactor produced by the two methods showed small variations on the optical cross sections. Two coating models were considered: concentric coating and droplet sphere. For the first model, DDA predicted larger absorption than the volume-equivalent core-shell Mie. The coating also caused increase in the discrepancy between the scattering predicted by DDA and the core-shell Mie. For the second model, the aggregates exhibited less absorption and more scattering compared to the concentrically coated aggregates with similar coating fraction, highlighting the importance of coating configurations on the optical properties of coated soot.Laboratory experiments on particles coated with transparent organic were conducted to investigate the changes in the aggregate structure and scattering. Palas particles (dmobility ≈ 118 nm) were employed as proxy for soot and oleyl alcohol was used as the coating. The results of the experiments confirmed that the aggregate-like particles underwent collapsing as the coating was added. The aggregate was fully collapsed (dmobility ≈ 78 nm) when coating mass ratios ≈ 1.75. The coating also enhanced the scattering of coated Palas by a factor of around 2 – 15 depending on the coating amount. The comparative study between the nephelometer scattering from the experiments and the corresponding volume-equivalent Mie were done. The scattering of the uncoated and coated aggregate when aggregate restructuring still occurred were significantly lower compared to the Mie estimations. As the particles fully collapsed, however, their scattering could be accurately predicted from the Mie theory.

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Master's Student Supervision (2010 - 2018)
Beam-tracing prediction of room-to-room sound transmission (2018)

Modeling sound transmission is a challenging task. An existing beam-tracing model for empty, parallelepiped rooms with specularly-reflecting surfaces is extended to predict room-to-room sound transmission between a source and receiver rooms separated by a common wall. This wall is modeled as one locally-reacting homogenous partition with frequency-independent transmission loss. Besides, sound transmission is modeled in Ray-Tracing (CATT-TM) and FEM (COMSOL). A reference configuration consists of two identical reverberation rooms is chosen following the recommendations of the literature and most of the prescriptions of the reverberation room standard, ASTM 3423. The capability of various room-to-room predictions models, in particular, the phase and energy-based beam tracing models (PBTM, EBTM) in reproducing the results of the diffuse-field theory is investigated. Both EBTM and CATT-TM are found to be reasonably accurate in reproducing the diffuse sound field for a reverberation room (i.e. for diffuse sound fields). However, the predicted levels deviate considerably from the diffuse-field theory with changes in the acoustical characteristics of the room (room aspect ratio, the magnitude of the surface absorption and surface absorption distribution (i.e. for non-diffuse sound fields). EBTM has been validated in both source and receiver rooms through existing results from ODEON in the literature and by comparing the prediction results with the new CATT-TM for the reference configuration. PBTM has been compared with finite element method (COMSOL) results in the low-frequency region. Both phase-based models match well in source room with a reasonable discrepancy. However, the PBTM has not reproduced the sound field predicted by COMSOL in the receiver room. Moreover, Waterhouse effect is studied by both PBTM and EBTM model in the reverberation rooms which is ignored in the classical diffuse-field concept. However, its significant effect is exhibited near the reflecting boundaries inside the reverberation room only in the PBTM predictions. Hence, based on recommendations of the ASTM standards during measuring sound transmission between rooms, sources and receivers should be placed sufficiently far away from the reflecting surfaces, edges and corners of the rooms to avoid the errors due to the Waterhouse effect.

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Rib-roughened heat and mass transfer enhancement in membrane-based energy recovery ventilators (2017)

Energy Recovery Ventilators (ERVs) save energy by recovering sensible and latent heat from exhaust ventilation streams. They consist of compact channels in a cross- or counter-flow arrangement separated by moisture-permeable membranes. This work employs computational fluid dynamics with experimental validation to study angled rib mixing features to enhance heat and mass transport in membrane-based ERVs. The model simulates air-to-air heat and mass exchange between two rectangular ducts in a counter-flow arrangement. Local results from these simulations are used in a mathematical model to predict the effectiveness of a cross-flow ERV. The flow is steady and laminar. The channels are modeled with and without ribs for various channel aspect ratios and flow rates. Periodic inlet/outlet conditions are assumed for all cases to highlight the effect of the ribs. Ribs are either on the membrane surface or the opposite wall, however ribs on the membrane surface are the focus of this work due to their superior performance. Results show that the ribs increase the channel Sherwood and Nusselt numbers by a larger fraction than the corresponding increase in friction factor. The improvement is larger for sensible recovery than latent recovery because the membrane’s mass-transfer resistance is higher than its thermal resistance. For a typical commercial grade, counter-flow ERV, total effectiveness can be improved by over 10% for an equal pressure drop by adding ribs and slightly increasing the channel height. Mass-transfer and pressure drop results from the simulations were validated experimentally for channels with and without ribs using a commercially available membrane (dPoint Technologies). Ribs were either formed into the membrane surface or made as extensions of the channel wall. The experimental and simulation results agree with one another within the experimental uncertainty of the test apparatus and variability of the membrane permeability.Typically, ERV performance targets (recovery effectiveness, pressure drop) are met by varying the channel dimensions or number of channels. The work presented here indicates that angled ribs could be used instead, which would not require altering the ERV footprint or using extra materials.

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CFD modeling of injection strategies in a high-pressure direct-injection (HPDI) natural gas engine (2015)

Direct injection of natural gas in compression-ignition engines offers benefits such as emissions reduction, fuel diversity, and energy security. However, in order to meet the upcoming stringent emissions regulations, further improvements in the performance of the High-Pressure Direct-Injection of Natural Gas (HPDI-NG) is needed. For this reason, different natural gas injection strategies and nozzle designs are numerically studied.The in-cylinder phenomena during the closed portion of the cycle is simulated using a Large-Eddy Simulation (LES) turbulence model and the Trajectory-Generated Low Dimensional Manifold (TGLDM) for chemistry coupling. Soot is modeled with a two-equation Hiroyasu model. To partially investigate the effect of LES variability, simulations with successive mesh refinements and infinitesimally varied inputs are carried out. Anticipated emission trends were observed for parametric sweeps with substantial variation of soot about the trend-line. This motivated the analysis of in-cylinder mixture, jet penetration and other more robust metrics.A novel paired-nozzle geometry was designed to increase the fuel-air mixing at the base of the jet, thus reducing soot. In reality, the paired jets increased exhaust PM. The CFD analysis revealed that the gas jet penetration was reduced compared to the baseline single-hole jet, while more air was entrained into the core of the jet. However, the effect of mixing due to impaired penetration dominates and results in more rich mixture and therefore more soot.CFD predicted the PM reduction benefits of “Late Post-Injection” (LPI) due to two major reasons: 1- the reduction in formed PM from the 1st pulse due to shortened pulse width, 2- negligible PM formation from the 2nd pulse for enough pulse separation. A second injection strategy, “Slightly Premixed Combustion” (SPC) also reduced PM in experiments. The CFD package had not been developed for such combustion regime, wherein the diesel-gas kinetic interactions should be resolved; hence perfect matching between the experimental and numerical combustion for SPC was not attained. Nevertheless, by optimizing the injection timing to resemble the phasing of experimental Heat Release Rate (HRR) curve, to the “best extent possible”, more premixing, higher rate of penetration, and less rich-mixture mass was observed.

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Emissions characterization of paired gaseous jets in a pilot-ignited natural-gas compression-ignition engine (2015)

Heavy-duty engines must meet strict emission standards and retain high fuel efficiency. This thesis examines a new type of fuel injector nozzle for a pilot-ignited direct-injection natural gas engine. The nozzle uses paired jets that increase mixing with air during combustion, which aims to reduce the amount of particulate matter (PM) formed. Tests were performed for different speeds and loads and over engine parameter sweeps (including timing, EGR, EQR, and diesel pilot mass) to compare the effects on the emissions to a single-hole nozzle. Low-PM strategies and morphology of the soot were compared as well.Contrary to expectations, the tests showed large increases in CO and PM from all the paired nozzles at all modes compared to the single-holed injector. Changing speed and load did not affect the relative emissions so further tests were only done with the paired nozzle that had the least emissions.The engine parameter sweeps at mid speed, high load (B75) showed similar emission patterns for the paired-hole nozzle and the single-hole nozzle. This suggests that the reasons for the high emissions lie in the characteristics of the jets, which are not changed much under normal HPDI operation.Injecting the natural gas before the pilot injection reduced PM. Late post-injection of some of the gas reduced PM by 50% without increasing other emissions for both injector types. Apparently, these strategies could work for other HPDI injectors.Compared to the reference injector, the paired-hole nozzle produced larger soot aggregates and larger numbers of particles but soot primary particle size showed different trends at different conditions. Soot fractal dimensions were the same and consistent with conventional diesel soot.CFD simulations showed that fuel packets moved through a richer high PM and CO forming zone during combustion for the paired nozzle. This high sooting zone had to be avoided either by further mixing or less mixing to avoid the high emissions produced.The results presented here were developed on a single-cylinder engine. While trends are expected to be similar to those from an equivalent multi-cylinder engine, emission levels and fuel consumption are not directly comparable to production multi-cylinder engines.

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Airborne disease infection risk modeling (2012)

A mathematical model which estimates spatial infection risk as a function of pulmonary rate and deposition region has been developed based on the does-response model. It is specifically designed for enclosed space with consideration of pathogen bio-properties, such as viability and infectivity.Firstly, eleven cases of Tuberculosis (TB) outbreaks in aircraft are studied to develop the optimal parameters set. It is then used to perform model validation and investigation of sample inpatient room spatial infection risk. Secondly, infection risk for eleven TB outbreaks are compared with modeling and Wells-Riley estimations. As a result, modeling results are within the calculated range of Wells-Riley prediction. To determine the importance of viability and ventilation rate regarding HVAC system design for health facilities, infection risks are calculated at different viability and ventilation rates. Based on the observation, ventilation rate or particle concentration in the space dominate the infection risk distribution, except when viability decays extreme rapidly. Thirdly, the spatial infection risk is investigated for TB in a typical 60 m³ inpatient room with displacement and well-mixed ventilation systems. Two room settings, a nurse standing close to the patient’s bed versus a visitor standing far away from the bed, and two coughing directions, horizontal versus vertical, are studied. The results show that for coughing horizontally, when the nurse stands beside the patient's bed, his/her breathing zone is the highest risk zone for displacement ventilation. Under displacement ventilation, the infection risk is lower when visitor stands away from the bed compared to stand close to the bed if the visitor is the only person present in the room besides the patient. The infection risk of the breathing zones in the two cases with horizontal coughing are both higher than 25%. However, when a patient coughs vertically, the displacement ventilation significantly reduces the infection risk. With 24 hours exposure, the infection risk for the nurse and the visitor are both less than 5%.

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Measurement of soot with organic coatings by laser-induced incandescence (2012)

Time-Resolved Laser-Induced Incandescence (TR-LII) uses a high-energy laser pulse to detect airborne soot particles. When a laser pulse encounters a light-absorbing particle, the energy will be absorbed, resulting in an increase in temperature. If the temperature is high enough, incandescence can be used to quantity of the soot mass (EC). TR-LII tracks the incandescent light as the particle cools, providing information on the particle structure. It is a common in LII research to assume that the soot aggregate particles contain only Elemental Carbon (EC) and if these soot aggregate particles are internally mixed with Organic Carbon (OC), the intense energy from the laser beam evaporates the OC instantly. Unfortunately, these assumptions are inaccurate because the existence of OC will alter the structure and heat transfer properties of the aggregate. The existence of OC also has an effect on the energy absorption by the soot particulates. An experiment was conducted using India ink particles as a soot surrogate and Oleyl Alcohol as a model OC coating. The experiment’s objective is to study the effect of coating (OC) on the LII detection. The coating increased the peak temperature, but the apparent primary particle diameter decreased when more coating was introduced, whereas the main output variable (volume fraction) showed a mixed response. Up until a thickness of 40 nm, the apparent volume fraction value was declining, but for a thicker coating condition, the value was increasing. Another experiment was conducted to study the effect of the coating on the particulate distribution downstream of the laser heating in the LII detecting chamber. The soot fragmentation phenomenon was found to occur in the LII system and the existence of coating has an effect on the soot fragmentation phenomenon. Compared to uncoated particle, which produces small fragments (
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Methods for the characterization of deposition and transport of magnetite particles in supercritical water (2012)

Generation IV CANDU Supercritical Water Reactor (SCWR) is being developed to use a light water coolant at high temperature and pressure beyond the critical point of water (374⁰C and 22.1 MPa). The dramatic decrease in the solubility of magnetite in supercritical water suggests that the precipitation of magnetite particles will occur in the reactor core which can deposit on the fuel cladding or be transported to the steam turbine. A once-through flow system was modified to develop experimental techniques for studying the deposition and transport of magnetite particles in supercritical water onto stainless steel 316L. Experiments were run with temperatures ranging from 200°C to 400°C and a pressure of 23.7 MPa. A hydrothermal method for synthesizing magnetite particles was adapted for producing simulated corrosion products in which a typical run had an iron concentration of 0.005 mol/L and lasted for 40 minutes. An online monitoring technique using thermal resistance to infer deposit loadings showed deposition and removal cycles of the corrosion product on the tube wall. Scanning electron microscope images of particles on the tube inner wall and those collected by the high temperature, high pressure filters revealed magnetite particles which were several hundred nanometers to several microns in diameter depending on the precursor and condition of the system. Ultrasound and acid wash cleaning methods were used to remove deposits from the test section for determining deposit thickness and adhesive strength. The strength of deposit adhesion was observed to increase along the tube, particularly under supercritical conditions suggesting precipitation of dissolved species may enhance the strength of the deposit. By comparing the results, a comprehensive approach was developed to study magnetite fouling in supercritical water conditions. Finally, comparison between a simulation model based on mass transport equations and experimental deposition suggests that mass transport alone can overestimate the deposition thickness when surface attachment and removal are significant as they were for many experiments in this study. The simulation predicted as an upper limit scenario that fouling in a CANDU SCWR could increase the fuel cladding temperature at certain locations by up to 23.9⁰C after one year of operation.

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A morphological survey of particulate matter emissions from spark-ignited engines (2011)

Spark-ignited engines are known to produce PM composed of solid, volatile or semi-volatile particles including spheres of carbon soot formed into agglomerates, other forms of carbonaceous particles, metal particles and charred droplets of engine oil. In this thesis, detailed observation has revealed that SI PM is partly composed of fully-formed carbon nanotubes and fullerenes in addition to known particle types previously presented in the literature. The purpose of this work is to ascertain the shape and size of particulate matter being emitted by SI engines. In this thesis, PM thermophoretic sampling and transmission electron microscopy were used to collect and analyze engine soot samples, respectively. Furthermore, the operation of the thermophoretic sampling device used in engine PM sample collection was characterized to identify the sampling efficiency based on particle deposition and sampling biases based on differences in particle thermoconductivity for various forms of carbon such as turbostratic soot, crystalline carbon nanotubes and calcium. In general, the efficiency of the TPS method was roughly estimated to be 30-80% efficient based on experimental results.In this thesis, carbon nanotubes and fullerenes have been identified as being emitted from in-use, spark-ignited natural gas and gasoline burning auto-rickshaw engines tested in New Delhi, India. Emission of fullerenes and CNTs was on the order of 10% +/- 7% of the non-volatile particulate matter. Agglomerates, dense spherical particles believed to be charred engine oil, and unidentified or compound particles were also cataloged. Confirmation that nanotubes are being produced by SI engines was achieved using PM samples collected from the Ricardo Hydra laboratory test engine at the University of British Columbia, Clean Energy Research Centre. Under more controlled conditions than can be achieved sampling in-use vehicles, SI engine PM is found to be a complex collection of dense, dark (possibly charred oil) spheres, small primary particle agglomerates, small particle deposits, volatile droplets, carbon nanotubes and fullerenes and large ‘other’ particles. High resolution TEM confirmed tube-shaped particles to be fully formed multi-walled carbon nanotubes.

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Combustion of natural gas with entrained diesel in a heavy-duty compression-ignition engine (2010)

High-pressure direct-injection of natural gas for use in compression-ignition engines has been found to reduce emissions without sacrificing performance relative to pure diesel operation. In the present work, prototype ‘co-injectors’ which inject a diesel and natural gas mixture from a single injector were tested in a heavy-duty, 6-cylinder Cummins ISX engine with 5 cylinders disabled. One prototype (‘B’) was tested under low-speed, low-load conditions, to determine the effects of fuel flows and in-cylinder conditions on the combustion characteristics of co-injection. Co-injector B, and a second prototype (Co-injector CS: A variation of Co-injector B which mixes the fuels differently) were tested at three engine modes using two injections per cycle to determine the effect of the duration of the first injection on emissions and combustion characteristics. The performance of the co-injectors was compared to Westport Innovation’s High Pressure Direct Injection (HPDI) J36 injector to determine if co-injection can produce comparable emissions.Single injection tests carried out with Co-injector B at 800 RPM over a range of diesel flows, gas flows, injection pressures, and cylinder temperatures & pressures were used to generate response surfaces for knock intensity, ignition delay, and combustion efficiency. It was found that diesel flow and the cylinder pressure at the time of injection had the largest effect of knock intensity and ignition delay, and that the knock/ignition delay relationship in co-injection is inverse. The double injection tests showed that the difference in diesel distributions within the gas plenums of CS and B results in more diesel being injected during the first injection in CS compared to B, which supports previous results. It was found that short first pulses resulted in the lowest emissions for both co-injectors, and that with low first gas pulse widths the performance of the co-injectors is comparable to that of Westport’s HPDI-J36 injector.

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Flow characteristics of gas-blast fuel injectors for direct-injection compression-ignition engines (2010)

Natural gas has a high auto-ignition temperature, therefore natural gas engines use anignition source to promote combustion. The high-pressure direction-injection (HPDI)systems available use small diesel injections prior to the main gas injection. A new seriesof HPDI injectors have been developed that inject diesel and gas simultaneously throughthe same holes. In order to understand and control injection and combustion behavior inan engine, it is essential to understand how injection mass is related to the diesel/gas ratioand injection command parameters.Three prototype injectors are examined. “Prototype B” most closely resembles a standardJ36 HPDI injector, but has a modified diesel needle that injects diesel internally into acommon diesel/gas reservoir. Prototypes “CS & CSX” have the diesel needle eliminatedand replaced with a flow restrictor. The pressure difference between the diesel and thegas controls the quantity of diesel injected. A single pulse width (GPW) for the gasneedle controls the fuel quantities.An injection visualization chamber (IVC) was developed for flow measurements andoptical characterization of injections into a chamber at pressures up to 80 bar. Diesel andnatural gas are replaced by VISCOR® and nitrogen to study non-reacting flows. A novelfeature of the IVC is a retracting shroud that allows the injector to reach steady-state priorto imaging.For low commanded injection duration (GPW less than 0.60 ms), the relation betweenGPW and injected mass is non-linear, for all injectors tested. For gas pulse widths greaterthan 0.65 ms the Co-injectors exhibit approximately linear behavior with higher dieselfuelling quantities lowering gas flow quantities. All Co-injectors are compared tobaseline gas flow quantities of a standard J36 to show design difference effects on flowquantities. The sensitivity of gas flow to diesel in injection quantities, as well as thedischarge coefficient are computed and theoretically modeled for each prototype. Resultssuggest differing diesel/gas distributions, dependent on method of diesel introduction andactuator response.Imaging indicates the mechanical delay of the injectors is independent of chamberbackpressure but dependent on fuel supply pressure. However, gas injection quantitiesare increased by higher chamber backpressure. Changes in the gas/liquid ratio arereflected in different jet image characteristics. These results are compared to theory usingan AMESim model developed for an existing production injector.

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