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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2020)
Its inherent economic and environmental advantages as a compression ignition (CI) engine fuel make natural gas (NG) an attractive alternative to diesel fuel. Limited optical studies of the NG combustion strategies have been reported in literature. The current work focused on developing optical characterization techniques to study in-cylinder processes in cleaner combustion strategies, such as those involving natural gas. An experimental facility supporting optical diagnostics via a Bowditch piston arrangement in a 2-litre, single-cylinder research engine was used in this study. In order to facilitate quantitative soot analysis for low soot combustion strategies, the performance of the pyrometric method was improved by nearly 40% increase in the resolved signal fraction through modifications in numerical algorithm, calibration and implementation of the method, and image processing. The enhanced pyrometry method was implemented simultaneously with high-speed OH* chemiluminescence imaging to pilot-ignited direct-injected natural gas (PIDING) combustion for the first time. The results revealed that a standard PIDING operation can be characterized by low-sooting non-premixed combustion of the NG along the jet axes and of a partially-premixed charge at the wall region, followed by onset of detectable soot at the points of NG jet impingement on the bowl wall. This results in formation of a soot cloud adjacent to the wall, which then grows towards the center with continued soot formation and reflected momentum of the NG jets impinging on the bowl wall. The relative timing between NG injection pulse and peak HRR, and the P_inj, showed strong influence in the rate and extent of soot formation and peak concentration levels. Rugged probe designs afford optical measurements from all-metal engines. Comparisons between 2D and probe based 0D pyrometry measurements were made under optical engine configuration, for the first time, to better characterize the 0D probe signal. The 2D and 0D results showed reasonable agreements, especially when field-of-view geometry differences were taken into account. 0D two-color pyrometry measurements in an all-metal engine led to similar conclusions on soot in-cylinder processes, albeit with signs of enhanced late-cycle soot oxidation, attributed to the conventional omega shaped piston bowl geometry.
Master's Student Supervision (2010 - 2018)
In recent years, government policies have mandated significant reductions in emissions of greenhouse gases (GHG) and particulate matter (PM) from heavy-duty, on-highway transportation applications. This has necessitated the development of clean engine technologies such as dual-fuel combustion of natural gas (NG) in compression ignition (CI) engines. With these new engine developments, the need to understand and optimize these technologies to meet emission regulations becomes crucial. Traditional engine research relies on thermodynamic methods and exhaust analysis to examine performance and emission trends present across real-world operating conditions – more recently, optical tools have become increasingly accessible and are providing new methods of understanding combustion phenomena. Interpretation however, is often not directly translatable between optical and thermodynamic engines due to the many mechanical differences between the two. This work aims to provide the foundations for a new “thermo-optical” approach which combines conventional thermodynamic analysis with optical insight into combustion phenomenon to bridge the gap between thermodynamic and optical engine studies.The development and application of an optical probe performing line of sight pyrometry for in-cylinder soot concentration and temperature measurements, as well as the implementation of a probe for in-cylinder local fuel concentration measurements is detailed. The probes are operated in a 2-litre single-cylinder research engine capable of thermodynamic (“all-metal”) and optical configurations and were utilized under two vastly different operating strategies. These strategies used premixed methane with a diesel pilot (DIDF), and High Pressure Direct Injection (HPDI) for non-premixed NG with a diesel pilot. The pyrometry probe demonstrated the effect of HPDI injection parameters on in-cylinder PM concentration while fuel concentration measurements were used to identify the combustion mode under DIDF conditions, and to provide insight to HPDI injection and combustion characteristics. The probes’ performance and capabilities were evaluated under thermodynamic and optical configurations, with high-speed cameras complementing the probes during optical operation. The framework for interpretation in the “thermo-optical” methodology was developed through analysis of the local fuel concentration, soot concentration and temperature, spatially resolved optical results, and conventional apparent heat release rate (AHRR) analysis.
This research sought to demonstrate the potential of biodiesel and softwood derived Fast Pyrolysis Oil (FPO) blends as an alternative low-carbon drop-in diesel fuel. FPO was supplied from an in-house fluidized bed reactor as well as a commercial source. Separate FPO-biodiesel blends from both FPO sources were prepared using initial volumetric ratios of 80:20 and 60:40 (biodiesel:FPO, by volume). Upon blending each performed volumetric ratio, mixing and a 24 hour settling period, two layers formed and the top, biodiesel-rich layers containing about 5 and 10 vol % FPO were decanted and characterized on the basis of a thermogravimetric analysis, viscosity, acid number, water content, elemental analysis, and heating value. Significant decreases in viscosity, acidity, and water content from the original FPO validated blending as means of extracting compounds suitable for use as fuels from pyrolytic liquids in biodiesel. A single cylinder, direct injection diesel engine was used to analyze the combustion performance of the FPO fuel blends against neat diesel and biodiesel. Fuel performance was characterized on the basis of a thermodynamic analysis and corresponding exhaust measurements for CO₂, CO, unburned hydrocarbons, particulate matter, and NOx. Two thermodynamic measurement campaigns were performed in order to provide insight into FPO fuel performance across various engine conditions. In addition to the thermodynamic measurements, in-cylinder high-speed photography was implemented to support the interpretation of thermodynamic combustion data. Engine testing revealed similar indicated efficiencies for biodiesel and diesel at all considered engine-operating modes, while blend fuels showed indicated efficiencies between 75 and 95% of diesel values. FPO fuels exhibited increased ignition delays and shorter combustion durations with greater FPO blend concentrations, though this could be partially compensated for using a pilot injection strategy. The longer ignition delays of the blend fuels resulted in overly lean regions of the cylinder, which produced largely premixed combustion events contributing to brake specific CO and uHC emissions up to 1.5 and 3.5 greater than diesel, respectively. Specific PM emissions were 41-62% lower for blend fuels than diesel. Both blends of in-house FPO showed similar PM emission performance, however at higher concentrations than low blend commercial fuel.
Diesel-ignited dual-fuel (DIDF) combustion of natural gas (NG) is a promising, and immediately available strategy to improve heavy-duty compression-ignition (CI) engine performance to meet challenging and evolving emissions regulations. The DIDF concept utilizes a combination of port-injected NG and direct-injected diesel to couple the relatively low-cost and low-emissions characteristics of NG combustion with the operational and performance characteristics that have made diesel CI engines ubiquitous. This combination of fuelling strategies permits a wide range of different operating modes, which are characterized by a number of fundamental combustion mechanisms. Combustion mechanisms specific to particular modes of DIDF operation have previously been addressed, however a comprehensive conceptual description of the combustion processes and modes of DIDF operation is lacking. A clear context for specific observed phenomena and DIDF operating modes is needed to bridge and extend the conclusions of investigations in this field. That need is addressed by this investigation through experimental analysis of thermodynamic and optical measurements of a broad range of DIDF fuelling modes. A 2-litre single-cylinder CI research engine capable of both conventional and optically-accessible operation was commissioned and operated with port-injected methane (CH₄). Fuelling modes were characterized using the global equivalence ratio (φglobal =0.55—0.88) and pilot fuel ratio (Rpilot =0.06—0.61) and were performed with combinations of pilot injection timing and pressure. A novel set of criteria, which used the measured apparent heat release rate (AHRR), defined sequential stages of DIDF combustion and mapped fundamental regimes of DIDF operation in the Rpilot-φglobal space. Flame propagation, and non-flame propagation DIDF operating regimes were distinguished by an apparent lean flame propagation limit observed at a CH₄ equivalence ratio (φCH₄) equal to 0.4. Pilot injection parameters were observed to be critical to combustion and emissions processes across all operating modes except for a unique subset of operating points with Rpilot=0.06. Spatially-resolved broadband visible light and OH*-chemiluminescence measurements supported the identified operating regimes, and indicated that the conventional conceptual model of DIDF combustion is not a complete description of the DIDF combustion process for all operating modes.