Patrick Kirchen

Associate Professor

Relevant Degree Programs

Affiliations to Research Centres, Institutes & Clusters


Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - April 2022)
Characterizing regimes of stratified pilot-ignited direct-injection natural gas combustion in an optically-accessible engine (2021)

Heavy-duty road transport is a significant contributor of greenhouse gases (GHG) and airborne pollutants, and remains challenging to decarbonize. Application of natural gas (NG) in pilot-ignited direct-injection NG (PIDING) engines has been proven to reduce emissions of pollutants and GHGs relative to conventional diesel engines. Recently, stratified-premixed NG combustion has been identified as a viable approach to further reduce PIDING pollutant emissions. However, there is insufficient experimental data on stratified-premixed PIDING combustion to guide its effective implementation. The objective of this work is to present a systematic evaluation of stratified-premixed PIDING combustion modes that span from fully-premixed to non-premixed conditions in terms of ignition, main combustion, and emissions behavior.To address these objectives, a single-cylinder research engine facility was operated in conventional all-metal and optically-accessible configurations. The facility was upgraded with a custom-designed cylinder head and high-pressure diesel/NG fuel system to investigate PIDING combustion and apply multiple simultaneous in-cylinder diagnostics to supplement existing in-cylinder OH*-chemiluminescence and 700nm imaging. Quantitative feature extraction from single-cycle combustion images was enhanced by developing a novel image segmentation algorithm to improve characterization of cyclic variability of combustion processes.Combined thermodynamic and optical analyses of injection timing, duration, and pressure effects for non-premixed PIDING combustion condition identified five distinct combustion processes, which were incorporated into an updated conceptual description of non-premixed PIDING combustion. Six regimes of stratified PIDING combustion distinguished by NG premixing time were identified and characterized for a wide range of injection pressures (14-22MPa) and equivalence ratios (0.47-0.71). Consistency of combustion regime characteristics with respect to injection pressure, equivalence ratio, and with the available literature provide confidence in the broad applicability of the identified combustion regimes (i.e. not engine-specific). NG mixture development, pilot-NG interactions, and reaction zone structure and growth rates were characterized using simultaneous in-cylinder imaging and local high-speed in-cylinder fuel concentration measurement. The conclusions of this work are summarized as a conceptual framework that parameterizes the spectrum of stratified PIDING combustion and highlights conditions where PIDING combustion performance may be improved. The key findings and novel analysis and experimental methods are broadly relevant to all pilot-ignited gaseous direct-injection combustion technologies and fuels.

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Gain-scheduling and preview control of selective catalytic reduction systems in diesel engines (2021)

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Machine learning modeling of a direct-injected dual-fuel engine based on low density experimental data (2021)

Automotive systems are constantly increasing in complexity, requiring advanced modeling methods with large data sets to analyze these systems. This work proposes a machine learning approach to rapidly developing, steady state, control oriented, engine models that use optimization methods and engineering knowledge to reduce the burden of data collection and improve model performance and reliability. Data is collected from a pilot ignited direct injection natural gas engine using a full factorial approach for a high density data set and a design of experiments approach for a low density training data set with randomized validation data. An optimization approach for selecting hyperparameters for neural network and Gaussian process regression models is proposed. Models for emissions and performance metrics are created and compared to response surface models. The hyperparameter optimized models show an improvement in robustness and model performance, reducing the normalized root mean square error by 26% compared to other hyperparameter configurations. Gaussian process regression hyperparameter optimization shows the lowest error, 46% lower than response surface models. The Gaussian process regression hyperparameter optimized models are further improved using multi-region modeling, sensitivity analysis based input reduction, layered modeling, and hybrid layered modeling. The sensitivity based input reduction reduces the normalized root mean square error for all models by an average of 8% and up to 19%. The layered models reduce the normalized root mean square error for the CO by 52%, NOₓ by 30%, and particulate matter by 33%. The multi-region models reduce the normalized root mean square error for the O₂ by 40% and thermal efficiency by 16%. Using the best techniques for each output, the error is reduced by 19%, compared to hyperparameter optimization alone and 45% compared to typical Gaussian process regression models. These results show that hyperparameter optimization combined with the other techniques presented here significantly reduce model error. Using these techniques, it is possible to reduce the reliance on data for engine modeling. Future research in energy conversion technologies can use these techniques to rapidly develop new technologies without the cost in time and funding typically reserved for extensive data collection.

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Single-cycle exhaust soot measurement from internal combustion engines (2021)

The black carbon particulate matter (soot) emissions from internal combustion engines have negative health and climate impacts. PM emissions are typically characterized with modest temporal resolutions; however, in-cylinder investigations have demonstrated significant variability and the importance of individual cycles. Detecting such variations in the exhaust requires measurements close to the exhaust valve, which are not possible with the current sensors. Here, a methodology for characterizing the cycle-specific PM concentration at the exhaust-port of a single-cylinder research engine is developed using a light-scattering sensor, the Fast Exhaust Nephelometer (FEN).The FEN light scattering is converted to soot mass concentration (Cₘ) and mass-mean mobility diameter (dm,g) using an inversion algorithm based on the Rayleigh-Debye-Gans model for fractal aggregates (RDGFA). The model incorporates the external mixing hypothesis (EMH) to correlate the diameter of primary particles with the aggregates. The inversion parameters are obtained from Transmission Electron Microscopy (TEM) and literature, resulting in Cₘ and dm,g that are within ±10% of the reference methods. The results could vary by ±40% due to uncertainties in the RDGFA parameters; however, by incorporating the EMH morphology model, the variations are reduced to within ~ ±25% of the reference measurements.The response time of the FEN, determined from a “skip-fired” scheme by disabling the fuel injection, is on average 55 ms. This is well below the engine cycle period (~100 ms) for the considered engine speeds. A cycle-specific PM mass averaging method was developed based on the characteristics of the exhaust-port signals. Using this cycle-resolved method, it is shown that the cycle-to-cycle coefficient of variation of Cₘ is 40%, while the in-cylinder gross indicated mean effective pressure (GIMEP) varies by 2%. Despite their different ranges of variation, the cycle-specific Cₘ and GIMEP are negatively correlated with R² ~ 0.2-0.7, where cycles with low GIMEP emit more soot. The physical causes of this association deserve further investigation, but are expected to be caused by local fuel-air mixing effects. The methods and findings of this work can further our understanding of the engine variability under transient conditions, and assist the interpretation of the in-cylinder variations observed in optical engine experiments.

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Developing pyrometric and chemiluminescence optical diagnostics for investigation of modern alternative CI engine combustion strategies (2019)

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.

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Master's Student Supervision (2010 - 2021)
Production and characterization of upgraded biomass fast pyrolysis oil for combustion in a swirl-stabilized burner (2020)

Biofuels have garnered attention because of their potential to displace conventional petroleum fuels with renewable feedstocks that lower greenhouse gas emissions. Bio-oil (fast pyrolysis oil) is a liquid made from thermal degradation of non-food-crop biomass and has been used as an alternative to heavy fuel oil on industrial scales. However, bio-oil is a complex mixture of biomass-derived compounds with different physical and chemical properties to petroleum fuels which affect the combustion performance.Bio-oil was produced from softwood pellets in a fast pyrolysis apparatus with a multi-stage condenser. Of the three bio-oil fractions collected, the sample from the third vessel had a viscosity of 30mPa-s and an HHV near 20 MJ/kg, thus was deemed appropriate for fuel testing. ZSM-5 was used as a catalyst in the fluidized bed reactor to produce bio-oil with 20wt% less oxygen and 5 MJ/kg higher in HHV. The two bio-oil samples produced, one with ZSM-5 catalyst (CAT) and the other without catalyst (NC), were compared to a commercially available bio-oil (COMM) and diesel. CAT had the highest HHV and lowest oxygen content but was the least volatile of the bio-oil samples, whereas COMM had the lowest energy density and highest volatility.The fuel samples were tested in a swirl-stabilized combustor to measure CO, NOx, particulate matter, and unburned hydrocarbon in the exhaust. COMM produced CO and NOx emissions near 95 and 97 ppm, respectively. The exhaust from NC had CO and NOx concentrations of approximately 185 and 50 ppm, respectively. Finally, the CAT flame was unstable, producing CO emissions around 300 ppm. Volatility appeared to have an outsize impact on emissions compared to properties like HHV or viscosity. Bio-oil/ethanol blends increased the volatile composition while having modest impacts on HHV or viscosity and produced CO and NOx concentrations of 18 and 105 ppm, respectively.Two-colour pyrometry measured flame temperature and soot concentration during combustion. The soot concentration in the flame was 56 times greater for diesel than bio-oil. In contrast, the average flame temperature for diesel and bio-oil were 1700 and 1900 K, respectively, although the bio-oil data may be uncertain due to flame heterogeneity.

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Characterization and system level study of air addition in a pilot ignited direct injection natural gas engine (2019)

The emissions from heavy duty engines must be reduced in light of their climate and health effects. Pilot-ignited direct injection natural gas engines (PIDING) allows cleaner combustion by using natural gas as the primary fuel instead of diesel. To achieve further emission reductions, the concept of air addition to natural gas, at various global equivalence ratio (Φ) and EGR rates was investigated in a heavy-duty mode of a PIDING engine. However, this concept requires compressed air over 300 bar, which may impose net compression work to the engine. Therefore, the system level implications were investigated by developing and characterizing a prototype compression system, and subsequently considering its compression work with the engine indicated efficiency. The investigations were carried out using a single cylinder research engine and an industrial reciprocating compressor. Fuel dilution by air addition was demonstrated to effectively reduce emissions of PM, CO, and THC. Particulate matter (PM) reduced exponentially, resulting in more than an order of magnitude reduction. Similarly, carbon monoxide (CO) was also reduced albeit with lower magnitude. The total unburnt hydrocarbons (THC) reductions with air addition were significant only at high EGR (> 12.5%). However, air addition significantly increased NOx emissions (up to factor of 2.5); but increasing the EGR rates by 6.5%-point may compensate for this. The net compression work was dependent on the engine operating conditions, number of compressor stages, and performance of the chosen compressor. Air addition resulted in indicated efficiency improvements on the order of 2.5%, which at high Φ were sufficient to compensate for the compression work of a three-stage reciprocating compressor. The same may be possible with even smaller and efficient 2-stage compressors. An optimization study suggests that air addition would be most effective at high values of Φ, EGR rates, and air addition. As an in-cylinder strategy, it has the potential to be used in conjunction with ultra-high EGR, to significantly reduce both PM and NOx emissions, while avoiding the typical issues of ultra-high EGR: combustion instabilities and high THC and CO emissions.

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Development of a fast methane sensor based on wavelength modulation spectroscopy for exhaust methane emission measurement (2019)

Natural gas is an attractive alternative fuel with a lower price and carbon dioxide emission compared to liquid fossil fuels. Methane (CH₄) in natural gas, however, has a high global warming potential (GWP), thus the emission of unburnt CH₄ can offset the cleaner combustion of natural gas and should be carefully monitored in dual-fuel natural gas/diesel engines. To develop cleaner engines, a high-speed methane sensor in the exhaust gas stream is required to capture emissions during real-world, transient engine operation. While CH₄ measurements using Fourier-transform infrared (FTIR) spectroscopy in dual-fuel engines have been demonstrated, its speed is insufficient for cycle-resolved measurements. To this end, a fast, robust, and inexpensive CH₄ sensor based on wavelength modulation spectroscopy (WMS) was developed using a relatively inexpensive IR diode laser with a centre wavelength of 1651 nm.The WMS sensor was assessed using gas standards and validated against a flame ionization detector (FID). The 508 mm heated gas cell reliably detects CH₄ from 50 ppm to over 2% at a temporal resolution of over 200 Hz. The WMS sensor can resolve transient methane emission with a time delay and time constant of 0.55 s and 0.44 s respectively. When demonstrated on a heavy-duty dual-fuel research engine, the WMS sensor and FID agreed with a mean percentage difference of 4.2%. The field measurement capability of this portable sensor, which can continuously measure for seconds to hours, was demonstrated on dual-fuel marine engines of a coastal vessel. The GWP of dual-fuel engine exhaust heavily depends on operational profiles, and the fast WMS methane sensor will assist engineers and policy makers to characterize and reduce in-use CH₄ emissions.

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Development and application of in-cylinder fuel concentration and pyrometry optical diagnostic tools in diesel-ignited dual-fuel natural gas engines (2017)

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.

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Production and characterization of biomass fast pyrolysis oil blends for combustion testing as drop-in fuel alternatives in a single cylinder diesel engine (2017)

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.

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Thermodynamic and Optical Investigation of the Combustion Mechanisms of Diesel-Ignited Dual-Fuel Natural Gas Combustion (2016)

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.

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