Morgan DeFoort

Biomass for thermochemical conversion: targets and challenges

Bioenergy will be one component of a suite of alternatives to fossil fuels. Effective conversion of biomass to energy will require the careful pairing of advanced conversion technologies with biomass feedstocks optimized for the purpose. Lignocellulosic biomass can be converted to useful energy products via two distinct pathways: enzymatic or thermochemical conversion. The thermochemical pathways are reviewed and potential biotechnology or breeding targets to improve feedstocks for pyrolysis, gasification, and combustion are identified. Biomass traits influencing the effectiveness of the thermochemical process (cell wall composition, mineral and moisture content) differ from those important for enzymatic conversion and so properties are discussed in the language of biologists (biochemical analysis) as well as that of engineers (proximate and ultimate analysis). We discuss the genetic control, potential environmental influence, and consequences of modification of these traits. Improving feedstocks for thermochemical conversion can be accomplished by the optimization of lignin levels, and the reduction of ash and moisture content. We suggest that ultimate analysis and associated properties such as H:C, O:C, and heating value might be more amenable than traditional biochemical analysis to the high-throughput necessary for the phenotyping of large plant populations. Expanding our knowledge of these biomass traits will play a critical role in the utilization of biomass for energy production globally, and add to our understanding of how plants tailor their composition with their environment.

Distributed biochar and bioenergy coproduction: a regionally specific case study of environmental benefits and economic impacts

Biochar has been advocated as a method of sequestering carbon while simultaneously improving crop yields and agro‐ecosystem sustainability. It can be produced from a wide variety of biomass feedstocks using different thermochemical conversion technologies with or without the recovery of energy coproducts, resulting in chars of differing quality and a range of overall system greenhouse gas (GHG) mitigation outcomes. This analysis expands on previous sustainability studies by proposing a mechanistic life cycle GHG and economic operating cost assessment model for the coproduction of biochar and bioenergy from biomass residue feedstocks, with a case study for north‐central Colorado presented. Production is modeled as a continuous function of temperature for slow pyrolysis, fast pyrolysis, and gasification systems. Biochar environmental benefits (C sequestration, N2O suppression, crop yield improvements) are predicted in terms of expected liming value and recalcitrance. System‐level net GHG mitigation is computed, and net returns are estimated that reflect the variable economic costs of production, the agronomic value of biochar based on agricultural limestone or fertilizer displacement, and the value of GHG mitigation, with results compared to the alternate use of char for energy production. Case study results indicate that slow pyrolysis systems can mitigate up to 1.4 Mg CO2eq/Mg feedstock consumed, provided a favorable feedstock is utilized, production air pollutant emissions are mitigated, and energy coproducts are recovered. The model suggests that while financial returns are generally greater when char is consumed for energy (biocoal) than when used as a soil amendment (biochar), chars produced through high‐temperature conversion processes will have greater GHG‐mitigation value as biochar. The biochar scenario reaches economic parity at carbon prices as low as

Use of hollow-core fibers to deliver nanosecond Nd:YAG laser pulses to form sparks in gases

50/Mg CO2eq for optimal scenarios, despite conservative modeling assumptions. This model is a step toward spatially explicit assessment and optimization of biochar system design across different feedstocks, conversion technologies, and agricultural soils.

The effect of air-fuel ratio control strategies on nitrogen compound formation in three-way catalysts

We report what is to our knowledge the first delivery of nanosecond laser pulses through flexible fibers to produce optical sparks in atmospheric-pressure gases. Our work employs a Nd:YAG laser beam (1.064 microm) delivered through a cyclic olefin polymer-coated silver hollow fiber. We studied the beam properties at the fiber exit as a function of the fiber launch geometry. We found that for a low-angle launch (approximately 0.01 rad half-angle), the exit beam has relatively high optical intensity (approximately 2 GW/cm2) and low light divergence (approximately 0.01 rad half-angle) and allows downstream spark formation. The effect of fiber bending on the exit beam and on the ability to make sparks is also investigated.

Towards Multiplexed Fiber Delivered Laser Ignition for Natural Gas Engines

Abstract The ability of three-way catalysts (TWCs) to effectively remove CO and NOx from the exhaust is directly controlled by the air-fuel ratio at which the accompanying engine is operated. In a stoichiometric engine, small variations in the air-fuel ratio have large effects on the catalyst performance. These effects include wide variations in removal efficiencies and catalytic production of ammonia. The effect of the air-fuel ratio on catalysts has been well studied on automotive engines; these studies show the importance of maintaining an air-fuel ratio close to stoichiometric conditions. In automotive systems a ‘dithering’ technique is used in which the air-fuel ratio is modulated to widen the window of control. The effect of dithering on industrial engines has not been studied. A research programme was conducted to evaluate the effects of the air-fuel ratio on the performance of three-way catalysts operating on natural gas-fuelled industrial engines, the test programme aims at optimizing the engine based on the performance of the catalyst. This project has shown that dithering is an effective technique for enhancing the performance of TWCs on industrial engines. These results show that the allowable air-fuel ratio deviations are much larger with dithering and that the production of ammonia is significantly reduced.

The Effects of Air Flow Rates, Secondary Air Inlet Geometry, Fuel Type, and Operating Mode on the Performance of Gasifier Cookstoves

The use of laser ignition for advanced gas engines may provide benefits including extension of the lean limit and higher efficiency operation at elevated pressures. This contribution provides a short review of efforts to develop a practical laser ignition system for advanced multicylinder gas engines. The approach is to use a single laser source with fiber optic cables delivering the high power pulses from the source to the engine cylinders. The optical requirements for the fiber delivery lead us to use coated hollow core optical fibers. Characterizations and results of spark delivery tests for the fibers are presented. Single-cylinder engine test results using fiber delivered laser ignition are summarized. For multicylinder operation, a multiplexer based on a moving mirror is used to route the laser output pulses to different fiber channels (cylinders). Benchtop testing and initial engine testing of the multiplexed system are presented.

Laser Ignition of Natural Gas Engines Using Fiber Delivery

Development of biomass cookstoves that reduce emissions of CO and PM2.5 by more than 50% and 95%, respectively, compared to a three-stone fire has been promoted as part of efforts to reduce exposure to household air pollution (HAP) among people that cook with solid fuels. Gasifier cookstoves have attracted interest because some have been shown to emit less CO and PM2.5 than other designs. A laboratory test bed and new test procedure were used to investigate the influence of air flow rates, stove geometry, fuel type, and operating mode on gasifier cookstove performance. Power output, CO emissions, PM2.5 emissions, fuel consumption rates, producer gas composition, and fuel bed temperatures were measured. The test bed emitted <41 mg·MJd–1 PM2.5 and <8 g·MJd–1 CO when operating normally with certain prepared fuels, but order of magnitude increases in emission factors were observed for other fuels and during refueling. Changes in operating mode and fuel type also affected the composition of the producer gas entering the secondary combustion zone. Overall, the results suggest that the effects of fuel type and operator behavior on emissions need to be considered, in addition to cookstove design, as part of efforts to reduce exposure to HAP.

Development of a Fiber Delivered Laser Ignition System for Natural Gas Engines

A practical impediment to implementation of laser ignition systems has been the open-path beam delivery used in past research. In this contribution, we present the development and implementation of a fiber-optically delivery laser spark ignition system. To our knowledge, the work represents the first demonstration of fiber coupled laser ignition (using a remote laser source) of a natural gas engine. A Nd:YAG laser is used as the energy source and a coated hollow fiber is used for beam energy delivery. The system was implemented on a single-cylinder of a Waukesha VGF 18 turbo charged natural gas engine and yielded consistent and reliable ignition. In addition to presenting the design and testing of the fiber delivered laser ignition system, we present initial design concepts for a multiplexer to ignite multiple cylinders using a single laser source, and integrated optical diagnostic approaches to monitor the spark ignition and combustion performance.Copyright

Fiber Delivered Systems for Laser Ignition of Natural Gas Engines

Laser ignition is viewed as a potential future technology for advanced high-efficiency low-emission natural gas engines. However, in order to make laser ignition systems more practical, thereby enabling them to transition from the laboratory to industrial settings, there is a need to develop fiber optically delivered ignition systems. Recent work at Colorado State University has shown the possibility of using coated hollow fibers for spark delivery and has demonstrated laser ignition and operation of a single engine cylinder using hollow fiber delivery. In order to practically operate a multiple cylinder engine, we envisage a simple and low-cost system based upon a single laser source being delivered (“multiplexed”) through multiple fibers to multiple engine cylinders. In this paper, we report on the design, development, and initial bench-top testing of a multiplexer. Bench-top testing showed that the multiplexer can be positioned with the required accuracy and precision for launching into fiber optics, and can be switched at the relatively high switching rates needed to operate modern natural gas engines. Another test employed the multiplexer to alternately launch laser pulses into a pair of hollow fibers in a way that allows spark creation downstream of the fibers.Copyright

Optical diagnostics integrated with laser spark delivery system

Past research has shown that laser ignition is capable of operating high bmep engines at high efficiency and with low emission levels. However, for laser ignition systems to be adopted by industry, one requires a practical (and economical) mode of beam delivery other than the conventional open-path beam delivery that has been used in much of the past research. One potential beam delivery method is via optical fibers capable of handling high peak power. This paper summarizes our recent efforts in this area. Using coated hollow fibers, our research group has demonstrated the delivery of laser pulses to form optical sparks both on the bench-top and for ignition and operation of a single cylinder of an ARES engine. When held relatively straight, the hollow fibers allow transmission of nanosecond pulse energies of 10s of milli-Joules with transmission above 90% and sufficient beam quality for spark formation. We have also been able to deliver optical sparks on the bench-top with high peak power pulsed fiber lasers. Pulse energies in those experiments were approximately 2 mJ. Other recent work has studied the transmission characteristics of recently developed photonic crystal fibers.Copyright