Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple "upstream" (i.e., lignin bioengineering, lignin isolation and "early-stage catalytic conversion of lignin") and "downstream" (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a "beginning-to-end" analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis.

Catalytic roles of metals and supports on hydrodeoxygenation of lignin monomer guaiacol

Relationship Between Diesel Fuel Spray Vapor Penetration/Dispersion and Local Fuel Mixture Fraction

Diesel spray experiments at controlled high-temperature and high-pressure conditions offer the potential for an improved understanding of diesel combustion, and for the development of more accurate CFD models that will ultimately be used to improve engine design. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but uncertainties about their operation exist because of the uniqueness of each facility. For the IMEM meeting, we describe results from comparative studies using constant-volume vessels at Sandia National Laboratories and IFP. Targeting the same ambient gas conditions (900 K, 60 bar, 22.8 kg/m{sup 3}, 15% oxygen) and sharing the same injector (common rail, 1500 bar, KS1.5/86 nozzle, 0.090 mm orifice diameter, n-dodecane, 363 K), we describe detailed measurements of the temperature and pressure boundary conditions at each facility, followed by observations of spray penetration, ignition, and combustion using high-speed imaging. Performing experiments at the same high-temperature, high-pressure operating conditions is an objective of the Engine Combustion Network (http://www.ca.sandia.gov/ECN/), which seeks to leverage the research capabilities and advanced diagnostics of all participants in the ECN. We expect that this effort will generate a high-quality dataset to be used for advanced computational model development at engine conditions.

Comparison of Diesel Spray Combustion in Different High-Temperature, High-Pressure Facilities

Recent progress in gasoline surrogate fuels

Combustion behavior of various oxygenated fuels has been studied in a DAF heavy-duty (HD) directinjection (DI) diesel engine. From these fuels, it is well-known that they lead to lower particle (PM) emissions; however, for a given fuel oxygen mass fraction, there are significant differences in PM reduction. Although this can be traced back to the specific molecular structure of the oxygenate in question, no consensus can be found in the literature as to the explanation hereof. In this study, the sooting tendency (smoke number) of three oxygenates [viz., tripropylene glycol methyl ether (TP), dibutyl maleate (DB), and cyclohexanone (X1)] was compared to that of commercial diesel fuel (EN590, D). The results suggest that the cetane number (CN) (i.e., fuel reactivity) may play an important role. More specifically, the low reactive oxygenate X1, with its cyclic carbon chain, was found to perform exceptionally well compared to the more reactive linear and branched oxygenates DB and TP, respectively. Cyclic oxygenates are abundant in nature. Cellulose, the most common organic compound on earth, is the best-known example. Although it is not trivial, liquid cyclic oxygenates can be made from lignocellulosic biomass. Particularly, the production of C6 oxygenates (e.g., guaiacol, cyclohexanone, phenol, etc.), which can be derived from lignin, is the subject of current investigation. Fuels produced from such biomass (e.g., plant waste or the nonedible part of plants) are referred to as secondgeneration biofuels and are expected to play a pivotal role in the near future.

http://www.mate.tue.nl/mate/pdfs/9419.pdf

Cyclic Oxygenates: A New Class of Second-Generation Biofuels for Diesel Engines

This paper first compares strengths and weaknesses of different options for performing optical diagnostics on HD diesel sprays. Then, practical experiences are described with the design and operation of a constant volume test cell over a period of more than five years. In this test rig, pre-combustion of a lean gas mixture is used to generate realistic gas mixture conditions prior to fuel injection. Spray growth, vaporization are studied using Schlieren and Mie scattering experiments. The Schlieren set-up is also used for registration of light emitted by the combustion process; this can also provide information on ignition delay and on soot lift-off length. The paper further describes difficulties encountered with image processing and suggests methods on how to deal with them. Results are presented that illustrate the wide range of capabilities of this test-rig when combined with high speed video registration, in particular its potential for studying issues related to vaporizing fuel spray dynamics.

http://www.mate.tue.nl/mate/pdfs/10123.pdf

Design and operation of a high pressure, high temperature cell for HD diesel spray diagnostics: guidelines and results

This paper reports on a study of a large number of blends of a low-sulfur EN-590 type diesel fuel respectively of a Swedish Class 1 fuel and of a synthetic diesel with different types of oxygenates. Oxygen mass fraction of the blends varied between 0 and 15%. For comparison, the fuel matrix was extended with non-oxygenated blends including a diesel/water emulsion. Tests were performed on a modern multi-cylinder HD DAF engine equipped with cooled EGR for enabling NO\dx levels between 2.0 and 3.5 g/kWh on EN-590 diesel fuel. Additional tests were done on a Volvo Euro-2 type HD engine with very low PM emission. Finally, for some blends, combustion progress and soot illumination was registered when tested on a single-cylinder research engine with optical access. The results confirm the importance of oxygen mass fraction of the fuel blend, but at the same time illustrate the effect of chemical structure: some oxygenates are twice as effective in reducing PM as other well-known oxygenates. In combination with conventional CI combustion with extended ignition delay, such fuel blends will produce extremely low PM levels without the necessity of very high amounts of EGR, suggesting a possible alternative pathway towards clean diesel combustion.

Peter J. M. Frijters

Papers

Cyclic Oxygenates: A New Class of Second-Generation Biofuels for Diesel Engines

Design and operation of a high pressure, high temperature cell for HD diesel spray diagnostics: guidelines and results

Oxygenated Fuel Composition Impact on Heavy-Duty Diesel Engine Emissions