Butanol is a very competitive renewable biofuel for use in internal combustion engines given its many advantages. In this review, the properties of butanol are compared with the conventional gasoline, diesel fuel, and some widely used biofuels, i.e. methanol, ethanol, biodiesel. The comparison of fuel properties indicates that n-butanol has the potential to overcome the drawbacks brought by low-carbon alcohols or biodiesel. Then, the development of butanol production is reviewed and various methods for increasing fermentative butanol production are introduced in detailed, i.e. metabolic engineering of the Clostridia, advanced fermentation technique. The most costive part of the fermentation is the substrate, so methods involved in renewed substrates are also mentioned. Next, the applications of butanol as a biofuel are summarized from three aspects: (1) fundamental combustion experiments in some well-defined burning reactors; (2) a substitute for gasoline in spark ignition engine; (3) a substitute for diesel fuel in compression ignition engine. These studies demonstrate that butanol, as a potential second generation biofuel, is a better alternative for the gasoline or diesel fuel, from the viewpoints of combustion characteristics, engine performance, and exhaust emissions. However, butanol has not been intensively studied when compared to ethanol or biodiesel, for which considerable numbers of reports are available. Finally, some challenges and future research directions are outlined in the last section of this review.

Progress in the production and application of n-butanol as a biofuel

Alcohol combustion chemistry

A comprehensive chemical kinetic combustion model for the four butanol isomers

The influence of n-butanol/diesel fuel blends utilization on a small diesel engine performance and emissions

Metabolic engineering is the enabling science of development of efficient cell factories for the production of fuels, chemicals, pharmaceuticals, and food ingredients through microbial fermentations. The yeast Saccharomyces cerevisiae is a key cell factory already used for the production of a wide range of industrial products, and here we review ongoing work, particularly in industry, on using this organism for the production of butanol, which can be used as biofuel, and isoprenoids, which can find a wide range of applications including as pharmaceuticals and as biodiesel. We also look into how engineering of yeast can lead to improved uptake of sugars that are present in biomass hydrolyzates, and hereby allow for utilization of biomass as feedstock in the production of fuels and chemicals employing S. cerevisiae. Finally, we discuss the perspectives of how technologies from systems biology and synthetic biology can be used to advance metabolic engineering of yeast.

Metabolic Engineering of Saccharomyces cerevisiae: A Key Cell Factory Platform for Future Biorefineries

This study was designed to evaluate a ‘what-if’ scenario in terms of using butanol as an oxygenate, in place of ethanol in an engine calibrated for gasoline operation. No changes to the stock engine calibration were performed for this study. Combustion analysis, efficiency and emissions of pure gasoline, 10% ethanol and 10% butanol blends in a modern, direct-injection four-cylinder, spark ignition engine were analyzed. Data was taken at engine speeds of 1000 RPM up to 4000 RPM with load varying from 0 Nm (idle) to 150 Nm. Relatively minor differences existed between the three fuels for the combustion characteristics such as heat release rate, 50% mass fraction burned, and coefficient of variation of indicated mean effective pressure at low and medium engine loads. However at high engine loads the reduced knock resistance of the butanol blend forced the engine control unit to retard the ignition timing substantially, compared to the gasoline baseline and even more pronounced compared to the ethanol blend. Brake specific volumetric fuel consumption which represented a normalized volumetric fuel flow rate, was lowest for the gasoline baseline fuel, due to the higher energy density. The 10% butanol blend had a lower volumetric fuel consumption compared to the ethanol blend, as expected based on energy density differences. Results showed little difference in regulated emissions between 10% ethanol and 10% butanol. The ethanol blend produced the highest peak specific NOx due to the high octane rating of ethanol and effective anti-knock characteristics. Overall, the ability of butanol to perform equally as well as ethanol from an emissions and combustion standpoint, with a decrease in fuel consumption, initially appears promising. Further experiments are planned to explore the full operating range of the engine and the potential benefits of higher blend ratios of butanol.Copyright © 2008 by UChicago Argonne LLC, Operator of Argonne National Laboratory

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A Comparison of Ethanol and Butanol as Oxygenates Using a Direct-Injection, Spark-Ignition (DISI) Engine

The new US Renewable Fuel Standard requires an increase of ethanol and advanced biofuels to 36 billion gallons by 2022 Due to its high octane number, renewable character and minimal toxicity, ethanol was believed to be one of the most favorable alternative fuels to displace gasoline in spark-ignited engines However, ethanol fuel results in a substantial reduction in vehicle range when compared to gasoline In addition, ethanol is fully miscible in water which requires blending at distribution sites instead of the refinery Butanol, on the other hand, has an energy density comparable to gasoline and lower affinity for water than ethanol Butanol has recently received increased attention due to its favorable fuel properties as well as new developments in production processes The advantageous properties of butanol warrant a more in-depth study on the potential for butanol to become a significant component of the advanced biofuels mandate This study evaluates the combustion behavior, performance, as well as the regulated engine-out emissions of ethanol and butanol blends with gasoline Two of the butanol isomers; 1-butanol as well as iso-butanol, were tested as part of this study The evaluation includes gasoline as a baseline, as well as various ethanol/gasoline and butanol/gasoline blends up to a volume blend ratio of 85% of the oxygenated fuel The test engine is a spark ignition, direct-injection, (SIDI), four-cylinder test engine equipped with pressure transducers in each cylinder These tests were designed to evaluate a scenario in terms of using these alcohol blends in an engine calibrated for pump gasoline operation Therefore no modifications to the engine calibration were performed Following this analysis of combustion behavior and emissions with the base engine calibration, future studies will include detailed heat release analysis of engine operation without exhaust gas recirculation Also, knock behavior of the different fuel blends will be studied along with unregulated engine out emissionsCopyright © 2009 by ASME

Effects of Blending Gasoline With Ethanol and Butanol on Engine Efficiency and Emissions Using a Direct-Injection, Spark-Ignition Engine

Air Separation Membranes (ASM) could potentially replace Exhaust Gas Recirculation (EGR) technology in engines due to the proven benefits in NOx reduction but without the drawbacks of EGR. Previous investigations of Nitrogen Enriched Air (NEA) combustion using nitrogen bottles showed up to 70% NOx reduction with modest 2% nitrogen enrichment. The investigation in this paper was performed with an ASM capable of delivering at least 3.5% NEA to a single cylinder spark ignited natural gas engine. Low Temperature Combustion (LTC) is one of the pathways to meet the mandatory ultra low NOx emissions levels set by regulatory agencies. In this study, a comparative assessment is made between natural gas combustion in standard air and 2% NEA. Enrichment beyond this level degraded engine performance in terms of power density, Brake Thermal Efficiency (BTE), and unburned hydrocarbon (UHC) emissions for a given equivalence ratio. The ignition timing was optimized to yield maximum brake torque for standard air and NEA. Subsequently, conventional spark ignition (SI) was replaced by laser ignition (LI) to extend lean ignition limit. Both ignition systems were studied under a wide operating range from ψ: 1.0 to the lean misfire limit. It was observed that with 2% NEA, for a similar fuel quantity, the equivalence ratio (Ψ) increases by 0.1 relative to standard air conditions. Analysis showed that lean burn operation along with NEA and alternative ignition source such as LI could pave the pathway for realizing lower NOx emissions with a slight penalty in BTE.Copyright © 2009 by ASME

Air separation membranes : an alternative to EGR in large bore natural gas engines.

A comparative analysis of nitrogen and oxygen enriched combustion is presented in this paper. Nitrogen enrichment of intake air is proposed as an alternative to Exhaust Gas Recirculation (EGR). NOx reduction by EGR is not very promising due to engine reliability concerns and increased maintenance costs. Air separation membrane, on the other hand, is a potential strategy for NOx reduction due to uncompromised reliability of engine performance. Oxygen-rich and nitrogen-rich streams are produced by passing air through a nonporous polymeric membrane. Nitrogen Enriched Air (NEA) reduces NOx formation by lowering in-cylinder combustion temperatures but with a compromise in Fuel Conversion Efficiency (FCE). However, advanced ignition timing improves FCE considerably. Oxygen Enriched Air (OEA), on the other hand, improves FCE due to the availability of extra oxygen for better combustion which results in higher bulk gas temperatures and NOx emissions. This behavior could be controlled by retarding the ignition timing. Experimental results of nitrogen and oxygen enriched combustion of a Kohler M12 generator (converted to operate with natural gas) is presented in this paper. A 68% reduction in NOx and a 0.8% drop in FCE were observed at −30 ATDC ignition timing (IT) with 2.1% N2 enrichment (40 slpm). A 9% O2 enrichment (40 slpm) at −30 ATDC IT improved FCE by 1% but with higher NOx emissions. The increase in NOx emissions was minimal with a 2% improvement in FCE at −10 ATDC IT and 9% O2 enrichment (40 slpm). Some of the drawbacks encountered were engine misfire at higher concentrations of nitrogen enriched air and retarded ignition timing resulting in poor FCE. This paper discusses both the approaches and highlights the benefits of nitrogen enrichment using an air separation membrane over its counterpart for NOx reduction.© 2005 ASME

Performance of a natural gas engine using variable air composition.

This paper is the first of three papers stemming from a dual fuel Chrysler prototype engine which uses both diesel and gasoline direct injection running at stoichiometric conditions, as part of a project to explore the viability of incorporating an engine platform which utilizes low temperature combustion regimes into a modern automotive application. The combustion system used high rates of EGR while maintaining combustion stability by using high charge motion intake port and a high energy ignition system. The engine ran highly dilute SI combustion at low loads, Diesel Assisted Spark Ignition at medium loads and a transition to Diesel Micro Pilot ignition at medium to high load. This paper explores diesel assisted spark ignited combustion at medium loads 6.5 bar to 12.7 bar BMEP. The second paper will explore the use of diesel micro-pilot ignition at high loads 10.6 bar to 14.5 bar BMEP and the third paper to be published in 2024 will explore fuel property effects (mainly Cetane and Octane) through the use of alternative fuels. In the diesel assisted spark ignited combustion regime combustion is initiated via a spark while using a diesel injection to provide a low octane fuel source early in combustion. Results were obtained at speed/load points ranging from 1500 to 3200 RPM and boost levels ranging from 95 to 200 kPa. Spark timing, diesel injection timing, and exhaust gas recirculation percentage were crucial variables affecting the performance of the engine. Brake thermal efficiency levels above 39% were possible at numerous operating conditions.

Steve McConnell

Papers

A Comparison of Ethanol and Butanol as Oxygenates Using a Direct-Injection, Spark-Ignition (DISI) Engine

Effects of Blending Gasoline With Ethanol and Butanol on Engine Efficiency and Emissions Using a Direct-Injection, Spark-Ignition Engine

Air separation membranes : an alternative to EGR in large bore natural gas engines.

Performance of a natural gas engine using variable air composition.

Combustion Regimes in the Chrysler Multi-Air Multi-Fuel Engine, Part 1 - Diesel Assisted Spark Ignited