Review of high efficiency and clean reactivity controlled compression ignition (RCCI) combustion in internal combustion engines

https://biblio.ugent.be/publication/8589931/file/8609217.pdf

Methanol as a fuel for internal combustion engines

Biofuels have grabbed the attention of engine researchers ever since the oil-crisis and escalating costs of petro-chemicals cropped up in the ׳70s. Ethanol and methanol were the most widely researched alcohols in IC engines. However, the last decade has witnessed significant amount of research in higher alcohols due to the development of modern fermentation processes using engineered micro-organisms that improved yield. Higher alcohols are attractive second/third generation biofuels that can be produced from sugary, starchy and ligno-cellulosic biomass feedstocks using sustainable pathways. The present work reviews the current literature concerning the effects of using higher alcohols ranging from 3-carbon propanol to 20-carbon phytol on combustion, performance and emission characteristics of a wide range of diesel engines under various test conditions. The literature is abound with evidence that higher alcohols reduce carcinogenic particulate emissions that are prevalent in diesel engines. NOx emissions either increased or decreased based on the domination of either cetane number or heat of evaporation. Brake specific fuel consumption (BSFC) of the engine usually suffered due to low energy content of alcohols. A notable feature is that the combination of higher alcohols (like butanol or pentanol), high exhaust gas recirculation (EGR) rates and late injection timing enabled low temperature combustion (LTC) in diesel engines that can simultaneously reduce smoke and NOx emissions with improved engine efficiency. It can be concluded that higher alcohols reduce smoke emissions with their fuel-borne oxygen; enhance air/fuel mixing by offering long ignition delay and eventually replace fossil diesel (partially or wholly) to enable a clean and efficient combustion in compression-ignition engines. The chief thrust areas include developing mutant strains with higher yield, higher tolerance to toxic inhibition and low-cost substrates for fermentation. Further work is required in stipulating optimum blend-fuel characteristics and ensuring the long-term durability of the engines using these fuels.

Use of higher alcohol biofuels in diesel engines: A review

Evolution, challenges and path forward for low temperature combustion engines

Potential of acetone-butanol-ethanol (ABE) as a biofuel

Development of Dual-Fuel Low Temperature Combustion Strategy in a Multi-Cylinder Heavy-Duty Compression Ignition Engine Using Conventional and Alternative Fuels

The U.S. Renewable Fuel Standard (RFS2) requires a drastic increases in production of advanced biofuels up to 36 billion gallons over the next decade while corn-based ethanol will be capped at 15 billion gallons. Currently ethanol is the predominant alternative fuel and is widely distributed at 10 vol % blends in gasoline (E10). However, certain properties of ethanol make it less desirable as a blending agent in particular at higher blend levels. Therefore the engine- and vehicle-related properties of longer chain alcohols are evaluated in comparison to gasoline to determine their suitability as blending agents for spark-ignition engine fuels. This analytical study aims at providing comprehensive property data for a range of alcohol isomers with a carbon count up to C8. Relevant physical property data is used to determine the general suitability of longer chain alcohol isomers as blending agents based on factors such as melting point and boiling. Based on initial findings the scope of the study was narrowed down to alcohols in the C2–C6 range. It was determined that the engine- and combustion-relevant information is missing from the literature for a wide range of longer chain isomers. Thus fuel testing for engine-relevant properties such as lower heating value, knock resistance (RON, MON) and Reid Vapour Pressure (RVP) for alcohols up to C6 was performed as part of this study. Data suggests that the melting point of alcohols increases with increasing carbon count and all C7 and C8 isomers exhibit melting points in excess of −40 °C making their use as vehicle fuel questionable. Boiling points increase with increasing carbon count and n-structures generally have slightly higher boiling points than their respective iso-structures. Latent heat of vaporization decreases with carbon count, the mass-specific value for ethanol is triple that of gasoline, the energy specific ratio increases to a factor of 5. Alcohol fuels generally have a significantly lower RVP than gasoline, RVP decreases with increasing carbon count. Stoichiometric air demand and fuel energy content increase with carbon count. Knock resistance expressed as Research Octane Number (RON) and Motor Octane Number (MON) decreases significantly with increasing carbon count, iso-structures show increased knock resistance compared to their respective n-structures. This study is limited to analytical results as well as fuel property testing according to ASTM standards. Only properties of neat alcohols are evaluated in comparison to gasoline certification fuel, gasoline blend stock for ethanol blending and E10. The analysis of the reported properties is further focused on spark-ignition engine applications only. Future phases of this project will include the assessment of properties of multi-component blends as well as efficiency, performance and emissions testing on a modern direct-injection engine. While data for a limited number of commonly used alcohols such as ethanol and iso-butanol is available in the literature, little or no data is available for a majority of other alcohols and their isomers. In addition, engine-related data published in the past occasionally disregards the significant differences between alcohol isomers of the same chain length. This study offers a comprehensive review of physical properties of alcohols and their common isomers in the C2–C8 range as they relate to in-vehicle use and spark-ignition combustion engine application. Data presented in this paper suggests that higher alcohols have certain physical properties that might be desirable for blending with gasoline. Due to their oxygen content all alcohols have an inherent disadvantage in terms of energy content compared to non-oxygenated fuels. While this disadvantage becomes less pronounced with increasing carbon count, other less desirable properties such as a low RVP and reduced knock resistance become more dominant with longer chain length alcohols. In addition to merely evaluating properties, the selection of promising alcohols and blend levels will ultimately depend on the introduction scenario and target properties.

Analytical Assessment of C2–C8 Alcohols as Spark-Ignition Engine Fuels

Stricter CO2 and emissions regulations are pushing spark ignition engines more and more towards downsizing, enabled through direct injection and turbocharging. The advantages which come with direct injection, such as increased charge density and an elevated knock resistance, are even more pronounced when using low carbon number alcohols instead of gasoline. This is mainly due to the higher heat of vaporization and the lower air-to-fuel ratio of light alcohols such as methanol, ethanol and butanol. These alcohols are also attractive alternatives to gasoline because they can be produced from renewable resources. Because they are liquid, they can be easily stored in a vehicle.
In this respect, the performance and engine-out emissions (NOx, CO, HC and PM) of methanol, ethanol and butanol were examined on a 4 cylinder 2.4 DI production engine and are compared with those on neat gasoline. Additionally, measurements were done for E85 and a methanol-gasoline blend with the same air-to-fuel ratio as E85 because this ‘iso-stoichiometric’ methanol-gasoline blend shows very few differences in physical properties to E85 and has the potential to be used as ‘drop-in’ fuel for flex-fuel vehicles. It is shown that the brake thermal efficiency when running on alcohol fuels is significantly better than with gasoline while emitting fewer emissions. In a knock limited case for gasoline, the brake thermal efficiency on methanol was more than 5 percentage points better than on gasoline. The engine test results also confirm that, from an engine control point of view, the ‘iso-stoichiometric’ methanol-gasoline blend can indeed be used as a ‘drop-in’ fuel for E85.

Andrew Ickes

Papers

Development of Dual-Fuel Low Temperature Combustion Strategy in a Multi-Cylinder Heavy-Duty Compression Ignition Engine Using Conventional and Alternative Fuels

Analytical Assessment of C2–C8 Alcohols as Spark-Ignition Engine Fuels

Experimental Investigation of a DISI Production Engine Fuelled with Methanol, Ethanol, Butanol and ISO-Stoichiometric Alcohol Blends

Impact of Cetane Number on Combustion of a Gasoline-Diesel Dual-Fuel Heavy-Duty Multi-Cylinder Engine

Comparison of RCCI Operation with and without EGR over the Full Operating Map of a Heavy-Duty Diesel Engine