A comparative analysis on combustion and emissions of some next generation higher-alcohol/diesel blends in a direct-injection diesel engine
Graphical abstract
Introduction
Diesel engines are more popular energy conversion devices because of their higher fuel conversion efficiency, higher torque capability, higher durability and lower hydrocarbon and carbon monoxide (HC & CO) emissions when compared to gasoline engines. Increasing concerns of fossil fuel depletion, oil-price volatility, burgeoning energy demands, global warming by GHG (green-house gases) emissions, toxic pollutants (smoke and NOx) and rigorous emission regulations are driving the scientific community to find alternative renewable biofuels for use in diesel engines. Recently higher alcohols have gathered interest among engine researchers to use them in diesel engines either as a neat fuel or as a blending component because they offer higher calorific value, higher cetane number, better blend stability and lower vapor pressure when compared to other widely-studied lower alcohols like ethanol and methanol. The term ‘higher alcohol’ refers to a series of straight and branched chain alcohols that consists of four or more carbon atoms like butanol (C4), pentanol (C5), hexanol (C6), heptanol (C7), octanol (C8), dodecanol (C12) and phytol (C20) [1]. The molecular structures of some higher alcohols are portrayed in Fig. 1.
Higher alcohols are found to be less corrosive on fuel injection and delivery systems due to their less hygroscopic nature than ethanol [2]. They have high flashpoints that offer safer storage and handling within the existing fuel distribution infrastructure. Their lower vapor pressures cause less evaporative emissions [3]. Though longer-chain alcohols have less oxygen content, they can still enhance the premixed combustion phase with their relatively longer ignition delays allowing sufficient mixing of air/fuel and also improve the diffusion combustion phase [1]. Furthermore, alcohols with longer carbon chains consume less energy during its production when compared to other lower alcohols since the biological process of breaking down large macromolecules can stop earlier [4]. The properties of higher alcohols in comparison with diesel and other lower alcohols are listed in Table 1.
The use of higher alcohols was earlier thwarted by high production costs, prolific use in food industry and limited production from non-petroleum resources [8]. Higher alcohols have never been able to be produced in larger quantities that make them potentially viable for use in diesel or gasoline engines until Atsumi et al. [9] achieved a high yield of 20 g/L of iso-butanol from glucose using the valine pathway in a lab-scale fermentor employing engineered Escherichia coli. Since then, bio-synthetic pathways have been extended to produce n-pentanol, n-hexanol, n-heptanol and n-octanol by employing larger substrates [10], [11]. Table 2 provides the details of microbial production of these alcohols from engineered micro-organisms with their yield data.
It could be inferred from Table 2 that the last decade has witnessed a significant amount of research to produce greater yields of higher alcohols through biosynthesis. To complement these efforts, several experimental and chemical kinetic modeling studies have been carried out. Fundamental combustion studies on iso-butanol [22], [23], [24], [25], [26], [27], n-pentanol [28], [29], [30], [31], [32], n-hexanol [30], [33], [34] and n-octanol [6], [35] were conducted which included information on its oxidation, laminar burning velocities, flame structure, reaction rates and pathways, species concentration data, stable intermediate species and ignition delay times.
The compatibility of these alcohols in diesel engines has prompted engine researchers to use them in their neat or blended form in diesel engines to analyze their combustion, performance and emission characteristics under various combustion strategies. Unlike n-butanol, which is heavily researched in the last 5 years, only a handful of research exists with iso-butanol [8], [36], [37], [38], [39], [40], [41] and n-pentanol usage [4], [41], [42], [43], [44], [45], [46] in diesel engines. These studies collectively demonstrated that ignition delay increased with increasing alcohol content in the blends as a result of their lower cetane number. The peaks of in-cylinder pressure and heat release rate increased with alcohol addition as a result of enhanced premixed combustion phase caused by the prolonged ignition delay. Smoke emissions generally decreased with increasing alcohol content in the blends. NOx emissions remained low with iso-butanol/diesel blends at all loads and n-pentanol/diesel blends only at low/medium loads. NOx emissions increased invariably at high loads with the addition of n-pentanol.
So far only one study has investigated the combustion, emission and performance of a diesel engine using n-hexanol/diesel blends up to 50% by vol [47]. Addition of n-hexanol also increased the ignition delay along with slightly higher peaks of pressure and HRR. NOx increased but the smoke was substantially reduced with n-hexanol addition. Till date, there have been far fewer studies that used n-octanol in considerable proportions in diesel engines. McCormick et al. [48] reported simultaneous reduction of PM and NOx by 12% and 3%, respectively, by adding 1-octanol at 2 wt% of oxygen with diesel in a 2-stroke diesel DI engine. Heuser et al. [49] used neat n-octanol in a compression-ignition engine and reported PM emissions to reduce by 20-fold than a diesel fuelled engine. Zhang et al. [50] tested n-octanol/diesel blend (30 vol%) with hydro-treated vegetable oil (HVO) or di-tertiary-butyl peroxide (DTBP) as cetane improvers at various operating points from the European stationary cycle and obtained less smoke and high NOx. Deep et al. [51] compared the use of 1-octanol at different blend ratios (10%, 20% and 30% v/v) with diesel in a medium capacity unmodified diesel engine. NOx levels were reduced with increasing octanol content in the blend and the engine efficiency was slightly affected. Heuser et al. [6] analyzed the combustion and emission behavior of 1-octanol and di-n-butyl ether in a single cylinder engine. Ignition delay prolonged with 1-octanol. Soot emissions reduced by 5-fold and a reduction in total particle number by up to 80% was achieved. Hoppe et al. [52] found favorable soot/NOx trade-off over the entire engine load range with n-octanol/diesel blends. For further reading on higher alcohols usage in diesel engines, a detailed and exhaustive review can be obtained from a recent article by this research group [1].
Filling a gap in the existing body of literature of higher alcohols, this research presents a vis-a-vis study that compares and analyzes four higher alcohol/diesel blends (iso-butanol, n-pentanol, n-hexanol and n-octanol) in the same light-duty, single cylinder, and direct injection diesel engine under similar operating conditions. To the authors’ knowledge, this is the first time that such a comparative evaluation is reported for many higher alcohol/diesel blends in the same engine and operating conditions concerning combustion and emission characteristics of the engine.
Section snippets
Test fuels
Iso-butanol (Purity: 99%, CAS No: 78-83-1) and n-pentanol (Purity: 98%, CAS No: 71-41-0) were procured from AVRA Synthesis, India. n-hexanol (Purity: 98%, CAS No: 108-93-0) and n-octanol (Purity: 99%, CAS No: 111-87-5) were procured from Merck Millipore, India. All these alcohols are certified to be of analytical grade. Ultra-low sulfur diesel (ULSD) fuel which forms the reference fuel for this study was obtained from Indian oil corporation, Chennai. The test fuels were prepared by mixing all
Results and discussion
The results of the combustion and emission characteristics are presented and discussed for higher alcohol/diesel blends with reference to baseline diesel operation. Some results were analyzed only at high load conditions for the sake of brevity of space of this paper and also because the fuel/air mixture has longer residence time at low speed and high load conditions.
Conclusions
This study was intended to compare and analyze the effects of some higher alcohol/diesel blends on combustion and emission characteristics of a DI diesel engine. Four test blends containing 30 vol% of iso-butanol, n-pentanol, n-hexanol and n-octanol (designated as ISB30, PEN30, HEX30 and OCT30, respectively) were prepared on an individual basis for this purpose and the following conclusions were drawn based on the experimental results with respect to ULSD:
- 1.
ISB30 experienced the longest ignition
Acknowledgements
The authors appreciate the support of the Management of Sri Venkateswara College of Engineering and Jeppiaar Institute of Technology, Sriperumbudur, Chennai, TN, India for facilitating this research. The authors acknowledge the assistance rendered by Polymeric Materials Research Lab at Alagappa College, Karaikudi, TN, India for estimating fuel properties.
References (82)
- et al.
Use of higher alcohol biofuels in diesel engines: a review
Renew Sustain Energy Rev
(2016) The influence of n-butanol/diesel fuel blends utilization on a small diesel engine performance and emissions
Fuel
(2011)- et al.
A comparison of performance of higher alcohols/diesel fuel blends in a diesel engine
Appl Energy
(2012) - et al.
Microbial production of 1-octanol: a naturally excreted biofuel with diesel-like properties
Metab Eng Commun
(2015) - et al.
Alcohol combustion chemistry
Prog Energy Combust Sci
(2014) - et al.
Genetic engineering to enhance the Ehrlich pathway and alter carbon flux for increased isobutanol production from glucose by Saccharomyces cerevisiae
J Biotechnol
(2012) - et al.
Butanol and hexanol production in Clostridium carboxidivorans syngas fermentation: medium development and culture techniques
Bioresour Technol
(2015) - et al.
A selection platform for carbon chain elongation using the CoA-dependent pathway to produce linear higher alcohols
Metab Eng
(2012) - et al.
An experimental and kinetic modeling study of combustion of isomers of butanol
Combust Flame
(2010) - et al.
A comprehensive chemical kinetic combustion model for the four butanol isomers
Combust Flame
(2012)
Detailed kinetic modeling of the combustion of the four butanol isomers in premixed low-pressure flames
Combust Flame
Combustion and pyrolysis of iso-butanol: experimental and chemical kinetic modeling study
Combust Flame
Experimental and detailed kinetic modeling study of 1-pentanol oxidation in a JSR and combustion in a bomb
Proc Combust Inst
A comparison of longer alkane and alcohol ignition including new experimental results for n-pentanol and n-hexanol
Proc Combust Inst
High temperature ignition delay times of C5 primary alcohols
Combust Flame
Experimental and kinetic modeling study of 1-hexanol combustion in an opposed-flow diffusion flame
Proc Combust Inst
An experimental and modeling study of n-octanol combustion
Proc Combust Inst
Performance and emission characteristics of a diesel engine using isobutanol–diesel fuel blends
Renewable Energy
Effects of iso-butanol/diesel and n-pentanol/diesel blends on performance and emissions of a DI diesel engine under premixed LTC (low temperature combustion) mode
Fuel
Performance tests of a diesel engine fueled with pentanol/diesel fuel blends
Fuel
Effect of n-pentanol addition on the combustion, performance and emission characteristics of a direct-injection diesel engine
Energy
Combustion and emission characteristics of diesel engine fueled with diesel/biodiesel/pentanol fuel blends
Fuel
Combustion and emissions of compression ignition in a direct injection diesel engine fueled with pentanol
Energy
Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends
Fuel
Microbial synthesis of n-butanol, isobutanol, and other higher alcohols from diverse resources
Bioresour Technol
Experimental study on diesel conventional and low temperature combustion by fueling four isomers of butanol
Fuel
Systematic study of the effect of the hydroxyl functional group in alcohol molecules on compression ignition and exhaust gas emissions
Fuel
Chemical kinetic modeling of dimethyl carbonate in an opposed-flow diffusion flame
Proc Combust Inst
Investigating the emissions during acceleration of a turbocharged diesel engine operating with bio-diesel or n-butanol diesel fuel blends
Energy
Alcohol–diesel fuel combustion in the compression ignition engine
Fuel
An experimental study on the performance parameters of an experimental CI engine fueled with diesel–methanol–dodecanol blends
Fuel
Combined effect of injection timing, EGR and injection pressure in NOx control of a stationary diesel engine fuelled with crude rice bran oil methyl ester
Fuel
Experimental investigation of performance, emission and combustion characteristics of waste plastic pyrolysis oil blended with diethyl ether used as fuel for diesel engine
Energy
The influence of various oxygenated functional groups in carbonyl and ether compounds on compression ignition and exhaust gas emissions
Fuel
Chemical kinetics of hydrocarbon ignition in practical combustion systems
Proc Combust Inst
Estimation of double-Wiebe function parameters using least square method for burn durations of ethanol-gasoline blends in spark ignition engine over variable compression ratios and EGR levels
Appl Therm Eng
Combustion characteristics of lemongrass (Cymbopogon flexuosus) oil in a partial premixed charge compression ignition engine
Alexandria Eng J
Experimental and numerical study on NOx and CO emission characteristics of dimethyl ether/air jet diffusion flame
Appl Energy
An experimental and modeling study of NOx and CO emission behaviors of dimethyl ether (DME) in a boiler furnace
Fuel Process Technol
Everything you need to know about NOx
Met Finish
Effect of injection timing on the exhaust emissions of a diesel engine using diesel–methanol blends
Renewable Energy
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