Biodiesel is being considered as a renewable fuel candidate to completely or partially replace fossil diesel. Understanding its combustion is key to assess its applicability in practical compression ignition engines. Significant progress has been made in understanding biodiesel combustion through experimental studies, development of reaction kinetics to describe its oxidation, and simulations in typical engine environments. The use of surrogates in place of the real biodiesels plays a crucial role in this endeavour. This chapter reviews the existing studies revolving around surrogate fuels for biodiesels. Thereafter, the challenges ahead in this context to further enhance our knowledge of biodiesel combustion are presented, and possible options to address these are discussed where appropriate. © 2017, Springer Nature Singapore Pte Ltd.

Krithika Narayanaswamy

Department of Mechanical Engineering

Krishnasamy V. Anand

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Surrogates for Biodiesel: Review and Challenges

Green Energy and Technology

Biodiesel is a potential alternative to fossil diesel. In combustion simulations, in order to circumvent the difficulty in integrating reaction schemes for biodiesels, which are typically of a large size and not well understood, a surrogate approach to simplify the representation of its long chain methyl ester components is adopted. In this work, a compact reaction scheme for methyl butanoate, which is a potentially important candidate for biodiesel surrogates, is derived from a detailed reference mechanism (Dooley et al., 2008). An existing well-validated model for n-dodecane (Narayanaswamy et al., 2014) oxidation, which is a suitable base to model biodiesel surrogates, is augmented with the oxidation pathways of methyl butanoate. The resulting combined mechanism is comprehensively assessed for methyl butanoate kinetic description. Several rate constants pertaining to methyl butanoate kinetics are updated in the resulting chemical mechanism based on recent rate recommendations from the literature in a consistent manner. The revised kinetic model has been validated comprehensively against a wide range of experimental data and found to be satisfactory. In addition, auto-ignition delay times of methyl butanoate have been measured in a rapid compression machine (RCM). The ignition delay time measurements cover a wide range of experimental conditions: temperatures of 850–1100 K and pressures of 10–40 bar. The impact of varying equivalence ratios on ignition delay times has also been investigated for ϕ = 0.5–1.5 and ignition delay times are reported for the rich mixtures for the first time as a part of this work. No two-stage ignition or negative temperature coefficient (NTC) behavior has been observed for methyl butanoate in the experimental investigation. The effect of addition of low-temperature chemistry pathways to the methyl butanoate chemical kinetic mechanism has also been explored. © 2018 The Combustion Institute

Combustion and Flame

Experimental and chemical kinetic modeling investigation of methyl butanoate as a component of biodiesel surrogate

An alternative way to formulate transportation fuel surrogates using model predictions of gas-phase combustion targets is explored and compared to conventional approaches. Given a selection of individual fuel components, a multi-component chemical mechanism describing their oxidation kinetics, and a database of experimental measurements for key combustion quantities such as ignition delay times and laminar burning velocities, the optimal fractional amount of each fuel is determined as the one yielding the smallest error between experiments and model predictions. Using a previously studied three-component jet fuel surrogate containing n-dodecane, methyl-cyclohexane, and m-xylene as a case study, this article investigates in a systematic manner how the surrogate composition affects model predictions for ignition delay time and laminar burning velocities over a wide range of temperature, pressure and stoichiometry conditions, and compares the results to existing surrogate formulation techniques, providing new insights on how to define surrogates for simulation purposes. Finally, an optimisation algorithm is described to accelerate the identification of optimal surrogate compositions in this context. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

Combustion Theory and Modelling

Simulation-driven formulation of transportation fuel surrogates

Biodiesel fuels comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats serve as a potential alternative to fossil diesel. The biodiesel fueled engine does not require any major hardware modifications in the existing configuration. Also, the uses of biodiesel in compression ignition engines are found to significantly lower soot emissions. Thus, the conventional nitric oxide-soot trade-off problem narrows down to a unidirectional control of nitric oxide emissions which are generally known to increase with several candidate biodiesel fuels. The formation of oxides of nitrogen (NOx) from biodiesel fuel is dependent on both fuel and engine characteristics. The present work reviews the effect of biodiesel fuel composition and properties on NOx emissions emanating from biodiesel fueled engines and describes fuel modifications and engine tuning measures for their mitigation. The other outcomes of biodiesel NOx control measures in terms of engine performance and emission changes are also highlighted and the best possible ways for achieving biodiesel-NOx neutrality are outlined. © 2016 Elsevier Ltd. All rights reserved.

Renewable and Sustainable Energy Reviews

Biodiesel NOx penalty and control measures - A review

Surrogate fuels are often used in place of real fuels in computational combustion studies. However, many different choices of hydrocarbons to make up surrogate mixtures have been reported in the literature, particularly for jet fuels. To identify the best choice of surrogate components, the capabilities of different surrogate mixtures in emulating the combustion kinetic behavior of the real fuel must be examined. To allow extensive assessment of the combustion behavior of these surrogate mixtures against detailed experimental measurements for real fuels, accurate and compact kinetic models are most essential. To realize this goal, a flexible and evolutive component library framework is proposed here, which allows mixing and matching between surrogate components to obtain short chemical mechanisms with only the necessary kinetics for the desired surrogate mixtures. The idea is demonstrated using an extensively validated multi-component reaction mechanism developed in stages (Blanquart et al., 2009; Narayanaswamy et al., 2010, 2014, 2015), thanks to its compact size and modular assembly. To display the applicability of the component library framework, (i) a jet fuel surrogate consisting of n-dodecane, methylcyclohexane, and m-xylene, whose kinetics are described in the multi-component chemical mechanism is defined, (ii) a chemical model for this surrogate mixture is derived from the multi-component chemical mechanism using the component library framework, and (iii) the predictive capabilities of this jet fuel surrogate and the associated chemical model are assessed extensively from low to high temperatures in well studied experimental configurations, such as shock tubes, premixed flames, and flow reactors. © 2015 The Combustion Institute.

Fulltext

A component library framework for deriving kinetic mechanisms for multi-component fuel surrogates: Application for jet fuel surrogates

The increased focus on alternative fuels research in the recent years are mainly driven by escalating crude oil prices, stringent emission norms and the concern on clean environment. The processed form of vegetable oil (biodiesel) has emerged as a potential substitute for diesel fuel on account of its renewable source and lesser emissions. The experimental work reported here has been carried out on a turbocharged, direct injection, multi-cylinder truck diesel engine fitted with mechanical distributor type fuel injection pump using biodiesel-methanol blend and neat karanji oil derived biodiesel under constant speed and varying load conditions without altering injection timings. The results of the experimental investigation indicate that the ignition delay for biodiesel-methanol blend is slightly higher as compared to neat biodiesel and the maximum increase is limited to 1 deg. CA. The maximum rate of pressure rise follow a trend of the ignition delay variations at these operating conditions. However, the peak cylinder pressure and peak energy release rate decreases for biodiesel-methanol blend. In general, a delayed start of combustion and lower combustion duration are observed for biodiesel-methanol blend compared to neat biodiesel fuel. A maximum thermal efficiency increase of 4.2% due to 10% methanol addition in the biodiesel is seen at 80% load and 16.67 s-1 engine speed. The unburnt hydrocarbon and carbon monoxide emissions are slightly higher for the methanol blend compared to neat biodiesel at low load conditions whereas at higher load conditions unburnt hydrocarbon emissions are comparable for the two fuels and carbon monoxide emissions decrease significantly for the methanol blend. A significant reduction in nitric oxide and smoke emissions are observed with the biodiesel-methanol blend investigated. © 2010 Elsevier Ltd.

Biomass and Bioenergy

Experimental investigations on combustion, performance and emissions characteristics of neat karanji biodiesel and its methanol blend in a diesel engine

Suitability of vegetable oil as an alternative to diesel fuel in compression ignition engines has become attractive, and research in this area has gained momentum because of concerns on energy security, high oil prices, and increased emphasis on clean environment. The experimental work reported here has been carried out on a turbocharged direct-injection multicylinder truck diesel engine using diesel fuel and jatropha methyl ester (JME)-diesel blends. The results of the experimental investigation indicate that an increase in JME quantity in the blend slightly advances the dynamic fuel injection timing and lowers the ignition delay compared with the diesel fuel. A maximum rise in peak pressure limited to 6.5 per cent is observed for fuel blends up to 40 per cent JME for part-load (up to about 50 per cent load) operations. However, for a higher-JME blend, the peak pressures decrease at higher loads remained within 4.5 per cent. With increasing proportion of JME in the blend, the peak pressure occurrence slightly advances and the maximum rate of pressure rise, combustion duration, and exhaust gas temperature decrease by 9 per cent, 15 per cent and 17 per cent respectively. Although the changes in brake thermal efficiencies for 20 per cent and 40 per cent JME blends compared with diesel fuel remain insignificant, the 60 per cent JME blend showed about 2.7 per cent improvement in the brake thermal efficiency. In general, it is observed that the overall performance and combustion characteristics of the engine do not alter significantly for 20 per cent and 40 per cent JME blends but show an improvement over diesel performance when fuelled with 60 per cent JME blend. © IMechE 2008.

Journal	Data powered by TypesetGreen Energy and Technology
Publisher	Data powered by TypesetSpringer Verlag
ISSN	18653529
Open Access	No