The high-temperature autoignition of biodiesels and biodiesel components (2023)

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Combustion and Flame

Volume 161, Issue 12,

December 2014

, Pages 3014-3021

Author links open overlay panelWeijingWangSandeepGowdagiriMatthew A.OehlschlaegerPersonEnvelope

(Video) Biodiesel Kinematic Viscosity

Abstract

Ignition delay time measurements are reported for two reference fatty-acid methyl ester biodiesel fuels, derived from methanol-based transesterification of soybean oil and animal fats, and four primary constituents of all methyl ester biodiesels: methyl palmitate, methyl stearate, methyl oleate, and methyl linoleate. Experiments were carried out behind reflected shock waves for gaseous fuel/air mixtures at temperatures ranging from 900 to 1350K and at pressures around 10 and 20atm. Ignition delay times were determined by monitoring pressure and ultraviolet chemiluminescence from electronically-excited OH radicals. The results show similarity in ignition delay times for all methyl ester fuels considered, irrespective of the variations in organic structure, at the high-temperature conditions studied and also similarity in high-temperature ignition delay times for methyl esters and n-alkanes. Comparisons with recent kinetic model efforts are encouraging, showing deviations of at most a factor of two and in many cases significantly less.

Introduction

Biodiesel fuels offer reductions in important pollutant emissions (carbon monoxide, unburned hydrocarbons, and particulates) when used as alternatives to petroleum-based fuels in diesel engines and offer a potential pathway to reduced green house gas emissions from the light- and heavy-duty transportation sectors [1]. In order to develop high-efficiency, clean, and robust engines operating on biodiesel, an understanding of biodiesel combustion characteristics is desired, including the fundamental chemical kinetic behaviors of biodiesels. Among macroscopic chemical kinetic properties, the ignition delay time, the time delay prior to ignition for a fuel/oxidizer mixture at specified conditions, has drawn special attention since it describes a process of fundamental importance to diesel engines, autoignition. Autoignition initiates combustion in diesel and other compression-ignition engines; hence, its prediction is important for the design of these engines with optimized performance and minimized pollutant emissions.

There are a variety of experimental methods available to study autoignition, including shock tubes, rapid compression machines, and flow reactors. While each method has its advantages and drawbacks, shock tubes have been widely used for the following reasons. First, the shock tube provides nearly stationary, spatially uniform, and homogeneous conditions behind the reflected shock wave, which are amenable to simplified zero-dimensional modeling. Second, conditions similar to practical combustion systems can be obtained in shock tubes including elevated pressures, a wide range of temperatures, and fuel/oxidizer mixtures. Third, the shock tube provides a relatively simple experimental platform offering highly reproducible experimental conditions for which quantitative measurements of chemical kinetic behaviors can be realized. Here we present a study of biodiesel autoignition using the shock tube technique.

Biodiesels are mixtures of long-chain mono-alkyl esters formed via the transesterification of fatty acids. Methanol is typically used in the transesterification process yielding fatty-acid methyl esters, which when derived from most feedstocks have carbon chains between 14 and 20 carbon atoms with zero to three double bonds found in the carbon chain. See Fig. 1 for the organic structures of several methyl esters found in large quantities in biodiesels and Table 1 for a compositional characterization of methyl ester biodiesels synthesized from different feedstocks [2]. The methyl ester components are described using a standard nomenclature for their organic structure, CXX:Y, where XX represents the length of the carbon chain attached to the methyl ester functionality and Y is the number of double bonds within the carbon chain.

As shown in Table 1, biodiesels synthesized via methanol-based transesterification of vegetable oils (rapeseed, sunflower, safflower, and soybean), animal fats (tallow and lard), and waste grease (yellow and brown grease) contain four predominate methyl esters (structures given in Fig. 1): methyl palmitate (C16:0), methyl stearate (C18:0), methyl oleate (C18:1), and methyl linoleate (C18:2).

The number of double bonds in the methyl ester carbon chain, or degree of saturation, influences the ignition quality of neat methyl esters or multi-component methyl ester biodiesel in diesel engines, with more highly saturated methyl esters being more reactive than less saturated methyl esters. The degree of variation in reactivity has been demonstrated through the variation in the cetane number (CN). For example, fully saturated methyl stearate has a CN=76, while methyl oleate (one double bond) and methyl linoleate (two double bonds) have CN=57 and 37, respectively [3]. Cetane numbers ranging from 44 to 70 have been reported for multi-component biodiesels derived from vegetable oils and animal fats [4].

As shown in Table 1, the compounds found in biodiesels are large in carbon number (C14+), complicating kinetic modeling due to the numerous species and reaction pathways needed to describe their oxidation. The large size of biodiesel compounds also complicates gas-phase experiments, necessary to elucidate the chemical kinetic behaviors unique to biodiesels, due to their low vapor pressures. Therefore, most kinetic investigations performed to date have focused on smaller surrogate compounds containing the chemical functionalities found in biodiesel but without the long carbon chain. For example, methyl butanoate (C4:0) has been the subject of a number of studies (e.g., [5], [6]) and a number of recent studies have investigated intermediate-sized methyl ester biodiesel surrogates, including methyl decanoate (C10:0) (e.g., [7], [8]).

Fewer studies have focused on the larger compounds found in biodiesel; however, Dagaut et al. [9] performed jet-stirred reactor oxidation studies on rapeseed biodiesel, Marchese et al. [10] studied the ignition of methyl oleate and commercial soy biodiesel fuel droplets, and Bax et al. [11] have studied methyl oleate oxidation in a jet-stirred reactor. Relevant to the present study, Campbell et al. [12] performed the first shock tube autoignition study of biodiesel compounds, measuring ignition delay times using an aerosol shock tube technique for methyl oleate and methyl linoleate at dilute conditions (4% O2), pressures of 3.5 and 7.0atm, and temperatures from 1100 to 1400K. In a following study Campbell et al. [13] made measurements of ignition delay times for methyl decanoate, laurate, myristate, and palmitate and a methyl oleate/FAME blend at similar high-temperature (1026–1388K) argon–dilute conditions.

Detailed kinetic models have been developed by several groups for large biodiesel components. Detailed kinetic models containing low- and high-temperature oxidation chemistry for methyl palmitate, stearate, oleate, linoleate, and linolenate (C18:3) have been reported by Westbrook et al. [14], [15] and for methyl palmitate and stearate by Herbinet et al. [16]. Saggese et al. [17] have reported kinetic models developed using a reaction and species lumping approach for saturated and unsaturated large biodiesel compounds, including methyl palmitate, stearate, oleate, linoleate, and linolenate. When used in combination, models from these authors can describe biodiesels comprised of mixtures of methyl esters (e.g., Table 1). Golovitchev and Yang [18] have reported a highly reduced kinetic model for rapeseed methyl ester biodiesel and diesel engine simulations performed with their model. See the reviews of Coniglio et al. [19] and Violi et al. [20] for details regarding kinetic modeling for biodiesel compounds.

To the authors’ knowledge, there have been no previous fundamental studies of autoignition for multi-component biodiesel fuels, other than those that have been performed in engines, and the only one previous autoignition study for the predominate biodiesel components given in Fig. 1 and Table 1, that of Campbell et al. [12], [13] who investigated methyl oleate and methyl linoleate autoignition at dilute conditions. Here we report shock tube ignition delay time measurements carried out at elevated-pressures and lean to stoichiometric fuel/air conditions for the four biodiesel components shown in Fig. 1, methyl palmitate, stearate, oleate, and linoleate, as well as for two reference multi-component methyl ester biodiesels, derived from soybean oil and animal fats.

Section snippets

Experimental method

Shock tube ignition delay time measurements were performed in the Rensselaer heated high-pressure shock tube (5.7cm inner diameter, 2.59m long driver, 4.11m long driven) [21]. There are five points relating to the shock tube experiments described here: shock tube heating, fuel/air mixture preparation, determination of post-shock conditions, measurement of ignition delay times, and the fuels studied and experimental conditions considered.

Results and discussion

Measured ignition delay times for methyl palmitate/air mixtures at variable equivalence ratio and pressure are shown in Fig. 4. The measurements demonstrate a reduction in apparent activation energy with decreasing temperature from 1300 to 900K, from a high-temperature value of approximately 170kJ/mol near 1200–1300K. The change in apparent activation energy is consistent with the entrance to the negative-temperature-coefficient (NTC) regime, due to contributions from low-temperature oxidation

Summary

Ignition delay time measurements made using a heated shock tube technique are reported for four neat methyl esters found in large quantities in methyl ester biodiesels, methyl palmitate, methyl stearate, methyl oleate, and methyl linoleate, and two reference methyl ester biodiesels, derived from soybean oil and animal fats. Measurements were carried out a range of conditions (fuel/air at ϕ=0.25, 0.5, and 1.0; 10 and 20atm; and 900–1300K) for methyl palmitate allowing the determination power-law

Acknowledgments

This work was supported by the National Science Foundation under Grant CBET-1032453.

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    The blending of biodiesel and dimethyl ether (DME) can compensate for the shortcomings of the physicochemical properties of each other, which can be used as an alternative fuel in internal combustion engines. A skeletal mechanism including 255 species and 1253 reactions has been developed herein for further in-depth research on the biodiesel-DME blends combustion in an engine. The mechanism consists of four sub-mechanisms associated with fuels, ester groups, small molecules and emissions. During the hierarchical construction of the mechanism, the methyl esters with long carbon chain and high polyunsaturated degree, including methyl-palmitate, methyl-stearate, methyl-linoleate, methyl-5-decenoate and n-decane were used to represent the biodiesel to accurately reflect the combustion behavior of different types of biodiesel fuels. The mechanism has been widely validated against zero-dimensional ignition delay, one-dimensional laminar flame speed, premixed flame species concentration, three-dimensional in-cylinder pressure, heat release rate and soot emissions. The findings reveal that the combustion and emissions characteristics of biodiesel-DME blends can be accurately reproduced by the mechanism. It has been observed that the increasing DME proportion resulted in the extended ignition delay, increasing in-cylinder pressure peak, NOx emissions, and decreasing soot emissions.

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  • Oxidation kinetics of methyl crotonate: A comprehensive modeling and experimental study

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Copyright © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

FAQs

What is the autoignition temperature of diesel? ›

MaterialAutoignition Temperature oFNotes
Diesel350-625Laboratory - ASTM
Diesel>1200Heated catalytic converter. No ignition, test stopped at 1200 degrees F
Diesel950-1000Heated pipe
Diesel1010-1125Recessed stainless steel plate
3 more rows

Which fuel has the highest auto-ignition temperature? ›

Coal has the highest ignition temperature compared to other fuels.

What is the autoignition temperature of gasoline? ›

Gasoline has a flash point of -45°F and an auto-ignition temperature of 536°F. [1] Gasoline's aviation fuel counterpart Kerosene holds a flash point of 100°F and an auto-ignition temperature of 428°F.

Which factors affect ignition temperature? ›

Environmental factors include air flow, surface condition, and availability of oxygen. Both air flow and surface condition may influence the potential for ignition on surfaces of the same temperature. Air flow may affect air/fuel mixture and the time for transfer of heat.

How is autoignition temperature determined? ›

Autoignition temperature tests are measured by placing the substance in a half-litre vessel and inside a temperature-controlled oven. As mentioned the current standard procedures for such tests are outlined in ASTM E659.

What is the difference between flash point and autoignition temperature? ›

While the flash point is the ambient temperature at which the chemical can spark or ignite (if it meets an ignition source), the auto-ignition temperature is the lowest ambient temperature at which the chemical will spontaneously combust (without an ignition source).

Why self ignition temperature of petrol is higher than diesel? ›

The calorific value of petrol is greater than diesel engine so that pre ignition temp of petrol is less than diesel.

What is the ignition temperature of petrol and diesel? ›

Examples
FuelFlash pointAutoignition temperature
Gasoline (petrol)−43 °C (−45 °F)280 °C (536 °F)
Diesel (2-D)>52 °C (126 °F)210 °C (410 °F)
Jet fuel (A/A-1)>38 °C (100 °F)210 °C (410 °F)
Kerosene>38–72 °C (100–162 °F)220 °C (428 °F)
4 more rows

What will happen if the temperature of a fuel is raised to its ignition temperature? ›

This temperature is sometimes referred to as the kindling point of the fuel. Raising the temperature of a fuel to its auto-ignition point provides the energy required to initiate the chemical reaction needed for combustion.

What is called ignition temperature? ›

The ignition temperature (sometimes called the autoignition temperature) is the minimum temperature at which the material will ignite without a spark or flame being present.

What is ignition temperature example? ›

» IGNITION TEMPERATURE : It means that a substance is the lowest temperature at which it spontaneously ignites in normal atmosphere without an external source of ignition. » BEST EXAMPLE : Candle flame & Fire.

Which fuel has lowest ignition temperature? ›

Among the given options, kerosene has the lowest ignition temperature. So, it catches fire relatively easily.

Which fuel has high ignition temperature petrol or diesel? ›

The Self Ignition Temperature of Diesel is 210°C and that of Petrol varies from 247°C to 280°C. The lower SIT of Diesel is the reason behind the absence of a spark plug in a diesel engine.

What is the ignition temperature of oil? ›

Auto-ignition of lubricating oil working in a compressor for an air conditioner is studied experimentally. The adopted lubricating oil is an unknown mixture with multi-components and known to have flash point temperature of 170 °C. First, its auto-ignition temperature is measured 365 °C at atmospheric pressure.

What is the autoignition temperature for hydrogen? ›

since the autoignition temperature of hydrogen is 585°C [8].

What is an example of autoignition? ›

Rapid compression of some materials can also result in autoignition. For example, diesel engines do not use spark plugs to ignite the fuel-air mixture, but rather a rapid compression that raises the temperature to the autoignition point.

How do you stop autoignition? ›

Get rid of any dust or sawdust as quickly as possible to prevent fire. If you're storing oil-soaked or flammable products indoors, make sure you don't pile too many items together or place them in a confined space. Keep any flammable items away from sources of heat, including radiators and windows.

What is the minimum temperature at which a liquid fuel will produce enough vapor to burn? ›

Flashpoint is the minimum temperature at which the vapor concentration near the surface of the liquid is high enough to form an ignitable mixture. Any liquid with a flashpoint less than 100oF is considered to be a flammable liquid. A liquid with a flashpoint between 100oF and 200oF is combustible.

Which is higher flash point or boiling point? ›

Flash point is the lowest temperature at which vapour of the material will ignite when given an ignition source. Boiling point is the temperature at which the vapour pressure of a liquid equals the external pressure surrounding the liquid.

Why is flash point and fire point important? ›

The flash point is an important concept in fire investigation and fire protection because it is the lowest temperature at which a risk of fire exists with a given liquid. It is crucial in many circumstances to establish the presence of some liquids and to know their flash point during the investigation process.

What is flash point and Firepoint? ›

The flash point of a liquid hydrocarbon is the temperature to which it must be heated to emit sufficient flammable vapor to flash when brought into contact with a flame. The fire point of a hydrocarbon liquid is the higher temperature at which the oil vapors will continue to burn when ignited.

What type of ignition system does a diesel engine use to ignite fuel? ›

One difference is that diesel engines have a compression-ignited injection system rather than the spark-ignited system used by most gasoline vehicles.

Why compression ratio of petrol engine is smaller than diesel engine? ›

The readiness of petrol to ignite translates to a petrol engine requiring lower compression ratios and instead relying on a spark plug to combust the air-fuel mixture. Diesel, on the other hand, requires the cylinder to compress the air to the point where injecting diesel fuel instantly combusts the air-fuel mixture.

Why compression ratio is higher in diesel engine? ›

Diesel engines use higher compression ratios than petrol engines, because the lack of a spark plug means that the compression ratio must increase the temperature of the air in the cylinder sufficiently to ignite the diesel using compression ignition.

Is diesel fuel flammable? ›

A room with diesel fuel that isn't stored securely could be full of flammable vapours. Not only is diesel considered a grade 4 flammable, it's also a combustible.

What is fire point of fuel? ›

The fire point of a fuel is the lowest temperature at which the vapour of that fuel will continue to burn for at least five seconds after ignition by an open flame of standard dimension.

What is the ignition temperature of water? ›

Water is not combustible, as its a stable molecule. So it has no ignition temperature. 2.

Why should the ignition temperature of a fuel not be below room temperature? ›

A good fuel should not spontaneously catch fire. Hence, its ignition temperature should be more than room temperature or else it will catche fire easily and can be very disastrous.

What will happen if the ignition temperature of a substance is lower than the room temperature? ›

If ignition temperature of a substance is lower than room temperature then it will undergo spontaneous combustion.

How many types of combustion are there? ›

There are 5 different types of combustion.

Which fuel has the highest calorific value? ›

LPG has the highest calorific value. LPG has a typical specific calorific value of 46100 kJ/kg. The calorific value of a fuel may be defined as the amount of heat energy (kJ) produced by complete combustion of 1 kg of fuel under the standard conditions.

Which is more difficult to ignite petrol or diesel? ›

That's because diesel is much less flammable than gasoline. In a car, it takes intense pressure or sustained flame to ignite diesel. On the other hand, if you toss a match into a pool of gasoline, it won't even touch the surface — it ignites the vapors above the surface.

What is the ignition temperature of alcohol? ›

The auto ignition temperature (AIT) is recorded for stoichiometric concentrations. The AITs for methanol and ethanol are 470 °C and 365 °C, respectively [31].

What is meant by the autoignition temperature? ›

Definition. In the context of a combustible fuel mixture, the auto-ignition temperature is the lowest temperature at which the fuel will spontaneously ignite in a normal atmosphere without an external source of ignition such as a flame or spark.

What is meant by autoignition? ›

Autoignition is defined as the self-ignition of the vapors emitted by a liquid heated above its ignition temperature and that, when escaping into the atmosphere, enter into their explosive range.

What is the ignition temp of oil? ›

A flashpoint is the temperature at which an oil creates flammable vapors that when exposed to heat can cause a fire. For most cooking oils, the flashpoint is around 600° F.

Can diesel ignite from a spark? ›

According to Skelton, “The difference in diesel is that diesel fuel doesn't ignite. A spark plug has no use with diesel fuel because there is no need to 'light' the diesel fuel. Instead, the glow plug only heats the combustion chamber.”

What is an example of autoignition? ›

Rapid compression of some materials can also result in autoignition. For example, diesel engines do not use spark plugs to ignite the fuel-air mixture, but rather a rapid compression that raises the temperature to the autoignition point.

Why self ignition temperature of petrol is higher than diesel? ›

The calorific value of petrol is greater than diesel engine so that pre ignition temp of petrol is less than diesel.

What is ignition temperature example? ›

» IGNITION TEMPERATURE : It means that a substance is the lowest temperature at which it spontaneously ignites in normal atmosphere without an external source of ignition. » BEST EXAMPLE : Candle flame & Fire.

How do you stop autoignition? ›

Get rid of any dust or sawdust as quickly as possible to prevent fire. If you're storing oil-soaked or flammable products indoors, make sure you don't pile too many items together or place them in a confined space. Keep any flammable items away from sources of heat, including radiators and windows.

Which fuel has lowest ignition temperature? ›

Among the given options, kerosene has the lowest ignition temperature. So, it catches fire relatively easily.

What is the temp of fire? ›

Orange flames range from around 1100°C to 1200°C. White flames are hotter, measuring 1300°C to about 1500°C. The brighter the white, the higher the temperature. For blue flames, or flames with a blue base, you can expect the temperature to rise dramatically, hitting roughly 2500°C to 3000°C.

What oils are flammable? ›

These include tea tree, lavender and citrus oils. Other popular oils have flashpoints between 102-130° F, including orange, tangerine, rosemary, bergamot, chamomile, eucalyptus, fir, frankincense, juniper berry, grapefruit, lemon, lime and spruce. By comparison, the flashpoint of kerosene is between 100-162° F.

What Colour is unburnt diesel? ›

"White smoke (contingent on its odor) signifies insufficient temperature. Blue smoke may indicate an uncontrolled variable entering the combustion process." According to Zack Ellison at Cummins, "White smoke is an indication of unburned diesel fuel.

Does biodiesel flammable? ›

Biodiesel is a combustible liquid which burns readiy when heated. However, blending with petroleum based diesel fuel or contamination by materials used in manufacturing can increase its flammability.

What is the color of diesel fuel? ›

The U.S. government now requires diesel gas to be sold within three different varieties: clear, red, and blue. Understanding the difference among these fuels – and among the tax and legal implications of each – is critical if you intend to purchase diesel fuel.

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