Characteristics of Efficient Bio-fuels and Bio-diesels

  Biodiesel is noteworthy for its similarity to petroleum-derived diesel fuel, while at the same time having negligible sulfur and ash content. Bioethanol (Bioethanol from Vogelbusch) has only about 70% the Heating Value of petroleum distillates such as gasoline, but its sulfur and ash contents are also very low. Both of these liquid fuels have lower vapor pressure (Vapor Pressure from Wikipedia) and flammability (Flammability – from Wikipedia) than their petroleum-based competitors – an advantage in some cases (e.g. use in confined spaces such as mines) but a disadvantage in others (e.g. engine starting at cold temperatures).

Despite their wide range of possible sources, biomass feedstocks (What is a Feedstock?) are remarkably uniform in many of their fuel properties, compared with feedstocks such as coal or petroleum. For example, there are many kinds of coals whose gross heating value (Heating Value Definition – from Taftan.com ) ranges from 20 to 30 GJ/T (giga joules per metric tonne). However, nearly all kinds of biomass feedstocks destined for combustion fall in the range 15-19 GJ/T. For most agricultural residues, the heating values are even more uniform – about 15-17 GJ/tonne (6450-7300 Btu/lb); the values for most woody materials are 18-19 GJ/tonne (7750-8200 Btu/lb).

However, in contrast to their fairly uniform physical properties, biomass fuels are rather heterogeneous with respect to their chemical elemental composition.

Most biomass materials are more reactive than coal, with higher ignition stability. This characteristic also makes them easier to process thermochemically into higher-value fuels such as methanol (Methanol as Fuel – from Ethanol GEC) or hydrogen (Hydrogen Fuel – Clean & Secure Energy – White House). 

Characteristics of Oils or Fats Affecting their Suitability for Use as Biodiesel

Calorific Value, Heat of Combustion – Heating Value or Heat of Combustion, is the amount of heating energy released by the combustion of a unit value of fuels.

One of the most important determinants of heating value is moisture content. Air-dried biomass typically has about 15-20% moisture, whereas the moisture content for oven-dried biomass is negligible. Moisture content in coals vary in the range 2-30%. However, the bulk density (and hence energy density) of most biomass feedstocks is generally low, even after densification – between about 10 and 40% of the bulk density of most fossil fuels. Liquid biofuels however have bulk densities comparable to those for fossil fuels.

Melt Point or Pour Point - Melt or pour point refers to the temperature at which the oil in solid form starts to melt or pour. In cases where the temperatures fall below the melt point, the entire fuel system including all fuel lines and fuel tank will need to be heated.

Cloud Point - The temperature at which an oil starts to solidify is known as the cloud point. While operating an engine at temperatures below an oil’s cloud point, heating will be necessary in order to avoid waxing of the fuel. (Cloud Point Definition – from Engineers Edge)

Flash Point (FP) - The flash point temperature of diesel fuel is the minimum temperature at which the fuel will ignite (flash) on application of an ignition source. Flash point varies inversely with the fuel’s volatility. Minimum flash point temperatures are required for proper safety and handling of diesel fuel. (Flash Point – from the MSDS Hyper Glossary, Flash Point – from Wikipedia)

Iodine Value (IV) - Iodine Value (IV) is a value of the amount of iodine, measured in grams, absorbed by 100 grams of a given oil.

Iodine value (or Iodine number) is commonly used as a measure of the chemical stability properties of different biodiesel fuels against such oxidation as described above. The Iodine value is determined by measuring the number of double bonds in the mixture of fatty acid chains in the fuel by introducing iodine into 100 grams of the sample under test and measuring how many grams of that iodine are absorbed. Iodine absorption occurs at double bond positions - thus a higher IV number indicates a higher quantity of double bonds in the sample, greater potential to polymerise and hence lesser stability.

Iodine Numbers for some plant oils (before conversion into biodiesel):

·         Coconut oil: 10

·         Rapeseed oil: 94-120

·         Soybean oil: 117-143

·         Sardine oil: 185

Iodine Numbers after conversion to biodiesel through Transesterification (approximate values):

·         Rapeseed Methyl Ester (Rapeseed Biodiesel): 97

·         Rapeseed Ethyl Ester (Another variety of Rapeseed biodiesel): 100

·         Soy Ethyl Ester (Soy biodiesel variety 1): 123

·         Soy Methyl Ester (Soy biodiesel variety 2): 133

One can hence see that the process of transesterification (conversion of plant oil int6o biodiesel) reduces the iodine value to a small extent.

• Determination of Iodine Value – from Bruker Optics
• Determination of the Iodine Value of Oils & Fats – IUPAC (PDF)
• How Relevant is the Iodine Value – USDA ARS (PDF)
• Iodine Value & Biodiesel – USDA ARS Research Abstract
  

Viscosity – Viscosity refers to the thickness of the oil, and is determined by measuring the amount of time taken for a given measure of oil to pass through an orifice of a specified size. Viscosity affects injector lubrication and fuel atomization. Fuels with low viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in leakage or increased wear. Fuel atomization (Atomization – from Wikipedia) is also affected by fuel viscosity. Diesel fuels with high viscosity tend to form larger droplets on injection which can cause poor combustion, increased exhaust smoke and emissions.

Aniline Point/Cetane Number (CN) - Is a relative measure of the interval between the beginning of injection and autoignition of the fuel.  The higher the cetane number, the shorter the delay interval and the greater its combustibility.  Fuels with low Cetane Numbers will result in difficult starting, noise and exhaust smoke. In general, diesel engines will operate better on fuels with Cetane Numbers above 50.

Cetane tests provide information on the ignition quality of a diesel fuel. Research using cetane tests will provide information on potential tailoring of vegetable oil-derived compounds and additives to enhance their fuel properties. (References – Cetane Number Testing of Bio-diesel – from Biodiesel.org (PDF), Cetane Number – from Sizes.com, How Does Cetane Number Affect Diesel Engine Operation? ).

Density – Is the weight per unit volume.  Oils that are denser contain more energy.  For example, petrol and diesel fuels give comparable energy by weight, but diesel is denser and hence gives more energy per litre. (Fuel Density)

The aspects listed above are the key aspects that determine the efficiency of a fuel for diesel engines. There are other aspects/characteristics which do not have a direct bearing on the performance, but are important for reasons such as environmental impact etc. These are:

Ash Percentage - Ash is a measure of the amount of metals contained in the fuel. High concentrations of these materials can cause injector tip plugging, combustion deposits and injection system wear. The ash content is important for the heating value, as heating value decreases with increasing ash content.

Ash content for bio-fuels is typically lower than for most coals, and sulphur content is much lower than for many fossil fuels. Unlike coal ash, which may contain toxic metals and other trace contaminants, biomass ash may be used as a soil amendment to help replenish nutrients removed by harvest.

Sulfur Percentage - The percentage by weight, of sulfur in the fuel Sulfur content is limited by law to very small percentages for diesel fuel used in on-road applications. (Ultra-low Sulfur Diesel - PDF)

Potassium Percentage - The percentage by weight, of potassium in the fuel

Engine Manufactures Association (EMA) Recommended Guideline on Diesel Fuel

Property	Test Method	FQP-1A EMA #1 DF(1)	FQP-1A EMA #2 DF(1)
Flash Point, °C min.	D 93	38	52
Water, ppm max	D1744	200	200
Sediment, ppm max	D2276 or D5452	10	10
Distillation % Vol. Recovery, °C	D 86
90%, max.		272	332
95%, max.		288	355
Kinematic Viscosity, 40 °C	D 445	1.3 - 2.4	1.9 - 4.1
Ash, % max.	D 482	0.01	0.01
Sulfur, % max.	D 2622	0.05	0.05
Copper Corrosion, max.	D 130	3b	3b
Cetane Number, min.	D 613	50	50
Cetane Index, min.	D 4737	45	45
Rams Carbon, 10% residue max.	D 524	0.15	0.15
API Gravity, max.	D 287	43	39
Lubricity, g. min.	D6078(2)	3100	3100
Accelerated Stability, mg/L max.	D 2274	15	15
Detergency - L10 Injector	CRC Rating	<10	<10
Depositing Test	% Flow Loss	<6	<6
Low Temperature Flow, °C	D2500 or D4539	(3)	(3)
Microbial Growth		(4)	(4)

 Source: Engine Manufacturers Association 

More Links on Biodiesel Properties

·         Chemical Properties of Biodiesel, Iowa State University

·         Biodiesel Analysis from Chancellor College

·         New Feedstocks for Biodiesel Production – Analysis of its Physico-Chemicals Properties (PDF)

·         Stability of Biodiesel and Its Iodine Value – Brevard Biodiesel

·         Physical & Chemical Characteristics of Biodiesel Blends – from Biodiesel.org (PDF)

·         Biodiesel Recipe – from Wikipedia

·         Chemistry of Biofuel – fom A42.com

·         Fuel Chemistry

·         Biodiesel Overview & Characteristics from University of North Dakota

·         The Kinematic Viscosity of Biodiesel & Its Blends with Diesel Fuel (PDF)

·         Contamination or Dilution of Lubricating Oils in Biodiesel Powered Vehicles

·         Technical Performance of Vegetable Oil Methyl Esters with High Iodine Number (PDF)

·         Biodiesel Energy Content – form Biodiesel.org (PDF)

·         Effect of Biodiesel Composition on NOx & PM Emissions (PDF)

·         Biodiesel Cold Flow Guidelines – Greencar Congress

·         Understanding Biofuel Fuel Quality & Performances (PDF)

·         Biodiesel FAQ – from Govt of Maryland – Provides Comparison of Biodiesel and Petro Diesel Characteristics

·         Lubricity of Biofuel ( see homepage: Biodiesel.de )

·         Biodiesel Specs & Requirements Listing, Office of the Federal Environmental Executive, Govt of USA (PDF)

·         Biodiesel Flash Point Forum from Biodiesel Now

·         Environmental & Safety Info for Biodiesel – from ABG Biodiesel (PDF)

·         Understanding Biodiesel Fuel Quality & Performance (PDF)

·         Flash Point Testing – the Definitive Test Method

·         Biodiesel Fuels Between Acceptance & Quality (PDF)

·         Cetane Number Testing of Biodiesel (PDF)

·         Cetane in Diesel Fuel – from Global Finest

·         Measuring Cetane Number – Options for Diesel & Alternative Diesel Fuels (PDF)

·         Bubblewashing Biodiesel & Emulsions – Especially for Homebrew Bioediesel

·         Process for Producing Biodiesel Fuel with Reduced Viscosity & Cloud Point Temperature

·         Business Management for Biodiesel Producers (PDF)

·         Biodiesel Use in Engines – North Dakota State University

·         Biodiesel Performance, Costs & Use – Dept of Energy, Govt of USA

·         Biodiesel Info from Biodiesel SA, South Africa

·         Biodiesel Resource

·         Ask Ben Biodiesel FAQ

·         Biodiesel & the Environment – from Navigating our Future

·         Instructions for the Transport of Biodiesel (PDF)

·         Biodiesel Handling & Use Guidelines (PDF)

·         Technique for Analysis of Biodiesel – Metrohm UK

·         Fatty Acid Methyl Esters with a High Iodine Number (PDF)

·         Animal Fats Perform Well in Biodiesel (PDF)

·         Production of Biodiesel from Multiple Feedstocks (PDF)

·         Standardisation of Biodiesel, Netherlands (PDF)

·         Tiny Microreactor Rethinks Biodiesel Production

·         Biodiesel in Oregon – from the Government of Oregon

·         Biodiesel Info from Biofuel Systems, UK (Biofuel Process, Biofuel Chemistry)

·         Biofuel Performance, Costs & Use – Department of Energy, Govt of USA

·         The Modern & Profitable Biodiesel Production Plant (PDF)

·         How to make Rape Biodiesel More Financially Feasible

·         Biodiesel Plant Info – from VegetableOilDiesel.co.uk

·         Biodiesel Equipment from Doctor Diesel

·         Description of the Biodiesel Production Unit from Biodiesel Technologies GmbH

·         Biodiesel Equipment & Supplies from Biofuel Systems

·         Making Biodiesel – from SchNews

·         Green Fuels – European Biodiesel Equipment Supplier

·         Biomass Oil Analysis – Research Needs & Recommendations (PDF)

·         Characterization of Biodiesel Oxidation & Oxidation Products (PDF)

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About Oilgae - Oilgae - Oil & Biodiesel from Algae has a focus on biodiesel production from algae while also discussing alternative energy in general. Algae present an exciting possibility as a feedstock for biodiesel, and when you realise that oil was originally formed from algae - among others - you think "Hey! Why not oil again from algae!"

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