Understanding biodiesel & synthetic fuels: Impact on current IC engines

This thread could be a valuable repository of information for anyone intrigued by biodiesel and synthetic fuels as sustainable alternatives.

BHPian revsperminute recently shared this with other enthusiasts.

Hello, fellow BHPians!

I'm currently pursuing a bachelor's degree in Mechanical Engineering. As a car enthusiast, it's no surprise that I've chosen a topic related to the automotive field for my final year CAPSTONE project. My friend (@santra) and I have decided to delve into the study of synthetic fuels and biofuels, specifically their impact on existing internal combustion engines. However, we've encountered challenges in connecting with reliable sources and organizations operating in this specialized field.

I'm reaching out to tap into the collective wisdom of this community. If you're well-versed in the world of biodiesel or synthetic e-fuel, I kindly ask you to share your insights, experiences, and any trustworthy sources you might be aware of. Here are a few specific points that I'm keenly interested in:

Biodiesel/EFuel Production Methods:

  • What are the various methods employed to produce biodiesel from different feedstocks?
  • Are there any groundbreaking or emerging production techniques associated with e-fuels that are currently gaining attention?

Diverse Raw Materials:

  • Which feedstocks are commonly utilized in the production of biodiesel?
  • How are carbon capture techniques integrated into the production of e-fuels?

Biodiesel/EFuel Manufacturers:

  • Could you recommend companies that are actively engaged in manufacturing bio-diesel or e-fuels and might be open to collaborating with students like us?

Trustworthy Resources:

  • Can you point us towards reliable websites, research papers, or organizations that offer accurate and up-to-date information about biodiesel and e-fuels?

Personal Experiences:

  • Have you personally connected with any organizations or individuals who could potentially assist us in our project?

By synergizing our knowledge and insights, we have the opportunity to construct a valuable repository of information for anyone intrigued by biodiesel and synthetic fuels as sustainable alternatives. Whether you're an expert in this domain or possess connections to experts, your contribution is of immeasurable value.

Let's immerse ourselves in a dialogue that's both productive and enlightening. By doing so, we'll collectively empower ourselves to make well-informed decisions regarding our transportation preferences.

Anticipating your valuable contributions and insights.

Long live IC engines,


Here's what BHPian NomadSK had to say about the matter:

Here's my 2 cents on Bio-fuels

The continuous demand for innovation implies the existence of future unsolved technological needs. The automobile industry has constantly raced against time to solve these technological issues successfully. For instance, the oil industry has supplied sulfur-free fuels to satisfy environmental regulations, and this change also needs low-sulfur lubricants or gasoline with redesigned volatility. These technology solutions need to be also economically competitive to become widely accepted by the industry.

Over the past decades, scientists around the world have foreseen serious threats for human life in the near future and have identified sustainable energy as a target for the 21st century. However, what exactly does sustainable energy mean? Sustainable energy must fully satisfy global energy demands, produced at the same rate at which it is consumed, and with an economic cost that guarantees availability in every country and social strata. Although this might be considered a utopia, the need is evident and has been one of the main legislation focuses in different world areas during the last decades.

Idea behind the Blending

The reduction should be obtained through an increase in the percentage of renewable fuel blended with conventional fuels for transportation. There are seven categories of “advanced bio-fuels” (other than corn derived Ethanol) that could be grouped into:

  • Cellulosic bio-fuels, including Ethanol derived from cellulose, hemicellulose or lignin
  • Biomass-based bio-diesel
  • Other advanced bio-fuels: Ethanol from sugar, non-corn starch or waste material; bio-gas, butanol and other alcohols from renewable biomass

How Bio-Fuels are produced

  • Synthetic liquid bio-fuels can be produced from a wide range of biomass feedstocks and different processes. The alternatives that received more interest during the last decades include:
  • Ethanol is the main bio-fuel, produced through the fermentation of a wide variety of feedstocks, mainly corn and sugar cane, but also from other feedstocks like cereals and lignocellulosic materials. Bio-butanol may also be produced from similar processes.
  • Bio-diesels are diesel fuels obtained by reacting vegetable oils with alcohol. The transesterification reaction produces Fatty Acid Methyl Ester (FAME) when methanol is the alcohol used or Fatty Acid Ethyl Ester (FAEE) when Ethanol is used, with properties very similar for both esters. Different vegetable oils used as feedstocks include rapeseed oil (canola), soybean oil, palm oil, and recently jatropha oil, but a wide variety of alternative oils are feasible: castor oil, sunflower oil, tallow, and even used cooking oils and animal fats.
  • Pure vegetable oils (PVOs) could be used directly in diesel engines with significant changes in the design of some parts of the engine, but the automobile industry is strongly opposed to this possibility.
  • Hydrogenated vegetable oil (HVO) is another alternative to produce fuel from vegetable oils or animal fats. HVO is produced through a hydrotreatment process followed by an isomerization step. HVO has similar properties to fossil diesel, with high cetane numbers and low aromatic contents.
  • Synthetic diesel from biomass to liquid (BTL) is produced through a biomass gasification process to carbon monoxide (CO) and H2 (syngas), followed by oligomerization processes. The process is similar to those currently used to produce liquid fuels from natural gas and coal.
  • Other compounds suitable for use as transport fuels can be produced from bio-syngas, such as methanol, dimethyl ether (DME), and synthetic naphtha. Biomass can also be transformed into bio crude (pyrolysis) and theoretically mixed into the crude basket in conventional refineries.

With these practical considerations, the two most common types of bio-fuels used today are bio-ethanol and bio-diesel.

Bio-fuel properties

The suitability of blending bio-fuels to be used as automotive fuel is currently an outdated topic. Bio-fuels have been blended in automotive fuels at low percentages for decades and have been demonstrated to be suitable components for automotive fuels without market problems. In the beginning, bio-fuels were very extensively tested. Analytical characterization and vehicle performance tests were performed in most of the countries involved in bio-fuel development.

Bio-fuel handling

Bio-fuels must be integrated into existing infrastructures and be compatible with existing vehicle fleets and refueling networks. Therefore, bio-fuels must be blended with hydrocarbons at refineries (or terminal plants) to maintain the primary property of conventional fuels: fungibility. Fungible fuels have common use, commingled distribution, specifications, and quality control that guarantee their substitution for each other without problems.

Bio-fuel Mixing

There are two alternative methods for blending bio-fuels: splash blending or banalization. Splash blending essentially involves adding bio-fuels to conventional fuel at the filling station. This practice is not recommended by the oil and automobile industries because the uncontrolled blending of bio-fuels and conventional fuels can lead to vehicle performance problems. Banalization involves mixing systems in tanks or lines before the loading rack facilities and can be carried out at the refinery or at the terminal. When possible, refinery blending is recommended, and either tank mixing or line blending may be preferred depending on the bio-fuel handled.

Bio-fuel end use

Bio-fuels are generally considered to reduce pollutants at the exhaust pipe, but in truth, the reduction occurs before the catalyzer. After the catalyzer, pollutant emissions do not depend on bio-fuel content. The most important factor in vehicle performance is vehicle technology. Bio-fuels (or conventional fuels) are not required to improve performance, but they must not be detrimental. Other performance aspects, such as startability, driveability, or the emission of nonregulated pollutants, vary from bio-fuel to bio-fuel.


Bio-ethanol is by far the most widely used bio-fuel for transportation purposes. Although it has been used for decades in countries like Brazil, the beginning of this century saw the worldwide expansion of this bio-fuel as a substitute for gasoline, with a well-established industry because of the availability of a wide range of feedstocks and production processes with well-established technologies.

Ethanol is currently produced primarily by the fermentation of sugars produced by plants (sugar cane, sugar beet, etc) or starches (corn, barley, sorghum). Ethyl alcohol from cellulosic feedstocks (such as wood) is expected to become increasingly important. Although research on the use of cellulosic feedstocks, including paper, wood, and other fibrous plant material, dates back to the early 20th century, only recently are large-scale demonstrating plants coming into production.

Roughly 48 % of world Ethanol production is from sugar cane and sugar beet. Most of the remainder comes from grain, with corn playing a dominant role. Brazil is the largest sugar Ethanol producer in the world, and the United States and Canada are the largest starch Ethanol producers. Ethanol is widely used in Brazil and the United States, and the two countries were responsible for 88 % of the world’s Ethanol fuel production till some years back.


The addition of Ethanol to gasoline raises three main concerns:

  • Effect of Ethanol on fuel volatility (vapor pressure and distillation)
  • Effect of Ethanol on fuel octane
  • Hygroscopic nature of Ethanol

In addition, there are other non-negligible challenges to consider:

  • Removal of solid contaminants, such as dirt or rust
  • Material compatibility
  • Minor contaminants such as sulfates in the Ethanol

Ethanol has a strong affinity for water due to its hygroscopic nature. As a result, Ethanol absorbs existing water in distribution, storage, and vehicle fuel systems, which can result in phase separation. When this occurs, the gasoline in the upper phase contains a reduced Ethanol concentration and may fail to meet specifications for octane or other key characteristics such as vapor pressure and distillation.

Higher Ethanol content in gasoline creates a greater capacity to absorb water but does not increase the risk of phase separation because the amount of water needed to cause phase separation is very large and less probable at higher Ethanol contents.

The solvent nature of Ethanol is well known. For this reason, Ethanol blends may remove sediment and sludge from tanks and filling lines due to the solvency of the blend. Special care should be taken in the distribution system, with filters to prevent the arrival of those sediments to the vehicle.

With respect to the compatibility of Ethanol blends with materials from various components in fuel distribution systems and vehicles, there are differences from normal hydrocarbon fuels. Ethanol is different from other fuel hydrocarbons in aspects such as the presence of polar groups, a relatively smaller size, and higher conductivity. These properties may create problems with the integrity of some polymers used in different parts of the supply and distribution chain and Ethanol diffusion through polymers, increasing volatile organic compound emissions. Ethanol can also contribute to the corrosion and wear of various metal components.


The concerns related to the use of gasoline formulated with Ethanol usually increase with Ethanol concentration. The main potential complications related to handling Ethanol blends are related to water content, vapor pressure, and energy content. Ethanol distribution is rather difficult because of its affinity with water and its solvent properties, which allow it to dissolve substances insoluble in gasoline. This solvent capability allows the dissolution of material accumulated in pipelines, storage tanks, and other parts of the distribution system and thereby introduces impurities into the fuel.

The affinity of Ethanol for water can also result in phase separation of blended alcohol/gasoline fuels. If phase separation occurs, the quality of the remaining gasoline phase will change and is not likely to meet specifications. The water-rich phase has no value and contains hydrocarbons, which makes it a waste to be treated with special handling according to local regulations. Phase separation is a function of water and Ethanol content, temperature, and gasoline properties.

To minimize potential phase separation problems, the Ethanol-fuel blend should be made as far down the chain as possible, maintaining the quality control that guarantees that the fuel meets standards. Distribution of Ethanol-blended gasoline via multiproduct pipelines is usually not recommended, due to concerns about water content and the serious potential risk of jet fuel contamination. Loading racks at terminals appear as convenient places for blending facilities. Bio-ethanol is usually blended in distribution networks by mixing with special gasoline basestock (blendstock for oxygenate blending [BOB]) (matched blends) or with conventional gasoline (splash blends).

A BOB is a base fuel formulated at the refinery with specifications already adjusted to account for the changes caused by Ethanol. To prevent the fuel from failing to fulfill volatility specifications, some countries tolerate extended limits for Ethanol blends (volatility waiver). At terminals, pure Ethanol can be stored in fixed-roof tanks with or without internal floating decks. Tanks with external floating decks are not recommended given the hygroscopic nature of the product. If no additional measures are taken, the vapor concentration above the liquid Ethanol will generally be flammable, so adequate safety measures must be implemented.

Special attention should be taken when Ethanol-blended gasoline is introduced to filling stations for the first time to account for the risks of phase separation and sediments (rust particles, etc.) dissolving into the fuel. It is recommended to install filters (preferably those resistant to water) in the fuel dispensers.

End Use

Ethyl alcohol (Ethanol) has long been used as an automotive fuel in two different ways: hydrous alcohol, which can completely replace gasoline in dedicated internal combustion engines, and anhydrous alcohol, as an effective “octane booster” when mixed with gasoline. Ethanol is an appropriate bio-fuel for Otto engines because of its high octane number and compatible volatility.

Challenges Refineries/Distribution Logistics/End users

  • As the heating value of Ethanol is lower than that of gasoline, both in mass and volumetric terms, the fuel consumption is higher—that is, the fuel economy is lower—when an engine consumes Ethanol (approximately 3.5 % less distance per litre in the case of E10).
  • Although engines can theoretically be designed to use the high octane number of Ethanol to achieve better performance, this is not usually the case in practice, particularly due to the need to revert to gasoline when Ethanol is not available.
  • Startability in cold conditions could also be worse because of the high heat of vaporization of Ethanol. On the other hand, the higher volatilities of Ethanolblends, slightly increase the evaporative emissions in older vehicles. However, modern vehicles with active coal canisters and new refueling facilities will practically eliminate this increase in emissions. Other exhaust emissions, particularly CO emissions, are improved in older vehicles.
  • Water phase separation in case of problems through the distribution system could cause engine damage or poor vehicle performance. Ethanol has been used in diesel engines, but this application has strong barriers, primarily the stability (Ethanolis not soluble with diesel at low temperatures) and bad ignition quality (cetane number) of diesel-Ethanol blends.

A special and less controversial way to blend Ethanol in gasoline is ETBE. ETBE is produced at refineries through reactions with isobutene. ETBE can be blended with gasoline to percentages defined by oxygen content legislation without any technical problem in vehicle performance.

Bio-diesel/FAME (Fatty Acid Methyl Esters)

FAME, also commonly known as bio-diesel, is the most common bio-fuel used in diesel engines. FAME is not a single molecule like Ethanol, but a mixture of several methylic esters of different fatty acids, depending on the original vegetable (or animal) oil used in the production process. Vegetable oils are primarily composed of triglycerides (glycerol esters of fatty acids). Theoretically, PVOs can be used in diesel engines but are strongly disapproved by the most important car and fuel injection equipment manufacturers for several reasons. The production of bio-diesel is more geographically dispersed than Ethanol. Germany leads the world's production. The esterification process for bio-diesel manufacture is relatively simple and takes place at normal pressure and ambient temperatures.

The reaction to produce FAME is in fact a set of three reactions: from triglycerides to diglycerides, from diglycerides to monoglycerides, and a final step to convert monoglycerides to FAME. Catalysts are used to improve reaction rate and yield.

FAME is mainly produced from rapeseed (canola), palm, soybean and sunflower oils feedstocks. Jatropha oil has also recently entered the market. There is also research into using other plants (brassica carinata, crambe abyssinica, camelina, jojoba, etc.). It is also possible to use used cooking oil and animal fats, and research on lipids originating from algae is currently underway.


FAME is a complex mix of compounds, and its specifications must regulate characteristics to ensure correct engine behavior (cetane number, cold filter plugging point [CFPP] or oxidation stability. FAME is fully soluble and compatible with diesel oil. The main differences between FAME and diesel oil are:

  • Lower heating value (equivalent to less energetic density)
  • Low temperature operability
  • Lower stability

As it happened with bio-ethanol, the heating value of bio-diesel is lower than conventional diesel. The difference in density creates a difference between the two products of about 8 % in volume and 12.5 % less energy per weight unit. This difference creates higher fuel consumption, which depends on the percentage of FAME in the fuel.

Low-temperature properties of bio-diesel are also a critical specification. Individual FAME products have different properties, related to their composition and impurities from the production process.

Stability is related to the fuel’s tendency to form deposits that could induce filter blocking or foul injector nozzles in vehicles, and also if the product can be stored during long periods. Stability depends on the original vegetable oil, which impacts the type of seed used for the raw material. Oils with more unsaturated fatty acid chains produce less stable FAME, and antioxidants must be added. Although additives may solve this technical barrier, additive response depends on the feedstock, with FAME from sunflower oil being the most difficult to treat.

In addition, the presence of metals increases the amount of insoluble deposits formed. In a vehicle it is very difficult to avoid the presence of trace copper or zinc, and therefore antioxidant additives may not be enough. When metals are present, FAME blends require stabilizing additives, and some reports strongly recommend the use of metal-deactivating additives in modern engine injection systems (small hole injectors, small tolerances, and extremely high working pressures).

FAEE has not been widely studied in vehicles, but it is expected to behave similarly to FAME.


FAME is usually blended with diesel fuel at refineries because FAME-diesel blends are compatible with delivery networks. Nevertheless, transportation of FAME blends in multi-product pipelines is highly restricted to prevent cross-contamination in the supply chain between diesel and other fuels that may only accept FAME traces, such as jet fuels, heating oil, and marine gasoil.

Due to its hygroscopic nature, FAME blends may contain more water than hydrocarbon fuels. As water separation is more difficult, proper water management is essential at the refineries and the terminals when FAME is handled. Because water exposure facilitates biological growth, particularly when FAME is present, tanks containing FAME and FAME-diesel blends should also be checked periodically for the presence of microbiological contamination.

FAME has a very good solvent capacity. Bio-diesel may dissolve accumulated sediments in storage tanks, which may lead to later injector and filter plugging. In addition, FAME also exhibits compatibility problems with some polymers (polyethylene, polypropylene) and rubbers (natural and nitrile rubbers). Some metallic components may also be affected by bio-diesel blends.

End Use

FAME is currently blended at low percentages (up to 7 %) with fossil diesel in Europe. Some vehicle manufacturers are opposed to exceeding this amount, but other vehicle manufacturers have proposed up to 30 %. Vehicle manufacturers and injection equipment manufacturers do have some concerns regarding FAME use in modern diesel vehicles, particularly in engines with common rail injection systems. Problems with the dilution of FAME into lubricants have been also noted in vehicles with particulate traps in the exhaust pipe. In the United States, B20 (20 % FAME) is the most commonly used bio-diesel. Higher blends are possible but may require equipment or engine modifications.

It is possible to use pure FAME in dedicated engines. FAME performs very similarly to conventional diesel in engines when all of the appropriate specifications (such as ASTM or EN) are observed. No problems with driveability or startability have been described. However, because the heating value of FAME is less than that of diesel fuel (92 % of energy content from conventional diesel in a volumetric basis), fuel consumption increases (fuel economy decreases) when the engine consumes FAME (approximately 1 % less distance per litre in the case of B10). Modern diesel vehicles are more sensitive to water and sediment in the fuel due to the very fine tolerances required by their high-pressure fuel injection systems. However, even after clean, dry fuel has been delivered, vehicle factors must also be considered to achieve problem-free operation. Because FAME is more aggressive to elastomers, its compatibility with certain materials must also be checked.

In general, regulated exhaust emissions decrease except for emissions of NOx, which increase slightly. Particulate matter emissions decrease even when compared with low aromatic, nonsulfur (S<10 ppm) diesel.


HVO, also referred to as “green diesel,” “hydrobiodiesel,” or “renewable diesel fuel,” is a bio-fuel produced by hydrogenation of vegetable oil, used oil, or animal fats. This bio-fuel is chemically comparable to fossil fuels, as it is a mixture of saturated hydrocarbons derived from triglycerides. While FAME quality is strongly dependent on the feedstock used, HVOs can be produced from many oils without compromising fuel quality.

Co-processing of vegetable oil in an existing unit at refineries is the least expensive way to obtain bio-fuels with low investment as only minor modifications are required. The amount of vegetable oil that can be coprocessed depends on hydrogen availability, compressor capacity, and
required cold properties for the product.

The obtained product exhibits improved properties, including density and cetane number, in diesel blends. HVO exhibits properties similar to gas-to-liquid (GTL) and BTL fuels. HVO is also reported to have benefits in term of reduced NOx and smoke emissions.

Because HVOs are hydrocarbons, they do not need to comply with bio-diesel specifications, but with conventional diesel fuel requirements (EN 590 and ASTM D975). HVO has no harmful effects in vehicle motors due to its similar chemical properties to conventional diesel, which is an advantage over FAME, and can be blended to conventional diesel at any percentage. In addition, the low density of HVO allows it to extend diesel production by including heavier fractions.

HVO production is currently more expensive than FAME production because of the price of vegetable oil and hydrogen consumption. HVO production is expected to use nonconventional vegetable oils and treated greases, considered as residues, thus improving the economy of the process. From the end use point of view, vehicle manufacturers prefer HVO to FAME.

I will not touch synthetic fuels here, such as Coal-to-liquid (CTL) or Gas-to-Liquid (GTL). The process takes place at high temperatures and pressures.

Looking at the Future

As transportation grows around the globe, transportation fuel consumption will also increase despite current and future improvements in vehicle efficiency. To support current working scenarios for future bio-fuels, there are some assumptions with a reasonable degree of consensus:

  • Developed countries will maintain their support for renewable energy, including transportation bio-fuels and GHG emissions reduction,
  • Sustainability exigencies will be maintained and increasingly regulated,
  • Certification schemes will be established and accepted around the world,
  • Bio-fuels should be economically competitive, with a decisive element in the price per ton of CO2 avoided,
  • The GHG savings of conventional bio-fuels must improve, or such bio-fuels are likely to disappear in short to mid-term,
  • To develop renewable energies, some type of carbon tax will be imposed on fossil fuels,
  • Waste as a raw material will be developed as much as possible as one of the highest priorities in R&D strategies.

Finally - Why all the Push for blended fuels "POLITICS and ECONOMICS" Under the garb of "ENVIRONMENT and EFFICIENCY."

Hope this was helpful for you and other readers.

PS - I have tried to keep "Chemistry" out from the whole content (as much as I could) for ease of understandability for general readers.

Good luck with your project.


Here's what BHPian FueledbyFury had to say about the matter:

Mentioned below are websites that provide credible research papers and journals.

  • IEEE Xplore - You can download the research papers by copying the URL of the specific research paper's home screen and paste it into the Sci-Hub Website.
  • MPDI
  • International Journal of Renewable Energy Research (IJRER)
  • Springer

PRO TIP: Always look for Transaction papers and Journals. Conference papers lack credibility.

Good luck with your project!

Here's what BHPian condor had to say about the matter:

Interesting topic that you have picked there, and I hope you are able to complete a good project. Would be waiting to hear about this and the learnings after you submit it.

I am not sure if this will help, but reach out to S Bioworld CNG Associate in Latur. I keep seeing their posts in one of my groups. I don't have much info about them or their work, and they may not be in the same line as your research area. But you could give it a try, and hopefully, you will at least get some leads that can help you progress in your project.

Check out BHPian comments for more insights and information.

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